HK1180766B - Increase of usable dynamic range in photometry - Google Patents

Description

Increase of available dynamic range in photometry

Technical Field

The present invention relates to the field of optical devices comprising a detection unit with wavelength dependent responsiveness for determining the presence and/or concentration of an analyte in a sample. The invention relates in particular to an optical device and a method for compensating said wavelength-dependent responsivity of a detection unit.

Background

Several analyzers for use in analyzing samples, such as biological samples, include a light source that illuminates the sample and a photodetector that performs photometric measurements. For example, in clinical chemistry analyzers, the transmission of light through a cuvette containing a liquid sample is measured. The result is used to generate extinction data as a ratio of the intensity of light input to the sample to the intensity of light output through the sample. Extinction may be caused by absorption or scattering of light by the sample. Both processes result in measurable extinction. In this way, by measuring the response signal of the detector, typically at a usable wavelength, the presence and/or concentration of an analyte in a sample that may be indicative of a diagnostic condition may be determined. These wavelengths are the wavelengths at which the analyte is typically absorbing or scattering light of the type being determined so that a small degradation can be detected.

Photodiodes are typically used as detectors because of their linearity of output current as a function of incident light, low noise, small size and light weight, long lifetime, high quantum efficiency, and lower cost compared to photomultiplier tubes. On the other hand, the overall sensitivity of photodiodes is lower compared to photomultiplier tubes, their area is smaller, there is no internal gain and the response time is generally slower. Therefore, photodiode arrays are more commonly used in order to allow higher speed parallel readout.

The material chosen to make a photodetector operable in the visible wavelength range is typically silicon. Silicon is capable of generating significant photocurrents in a wavelength range comprised between about 190 nanometers and about 1100 nanometers, which is a useful range for analyzing biological samples.

However, the response of silicon-based photodetectors to the wavelength of incident light is variable. In other words, the responsivity of the photodetector is wavelength dependent. This means that the measurement signal or the baseline signal varies along a curve similar to the responsiveness curve over the wavelength range, provided that the same optical power is input into the photodetector over the entire wavelength range.

Responsivity is defined as the ratio of the generated photocurrent (a) to the incident optical power (W), usually expressed in a/W (amperes/watt). The responsivity can also be expressed as quantum efficiency, or the ratio of the number of photogenerated carriers to the incident photons.

A "baseline signal" is defined as the signal resulting from the conversion of electromagnetic energy directed from the light source to the detector through the optical path without passing through the sample or replacing the sample with a blank or reference solution. Thus, the baseline signal is a function of the light source intensity and photodetector responsivity at different wavelengths. In other words, the baseline signal over each selected usable wavelength range may be defined as a blank signal, any deviation from the blank signal being interpreted as signal attenuation caused by the analyte present in the sample.

Furthermore, not only the photodetector has wavelength dependent responsivity. Like the lens and the dispersive element, most components that may be part of the optical path have different properties at different wavelengths, so that the overall baseline signal is a function of the several components used in the detection unit.

Wavelength dependent responsivity is an inherent property of a detection unit, which means at least some of the components of the detector and optical path, typically all components having the effect of transmitting, reflecting, diffracting, refracting, scattering, etc. light en route, which may vary with the wavelength used.

With respect to detectors, "intrinsic properties" refer to material intrinsic properties, such as the silicon wavelength dependent responsivity of silicon-based detectors, which are well known to generate variable photocurrents over the typical wavelength range of silicon materials.

With respect to the optical path components, the wavelength dependent responsivity may be caused by both the material and form or geometry of the components (e.g., the material and geometry of the lens, the material and spatial resolution of the grating, etc.), which may cause different wavelengths of light to reach the detector at different intensities, at the same source intensity. In extreme cases, it is even possible to block or deviate the wavelengths from a certain range in such a way that light of those wavelengths never reaches the detector.

Furthermore, the sample container itself placed in the optical path may have a wavelength dependent responsiveness. For example, if glass or plastic cuvettes are used, it is well known that those cuvettes will absorb part of the radiation, for example in the ultraviolet range.

Furthermore, currently used light sources like halogen lamps have a variable intensity spectrum that is low at certain wavelengths, typically sloping downwards towards the ultraviolet and/or infrared on the border of the range, and has a peak of about 700 nm in the central part of the wavelength range.

Generally, near the range boundary, especially in the UV range, the detector has a lower responsiveness where the relative intensity of the light source is low, and a higher responsiveness where the relative intensity of the light source is high. As a result, at comparable concentrations, the response signal of an analyte being detected at a wavelength near the range boundary may be too weak, while the response signal of another analyte being detected at a wavelength where both the intensity of the light source and the responsiveness of the detector are high may result in signal saturation. For this reason, the dynamic range of the measurement is limited when the baseline signal is typically set in terms of the relative intensity of the light source and the available wavelength at which the responsivity of the detector is lowest. This is done in order to be able to measure small concentrations of the analyte.

However, this means that a very wide detector dynamic range is required, whereas the available dynamic range is small. In some cases, this may result in the need to dilute the sample being analyzed and repeat the measurement if the measured extinction is too high.

Photodiodes with one preamplifier per pixel are typically used to best address this problem, but at the cost of complexity and high cost. An alternative is to vary the integration time over different wavelengths, but this method is not suitable when fast measurements are required.

It is an object of the invention to provide an optical device that is simple and cost-effective and less dependent on the dynamic range of the detector.

According to an embodiment of the invention, this may be achieved by providing a light source comprising a plurality of light emitting elements emitting light of different respective usable wavelength ranges, wherein the intensity of at least some of the light emitting elements is adjusted to at least partially compensate the wavelength dependent responsivity of the detection unit for at least the selected usable wavelength. According to another embodiment, this may be achieved by providing at least one light modulator in the light path to at least partially compensate the wavelength dependent responsivity of the detection unit for at least the selected available wavelength. According to another embodiment, this may be achieved by sequentially adjusting the intensity of the light source to at least partially compensate the wavelength dependent responsivity of the detection unit for at least the selected available wavelength.

An advantage of the present invention is that it is possible to use the available dynamic range of the detector almost entirely for measurements, i.e. for determining the presence and/or concentration of an analyte in a sample. Another advantage of the invention is that it is possible to use a cheaper detector like a CCD or CMOS type detector. Another advantage is that although the dynamic range of the detector may be small, the dynamic range available for detection can be maximized to cover almost the entire available dynamic range of the detector. Another advantage is that it can be prevented that dilution of the sample and repeated analysis are required if the measurement signal is too high.

Another advantage of the present invention is that stray light in the optical device can be reduced.

Disclosure of Invention

The present invention relates to an optical device for determining the presence and/or concentration of an analyte in a sample, said optical device comprising a detection cell comprising a light path component and a detector, said detection cell having a wavelength dependent responsivity. The optical device further comprises a light source comprising at least two light emitting elements emitting light of different respective usable wavelength ranges. The optical device is arranged such that light from the light source is directed through the optical path to the detector so as to generate a baseline signal over the respective usable wavelength range and a response signal relative to the baseline signal when the sample is in the optical path, the response signal being indicative of the presence and/or concentration of the analyte in the sample. The optical device is arranged such that the intensity of the at least first and second light emitting elements is inversely proportional to the wavelength dependent responsivity of the detection unit for at least a first and a second available wavelength range, respectively, the responsivity of the detection unit being higher over the first available wavelength range than over the second available wavelength range such that the ratio between the first baseline signal over the first available wavelength range and the baseline signal over the second available wavelength range is smaller than the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range, preferably 50% or less of the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range.

According to another embodiment, the optical device comprises a detection unit comprising an optical path member and a detector, the detection unit having a wavelength dependent responsivity. The optical device further comprises at least one light source emitting light in a usable wavelength range. The optical device is arranged such that light from the light source is directed through the optical path to the detector so as to generate a baseline signal over the usable wavelength range and a response signal relative to the baseline signal when the sample is in the optical path, the response signal being indicative of the presence and/or concentration of the analyte in the sample. The optical device further comprises at least one light adjuster in the light path for compensating the wavelength dependent responsivity of the detection unit for at least a first and a second available wavelength range, respectively, the responsivity of the detection unit being higher over the first available wavelength range than over the second available wavelength range such that the ratio between the first baseline signal over the first available wavelength range and the baseline signal over the second available wavelength range is smaller than the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range, preferably 50% or less of the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range.

According to the present invention, an "optical device" is a stand-alone instrument, an integrated component within an analyzer, or a module in an analysis system adapted to optically analyze an analyte present in a sample, particularly adapted to measure light transmission through the sample.

The optical device is particularly suitable for analyzing biological samples. The sample is preferably a liquid solution that can potentially find one or more analytes of interest, such as a body fluid like blood, serum, plasma, urine, milk, saliva, cerebrospinal fluid, and the like. The sample may be analyzed as such, or after dilution with another solution or after mixing with reagents, e.g., to perform one or more diagnostic assays such as, for example, clinical chemistry assays and immunoassays. Thus, the optical device may advantageously be used for detecting the result of or monitoring the progress of a chemical or biological reaction, e.g. in coagulation analysis, agglutination analysis, turbidimetric analysis. Other diagnostic assays include, for example, qualitative and/or quantitative assays for analytes such as albumin, alkaline phosphatase (ALP), alanine transaminase, ammonia, amylase, aspartate transaminase, bicarbonate, bilirubin, calcium, cardiac markers, cholesterol, creatine kinase, D-dimer, ethanol, gamma glutamyltransferase, blood glucose, glycated hemoglobin (HBA 1 c), high density lipoprotein (HDL-) cholesterol, iron, lactate dehydrogenase, LDL-cholesterol, lipase, magnesium, inorganic phosphorus, potassium, sodium, total protein, triglycerides, urea, uric acid. This list is of course not exhaustive.

A "detection unit" is herein defined as a system within an optical device comprising light path components and a detector which makes it possible to direct light through a sample and measure light transmission or reflection, such as absorption and/or scattering, in a controlled manner. However, the detection unit may be configured to perform any other spectral measurement. Time-stationary measurements, time-resolved measurements, or both may also be required.

The optical path may contain components such as lenses, mirrors, apertures, filters, shutters, thermal shields, optical fibers, dispersive elements, etc. The dispersive element may be a transmissive or reflective diffraction grating, and may be a scanning monochromator or polychromator configured to receive the transmitted light and disperse it into a plurality of spectral components. The dispersive element may also be a refractive element like a prism.

A "detector" according to the present invention is a photodetector or photodetector that includes both single element and multi-element or array photodetectors as a means of converting electromagnetic energy into an electrical signal. Thus, a photodetector is a device capable of monitoring a photo-electromagnetic signal and providing an electrical output signal or response signal indicative of the presence and/or concentration of an analyte in a sample present in an optical path relative to a baseline signal. Such devices include, for example, photodiodes including avalanche photodiodes, phototransistors, photoconductive detectors, linear sensor arrays, CCD detectors, CMOS photodetectors including CMOS array detectors, photomultiplier tubes, and photomultiplier tube arrays. According to some embodiments, the light detector, such as a photodiode or photomultiplier tube, may contain additional signal definition or processing electronics. For example, the light detector may comprise at least one preamplifier, electronic filter or integrating circuit. Suitable preamplifiers include integral, transimpedance, current gain (current mirror) preamplifiers. According to a preferred embodiment, the detector is of the CCD or CMOS type. According to another embodiment, the detector is of the photodiode or PMT type.

The light source according to the invention is a unit in an optical device comprising at least one light-emitting element capable of emitting usable light. The term "available" refers to one or several wavelengths, or one or several wavelength ranges within a broader wavelength range, at which light directed through the sample can be used to measure with sufficient sensitivity the concentration of an analyte present in the sample and/or the small variation of the minimum concentration from a baseline signal. Of course, at least one light-emitting element may emit light in an unavailable range, insofar as it emits light in at least one available range. Furthermore, the term "available" must be intended as a relative term in the sense that a certain wavelength range may be available for measuring one or a group of analytes, and for other analytes may be less available, which means that if a loss of sensitivity is accepted, it may still be available for other analytes. On the other hand, if optimal measurement conditions are required, different available wavelength ranges need to be selected.

The term "wavelength range" must also be interpreted in a broad manner including both a narrow range of, for example, a few nanometers, e.g., 2-20 nanometers, and a broader range of, for example, 20-100 nanometers or more. It is also to be understood that these ranges may at least partially overlap.

A "light emitting element" is a source of electrically powered radiation such as an incandescent lamp, an electroluminescent lamp, a gas discharge lamp, a high intensity discharge lamp, a laser source.

According to one embodiment, the at least one light emitting element is, for example, a halogen lamp, which, like all incandescent light bulbs, produces a continuous broad spectrum from near ultraviolet to deep to infrared.

According to a preferred embodiment, the at least one light emitting element is a light emitting diode. The term "light emitting diode" or "LED" is used herein to refer to a conventional light emitting diode, i.e., an inorganic semiconductor diode that converts applied electrical energy into light. Such conventional LEDs include, for example, aluminum gallium arsenide (AlGaAs) which generally generates red light and infrared light, gallium aluminum phosphide which generally generates green light, gallium arsenide/phosphide (GaAsP) which generally generates red light, orange light, and yellow light, gallium nitride which generally generates green light, pure green light (or bright green light), and blue light, gallium phosphide (GaP) which generally generates red light, yellow light, and green light, zinc selenide (ZnSe) which generally generates blue light, indium gallium nitride (InGaN) which generally generates blue-green light and blue light, aluminum indium phosphide which generally generates orange light, yellow light, and green light, silicon carbide (SiC) which generally generates blue light, diamond which generally generates ultraviolet light, and silicon (Si) which is being developed. The LED is not limited to a narrow-band or monochromatic light LED; LEDs may also include broadband, multi-band, and generally white LEDs.

The term "LED" is also used herein to refer to Organic Light Emitting Diodes (OLEDs), edge emitting diodes (ELEDs), thin film electroluminescent devices (TFELDs), quantum dot based inorganic "organic LEDs", and phosphorescent OLEDs (pholeds), which may be polymer based or small molecule based (organic or inorganic).

Thus, according to some embodiments, the LED may be a standard semiconductor device, an organic LED, or an inorganic LED. Examples of organic LEDs are QDOT-based LEDs and nanotube-based LEDs. The LED may be a stack of LEDs such as a stack of organic LEDs or a stack of organic LED layers.

According to a preferred embodiment, the light source comprises a plurality of light emitting elements having respectively different available wavelengths or wavelength ranges. For example, the light source includes a combination of two, three, or more LEDs, such as an LED having a first available relatively shorter wavelength spectrum (e.g., UV-blue light), a second available "reddish" or longer wavelength spectrum, a third available further reddish or longer wavelength spectrum, depending on the number and type of available wavelengths desired, and so forth, ultimately up to infrared wavelengths.

Each LED may be configured to generate an emission energy of, for example, about 500 μ W and about 1W. Alternatively or in combination, some of the LEDs of the array may be configured to generate low emission energy, some medium emission energy, some high emission energy.

The light source may comprise a cooling device, such as a heat sink or a fan, in order to carry away heat generated by the light emitting elements or to prevent fluctuations in illumination and/or spectral shifts.

The light source and the light path components are configured to direct light from the light source through the light path to the detector so as to generate a baseline signal over the respective usable wavelength range, and to generate a response signal relative to the baseline signal when the sample is in the light path, the response signal being indicative of the presence and/or concentration of the analyte in the sample. The sample may be in, for example, a cuvette, flow cell, etc. located in the light path.

According to some embodiments, the optical device comprises a light mixing element consisting of light shaping and homogenizing optical elements, such as for example mixing rods, which homogenize the light emitted by the plurality of light emitting elements and improve the uniformity of the illumination before illuminating the sample located in the light path.

The light mixing element may be part of the light path or the light source.

According to one aspect of the invention, the light source comprises a plurality of light emitting elements, for example, at least two light emitting elements. In particular, the intensity of the at least first and second light-emitting elements is adjusted in inverse proportion to the wavelength-dependent responsivity of the detection unit for at least a first and a second usable wavelength range, respectively, the responsivity of the detection unit being higher over said first usable wavelength range than over said second usable wavelength range. In this way, a ratio between the first baseline signal over the first usable wavelength range and the baseline signal over the second usable wavelength range is obtained, which is smaller than the ratio between the responsiveness of the detection unit over the first usable wavelength range and the responsiveness of the detection unit over the second usable wavelength range.

Expressed in mathematical terms, the baseline signal BL (λ) is the spectrum S (λ) of the light source as a function of wavelength λ, multiplied by the detector responsivity Rd (λ), which is also a function of wavelength λ, and multiplied by the optical path responsivity Rop (λ), which is also a function of wavelength λ. Therefore, the formula can be written as BL (λ) = S (λ) × Rd (λ) × Rop (λ). This formula can be abbreviated as BL (λ) = S (λ) × Rdu (λ), where Rdu (λ) is the responsiveness of the detection unit corresponding to Rd (λ) × Rop (λ). S (λ) is represented by Watt (W). Rdu (. lamda.) is expressed in ampere/watt (A/W). BL (λ) is therefore expressed in amperes (a), which is the current measured by the detector and converted into a baseline signal.

The level of the baseline signal may vary in a wavelength-dependent manner according to the above formula. This means that, in a set of selected available wavelength ranges, there is a wavelength range where the baseline has the maximum level and a wavelength range where the baseline has the minimum level. Thus, the baseline signal at all selected available wavelengths can be normalized by dividing by the maximum baseline signal. Thus, the maximum baseline signal is given a value of 100%, while all other baseline signals are expressed as a fraction or percentage of the maximum baseline signal. The ratio between the maximum baseline signal and the minimum baseline signal among the selected wavelength range defines the dynamic range of the baseline signal. If the light source S is not a function of the wavelength λ, that is, if the light source is constant at all wavelengths, e.g., 1W, the spectrum of the baseline signal coincides with the responsivity curve Rdu (λ) of the detection unit.

Adjusting the intensity of the light-emitting elements in inverse proportion to the wavelength-dependent responsivity of the detection unit in order to compensate for the wavelength-dependent responsivity means that the light source is configured such that, at least for a selected usable wavelength, the individual light-emitting elements emit light with an intensity which is higher in case the responsivity of the detection unit is lower and lower in case the responsivity of the detection unit is higher, respectively. This means that by choosing, for example, the first and second wavelength ranges λ 1 and λ 2, respectively, when the responsivity of the detection unit is higher over the first usable wavelength range than over the second usable wavelength range, i.e. Rdu (λ 1) > Rdu (λ 2), the intensity of the light source S (λ 2) (i.e. the intensity of the second light-emitting element emitting light in that second wavelength range) is increasing compared to the first light source S (λ 1) (i.e. the intensity of the first light-emitting element emitting light in the first wavelength range). In particular, the formula for λ 1 is BL (λ 1) = S (λ 1) × Rdu (λ 1). The formula for λ 2 is BL (λ 2) = S (λ 2) × Rdu (λ 2). The relationship between λ 1 and λ 2 is given by the formula BL (λ 1)/BL (λ 2) = S (λ 1)/S (λ 2) × Rdu (λ 1)/Rdu (λ 2). If S (λ 1) is equal to S (λ 2), the ratio between BL (λ 1) and BL (λ 2) is equal to the ratio between Rdu (λ 1) and Rdu (λ 2).

Obtaining a ratio between the first baseline signal over the first usable wavelength range and the baseline signal over the second usable wavelength range, which is, for example, 50% or less of a ratio between the responsiveness of the detection unit over the first usable wavelength range and the responsiveness of the detection unit over the first usable wavelength range, means that the intensity of the second light-emitting element S (λ 2) with respect to the first light-emitting element S (λ 1) is adjusted so that BL (λ 1)/BL (λ 2) × Rdu (λ 2)/Rdu (λ 1) is 0.5 or less, preferably 0.1 or 10%. By adjusting S (λ 1) and S (λ 2) in inverse proportion to Rdu (λ 1) and Rdu (λ 2), respectively, the same baseline BL (λ 1) as the baseline BL (λ 2) concerning λ 2 is obtained for λ 1, that is, BL (λ 1)/BL (λ 2) = 1.

Preferably, S (λ n) (where λ n represents any selected wavelength range) is adjusted so as to reduce the dynamic range of the baseline signal, which is the ratio between the maximum baseline signal BL (λ max) and the minimum baseline signal BL (λ min) among the selected wavelength range, by at least 50%, preferably at least 90% up to 100%, compared to the baseline generated by the light source, which is constant over all wavelength ranges. In other words, BL (λ max)/BL (λ min) × Rdu (λ min)/Rdu (λ max) is 0.5 or less, preferably less than 0.1. By adjusting S (λ n) which is inversely proportional to Rdu (λ n), a baseline BL (λ n) which is the same at any selected wavelength is obtained.

Adjusting the intensity of the light-emitting element to compensate for the wavelength dependent responsivity of the detection cell also helps to minimize the frequently encountered and undesirable stray light problems. "stray light" is defined as light in the optical device, in particular in the detection unit, that reaches the detector at a wavelength (λ n) other than the predetermined wavelength(s). As a result, the baseline signal and/or the response signal generated by the detector is not only caused by light of e.g. a predetermined wavelength λ n, but also by light of a non-predetermined wavelength other than λ n, and is therefore chosen as an error deviating the measured value, i.e. a deviation from the correct signal. Such an error caused by stray light is negligible in the case where a signal caused by predetermined light is much larger than that caused by stray light. However, in the case where the responsivity of the detector is low at the predetermined wavelength and high at one or more wavelengths other than the predetermined wavelength, the error caused by stray light may be significant. The effect of stray light may be even more severe when the intensity of light at the predetermined wavelength is lower than the intensity of light at the non-predetermined wavelength, in addition to having a lower responsiveness at the predetermined wavelength than at the non-predetermined wavelength. Therefore, compensating the wavelength dependent responsivity of the detection unit according to the invention also reduces possible errors caused by stray light. According to an embodiment, at least for the wavelength or wavelengths where the stray light problem is more severe, the intensity of the respective light emitting element is further adjusted compared to the intensity of other light emitting elements emitting light in other usable wavelength ranges, i.e. the intensity of the respective light emitting element is further increased and/or the intensity of other light emitting elements emitting light in other usable wavelength ranges may be further reduced. This means that by selecting, for example, the first and second wavelength ranges λ 1 and λ 2, respectively, when the responsiveness of the detection unit is higher over the first usable wavelength range than over the second usable wavelength range, i.e., Rdu (λ 1) > Rdu (λ 2), the intensity S (λ 1) with the first light-emitting element can increase the intensity S (λ 2) of the second light-emitting element and/or the intensity S (λ 2) with the second light-emitting element can decrease the intensity S (λ 1) of the first light-emitting element, so that BL (λ 1)/BL (λ 2) < 1.

Adjusting the intensity of the light-emitting elements is for example achieved by varying the input electrical power of the individual light-emitting elements, for example by supplying more input electrical power to the light-emitting elements emitting light of the available wavelength or wavelength range of the detection unit with lower responsiveness, and optionally by supplying less input electrical power to the light-emitting elements emitting light of the available wavelength or wavelength range of the detection unit with higher responsiveness. For a selected usable wavelength range, for example, where the responsivity of the detection unit is low, it may be sufficient to adjust the intensity of only one light-emitting element. Generally, the closer the selected available wavelength range is, the smaller the difference in the value or level of the respective baseline signals, which means that it is less important to compensate for this difference. Thus, adjusting the intensity of at least two light-emitting elements must be understood in a relative manner, which includes setting or fixing the intensity of a first light-emitting element, and adjusting the intensity of a second light-emitting element relative to the first light-emitting element, regardless of whether the first light-emitting element is used for that particular analysis. Alternatively, since the wavelength dependent responsivity is an inherent property of the detection unit, different light emitting elements of respectively different powers according to the emission wavelength may be used.

Depending on the nature of the light-emitting elements, the number of light-emitting elements and the emission wavelength, a continuous broadband emission spectrum containing the available wavelengths or a discrete narrow-band emission spectrum containing the selected available wavelengths may be generated. Thus, the baseline signal may also be continuous or discontinuous with signal regions and gaps therebetween per selected usable long wave. The light source may also be configured to turn on or use only selected light-emitting elements, e.g., those that may be used to detect a selected analyte, while other light-emitting elements may remain off.

Ideally, for each of the selected available wavelengths, a baseline signal can be obtained with a dynamic range of 1, nearly flat, and/or nearly at the same level. In practice, then, any reduction in baseline signal degradation brings considerable benefit, as this increases the dynamic range available for measurement by an equal amount.

The dynamic range of an analyte is defined as the range of concentrations typical for that analyte in a sample. The dynamic range of the detector is defined as the ratio between the maximum detectable light at or near saturation and the lowest detectable light, which is typically limited by noise levels. The dynamic range of the baseline signal is defined as the ratio between the maximum baseline signal BL (λ max) and the minimum baseline signal BL (λ min) for a selected set of available wavelength ranges. The dynamic range available for measurement is the dynamic range that can be effectively used for detection, in other words, the available dynamic range. This is defined as the ratio between the maximum detectable change in the concentration of the analyte and the minimum detectable change in the concentration of the analyte limited by BL (λ min). Thus, the available dynamic range is the dynamic range of the detector minus the dynamic range of the baseline signal. Therefore, it is smaller than the dynamic range of the detector. The dynamic range of the analyte may thus exceed the available dynamic range for measurement, which means that the highest concentration of the analyte may not be measurable. That is why it is important to reduce the dynamic range of the baseline signal.

To be closer to the ideal state, the detector-side electronic compensation, e.g. by a preamplifier or an electronic filter, can also be combined with the compensation of the light intensity.

According to another embodiment, the at least one light adjuster is arranged in the light path for compensating the wavelength-dependent responsiveness of the detection unit at least for the selected usable wavelength in order to obtain a ratio between a first baseline signal over the first usable wavelength range and a baseline signal over the second usable wavelength range which is smaller than, preferably 50% or less of, the ratio between the responsiveness of the detection unit over the first usable wavelength range and the responsiveness of the detection unit over the second usable wavelength range.

A light modulator is an optical element that is capable of reducing the amount of light reaching a detector for a selected wavelength. The light modulator may be, for example, a filter or a barrier like a slit or a diaphragm.

The optical filter may be a patterned filter, e.g. a hybrid filter comprising a multi-band filter on a patterned filter layer, or may comprise a plurality of filters, e.g. an array or stack of filters, in order to compensate for the wavelength dependent responsivity of the detection unit at least for selected usable wavelengths for different wavelengths. This means that the light is dimmed at those wavelengths at which the responsivity of the detection unit is high, i.e. in a manner that is inversely proportional to the responsivity of the detection unit at least for the selected usable wavelengths.

At least one light modulator may be mounted on the detector, e.g. at least partially covering the sensor surface of the detector. Alternatively, the light conditioner may be coupled with the light source so as to at least partially cover the at least one light emitting element, or as part of the light path.

The at least one light source may be a broadband light source, e.g. comprising a broadband light emitting element. However, the light source may comprise a plurality of light emitting elements emitting in a narrow band or a broad band.

The optical modifier compensation may be combined with the compensation of the light intensity and/or with the electronic compensation to obtain a baseline signal for each of said selected usable wavelengths with even less variation.

The invention also relates to an analyzer for determining the presence and/or concentration of an analyte in a sample, the analyzer comprising said optical device. The analyzer according to the present invention is a device that assists the user in detecting, e.g., qualitatively and/or quantitatively optically evaluating, a sample for diagnostic purposes. Examples of such analyzers are: as a stand-alone instrument or as a module within a system comprising a plurality of modules, a clinical chemistry analyzer for detecting the results of or monitoring the progress of a chemical or biological reaction, a coagulation chemistry analyzer, an immunochemistry analyzer, a urine analyzer.

In particular, the analyzer may comprise a unit for facilitating pipetting, dosing, mixing of samples and/or reagents, a unit for loading and/or unloading and/or transporting and/or storing sample tubes or racks comprising sample tubes, a unit for loading and/or unloading and/or transporting and/or storing reagent containers or cassettes. The analyzer may also include an identification unit containing a sensor, such as a bar code reader. Alternative technologies like RFID may also be used for identification.

The pipetting unit may comprise a reusable washable needle, e.g. a steel needle, or a disposable tip. Typically, the pipetting unit is operatively coupled to an automatic positioning device for moving the pipette tip or needle relative to the analysis device, for example, may be mounted on a transport head which can be moved in two directions of travel in one plane, for example, by means of guide rails and in a third direction of travel perpendicular to the plane, for example, by means of a spindle drive.

The analyzer may further comprise a cuvette handling unit for transporting cuvettes containing samples to be analyzed, including the reaction mixture, to a detection position in the optical path of the detection unit. The cuvette handling unit may be embodied as a conveyor moving along at least one way, for example a linear or motor-like conveyor, or as a robotic arm driven by one or more electric motors, capable of translational movement along one or more possibly orthogonal axes. According to one embodiment, the test tube management unit comprises several test tube sections for simultaneously receiving and transporting at least one test tube to at least one detection unit.

According to one embodiment, the optical path may comprise a plurality of detection positions for receiving a plurality of cuvettes for parallel analysis of a plurality of samples.

According to one embodiment, the analyzer comprises a plurality of optical devices.

The analyzer may further comprise an incubation unit to maintain the sample/reagent mixture at a certain temperature during the reaction, a washing station to wash the pipette tip or needle, a stirring paddle, etc.

The analyzer preferably includes a controller that controls the automated analysis of the sample according to a predetermined process operation plan, which may be embodied, for example, as a programmable logic controller running a computer readable program having instructions for performing operations according to the process operation plan.

The present invention also relates to a method of determining the presence and/or concentration of an analyte in a sample, the method comprising the steps of:

-directing light from a light source comprising at least two light-emitting elements emitting light of different respective usable wavelength ranges to a detection unit comprising an optical path and a detector for generating a baseline signal over the respective usable wavelength ranges, the detection unit having a wavelength dependent responsivity;

-adjusting the intensity of the at least first and second light-emitting elements in inverse proportion to the wavelength dependent responsivity of the detection unit for at least a first and a second usable wavelength range, respectively, the responsivity of the detection unit being higher over said first usable wavelength range than over said second usable wavelength range, so as to obtain a ratio between a first baseline signal over the first usable wavelength range and a baseline signal over the second usable wavelength range that is smaller than, preferably 50% or less of, the ratio between the responsivity of the detection unit over the first usable wavelength range and the responsivity of the detection unit over the second usable wavelength range;

-generating a response signal relative to the baseline signal when the sample is in the optical path, and correlating the response signal with the presence and/or concentration of the analyte in the sample.

The term "relative to the baseline signal" is used herein to refer to any deviation from the baseline signal caused by the sample being analyzed, which may be above or below the baseline signal, typically below as transmission values are recorded as extinction.

According to a preferred embodiment, adjusting the intensity of the light-emitting element comprises the step of adjusting the level of the baseline signal so that the dynamic range of the detector comprises the dynamic range of the analyte concentration being determined, at least for selected available wavelengths. This means that at least for selected available wavelengths, the light intensity of the light-emitting elements emitting light at those wavelengths can be adjusted so that the baseline signal is near the saturation limit of the detector. In this way, the entire dynamic range of the detector up to the detection limit of the detector can be used to determine the concentration of the analyte without the need for final dilution of the sample even if the concentration of the analyte is too high. For example, if a detector is used, for example of the CCD or CMOS type, the dynamic range of this detector type is typically about 1000: 1. if the intensity of the light-emitting element is not so adjusted to compensate for the wavelength-dependent responsivity of the detection cell, the reliable dynamic range for determining analyte concentration over the entire available wavelength range will be reduced to 4: 1 below, this type of detector is not made available for detection with a dynamic range of 1000 because a significant portion of this dynamic range has been used up by the baseline: a change in analyte concentration of the order of 1. Thus, by compensating the wavelength dependent responsivity of the detection unit, the available dynamic range of the measurement can be maximized by almost covering the dynamic range of the detector, thus making it possible to use a detector with a smaller dynamic range, which means that a cheaper detector can be used. Of course, detectors like photodiode arrays and photomultiplier tubes can still be used, wherein the available dynamic range of measurement is even larger, thus making it possible to detect analytes over a wider concentration range without, for example, diluting the sample for high concentration samples.

According to one embodiment, adjusting the level of the baseline signal is performed depending on the type of sample or the type of analyte being determined, which means that the baseline signal can be adjusted for each available wavelength or range according to the analyte being detected and/or according to the typical expected dynamic range of the sample and/or the analyte present in the sample. For example, where low analyte concentrations or small concentration variations are expected, the baseline signal may also be moved toward the center portion of the detector's dynamic range so as to be sufficiently far from the saturation and detection limits of the detector. In other words, not only can the level of the baseline signal be adjusted so that the dynamic range of the detector encompasses the dynamic range of the analyte concentration being determined, but the baseline signal can be set at an optimal level within this range, for example, by concentrating the dynamic range of the analyte concentration relative to the center of the dynamic range of the detector for at least the selected wavelengths available.

The present invention also relates to a method of determining the presence and/or concentration of an analyte in a sample, the method comprising the steps of:

-directing light from a light source emitting in a usable wavelength range to a detection unit comprising an optical path and a detector for generating a baseline signal over said respective usable wavelength range, said detection unit having a wavelength dependent responsivity;

-compensating the wavelength dependent responsivity of the detection unit by sequentially adjusting the intensity of the light source for at least a first and a second available wavelength range, respectively, in order to obtain a ratio between a first baseline signal over the first available wavelength range and a baseline signal over the second available wavelength range which is smaller than, preferably 50% or less of, the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range;

-sequentially generating a response signal relative to said baseline signal while the sample is in the optical path and correlating said response signal with the presence and/or concentration of the analyte in the sample.

According to some embodiments, the method comprises the step of at least partially compensating the wavelength dependent responsiveness of the detection unit at least for the selected usable wavelength by placing at least one light conditioner in the light path, that is to say combining the compensation achieved by adjusting the intensity of the light source with the compensation achieved by the light conditioner.

The present invention also relates to a method of determining the presence and/or concentration of an analyte in a sample, the method comprising the steps of:

-directing light from at least one light source emitting in a usable wavelength range to a detection unit comprising an optical path and a detector for generating a baseline signal over the respective usable wavelength range, the detection unit having a wavelength dependent responsivity;

-compensating for a wavelength dependent responsivity of the detection unit over at least a first and a second available wavelength range, respectively, by placing at least one light modulator in the light path, the responsivity of the detection unit being higher over said first available wavelength range than over said second available wavelength range, so as to obtain a ratio between a first baseline signal over the first available wavelength range and a baseline signal over the second available wavelength range which is smaller than a ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range, preferably 50% or less of the ratio;

-generating a response signal relative to the baseline signal when the sample is in the optical path, and correlating the response signal with the presence and/or concentration of the analyte in the sample.

This means that the compensation achieved by adjusting the intensity of the light source and/or the compensation achieved by the light adjuster can still further be combined with electronic compensation in order to achieve even lower variation of the baseline signal.

According to a preferred embodiment, a ratio between the first baseline signal over the first usable wavelength range and the baseline signal over the second usable wavelength range is obtained which is less than 10% of the ratio between the responsiveness of the detection unit over the first usable wavelength range and the responsiveness of the detection unit over the second usable wavelength range.

Other and further objects, features and advantages of the present invention will be apparent from the following detailed description and drawings which illustrate preferred embodiments and serve to explain the principles of the invention in greater detail.

Drawings

FIG. 1 schematically depicts an optical apparatus for determining the presence and/or concentration of an analyte in a sample in an optical path according to certain embodiments of the present invention;

FIG. 2 schematically depicts an optical apparatus for determining the presence and/or concentration of an analyte in a sample in an optical path according to further embodiments of the present invention;

FIG. 3a depicts on the same graph the wavelength dependent responsivity typical of a prior art detection unit and the wavelength dependent intensity typical of a prior art broad spectrum light source simulated with a plurality of light emitting elements each emitting light in a usable wavelength range;

FIG. 3b depicts the prior art baseline signal of FIG. 3a over each of the available wavelength ranges as a function of the wavelength-dependent responsivity of the detection unit and the intensity of the light source at the respective wavelength;

FIG. 4a depicts on the same graph the wavelength dependent responsivity of the detection unit and the light intensity of each of the plurality of light emitting elements emitting light in the respective available wavelength range, wherein the intensity is adjusted in inverse proportion to the wavelength dependent responsivity of the detection unit;

FIG. 4b depicts the baseline signal of FIG. 4a over each of the available wavelength ranges;

FIG. 4c shows how the intensity of each of the plurality of light-emitting elements can be adjusted in comparison to FIG. 4a to further reduce the effects of stray light over a usable wavelength range;

FIG. 4d shows how the baseline signal obtained from the light intensity of FIG. 4c varies compared to FIG. 4 b;

FIG. 5 illustrates how to calculate a ratio between a first baseline signal over a first usable wavelength range and a baseline signal over a second usable wavelength range that is equal to 50% of a ratio between the responsivity of the detection unit over the first usable wavelength range and the responsivity of the detection unit over the second usable wavelength range;

FIG. 6a schematically illustrates a typical prior art relationship between the dynamic range of the detector, the dynamic range of the baseline, and the dynamic range of the analyte concentration; and

figure 6b schematically shows the relationship between the dynamic range of the detector, the dynamic range of the baseline and the dynamic range of the analyte concentration after reducing the dynamic range of the baseline.

Detailed Description

Fig. 1 schematically depicts an optical apparatus 100 for determining the presence and/or concentration of an analyte in a sample 10 contained in an optical cuvette 20 in the optical path 51 of a detection unit 50. The detection unit 50 includes optical path components such as a lens 52, an aperture 53, a mirror 54, a shutter 55, and a diffraction grating 65, which are configured to receive light 67 transmitted through the sample 10 and disperse it into a plurality of spectral components 68. The detection unit 50 further comprises a light detector 70, which light detector 70 comprises an array of light sensors 71, like CCD sensors, converting electromagnetic energy from the light 68 into electrical signals. The sensors 71 are divided in sectors, each sector being dedicated to one available wavelength range. Optical device 100 further comprises a light source 60, light source 60 comprising an array of light-emitting elements (in this case, LEDs 61) that emit light in different respective usable wavelength ranges, wherein the light from the LEDs is mixed by mixing rod 62 and directed through optical path 51 to detector 70 to generate a response signal indicative of the presence and/or concentration of an analyte in sample 10 relative to the baseline signal. The light source further comprises a heat shield 63 preventing heat from entering the detection unit 50, and a heat sink 64 taking away heat generated by the LED 61. The direction of the light is indicated by the arrow along the light path 51.

The light source 60 is configured such that the intensity of light emitted by each LED61 is adjusted in inverse proportion to the wavelength-dependent responsivity of the detection unit 50 at those respective wavelengths, which is dependent on both the optical components and the detector sensor 71. By this compensation a reduction of the ratio between the maximum baseline signal over one of the selected available wavelength ranges and the minimum baseline signal over the other selected available wavelength range is achieved. In other words, a reduction in baseline dynamic range is achieved.

Fig. 2 schematically depicts another optical apparatus 200 for determining the presence and/or concentration of an analyte in a sample 10 contained in an optical cuvette 20 in the optical path 51 of a detection unit 50. Since most of the features of this embodiment are the same as those of fig. 1, only the differences will be explained. In particular, the light source 60 comprises a light emitting element, in this example a halogen lamp, emitting light over a wide range of usable wavelengths. The optical device 200 further comprises a light adjuster 72 in the light path to compensate for the wavelength dependent responsiveness of the detection unit at least for a selected usable wavelength range. In this example, the light conditioner 72 is a patterned blocking filter that extends over the surface of the detector sensor 71. The light modulator 72 dims the light reaching the sensor 71 at those wavelengths where the responsivity of the detection unit 50 is high, to an extent that is inversely proportional to the responsivity of the detection unit 50 at least for the selected usable wavelength.

The effect of compensating the wavelength dependent responsivity of the detection unit 50 can best be understood by comparing fig. 3a with fig. 4a and fig. 3b with fig. 4b, respectively.

The graph of fig. 3a indicates on the left axis the intensity values of the light source in milliwatts (mW) at different wavelengths, in particular over the selected usable wavelength range (on the abscissa). The discrete emission 67 is obtained using a set of LEDs each emitting in a respective usable wavelength range, the resulting intensity spectrum being approximately equal to that emitted by a typical halogen broad-spectrum lamp used in similar applications. Referring to the right coordinate axis, where the units are amperes per watt (a/W), the wavelength dependent responsivity Rdu (λ) of a typical prior art detection unit is indicated by the curve Rdu (λ).

Fig. 3b depicts a normalized baseline signal 90, indicated in percent (%), obtained over each available wavelength range of fig. 3a, in accordance with the formula BL (λ) = S (λ) × Rdu (λ). The term "normalization" herein refers to giving the maximum baseline signal a relative value of 100%, all other baseline signals being expressed as a fraction or percentage (%) of this relative value. It can be seen that the baseline signal 92 at 340nm is only 0.3% of the baseline signal 91 (100%) at 660nm, which represent the minimum and maximum baseline signals, respectively, in this range of selected usable wavelengths. The dynamic range of the baseline is 330 in this case: 1.

when comparing fig. 4a with fig. 3a, the difference is that the intensity of the emitted light 67 of the individual LEDs 61 is adjusted in inverse proportion to the wavelength dependent responsivity Rdu (λ) of the detection unit 50.

Fig. 4b depicts a normalized baseline signal 90, indicated in percent (%), obtained over each available wavelength range of fig. 4a, in accordance with the formula BL (λ) = S (λ) × Rdu (λ). In comparison to fig. 3b, it can be seen that the same baseline signal 90 is obtained at each selected usable wavelength. The dynamic range of the baseline is now reduced to 1: 1.

fig. 4c shows for comparison the same wavelength dependent responsivity Rdu (λ) of the detection unit as shown in fig. 4a and the same intensity of the emitted light 67 of each of the plurality of light emitting elements emitting light in the respective usable wavelength range (dashed lines). Additionally, on the same graph, FIG. 4c shows, with a continuous line, an example of how the intensity of the emitted light 67 of each of the plurality of light-emitting elements can be adjusted to further reduce the effects of stray light over a useful wavelength range, in this case, at 340 nm. In particular, it can be noted that the intensity of the light-emitting element at 340nm is higher than in fig. 4a, while all other intensities are proportionally lower than in fig. 4 a.

This difference in light intensity causes a difference in the baseline signal 90 as shown in fig. 4d when compared to fig. 4 b. If the first wavelength range at 340nm is not considered, the dynamic range of the baseline is still 1: 1. if the first wavelength range is also considered, it is slightly larger, but still smaller if compared to that of fig. 3 b. Such a slight increase in the dynamic range of the one or more usable wavelength ranges is acceptable when considering the advantages of stray light reduction.

Fig. 5 depicts a normalized baseline signal 90, indicated in percent (%), obtained over each of the available wavelength ranges as in fig. 3a and 4a, according to the formula BL (λ) = S (λ) × Rdu (λ) and assuming that the intensity of the light source is constant over all wavelengths. The baseline signal thus coincides with the responsivity curve Rdu (λ) of the detection unit. It can be seen that the baseline signal 92 at 340nm is only 11% of the baseline signal 91 (100%) at 550nm, which represent the minimum and maximum baseline signals, respectively, in this range of selected available wavelengths. In this case, 11% is also the ratio between Rdu at 550nm and Rdu at 340 nm. By increasing the intensity of the light-emitting element in the range of 340nm so that the minimum baseline signal 92 becomes 22% of the maximum baseline signal at 550nm, the ratio between the maximum baseline signal and the minimum baseline signal is 50% of the ratio between the responsiveness of the detection unit at 550nm and the responsiveness of the detection unit at 340 nm.

Fig. 6a schematically depicts a typical prior art relationship between the dynamic range AC of the detector (between lines a and C), the dynamic range AB of the baseline (between lines a and B), and the dynamic range BD of the analyte concentration (between lines B and D). It can be seen that a significant portion of the dynamic range AC of the detector is used up by the baseline, thus reducing the dynamic range of the detector from AC to BC (between lines B and C). BC may also be defined as the available dynamic range, or indeed the dynamic range available for measuring analyte concentrations. If the dynamic range of analyte concentration BD exceeds the available dynamic range of the detector BC, signal saturation may occur and repeated measurements after dilution of the sample are required. In an alternative embodiment, more complex and expensive detectors with wider dynamic ranges may be used.

Fig. 6B schematically depicts the effect of reducing the dynamic range AB '(between lines a and B') of the baseline signal according to any embodiment of the invention. In particular, it can be seen that the usable dynamic range B 'C of the detector (between lines B' and C) increases accordingly. The dynamic range of the analyte concentration B 'D' (between lines B 'and D') remains the same as BD in fig. 6a, but the line has moved to be contained within the dynamic range AC of the detector, which may also remain unchanged.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically contemplated.

Claims (15)

1. An optical apparatus (100) for determining the presence and/or concentration of an analyte in a sample (10), the optical apparatus (100) comprising:

-a detection unit (50), the detection unit (50) comprising optical path components and a detector (70), the detection unit (50) having a wavelength dependent responsivity (Rdu (λ));

-a light source (60), the light source (60) comprising at least two light emitting elements (61) emitting light (67) of different respective usable wavelength ranges, wherein light from the light source (60) is directable to the detector (70) through the light path (51) so as to generate a baseline signal (90, 91, 92) over the respective usable wavelength ranges, and a response signal relative to the baseline signal (90, 91, 92) when the sample (10) is in the light path (51), the response signal being indicative of the presence and/or concentration of the analyte in the sample (10),

characterized in that the light source is configured such that the intensities (67) of at least the first and the second light-emitting element (61) are inversely proportional to the wavelength-dependent responsivity (Rdu (λ)) of the detection unit (50) over at least the first usable wavelength range (λ 1) and the second usable wavelength range (λ 2), respectively, the responsivity (Rdu (λ 1)) of the detection unit (50) being higher over the first usable wavelength range (λ 1) than over the second usable wavelength range (λ 2), whereby the single light-emitting element (61) is configured to emit light with an intensity that is higher in case the responsivity (Rdu (λ 2)) of the detection unit (50) is lower and lower in case the responsivity (Rdu (λ 1)) of the detection unit (50) is higher in case the responsivity (Rdu (λ 1)) is higher in case the intensity is lower in case the baseline signal (91) over the first usable wavelength range (λ 1) and the baseline signal (92) over the second usable wavelength range (λ 2) is such that the ratio between the baseline signal (91) over the first usable wavelength range (λ 1) and the second usable wavelength range (λ 2) is lower And is smaller than the ratio between the responsivity of the detection unit (50) over the first usable wavelength range (Rdu (λ 1)) and the responsivity of the detection unit over the second usable wavelength range (Rdu (λ 2)).

2. The optical device (100) according to claim 1, wherein the light source (60) comprises a plurality of light emitting diodes (61).

3. An optical apparatus (200) for determining the presence and/or concentration of an analyte in a sample (10), the optical apparatus (200) comprising:

-a detection unit (50), said detection unit (50) comprising optical path components and a detector (70), said detection unit having a wavelength dependent responsivity (Rdu (λ));

-at least one light source (60), the at least one light source (60) emitting light in a usable wavelength range, wherein light (67) from the light source is directable through an optical path (51) to a detector (70) for generating a baseline signal (90, 91, 92) in the usable wavelength range and a response signal relative to the baseline signal (90, 91, 92) when the sample (10) is in the optical path (51), the response signal being indicative of the presence and/or concentration of an analyte in the sample (10);

characterized in that the optical device (200) further comprises:

at least one light adjuster (72) in the light path to compensate for a wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) over at least first and second available wavelength ranges, respectively, the responsivity of the detection unit being higher over the first available wavelength range than over the second available wavelength range such that a ratio between a first baseline signal (91) over the first available wavelength range and a baseline signal (92) over the second available wavelength range is less than a ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range.

4. The optical device (200) according to claim 3, wherein the at least one light modulator (72) is a filter or a shutter.

5. The optical device (200) according to claim 3 or 4, wherein the optical filter (72) is a patterned filter, or comprises a plurality of filters of different wavelengths to compensate the wavelength dependent responsivity (Rdu (λ)) of the detection unit at least for selected usable wavelengths.

6. The optical device (100, 200) according to any one of the preceding claims, wherein the detector (70) is of the CCD or CMOS type.

7. An analyser for determining the presence and/or concentration of an analyte in a sample (10), the analyser comprising an optical device (100, 200) according to any one of claims 1 to 6.

8. A method of determining the presence and/or concentration of an analyte in a sample (10), the method comprising the steps of:

-directing light from a light source (60) comprising at least two light emitting elements (61) emitting light (67) of different respective usable wavelength ranges to a detection unit (50) comprising an optical path (51) and a detector (70) for generating a baseline signal (90, 91, 92) over said respective usable wavelength ranges, said detection unit (50) having a wavelength dependent response (Rdu (λ));

characterized in that the method further comprises the steps of:

-adjusting the intensity (67) of at least the first and the second light emitting element in such a way that it is inversely proportional to the wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) over said first usable wavelength range, respectively, the responsivity of said detection unit being higher over said first usable wavelength range than over said second usable wavelength range, thereby adjusting the emission of light with an intensity by a single light emitting element (61), said intensity being higher in case the responsivity (Rdu (λ 2)) of the detection unit (50) is lower, and said intensity being lower in case the responsivity (Rdu (λ 1)) of the detection unit (50) is higher, in order to obtain a ratio between the first baseline signal (91) over the first usable wavelength range and the baseline signal (92) over the second usable wavelength range, which is smaller than the ratio between the responsivity of the detection unit over the first usable wavelength range and the responsivity of the detection unit over the second usable wavelength range (ii) a And

-generating a response signal relative to said baseline signal (90, 91, 92) when the sample (10) is in the light path (51) and correlating said response signal with the presence and/or concentration of the analyte in the sample (10).

9. The method of claim 8, wherein adjusting the intensity (67) of the light-emitting element comprises the step of adjusting the level of the baseline signal (90) over a selected available wavelength range such that the dynamic range (AC) of the detector comprises the dynamic range (B 'D') of the analyte concentration being determined.

10. The method of claim 9, wherein adjusting the level of the baseline signal is performed depending on the type of sample (10) or the type of analyte being determined.

11. A method of determining the presence and/or concentration of an analyte in a sample (10), the method comprising the steps of:

-directing light from one light source (60) emitting in a usable wavelength range to a detection unit (50) comprising an optical path (51) and a detector (70), said light source (60) comprising at least two light emitting elements (61) emitting light (67) of different respective usable wavelength ranges for generating a baseline signal (90, 91, 92) over said respective usable wavelength ranges, said detection unit (50) having a wavelength dependent response (Rdu (λ));

characterized in that the method further comprises the steps of:

-compensating the wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) for at least the first and second available wavelength ranges, respectively, by sequentially adjusting the intensity of the light source (60) so as to obtain a ratio between a first baseline signal (91) over the first available wavelength range and a baseline signal (92) over the second available wavelength range, which ratio is smaller than the ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range; and

-sequentially generating a response signal relative to said baseline signal (90, 91, 92) when the sample (10) is in the light path (51) and correlating said response signal with the presence and/or concentration of the analyte in the sample (10).

12. Method according to any one of claims 8 to 11, comprising the step of at least partially compensating the wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) at least for the selected usable wavelength by placing at least one light modulator (72) in the optical path (51).

13. A method of determining the presence and/or concentration of an analyte in a sample (10), the method comprising the steps of:

-directing light from at least one light source (60) emitting light (67) in a usable wavelength range to a detection unit (50) comprising an optical path (51) and a detector (70), the light source (60) comprising at least two light emitting elements (61) emitting light (67) of different respective usable wavelength ranges for generating a baseline signal (90, 91, 92) over the respective usable wavelength ranges, the detection unit (50) having a wavelength dependent response (Rdu (λ));

characterized in that the method further comprises the steps of:

-compensating a wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) over at least a first and a second available wavelength range, respectively, by placing at least one light adjuster (72) in the optical path (51), the responsivity of the detection unit being higher over said first available wavelength range than over said second available wavelength range, so as to obtain a ratio between a first baseline signal (91) over the first available wavelength range and a baseline signal (92) over the second available wavelength range, which ratio is smaller than a ratio between the responsivity of the detection unit over the first available wavelength range and the responsivity of the detection unit over the second available wavelength range;

-generating a response signal relative to said baseline signal (90, 91, 92) when the sample (10) is in the light path (51) and correlating said response signal with the presence and/or concentration of the analyte in the sample (10).

14. Method according to any one of claims 8 to 13, comprising the step of at least partially compensating the wavelength dependent responsivity (Rdu (λ)) of the detection unit (50) for at least the selected available wavelength by means of a preamplifier or an electronic filter.

15. A method according to any one of claims 8 to 14, wherein a ratio between a first baseline signal (91) over a first usable wavelength range and a baseline signal (92) over a second usable wavelength range is obtained, which is 50% or less of the ratio between the responsiveness of the detection unit over the first usable wavelength range and the responsiveness of the detection unit over the second usable wavelength range.