WO2013141692A1

WO2013141692A1 - Sensors for detecting heavy metals

Info

Publication number: WO2013141692A1
Application number: PCT/MY2013/000053
Authority: WO
Inventors: Rais Ahmad MOHD; Azera Tuhaime NUR
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2012-03-21
Filing date: 2013-03-18
Publication date: 2013-09-26
Anticipated expiration: 2014-09-21
Also published as: MY155093A

Description

SENSORS FOR DETECTING HEAVY METALS

FIELD OF INVENTION

The present invention relates to an apparatus and method for detecting ions of heavy metallic element through ion recognizing molecule or ionophores without using reference electrode. BACKGROUND ART

At trace quantities heavy metals such as mercury and lead are considered fatal to human. Heavy metals in the environment get into human through food especially fish, and from drinking contaminated water. When consumed by fish in the form of contaminated food or directly taken from polluted water the heavy metals are retained in human body.

In order to protect the environment from heavy metal pollutants and to improve the quality of drinking water we propose development of miniaturized and self-powered sensor system to monitor industrial discharge and quality of water in the rivers, especially those used to supply fresh water for daily use. Lead is heavily used in the battery industry and it presumably is the main source of the polluted industrial discharge. Leakage of the liquid electrolyte in the reference electrode and contamination from analytes cause dilution of the internal reference (such as saturated chloride solution) and change in its concentration. The electromagnetic force (emf) of the reference electrode is no longer maintained at a stable potential because the reversible electrode such as silver-silver chloride electrode now "sees" changing concentrations of chloride ion. This is presumably the main cause for signal drift in potentiometric chemical sensor that originates from reference electrode.

The present invention proposes selective lead (II) ion sensor based on ionophore without using reference electrode. The lead (II) ion recognizing molecule is immobilized onto ion sensing channels sandwiched by conductive pads for electrical communication. The lead ionophore is secured on the channel with low impedance polymeric matrix such as ethyl cellulose. The baseline conductivity of the channel is adjusted by adding sufficient amount of conductive particles such as carbon nanotubes.

Ion recognizing molecules or ionophores are most widely used in ion-detecting chemical sensors to achieve selectivity on target ion. The recognizing agents are almost always neutral large molecules showing preferential binding to specific ion. In the presence of interfering ions, ionophore selectively holds on the target ion and "carries" the ions across polymeric sensing matrix. In a potentiometric measurement the sensing electrode, either an ion selective electrode (ISE) or ion sensitive field effect transistor (ISFET), is coupled to a reference electrode to measure potential difference between the two electrodes.

The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practice.

SUMMARY OF INVENTION

The present invention provides an apparatus (100) for detecting ions of heavy metallic element comprising at least one polymeric binder (102) to secure and immobilize lead (II) ion recognizing molecule onto ion sensing channels. The apparatus (100) comprising conductive filler particles (104) to reduce impedance across channel and adjust baseline of electrical conductivity; ion recognizing molecule or ionophores (106) with preferential binding to bind lead (II) ion selectively in the presence of interfering ions; and at least one channel on a substrate (108) in communication with at least two electrodes (110) to allow passage of current across channel through at least one channel on substrate (108) in communication with at least two electrodes (110).

A further aspect of the present invention provides a method (200) for detecting ions of heavy metallic element using ion recognizing molecule or ionophores with preferential binding to specific ion. The method comprising steps of securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202); reducing impedance across channel and adjusting baseline of electrical conductivity (204); binding lead (II) ion selectively in the presence of interfering ions (206); and allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes (208).

Preferably, the method for securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202) further comprises carrying selected ions across polymeric sensing matrix. Further, the method for reducing impedance across channel and adjusting baseline of electrical conductivity (204) further comprises adding conductive particles to reduce impedance across channel beyond limit of organic binder.

Preferably, the method for allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes further comprises measuring differential conductance and analyte concentration to determine response and sensitivity of sensor (302); and plotting conductance against analyte concentration to determine conductance of channel (304). The present invention consists of features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

To further clarify various aspects of some embodiments of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the accompanying drawings where: FIG. 1 illustrates lead (II) sensor without using reference electrode.

FIG. 2 is a flowchart illustrating a method for detecting ions of heavy metallic element using ion recognizing molecule or ionophores with preferential binding to specific ion. FIG. 3 is a flowchart illustrating a method for allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes.

FIG. 4 illustrates a plot of conductance versus logarithmic of lead concentration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an apparatus and a method for detecting ions of heavy metallic element comprising at least one polymeric binder to secure and immobilize lead (II) ion recognizing molecule onto ion sensing channels. Hereinafter, this specification will describe the present invention according to the preferred embodiments. It is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned without departing from the scope of the appended claims.

Reference is first being made to FIG. 1. FIG. 1 illustrates lead (II) sensor without using reference electrode. Miniaturized and self-powered sensor which is used to monitor industrial discharge and quality of water in the rivers, especially those used to supply fresh water for daily use is illustrated in FIG. 1. The present invention proposes selective lead (II) ion sensor based on ionophore without using reference electrode.

As illustrated in FIG. 1 , an apparatus (100) for detecting ions of heavy metallic element comprising at least one polymeric binder (102) to secure and immobilize lead (II) ion recognizing molecule onto ion sensing channels; conductive filler particles (104) to reduce impedance across channel and adjust baseline of electrical conductivity; ion recognizing molecule or ionophores (106) with preferential binding to bind lead (II) ion selectively in the presence of interfering ions; and at least one channel on a substrate (108) in communication with at least two electrodes (110) to allow passage of current across channel through at least one channel on substrate (108) in communication with at least two electrodes (110).

The lead (II) ion recognizing molecule or ionophores (106) is immobilized onto ion sensing channels sandwiched by conductive pads for electrical communication. The lead ionophore (106) is secured on the channel with low impedance polymeric matrix such as ethyl cellulose. Sufficient amount of conductive particles (104) such as carbon nanotubes are added to adjust the baseline conductivity of the channel.

The lead (II) sensor (100) of the present invention is field deployed in a miniaturized sensor system that automatically analyzes the trace-level of the toxicity of lead (II) ions in rivers and industrial discharge in order to transmit the data via wireless means. As illustrated in Fig. 1 , the lead (II) sensor (100) comprises multiple narrow and elongated channels filled with lead recognizing molecule (106), immobilized by low impedance polymeric binder (102). The binder preferably contains polar group and can be cured with mild heating. It is also desired that the organic binder contains cross-linkable moiety that cross links upon heat treatment. The at least one polymeric binder (102) may comprise of at least one combination of cellulose acetate, ethyl cellulose, cellulose, (methyl methacrylate-glycidyl methacrylate) copolymer, (methyl methacrylate-glycidyl methacrylate-tetrahydrofurfuryl acrylate) copolymer.

The sensing channel is sandwiched between at least two electrodes to measure the current and conductance across the channel. The said electrodes are screen printed silver on printed circuit board (PCB) substrate. The at least one channel of the sensor system may comprise of 0.5 to 8 % lead ionophore, 80 to 90% polymeric binder and 10 to 20% conductive filler, all by weight.

The baseline conductance of the channel is adjusted using conductive particles (104) which may comprise of at least one combination of platinum, silver, gold, carbon nanotubes, graphite, pyrolitic carbon, glassy carbon. The substrate (108) in communication with at least two electrodes (110) may comprise of at least one of the following materials; alumina, glass, paper, silicon dioxide, silicon nitride.

The detection limit and linear range of the lead sensor (100) can be optimized by changing the composition of the main components; lead ionophore (106), low impedance binder (102) and conductive filler (104).

The presence of trace amount of lead ion can be detected from the change in the conductivity across the channel while the presence of lead ions linearly increases the conductivity of the sensing channel.

Reference is now being made to FIG. 2 and FIG. 3 respectively. FIG. 2 is a flowchart illustrating a method for detecting ions of heavy metallic element using ion recognizing molecule or ionophores with preferential binding to specific ion and FIG. 3 is a flowchart illustrating a method for allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes. As illustrated in FIG. 2, a method (200) for detecting ions of heavy metallic element using ion recognizing molecule or ionophores with preferential binding to specific ion comprising steps of securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202). Lead (II) ion recognizing molecule is secured and immobilized onto ion sensing channels (202) wherein securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202) further comprises carrying selected ions across polymeric sensing matrix. Thereafter, impedance across channel is reduced and baseline of electrical conductivity is adjusted (204) by adding conductive particles to reduce impedance across channel beyond limit of organic binder. Lead (II) ion is selectively bound in the presence of interfering ions (206). Subsequently, passage of current across channel is allowed through at least one channel on substrate in communication with at least two electrodes (208). The passage of current across channel is allowed through at least one channel on substrate in communication with at least two electrodes (208) further comprises measuring differential conductance and analyte concentration to determine response and sensitivity of sensor (302); and plotting conductance against analyte concentration to determine conductance of channel (304).

The present invention is further described but not limited to the following example. Example 1 Preparation and Characterization of Selective Lead (II) Sensor

Lead ionophore (Fluka, 2mg), 2 mg of carbon nanotubes and 50mg of cellulose acetate are added into a 5-mL transparent glass vial with air-tight cap. Tetrahydrofuran (THF, 1 mL) is added into the vial and the mixture is sonicated for 5 minutes at 35 °C to achieve homogenous cocktail containing 4 weight percent (compared to cellulose acetate) of lead ionophore and 5% solution of cellulose acetate in THF.

Interdigitated multiple channels are defined by screen printing comb structures of silver electrodes. The distance across the channel is 1mm and the length of the channel is 3mm. The entire surface of the device is covered with screen printed solder mask or epoxy insulating materials, exposing only the contact windows to silver electrodes. The screen printed layers are oven cured at 120 °C under blanket of nitrogen gas for 30 minutes. The cocktail composition is dispensed to cover the channel windows and dried under continuous flow nitrogen gas for 30 minutes and further air dried overnight.

One of the electrodes is grounded while the other is applied with DC voltage from 0.5V to 1.5V with 0.1V increment. The current across the channel is measured at each applied voltage.

The difference in current between each step is calculated and the ratio of this value to the voltage step gives the conductance of the channel. The plot of conductance versus logarithmic of lead concentration is shown in FIG. 4. Therefore, the approach of the present invention lies in the detection of the trace amount of lead which is detected by the change of conductivity of the sensing channel wherein the selectivity towards lead ion is achieved by ionophore.

The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore indicated by the appended claims rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the claims, are to be embraced within their scope.

Claims

1. An apparatus (100) for detecting ions of heavy metallic element comprising:

at least one polymeric binder (102) to secure and immobilize lead (II) ion recognizing molecule onto ion sensing channels;

conductive filler particles (104) to reduce impedance across channel and adjust baseline of electrical conductivity;

ion recognizing molecule or ionophores (106) with preferential binding to bind lead (II) ion selectively in the presence of interfering ions; and at least one channel on a substrate (108) in communication with at least two electrodes (110) to allow passage of current across channel through at least one channel on substrate (108) in communication with at least two electrodes (110).

2. An apparatus (100) according to Claim 1 , wherein the at least one polymeric binder (102) may comprise of at least one combination of cellulose acetate, ethyl cellulose, cellulose, (methyl methacrylate-glycidyl methacrylate) copolymer, (methyl methacrylate-glycidyl methacrylate-tetrahydrofurfuryl acrylate) copolymer.

3. An apparatus (100) according to Claim 1, wherein the conductive filler particles (104) may comprise of at least one combination of platinum, silver, gold, carbon nanotubes, graphite, pyrolitic carbon, glassy carbon.

4. An apparatus (100) according to Claim 1 , wherein the at least one channel of the sensor system may comprise of 0.5 to 8 % lead ionophore, 80 to 90% polymeric binder and 10 to 20% conductive filler, all by weight.

5. An apparatus (100) according to Claim 1 , wherein the substrate (108) in communication with at least two electrodes (110) may comprise of at least one of the following materials; alumina, glass, paper, silicon dioxide, silicon nitride.

6. An apparatus according to Claim 1, is readily adapted for environmental monitoring.

7. A method (200) for detecting ions of heavy metallic element using ion recognizing molecule or ionophores with preferential binding to specific ion comprising steps of:

securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202);

reducing impedance across channel and adjusting baseline of electrical conductivity (204);

binding lead (II) ion selectively in the presence of interfering ions (206); and

allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes (208).

8. A method (200) according to Claim 13, wherein securing and immobilizing lead (II) ion recognizing molecule onto ion sensing channels (202) further comprises carrying selected ions across polymeric sensing matrix.

9. A method (200) according to Claim 13, wherein reducing impedance across channel and adjusting baseline of electrical conductivity (204) further comprises adding conductive particles to reduce impedance across channel beyond limit of organic binder.

10. A method (200) according to Claim 13, wherein allowing passage of current across channel through at least one channel on substrate in communication with at least two electrodes (208) further comprises:

measuring differential conductance and analyte concentration to determine response and sensitivity of sensor (302); and

plotting conductance against analyte concentration to determine conductance of channel (304).