CN1141680C - Quantum dot security devices and methods - Google Patents

Abstract

Quantum dots are used as fluorescent markers in security inks, paper, plastics, explosives, or any other article or substance where it is desirable to provide a unique signature or mark. Quantum dots of a particular size, composition and structure can be used to produce a particular fluorescence, mixtures of quantum dots can be used to produce random patterns of spectrally variable fluorescence, and particular quantum dot structures can be used to provide desired physical and optical properties. The quantum dots may be read by an optical reader, which may be combined with readers using other technologies.

Description

Quantum dot security device and method

technical field

The present invention relates to quantum dots, and in particular to quantum dots for security applications.

Background technique

Quantum dots, including their optical and physical properties and fabrication methods, have been described and disclosed in the following publications:

1. Warren C.W.Chan, Shuming Nie, "Quantum dot biosynthesis for ultrasensitive anisotropy detection", Science 281(5385): 2016

2. Marcel Burchez Jr., Mario Moronne, Peter Gin, Shimon Weiss, A. Paul Alivisators, "Semiconductor Nanocrystals as Fluorescent Biolabels", Science 281(5385): 2013

3.L.E.Brus, "Applied Physics" A53, 465 (1991)

4. W.L. Wilson, P.F. Szajowski, L.E. Brus, Science 262, 1242

(1993) 5. A. Henglein, Chem. Rev. 89, 1861 (1989)

6. H. Weller, Angew. Chem. Int. Ed. Engl. 32, 41 (1993)

7. M.A. Hines and P. Guyot-Sionnest, J. Phys. Chem. 100, 468 (1996)

8.B.O.Dabbousi, et al., J.Phys.Chem.B101, 9463 (1997)

9. C.B. Murray, D.J. Norris, M.G. Bawendi, J.Am.Chem.Soc.115, 8706 (1993)

10. X.G. Peng, J. Wickham, A.P. Alivasatos, J. Am. Chem. Soc. 120, 5343 (1998)

11. L.M. Lizmarzan, M. Giersig, P. Mulvaney, Langmuir 12, 4329 (1996)

12. M.A.CorreaDuarte, M.Giersig, L.M.LizMarzan, Chem.Phys.Lett.286, 497 (1998)

13. Marcel Bruchez Jr., Mario Moronne, Peter Gin, Shimon Weiss, and A. Paul alivisatos, "Semiconductor Nanocrystals as Fluorescent Biolabels," Science 1998 September 25; 281: 2013-2016.

14. Warren C.W.Chan and Shuming Nie, "Quantum dot biosynthesis for ultrasensitive anisotropy detection," Science 1998 September 25; 281: 2016-2018.

The aforementioned publications describe methods for fabricating quantum dots, such as CdSe-CdS and ZnS-covered CdSe crystals at the nanometer scale. The publication also describes the physical and optical properties of these quantum dots. In particular, in the articles by Chan et al. (Publication 1) and in the article by Burchez Jr. et al. (Publication 2), quantum dots with the following fluorescent properties are described:

High fluorescence intensity, comparable to Rhodamine 6G with 20 molecules;

The emission spectrum is equivalent to one-third of a typical organic dyed label latex ball;

Compared with typical organic dyes, its light fading rate is 100 times lower;

Long fluorescence lifetime, on the order of hundreds of nanoseconds;

There is a close correlation between the peak fluorescence spectrum and the diameter of quantum dots.

Contents of the invention

According to one aspect of the invention, quantum dots can be used as fluorescent markers in security inks, paper, plastics, explosives or any other item or substance that needs to provide a unique signature or mark. Because quantum dots have the characteristics of controllable fluorescence peak color, unique narrow fluorescence spectrum, remarkable long fluorescence lifetime, and the ability to make their fluorescence characteristics basically independent of the environment they are in contact with, so quantum dots are used in the above applications Outperforms standard fluorophores. Quantum dots of desired size, composition and structure can be used to generate desired fluorescence, mixtures of quantum dots can be used to generate arbitrary patterns with spectrally variable fluorescence, and special quantum dot structures can be used to provide desired physical and optical properties.

Description of drawings

Figure 1 is a schematic diagram of the inclusion of quantum dots in a plastic to mark products.

Figure 2 is a schematic diagram of a capped quantum dot, showing that a quantum dot has a capping layer and another layer of organic molecules. The organic molecules are combined together, or combined with suitable organic molecules.

Figure 3 is a plan view of a security label with a peel-off liner, a pressure-sensitive adhesive coating, a paper substrate printed with fluorescent quantum dot ink, and a transparent A hologram of the "window" through which strings are printed on the paper base layer.

Figure 4 is a schematic diagram of the optical module of a holographic reader for reading security markings in the form of holograms and/or fluorescent patterns with unique emission spectra or fluorescence lifetimes, such as those characteristic of quantum dots.

Figure 5 is a perspective view of a combined reader for reading a hologram and fluorescent quantum dots on a printed card.

Figure 6 is a graph showing the difference between quantum dot fluorescence and that of typical organic dyes.

7 is a flow diagram of a system for preventing and/or detecting counterfeit products via a security indicia reader, a string printer, a string and security indicia reader, and a communications network.

Detailed ways

According to one embodiment of the invention, the fluorescent properties of quantum dots can be used to provide a method of storing information on a surface or in a substance, thereby distinguishing valid products or documents from invalid products or documents. For example, as shown in FIG. 1, quantum dots 200 are contained within an eye 210 made of a suitable material, such as plastic. According to various embodiments of the invention as will be described below, the eye 210 can distinguish authorized products, such as teddy bears, from unauthorized products.

Applications of quantum dots according to various embodiments of the present invention will be described in the following examples. As shown in FIG. 2 , a quantum dot marking UV-curable ink for anti-counterfeiting/security applications can be fabricated using CdSe quantum dots 500 surrounded by ZnSe as a cap 520 . The ZnSe-capped CdSe quantum dots are prepared by existing methods, and the light 510 emitted by the quantum dots has a unique size distribution and optical properties. For example, since quantum dots have a size-dependent precipitation rate, centrifugation can be applied to separate quantum dots by their size. Alternatively, different conditions can be used to cause the batches of subdots to deviate from their size during growth, and then the batches of subdots can be selectively mixed together to prepare a mixture with a particular size distribution.

As shown in FIG. 3, a batch of prepared quantum dot mixture 410 can be suspended in a transparent UV-curable resin by stirring for an appropriate time, such as four hours, to make a fluorescent UV-curable resin. Freezing Ink 415. Many UV-curable resins and inks are commercially available from manufacturers in the US and Europe. The amount of quantum dots in the ink can be high or low. This ink is printed in a pattern on paper stock with an adhesive coating and a release paper liner 420 and then cured by exposure to UV light. The printed paper is then die cut to make rolls of self-adhesive labels 435 .

The tag 435 can be read by a reader, as shown in FIG. 4 . The reader includes an optical system that illuminates a selected area of the label with light of an appropriate wavelength, such as 514nm light. The light is used to read an area on the label 690 printed with quantum dot marking ink 415 . The reader collects the emitted fluorescent light 660 from the illuminated tag and analyzes its spectral and temporal characteristics. A lens system 635 focuses the fluorescent light source to a point and a diffraction grating 615 expands the fluorescent light source to its spectrum across a linear array 625 of photodetectors. The electronic circuit analyzes the temporal behavior of the fluorescent light by modulating the illuminating light and comparing the modulation of the illuminating light with the changes in the emitted fluorescent light due to the modulation.

The reader shown in FIG. 4 may be combined with readers using other technologies, such as the magnetic stripe reader shown in FIG. 5 .

Time-resolved fluorescence can be measured by applying a short pulse of activating light to a sample and observing the intensity of the emitted fluorescence over a period of hundreds of nanoseconds. Herein, "short" is compared with the fluorescence lifetime. Most phosphors only emit light for a few nanoseconds after activation, but CdSe500 quantum dots with ZnS capping 520 typically emit light for hundreds of nanoseconds after activation, as shown on the right side of Figure 6. The left side of Figure 6 shows the difference between quantum dot fluorescence and typical organic dye fluorescence. Another method of measuring time-resolved fluorescence is to modulate the activation light at one or more frequencies (eg, kHz-mHz) and observe the phase relationship between the modulation of the activation light and the modulation of the emitted fluorescent light source. Both of the above methods can clearly distinguish quantum dot fluorescence from organic dye fluorescence.

By observing the stereoscopically extended spectrum of fluorescence, the quantum dots can be distinguished from other kinds of fluorophores according to the bandwidth of the quantum dot fluorescence. The combined spectral and temporal analysis of the fluorescence clearly distinguishes the quantum dots from any other fluorophore that a counterfeiter might use to achieve the same fluorescent properties. The combination of spectral and temporal fluorescence properties can be referred to as a fluorescence signature.

The reader shown in Figure 4 reads the fluorescent signature of each spot in a series of small spots on the label as the label moves past the reader. If the quantum dots are present in such a high concentration that each spot contains a typical sample of the quantum dot mixture, each spot will produce the same fluorescent signature, which can only be reproduced by replicating the quantum dot mixture. Therefore, this fluorescent signature provides evidence of label origin.

If the quantum dots are separated so far apart that on average only one or a few quantum dots are present in each spot, each spot will have its own fluorescent signature. This series of fluorescent signatures is measured from a series of spots across the tag, then determined by the random placement of the various quantum dots on the tag, and is unique to each tag. This series of fluorescent signatures can be called "fluorescent pattern".

Because the fluorescent pattern on each label is unique, the fluorescent pattern on the label can be read during manufacturing or application and entered into a database. Then at the point of sale or distribution, these fluorescent patterns can be read and matched to patterns in a database. If a pattern is detected that is not in the database, it is evidence that a counterfeiter has counterfeited the manufacturing method of the quantum dot-marked tags.

Instead of using a database as it may require a large communication network, the label may additionally include a printed string. The string contains encrypted information representing the fluorescent pattern. For example in a public key encryption scheme using the fluorescent pattern as a key to generate the string, the encrypted information can identify the label printer and the date the information was encrypted and the string was printed on the label. Therefore, in the sales process of tagged products, the reader can read both the fluorescent pattern and the string, decrypt the string, and extract the encrypted information to verify the validity of the label and the product .

A system for preventing and/or detecting counterfeit products using a security tag reader is shown in FIG. 7 . The system includes the use of a string printer (not shown), a string and security tag reader (not shown), and a communication network (not shown).

Mixtures of quantum dots could be used as markers in explosives. According to this embodiment of the invention, quantum dots having a predetermined size distribution can be added to explosives or other substances during the manufacturing stage, thereby marking these substances according to the time and/or place of manufacture.

According to another embodiment of the invention, quantum dots may be disposed on a surface to provide information storage. In particular batches of quantum dots can be prepared, each batch having a unique small range of dot sizes. Each batch of dots is coated with a photosensitive adhesive such as dichromate gel. An optical system focuses a laser beam onto a surface coated with the first batch of quantum dots into very small spots, approximately a micron in diameter, which scans the entire surface, switching on and off according to position, so that While the beam is on, the first dots are bonded, and the surface is rinsed to remove unbonded quantum dots. The surface is then painted with a second batch of dots, repeating the process with a different pattern of illumination. Subsequent batches of dots and irradiation patterns provided further bonding of different quantum dot sizes, each with its own unique pattern.

Because the size of a quantum dot is generally less than 4 nanometers, a surface can accommodate 6,250,000 quantum dots/square micron or 6,250,000,000,000 dots/square centimeter. Quantum dots can be prepared in 20 or more specific sizes by precise control of growth time and conditions or by physical separation methods, yielding approximately 100,000,000,000,000 bits/cm2 compared to current high-density magnetic storage densities of approximately 50,000,000 bits/cm2 of total storage.

Using a near-field scanning optical probe with a probe size comparable to that of a quantum dot, the information stored on the tag can be read.

To mass-produce replicas of a quantum dot pattern, a master pattern can be prepared by using quantum dots labeled with a DNA sequence unique to the size of the quantum dot to generate the original quantum dot pattern. Then prepare a replica after the master pattern is prepared by following these steps:

1. Filling the master pattern with quantum dots coated with thiol-delimited DNA that is complementary to the DNA on the corresponding spot on the master pattern and allowing synthesis of complementary DNA strands.

2. Rinse off excess quantum dots from the main pattern.

3. prepare a piece of flat glass sheet, vapor deposition a gold coating on its surface, this glass sheet is immersed in the ethanol solution of 11-hydrogen mercaptoundecanoic acid (MUA) of a milligram molecular weight and soaks 18 hours, so that A monolayer of MUA was combined with a gold coating, then, in the presence of NaHCO3, polybasic L-lysine was adsorbed to the monolayer of MUA, and then, thiosuccinimide-4-(N -maleimidomethyl)cycloethane-1-carboxylate (SSMCC) to the monolayer MUA. The SSMCC reacts with residual lysine to generate a surface comprising reactive maleimide groups.

4. Pressing the treated gold surface of the glass slide against the master pattern, thereby bringing a portion of the thiol-delimited DNA on each quantum dot into contact with the reactive maleimide group. The master pattern and glass slide were pressed together for 12 hours to allow the thiol-delimited DNA to react with the maleimide group and bind together.

5. Heat the assembly to separate the complementary DNA strands and detach the glass sheet from the master pattern. The glass sheet will then bear a pattern of quantum dots, which is a mirror image of the master pattern.

The replica contains the same (or corresponding) quantum dots in the same pattern as the master pattern. Through the same steps, multiple replicas can be made from a master pattern, and replicas can be made from replicas, so that a large number of replicas can be produced from a single master pattern.

RNA has specific binding properties similar to DNA, as do antibody/antigen combinations; these or any other specific binding methods can be used in essentially the same way.

The fluorescent inks described here can be applied to any standard printing method as long as it is suitable for the carrier in which the quantum dots can be suspended. A preferred printing method is inkjet printing because it can print variable information in the form of different types of quantum dots in different printing spots.

The methods described here can be modified and adapted in various ways. For example:

The composition and structure of quantum dots, such as the choice of materials, and the presence or absence of different material layers, can be changed to produce different absorption and fluorescence properties;

The photosensitive adhesive can be selected from any of the many known photosensitive adhesives;

The density of quantum dots on the label or in the substance can be varied over any range of detectable densities; the activation light can be varied between the longest and shortest wavelengths that activate the particular quantum dots used;

The pattern of quantum dots on the label can be predetermined, periodic, quasi-periodic or random;

Any device capable of detecting fluorescence spectra and/or time-resolved fluorescence of quantum dots can be used;

Any fluorescent ink, particle, fiber or other structure or substance can be used in opaque reflection holograms or in or under transmission holograms;

Quantum dots can be combined with any other optically, electromagnetically, chemically, acoustically or mechanically detectable signature to provide further enhanced anti-counterfeiting security mechanisms;

Any substance or structure with adhesive properties can be used in the replication process of the quantum dot pattern;

A near-field optical scanning probe microscope, a conventional microscope, a fluorescence microscope, an epifluorescence microscope, a spectrofluorometer, or any other method that enables the distribution or arrangement, position, or Characteristically differentiated devices to read quantum dot patterns or distributions;

Time-resolved fluorescence can be detected using activation of simple pulses, square wave pulses, sinusoidally modulated light, or adaptively modulated light;

Activation can be achieved by laser light source, incandescent lamp, metal vapor discharge light, or any other light and light source that can activate the fluorescence in quantum dots;

Photoconductivity or absorption spectra of semiconductor quantum dots can be used to detect the presence and properties of quantum dots;

In the present invention, the labels do not require holograms; they can be simply printed using quantum dot inks, combinations of quantum dot inks and other inks, and can be printed on paper or other quantum dot-containing or layered with quantum dots. coated or covered substrates.

It should be understood that, even though various embodiments and advantages of the invention have been given in the above description, the above disclosure is illustrative only and changes may be made in detail while remaining within the broad principles of the invention. . Accordingly, the invention is limited only by the appended claims.

Claims (25)

CLAIMS 1. An anti-counterfeiting device comprising quantum dots applied in a predetermined pattern, in predetermined portions of the pattern, the quantum dots have desired optical or physical properties. 2. An anti-counterfeiting device comprising quantum dots applied to a surface, the quantum dots having properties in a detectable range such that these properties vary randomly from point to point on the surface. 3. The anti-counterfeiting device according to claim 2, wherein the quantum dots are arranged in clusters. 4. The anti-counterfeiting device according to claim 2, wherein the surface comprises a paper surface having a surface overcoated with a transparent layer. 5. An anti-counterfeiting device according to claim 4, wherein the transparent layer comprises a transmission hologram thermally embossed onto paper. 6. The anti-counterfeiting device according to claim 2, wherein the quantum dots are mixed into a liquid carrier, and then the liquid carrier is applied on the surface, and the carrier is hardened by drying or solidification, and to be applied. 7. A data recording medium comprising randomly sized quantum dots arranged on a surface area, the quantum dots being selectively altered such that information is encoded according to the selection of distribution or properties of the quantum dots in each area. 8. The data recording medium of claim 7, wherein selectively altering the behavior of the quantum dots comprises selectively altering the quantum dots by illuminating selected areas with light having a controllable and variable wavelength. 9. A data-recording medium comprising quantum dots of a desired characteristic combined with selected regions on a surface such that information is encoded according to the distribution or selection of the characteristics of the quantum dots in each region. 10. A data recording medium according to claim 9, wherein the quantum dots are bonded to selected areas on the surface by optically controlled chemical means or physically controlled adhesive means. 11. An anti-counterfeiting/security system comprising: a document with quantum dots arranged in a detectable range arrangement, and A reader adapted to detect the presence and arrangement of at least a portion of the quantum dots on the document. 12. An anti-counterfeiting/security system comprising: means for applying quantum dots to a document in a detectable arrangement; means for detecting the presence and arrangement of at least a portion of the quantum dots on the document; A means of comparing the arrangement with a reference. 13. A method of labeling a substance comprising incorporating quantum dots in the substance, the quantum dots having a property distribution within a predetermined detectable range, whereby the absence or change of the property distribution in a sample can be detected. 14. A product produced by the method of claim 13. 15. A fluorescent ink comprising quantum dots having a desired size distribution suspended in a dryable or solidifiable liquid carrier. 16. The fluorescent ink according to claim 15, wherein the carrier comprises a UV-curable resin. 17. A product produced by printing the fluorescent ink of claim 16 on a surface. 18. A product with enhanced counterfeit resistance manufactured by combining quantum dots with at least one other printing, embossing, marking, marking, or anti-counterfeiting feature or composition. 19. A marker comprising quantum dots contained in a dryable or settable adhesive matrix liquid. 20. A fluorescent coating comprising a layer of hardenable liquid containing suspended quantum dots disposed on a surface and hardened. 21. A security thread for securely marking an object comprising a thread coated with a collection of quantum dots. 22. A security tag reader comprising: means for illuminating a group of areas on the label; means for detecting the fluorescence emitted by the quantum dots on the label, and A device for determining whether emitted fluorescence has characteristics characteristic of quantum dot fluorescence. 23. A security tag reader comprising: A device for illuminating a small area on the label; means for detecting the fluorescence emitted by the quantum dots on the label; means for measuring the fluorescent characteristic; means for moving the reader relative to the tag such that the reader reads a plurality of locations on the tag in approximately a predetermined pattern and sequence, and Means for representing the order and characteristics of this fluorescence as a string. 24. The security tag reader of claim 23, wherein the means for measuring the characteristic of the fluorescence comprises means for measuring the fluorescence lifetime of the fluorescence. 25. The security tag reader of claim 23, wherein the means for measuring the fluorescent characteristic comprises means for measuring a fluorescence spectrum of the fluorescence.

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