HK1037049B - Quantum dot security and method - Google Patents

Description

Quantum dot security devices and methods

Technical Field

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

Background

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

"Quantum dot biosynthesis from Warren C.W.Chan, Shuming Nie for ultrasensitive anisotropy detection" [ science ] 281 (5385): 2016

"semiconductor nanocrystals as fluorescent biological labels" by Marcel Burchez jr., Mario monne, Peter Gin, Shimon Weiss, a. paul alivisas, science 281 (5385): 2013

L.E.Brus, applied Physics A53, 465(1991)

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)

Marcel Bruchez Jr., Mario Morone, Peter Gin, Shimon Weiss, and A.Paul alivisatos, "semiconductor nanocrystals used as fluorescent biomarkers" science 1998September 25; 281: 2013-2016.

"Quantum dot biosynthesis for ultrasensitive anisotropy detection" science 1998September 25; 281: 2016-2018.

The above publications describe methods of making quantum dots, such as nano-sized CdSe-CdS and ZnS capped CdSe crystals. This publication also describes the physical and optical properties of these quantum dots. In particular, in the article by Chan et al (publication 1) and the article by Burchez jr. et al (publication 2), quantum dots with the following fluorescence properties are described:

high fluorescence intensity, comparable to 20 molecules of rhodamine 6G;

the emission spectrum is equivalent to one third of that of a typical organic dyeing label latex ball;

compared with typical organic dyes, the light fading rate is 100 times lower;

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

the fluorescence spectrum peak value has a close correlation with the diameter of the quantum dot.

Disclosure of Invention

According to one aspect of the present invention, quantum dots can be 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 are superior to standard fluorophores in the above applications because of their controllable peak fluorescence color, unique narrow fluorescence spectrum, significantly long fluorescence lifetime, and the ability to make their fluorescence characteristics substantially independent of the environment to which they are exposed. Quantum dots of desired size, composition and structure can be used to produce the desired fluorescence, mixtures of quantum dots can be used to produce any pattern with spectrally variable fluorescence, and particular quantum dot structures can be used to provide the desired physical and optical properties.

Drawings

Fig. 1 is a schematic illustration of the inclusion of quantum dots in a plastic to mark a product.

Fig. 2 is a schematic view of a capped quantum dot showing a quantum dot having a capping layer and another layer of organic molecules that function to bind the quantum dot to additional organic molecules, or to suitable organic molecules, in the presence of light of a particular wavelength.

FIG. 3 is a plan view of a security tag having a release liner, a coating of pressure sensitive adhesive, a paper substrate layer printed with fluorescent quantum dot ink, and a transparent hologram with a "window" through which a string of characters is printed on the paper substrate layer.

FIG. 4 is a schematic view of an optical module of a holographic reader for reading a security mark in the form of a hologram and/or a fluorescent pattern having a unique emission spectrum or fluorescent lifetime, such as those of quantum dots.

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

Fig. 6 is a graph showing the difference between the fluorescence of quantum dots and the fluorescence of typical organic dyes.

FIG. 7 is a flow chart 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 communication network.

Detailed Description

According to one embodiment of the invention, the fluorescent properties of quantum dots may 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 in an eye 210 made of a suitable material, such as plastic. The eye 210 may distinguish authorized products, such as teddy bears, from unauthorized products, according to various embodiments of the present invention, as will be described below.

Applications of the 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 capping 520. The ZnSe capped CdSe quantum dots are prepared by existing methods, and the light 510 emitted by the quantum dots has unique size distribution and optical characteristics. For example, since quantum dots have a size-dependent precipitation rate, a centrifugation method may be applied to separate the quantum dots by their size. Alternatively, different conditions may be used to cause the individual batches of sub-dots to deviate from their size during growth, and then the individual batches may be selectively mixed together to prepare a mixture having a particular size distribution.

As shown in fig. 3, a batch of prepared quantum dot mixture 410 may be suspended in a clear UV-curable resin by stirring for a suitable period of time, such as four hours, to produce a fluorescent UV-curable ink 415. Many UV-curable resins and inks are commercially available from manufacturers in the united states and europe. The amount of quantum dots in the ink can be high or low. This ink is printed in a pattern on the stock with an adhesive coating and a release paper liner 420, and then cured by uv exposure. The printed paper is then die cut to produce a roll 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, for example 514 nm. This light is used to read an area on a label 690 printed by the quantum dot marking ink 415. The reader collects the emitted fluorescence 660 from the illuminated labels and analyzes their spectral and temporal characteristics. A lens system 635 focuses the fluorescent light source to a point and a diffraction grating 615 spreads the fluorescent light source into its spectrum over a linear array 625 of photodetectors. The electronic circuit analyzes the time behavior of the fluorescence by modulating the illumination light and comparing the modulation of the illumination light with the change of the emitted fluorescence due to the modulation.

The reader shown in fig. 4 may be combined with readers using other technologies, such as a magnetic stripe reader as 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. In this context, "short" is in comparison to the fluorescence lifetime. Most phosphors emit only a few nanoseconds of light after activation, but the CdSe500 quantum dots of the ZnS capping 520 are typically capable of emitting hundreds of nanoseconds of light after activation, as shown on the right side of fig. 6. The left side of fig. 6 shows the difference between quantum dot fluorescence and typical organic dye fluorescence. Another method of measuring time-resolved fluorescence is to modulate the activating light at one or more frequencies (e.g., kHz-mHz) and observe the phase relationship between the activating light modulation and the emitted fluorescent light source modulation. Both of the above methods can clearly distinguish quantum dot fluorescence from organic dye fluorescence.

By observing the stereo-extended spectrum of fluorescence, quantum dots can be distinguished from other types of fluorophores based on the bandwidth of the quantum dot fluorescence. The spectral and temporal combined analysis of fluorescence can clearly distinguish quantum dots from fluorophores that any counterfeiter might use to achieve the same fluorescence characteristics. The combination of spectral and temporal fluorescence characteristics may be referred to as a fluorescence signature.

The reader shown in fig. 4 reads the fluorescent signature of each spot in a series of small spots on the tag as the tag moves past the reader. If the quantum dots are present in such high concentrations that each spot contains a typical sample of a mixture of quantum dots, each spot will produce the same fluorescence signature that can only be replicated by replicating the mixture of quantum dots. Thus, the fluorescent signature provides evidence of the origin of the tag.

If these quantum dots are so far apart from each other that on average only one or a few quantum dots are present in each spot, each spot will have its own fluorescence signature. The series of fluorescent signatures can be measured from a series of spots throughout the label and then determined by the random location of the various quantum dots on the label and unique to each label. This series of fluorescent signatures may be referred to as a "fluorescent pattern".

Because the fluorescent pattern on each tag is unique, the fluorescent pattern on the tag can be read at the point of manufacture or application and entered into a database. These fluorescent patterns can then be read and matched to patterns in a database at the point of sale or distribution. If a pattern is detected that is not in the database, it is proof that a counterfeiter has counterfeited the method of manufacture of the quantum dot marking tag.

Instead of using a database, which may require a large communication network, the tag may additionally comprise a printed string. The string contains encrypted information representing the fluorescent pattern. The string may be generated, for example, using a fluorescent pattern as a key in a public key encryption scheme, the encryption information may identify the label printer and the date the information was encrypted and the string printed on the label. Therefore, in the selling link of the product subjected to label processing, the reader can read the fluorescent pattern and the character string, decrypt the character string and extract the encrypted information, so that the validity of the label and the product is verified.

A system for preventing and/or detecting counterfeit products using a security mark 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 communications network (not shown).

Mixtures of quantum dots can be used as markers in explosives. According to this embodiment of the invention, quantum dots having a predetermined size distribution may be added to the explosive or other substance at the manufacturing stage, thereby marking the substance 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, each with a unique small range of dot sizes, can be prepared. Each batch of dots is coated with a light-sensitive binder such as dichromic acid gel. An optical system focuses a laser beam into a very small spot, on a surface coated with a first plurality of quantum dots, approximately microns in diameter, the laser beam scanning the entire surface, turning on and off depending on the position, thereby bonding the first plurality of dots while the laser beam is on, and rinsing the surface to remove unbonded quantum dots. The surface is then coated with a second series of dots and the process is repeated with a different illumination pattern. Subsequent batches of dots and illumination patterns, each with its own unique pattern, provide further bonding of different quantum dot sizes.

Since the size of a quantum dot is typically less than 4 nanometers, a surface can accommodate 6,250,000 quantum dots per square micron or 6,250,000,000,000 dots per square centimeter. Quantum dots can be prepared at 20 or more specific sizes by precisely controlling growth time and conditions or by physical separation methods, which can yield a total storage volume of approximately 100,000,000,000,000 bits/cm compared to the current high density magnetic storage densities of approximately 50,000,000 bits/cm.

The information stored on the tag can be read using a near field scanning optical probe with a probe size comparable to one quantum dot size.

In order to mass-produce a copy of the quantum dot pattern, a main pattern can be prepared by a method of generating an original quantum dot pattern using quantum dots labeled with a DNA sequence unique to the size of the quantum dots. A replica is then prepared after the host preparation is complete by:

1. the host is filled with quantum dots coated with thiol-delimited DNA that is complementary to the DNA at the corresponding dots on the host and allows complementary DNA strand synthesis.

2. And rinsing the redundant quantum dots from the main pattern.

3. Preparing a flat glass sheet, vapor depositing a gold coating on its surface, immersing the glass sheet in a milligram molecular weight ethanol solution of 11-mercaptoundecanoic acid (MUA) for 18 hours to bond the single layer of MUA to the gold coating, adsorbing the poly-L-lysine to the single layer of MUA in the presence of NaHCO3, and adding thiosuccinimide-4- (N-maleimidomethyl) cyclohexane-1-carboxylate (SSMCC) to the single layer of MUA. The SSMCC is reacted with residual lysine to produce a surface comprising a reactive set of maleimides.

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

5. The assembly device is heated to separate the complementary DNA strands and detach the glass slide from the host. The glass sheet will bear a quantum dot pattern that is a mirror image of the host pattern.

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

RNA has similar specific binding properties as DNA, as do antibody/antigen combinations; these or any other particular combination of methods may be used in substantially the same manner.

The fluorescent inks described herein can be applied to any standard printing method, as long as they are suitable for a carrier in which the quantum dots can be suspended. One preferred printing method is ink jet printing because it allows variable information to be printed in the form of different types of quantum dots in different printed dots.

The methods described herein may be modified and adapted in various ways. For example:

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

the photosensitive binder may be selected from any of a number of known photosensitive binders;

the density of quantum dots on the label or in the substance can vary within any detectable density range; the activating light may vary between the longest wavelength and the shortest wavelength that can activate the particular quantum dot used;

the pattern of quantum dots on the label may 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 the opaque reflection hologram or in or below the transmission hologram;

quantum dots can be combined with any other optically, electromagnetically, chemically, acoustically or mechanically detectable feature to provide a further enhanced anti-counterfeiting security mechanism;

any substance or structure having adhesive properties can be used in the replication of the quantum dot pattern;

the quantum dot pattern or distribution can be read using a near-field optical scanning probe microscope, a conventional microscope, a fluorescence microscope, an epifluorescence microscope, a spectrofluorimeter, or any other device capable of distinguishing the distribution or arrangement, location or characteristics of the quantum dots in an individual or coordinated state;

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

activation may be achieved by a laser light source, incandescent lamp, metal vapor discharge light, or any other light and light source capable of activating fluorescence in quantum dots;

the photoconductivity or absorption spectrum of semiconductor quantum dots can be used to detect the presence and characteristics of quantum dots;

in the present invention, the label does not require a hologram; they may be simply printed with quantum dot inks, combinations of quantum dot inks and other inks, and may be printed on paper or other substrates containing quantum dots or coated or overlaid with layers containing quantum dots.

It is to be understood that even though various embodiments and advantages of the present invention have been set forth in the foregoing description, the foregoing disclosure is illustrative only, and changes may be made in detail, while remaining within the broad principles of the present invention. Accordingly, the invention is not to be restricted except in light of the attached claims.

Claims (25)

1. An anti-counterfeiting device comprises quantum dots applied in a predetermined pattern, the quantum dots having desired optical or physical properties in a predetermined portion of the pattern.

2. An anti-counterfeiting device comprises quantum dots applied to a surface, the quantum dots having properties within a detectable range such that the properties can vary randomly from dot to dot 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, one surface of the paper surface being overcoated with the transparent layer.

5. The anti-counterfeiting device according to claim 4, wherein the transparent layer comprises a transmission hologram hot-embossed onto the paper.

6. The anti-counterfeiting device according to claim 2, wherein the quantum dots are applied by mixing them into a liquid carrier, coating the liquid carrier on the surface, and hardening the carrier by drying or solidifying.

7. A data recording medium comprising randomly sized quantum dots arranged on a surface region, the quantum dots being selectively altered such that information is encoded according to a selection of the distribution or characteristics of the quantum dots in each region.

8. The data recording medium of claim 7, wherein the act of selectively altering the quantum dots comprises illuminating selected areas by using light having a controllable and variable wavelength to selectively alter the quantum dots.

9. A data recording medium comprising quantum dots of a desired character combined with selected regions on a surface such that information is encoded according to the selection of the distribution or character of the quantum dots in each region.

10. The data recording medium of claim 9, wherein the quantum dots are bonded to the selected regions on the surface by an optically controlled chemical process or a physically controlled bonding process.

11. An anti-counterfeiting/security system comprising:

a document with quantum dots arranged in an arrangement within a detectable range, 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 the quantum dots to a document in an arrangement within a detectable range;

means for detecting the presence and arrangement of at least a portion of the quantum dots on the document;

means for comparing the arrangement with a reference.

13. A method of labelling a substance comprising incorporating quantum dots into the substance, the quantum dots having a property profile within a predetermined detectable range, whereby the absence or change of the property profile in a sample can be detected.

14. A product made according to the method of claim 13.

15. A fluorescent ink comprising quantum dots having a desired size distribution and suspended in a dryable or settable liquid carrier.

16. The fluorescent ink of claim 15, wherein the carrier includes a UV-curable resin.

17. A product made by printing the fluorescent ink of claim 16 onto a surface.

18. A product having enhanced anti-counterfeiting capabilities, the product being made by a method that combines quantum dots with at least one other printed, embossed, marked, identified, or anti-counterfeiting feature or ingredient.

19. A label comprising quantum dots contained in a dryable or settable binder matrix liquid.

20. A phosphor coating comprising a layer of a hardenable liquid containing suspended quantum dots, which is disposed on a surface and hardened.

21. A security thread for security marking an object, comprising a thread coated with a batch of quantum dots.

22. A security tag reader, comprising:

means for illuminating a set of areas on the label;

means for detecting fluorescence emitted by quantum dots on a label, and

means for determining whether the emitted fluorescence has a characteristic that is characteristic of quantum dot fluorescence.

23. A security tag reader, comprising:

means for illuminating a small area on the label;

means for detecting fluorescence emitted by the quantum dots on the label;

means for measuring the fluorescence signature;

means for moving the reader relative to the tags such that the reader reads a plurality of locations on the tags in approximately a predetermined pattern and sequence, and

means for representing the sequence and characteristics of the fluorescence as a string of characters.

24. The security tag reader of claim 23, wherein the means for measuring the fluorescent light characteristic comprises means for measuring a fluorescent lifetime of the fluorescent light.

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.