U.S. patent application number 13/635559 was filed with the patent office on 2013-01-10 for wavelength selective sers nanotags.
This patent application is currently assigned to CABOT SECURITY MATERIALS, INC.. Invention is credited to William E. Doering, Richard G. Freeman, Michael J. Natan, Marcelo E. Piotti.
Application Number | 20130009119 13/635559 |
Document ID | / |
Family ID | 44673572 |
Filed Date | 2013-01-10 |
United States Patent
Application |
20130009119 |
Kind Code |
A1 |
Natan; Michael J. ; et
al. |
January 10, 2013 |
WAVELENGTH SELECTIVE SERS NANOTAGS
Abstract
Wavelength selective particles such as SERS nanotags modified
for wavelength selectivity. As used herein, a wavelength selective
particle is one which cannot be effectively excited or interrogated
at one or more wavelengths where a reporter molecule associated
with the particle would normally produce a spectrum. Also disclosed
are methods of manufacturing wavelength selective particles and
methods of tagging materials or objects with wavelength selective
particles.
Inventors: |
Natan; Michael J.; (Los
Altos, CA) ; Freeman; Richard G.; (Mountain View,
CA) ; Doering; William E.; (Santa Clara, CA) ;
Piotti; Marcelo E.; (Fremont, CA) |
Assignee: |
CABOT SECURITY MATERIALS,
INC.
Mountain View
CA
|
Family ID: |
44673572 |
Appl. No.: |
13/635559 |
Filed: |
March 22, 2011 |
PCT Filed: |
March 22, 2011 |
PCT NO: |
PCT/US11/29395 |
371 Date: |
September 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61316284 |
Mar 22, 2010 |
|
|
|
Current U.S.
Class: |
252/582 ;
427/162 |
Current CPC
Class: |
G01N 2201/06113
20130101; H01S 3/30 20130101; Y10S 977/834 20130101; B82Y 20/00
20130101; G01N 21/658 20130101; B82Y 30/00 20130101; Y10S 977/81
20130101 |
Class at
Publication: |
252/582 ;
427/162 |
International
Class: |
G02B 5/20 20060101
G02B005/20; B05D 5/06 20060101 B05D005/06 |
Claims
1. A wavelength selective SERS nanotag comprising: a SERS enhancing
core; a SERS active reporter molecule associated with the core; an
encapsulant encapsulating the core and reporter association; and a
blocking material associated with the encapsulant that wholly or
partially blocks the passage of light energy at a selected
wavelength to the reporter molecule, or wholly or partially blocks
the radiation of light energy at a selected wavelength from the
reporter molecule.
2. The wavelength selective SERS nanotag of claim 1 wherein the
blocking material comprises a nanorod associated with the
encapsulant.
3. The wavelength selective SERS nanotag of claim 2 wherein the
nanorod is an Au nanorod.
4. The wavelength selective SERS nanotag of claim 2 wherein the
nanorod is electrostaticly associated with the encapsulant.
5. The wavelength selective SERS nanotag of claim 4 further
comprising a charged polymer associated with the nanorod; and an
oppositely charged polymer associated with the SERS nanotag.
6. The wavelength selective SERS nanotag of claim 1 wherein the
blocking material is a dye.
7. The wavelength selective SERS nanotag of claim 6 wherein the
encapsulant comprises a mesoporous surface.
8. The wavelength selective SERS nanotag of claim 6 wherein the
blocking material is a fluorescent dye.
9. A wavelength selective SERS nanotag comprising: a SERS enhancing
core; a SERS active reporter molecule associated with the core; an
encapsulant encapsulating the core and reporter association; and a
masking material associated with the encapsulant that wholly or
partially masks light energy radiated at a selected wavelength from
the reporter molecule.
10. A method of manufacturing a wavelength selective SERS nanotag
comprising: providing a SERS enhancing core; associating a SERS
active reporter molecule with the core; encapsulating the core and
reporter association with an encapsulant; and associating a
blocking material with the encapsulant that wholly or partially
blocks the passage of light energy at a selected wavelength to the
reporter molecule, or wholly or partially blocks the passage of
light energy at a selected wavelength radiated from the reporter
molecule.
11. A method of manufacturing a wavelength selective SERS nanotag
comprising: providing a SERS enhancing core; associating a SERS
active reporter molecule with the core; encapsulating the core and
reporter association with an encapsulant; and associating a masking
material with the encapsulant that wholly or partially masks light
energy radiated at a selected wavelength from the reporter
molecule.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a 371 national phase application of
PCT/US2011/029395, filed on Mar. 22, 2011, which claims priority to
U.S. Provisional Patent Application No. 61/316,284, filed on Mar.
22, 2010, both hereby incorporated by reference in their
entirely.
BACKGROUND
[0002] SERS nanotags have proved useful for marking objects for
identification and tracking. SERS nanotags are nanoparticulate
optical detection tags which function through surface enhanced
Raman scattering (SERS). SERS is a laser-based optical spectroscopy
that, for molecules or other materials, generates a
fingerprint-like vibrational spectrum with features that are much
narrower than typical fluorescence.
[0003] Typically, a SERS active molecule associated with a tag is
excited by laser light at a specific excitation wavelength. Many
SERS active molecules can be excited at several alternative
wavelengths with each wavelength causing the emission of a
characteristic SERS spectrum. In some marking uses the ability of a
known SERS nanotag to be interrogated at multiple suitable
interrogation wavelengths is an advantage. In other
implementations, such as covert item marking, the ability to excite
a SERS nanotag at multiple wavelengths is potentially a
disadvantage, since this makes covert tags easier to detect by
third parties. It is difficult however to manufacture a SERS
nanotag that can be interrogated at a limited number of otherwise
suitable wavelengths with conventional SERS reporter molecules.
[0004] The embodiments disclosed herein are directed toward
overcoming these or other problems associated with known surface
enhanced spectroscopy particles.
SUMMARY OF THE EMBODIMENTS
[0005] Selected embodiments include wavelength selective particles
such as SERS nanotags modified as described. As used herein, a
wavelength selective particle is one which cannot be effectively
excited or interrogated at one or more wavelengths where a reporter
molecule associated with the particle would normally produce a SERS
spectrum. For example, a wavelength selective SERS nanotag might be
SERS active when using a 1064 nm excitation wavelength but inactive
at 785 nm, where activity at 785 nm would otherwise be expected
based upon the reporter molecule present in the SERS nanotag or the
plasmonic properties of the metal nanoparticle.
[0006] One embodiment of SERS nanotag which is wavelength selective
includes a SERS enhancing core and a SERS active reporter molecule
associated with the core. The wavelength selective SERS tag also
includes an encapsulant surrounding the core/reporter association.
Wavelength selectivity may be imparted by a blocking material
associated with the encapsulant which fully or partially blocks the
passage of light energy at a specific wavelength to the reporter
molecule and plasmonic particle. Alternatively, the blocking
material could wholly or partially block the radiation of light
energy at a selected wavelength from the reporter molecule or
plasmonic particle.
[0007] The blocking material could be a nanorod, for example, a
gold nanorod associated with the encapsulant. Alternatively, the
blocking material could be a molecule of any type which serves to
selectively block a relevant wavelength. For example, the blocking
material could be an organic or inorganic dye or a quantum dot
particle. Alternatively, the blocking material could be a metal
oxide, metal sulfide, metal nitride, or other similar material.
[0008] In embodiments where the blocking material is a nanorod, the
nanorod may be electrostaticly associated with the encapsulant. For
example, the nanorod may be coated with a charged polymer and the
SERS nanotag coated with an oppositely charged polymer.
Alternatively, the nanorod may be covalent attached to the
encapsulant.
[0009] In embodiments where the blocking material is a molecule
such as a dye, an increased quantity of blocking material may be
associated with the encapsulant by forming the encapsulant as a
porous or mesoporous surface.
[0010] An alternative embodiment includes a SERS nanotag as
described above with a masking material associated with the
encapsulant. A masking material will wholly or partially mask light
energy emitted at a given wavelength by the reporter molecule. In a
masking embodiment, the reporter associated with the SERS nanotag
will still emit a Raman spectrum when excited but the emission is
masked or otherwise made undetectable. For example, a fluorescent
molecule associated with the SERS nanotag may be selected to
fluoresce at a particular wavelength, thus masking the SERS
spectrum at that wavelength.
[0011] Alternative embodiments include methods of manufacturing a
wavelength selective SERS nanotag as described above. Alternative
methods also include using a wavelength selective SERS nanotag to
mark or tag an item, substance, document or article, such that the
tag may be detected at fewer interrogation frequencies than would
be expected based upon the nature of the reporter molecule used
with the SERS nanotag.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a graphic representation of the SERS activity and
absorbance of the mixture of SERS nanotags and Au nanorods of
Example 1.
[0013] FIG. 2 is a composite of multiple TEM images of the
particles of Example 2 featuring Au nanorods electrostaticly
associated with SERS nanotags.
[0014] FIG. 3 is a graphic representation of UV-visible light
extinction characteristics and normalized SERS responses at
selected wavelengths of the particles of Example 2.
[0015] FIG. 4 is a composite of multiple SEM images of the
particles of Example 3.
[0016] FIG. 5 is a graphic representation of UV-visible light
extinction characteristics and SERS activity at selected
wavelengths for the particles of Example 3.
[0017] FIG. 6 is a graphic representation of the SERS activity of
the particles of Example 4.
[0018] FIG. 7 is a SEM image of the particles of Example 4.
[0019] FIG. 8 is a graphic representation of SERS activity of the
particles of Example 5.
[0020] FIG. 9 is a graphic representation of SERS activity at
selected wavelengths for the particles of Example 6.
[0021] FIG. 10 is an SEM image of SERS nanotags featuring a
mesoporous silica encapsulant as described in Example 7.
[0022] FIG. 11 is a graphic representation of the Ramen spectra at
selected wavelengths of SERS nanotags after mixture with a
fluorescent masking agent as Described in Example 8.
DETAILED DESCRIPTION
[0023] The embodiments disclosed herein relate to particles that
are spectroscopically active. In particular, the disclosed
particles and methods are surface-enhanced spectroscopy (SES)
active. Representative SES techniques include but are not limited
to SERS, SERRS and others. Surface enhancement in various other
spectroscopy methods or systems has been observed. The most widely
studied have been surface-enhanced Raman scattering and
surface-enhanced fluorescence (SEF). But a variety of other surface
enhanced phenomena have been observed including surface-enhanced
hyper Raman scattering (SEHRS), surface-enhanced hyper Raman
resonance scattering (SEHRRS), surface-enhanced Rayleigh
scattering, surface-enhanced second harmonic generation (SHG),
surface-enhanced infrared absorption reflectance (SEIRA), and
surface-enhanced laser desorption ionization (SELDI). These are
part of a wider field known as plasmon enhancement or
plasmon-enhanced spectroscopy, which in addition to the phenomena
mentioned above includes surface plasmon enhanced emission (such as
SPASERS--surface plasmon amplification of spontaneous emission of
radiation), plasmon enhanced diffraction, and plasmon enhanced
optical transmission. Plasmon enhancement is also a method to
increase the efficiency of solar cells. As used throughout this
disclosure SES includes the above listed and any related or similar
spectroscopic technique.
[0024] Many of the examples herein are described with respect to
SERS. It must be noted however that the methods, compositions and
particles disclosed herein are equally applicable to SERRS, SEHRS,
SEF, SEHRRS, SHG, SEIRA, SPASERS, or other surface enhanced or
plasmon enhanced SES technique.
[0025] In general, taggants are materials, substances, molecules,
ions, polymers, nanoparticles, microparticles, or other matter,
incorporated into, onto or otherwise associated with objects for
the purposes of identification or quantitation. More specifically,
taggants are used in activities and products including but not
limited to detection, analysis, and/or quantification measurements
related to brand security, brand protection, trademark protection,
product security, product identification, brand diversion,
bar-coding, grey market remediation, friend-or-foe analysis,
product life cycle analysis, counterfeiting, anti-counterfeiting,
forensic analysis of authenticity, authentication, biometrics,
object tracking, chain-of-custody analysis, product tampering,
anti-smuggling, smuggling detection, supply-chain tracking, product
tracking, lost revenue recovery, product serialization, serialized
authentication, freshness tracking, sell-by date tracking, use-by
date tracking, and standoff detection/identification.
[0026] Taggants can be added to all forms of matter, including but
not limited to solids, liquids, gases, gels, foams, semi-solids,
glasses, plasmas, liquid crystals, amorphous and
magnetically-ordered solids, superconductors, superfluids,
Bose-Einstein condensates, and supersolids.
[0027] Many known methods of detecting taggants utilize one of
several spectroscopic techniques, for example a surface-enhanced
spectroscopy (SES) techniques such as SERS or SERRS. Broadly
speaking, suitable materials fall in two categories:
nano/microscale and macroscopic. For example, certain sizes and
shapes of Ag and Au nanoparticles, and aggregates thereof, are
known to support SERS. Likewise, a large variety of macroscopic
SERS substrates have been described in the literature, including
electrodes, evaporated films, Langmuir-Blodgett films,
2-dimensional planar arrays, and so forth.
[0028] Known prior art tagging methods which utilize SERS-active
tags typically include a reporter molecule or dye with known
SERS-active characteristics. For example, a known SERS-active
chemical can be added as a dye to mark fuel and a subsequent SERS
spectrum obtained when the SERS-active dye is associated with a
SERS-active metal particle or substrate. Only a limited number of
SERS active chemicals are known.
[0029] Many of the embodiments disclosed herein feature the use of
a surface-enhanced spectroscopy (SES) active taggant. The most
widely studied have been surface-enhanced Raman scattering and
surface-enhanced fluorescence (SEF). But a variety of other surface
enhanced phenomena have been observed including surface-enhanced
hyper Raman scattering (SEHRS), surface-enhanced hyper Raman
resonance scattering (SEHRRS), surface-enhanced Rayleigh
scattering, surface-enhanced second harmonic generation (SHG),
surface-enhanced infrared absorption reflectance (SEIRA), and
surface-enhanced laser desorption ionization (SELDI). These are
part of a wider field known as plasmon enhancement or
plasmon-enhanced spectroscopy, which in addition to the phenomena
mentioned above includes surface plasmon enhanced emission (such as
SPASERS--surface plasmon amplification of spontaneous emission of
radiation), plasmon enhanced diffraction, and plasmon enhanced
optical transmission. Plasmon enhancement is also a method to
increase the efficiency of solar cells. As used throughout this
disclosure SES includes the above listed and any related or similar
spectroscopic technique.
[0030] Many of the examples herein are described with respect to
SERS. It must be noted however that the methods, compositions and
particles disclosed herein are equally applicable to SERRS, SEHRS,
SEF, SEHRRS, SHG, SEIRA, SPASERS, or other surface enhanced or
plasmon enhanced SES technique.
[0031] Surface enhanced Raman scattering (SERS)-active particles
are useful in a variety of applications. One interesting
application is anti-counterfeiting, and more specifically to verify
the authenticity, source, age, and/or distribution path of
banknotes, tax stamps, banderols, passports, identification cards,
driver's licenses, work permits, fiduciary documents, stock and
bond certificates, and other valuable documents that contain ink.
Likewise, SERS-active particles can be used for similar purposes to
mark or tag a variety of other materials that contain print or
lettering composed of ink or lacquer, including but not limited to
software, machine parts such as airplane parts or automobile parts,
instrumentation, pharmaceutical and diagnostic products, medical
devices, luxury goods, fast-moving consumer goods, CD's, DVD's and
other electronic storage components, and so forth. Moreover, any
ink- or lacquer-containing packaging for any type of product is a
viable location for introduction of SERS-active particles for
anti-counterfeiting, or authentication purposes. Additional closely
related applications for SERS-active particles include: brand
security, brand protection, trademark protection, product security,
product identification, brand diversion, barcoding, grey market
remediation, friend-or-foe analysis, product life cycle analysis,
counterfeiting, forensic analysis of authenticity, biometrics,
document tracking, chain-of-custody analysis, product tampering,
anti-smuggling, smuggling detection, supply-chain tracking, product
tracking, lost revenue recovery, product serialization, serialized
authentication, freshness tracking, sell-by date tracking, use-by
date tracking, object tracking, standoff detection, and/or standoff
identification. In addition, SERS-active particles can be used for
combinations of these applications, including but not limited to a
combination of authentication and sell-by-date tracking.
Collectively, these applications are referred to as Industrial
Security.
[0032] One non-exclusive and non-limiting type of tag which is
described herein and which may be modified according to the
disclosed methods and with the disclosed materials is a SERS
nanotag also referred to as a SERS tag. SERS nanotags are
nanoparticulate optical detection tags which function through
surface enhanced Raman scattering (SERS). SERS is a laser-based
optical spectroscopy that, for molecules, generates a
fingerprint-like vibrational spectrum with features that are much
narrower than typical fluorescence.
[0033] A typical SERS nanotag includes a metal nanoparticle core
and a SiO.sub.2 (glass) or other silicon containing encapsulant.
Other materials including but not limited to various types of
polymers may also be used as an encapsulant or shell. Details
concerning the use, manufacture and characteristics of a typical
SERS nanotag are included in U.S. Pat. No. 6,514,767, entitled
"Surface Enhanced Spectroscopy-Active Composite Nanoparticles;"
U.S. Pat. No. 7,192,778, entitled "Surface Enhanced
Spectroscopy-Active Composite Nanoparticles;" U.S. Pat. No.
7,443,489, entitled "Surface Enhanced Spectroscopy-Active Composite
Nanoparticles;" and U.S. Published Patent Application No. US
2006-0054506, entitled "Surface Enhanced Spectrometry-Active
Composite Nanoparticles;" each of which patents and publications is
incorporated herein by reference for all matters disclosed
therein.
[0034] Although the embodiments disclosed herein are described in
terms of SERS nanotags prepared from single nanoparticle cores, it
is to be understood that nanoparticle core clusters or aggregates
may be used in the preparation of SERS nanotags. Methods for the
preparation of clusters of aggregates of metal colloids are known
to those skilled in the art. The use of sandwich-type particles as
described in U.S. Pat. No. 6,861,263 entitled "Surface Enhanced
Spectroscopy-Active Sandwich Nanoparticles" is also contemplated,
which patent is incorporated herein by reference for all matters
disclosed therein.
[0035] The nanoparticle core may be of any material known to be
Raman-enhancing, via plasmonic (electromagnetic) factors, chemical
factors or a combination of factors. The nanoparticle cores may be
isotropic or anisotropic. Nanoparticles suitable to be the core of
a SERS nanotag include colloidal metal, hollow or filled nanobars,
magnetic, paramagnetic, conductive or insulating nanoparticles,
synthetic particles, hydrogels (colloids or bars), and the like.
The nanoparticles can exist as single nanoparticles, or as clusters
or aggregates of the nanoparticles.
[0036] Nanoparticles can exist in a variety of shapes, including
but not limited to spheroids, rods, disks, pyramids, cubes,
cylinders, nanohelixes, nanosprings, nanorings, rod-shaped
nanoparticles, arrow-shaped nanoparticles, teardrop-shaped
nanoparticles, tetrapod-shaped nanoparticles, prism-shaped
nanoparticles, and a plurality of other geometric and non-geometric
shapes. Another class of nanoparticles that has been described
includes those with internal surface area. These include hollow
particles and porous or semi-porous particles. While it is
recognized that particle shape and aspect ratio can affect the
physical, optical, and electronic characteristics of nanoparticles,
the specific shape, aspect ratio, or presence/absence of internal
surface area does not bear on the qualification of a particle as a
nanoparticle. A nanoparticle as defined herein also includes a
nanoparticle in which the metal portion includes an additional
component, such as in a core-shell particle.
[0037] Each SERS nanotag is typically encoded with one or multiple
unique reporters, comprising an organic or inorganic molecule or an
organic or inorganic material at the interface between the
nanoparticle core and shell of glass or other suitable encapsulant.
This approach to detection tags leverages the strengths of Raman
scattering as a high-resolution molecular spectroscopy tool and the
enhancements associated with SERS, while bypassing the shortcomings
often encountered when making stand-alone SERS substrates such as
difficult reproducibility and lack of selectivity. SERS nanotags
exhibit intense spectra (enhancement factors in excess of 10.sup.6)
at 633 nm, 785 nm, 1064 nm or other suitable excitation
wavelengths, which wavelengths can be selected to avoid intrinsic
background fluorescence in biological samples such as whole blood
and in matrices like glass and plastic.
[0038] The encapsulant, which is essentially SERS-inactive or
relatively weakly SERS-active, stabilizes the particles against
aggregation, prevents the reporter from diffusing away, prevents
competitive adsorption of unwanted species, and provides an
exceptionally well-established surface. Glass, silica, silicates or
other silicon-containing species are well suited as
encapsulants.
[0039] Typical SERS nanotags do not exhibit wavelength dependent
response. Thus, known tags will return an identifiable spectrum
when excited at one of several excitation wavelengths. For example,
a known tag might be excitable and return a detectable SERS
spectrum at both 785 nm and 1064 nm excitation wavelengths. A
wavelength selective tag would be useful for many purposes,
including but not limited to covert marking of materials or
documents. As used herein, a wavelength selective particle is one
which cannot be effectively excited or interrogated at one or more
wavelengths where the selected reporter molecule/metal nanoparticle
combination would normally produce a SERS spectrum.
[0040] For example, a wavelength selective SERS nanotag might be
SERS active when using a 1064 nm excitation wavelength but inactive
at 785 nm, where activity at 785 nm would be expected based upon
the reporter. It is important to note that many of the examples
discussed herein feature tags which would not be SERS-active at 785
nm, but would be easily recognized using 1064 nm excitation. This
particular wavelength selectivity is representative only. The
disclosed or similar methods might be used to fabricate the reverse
tag, showing a spectrum at 785 nm but none at 1064 nm. In addition
the methods and materials described may be adaptable to other
suitable wavelengths. Moreover, combinations of effects (or
materials) can be used to generate more complex wavelength-response
profiles. For example, a SERS tag might excitable at 633, 785, and
1064 nm. The particle is then coated with materials that adsorb
light strongly at 633 and 1064 nm, but not 785 nm. Excitation at
either of the former frequencies would not yield a spectrum, but
excitation at the latter would. Alternatively, the profile could be
reversed so that SERS spectra are obtainable at 633 nm and 1064 nm
excitation but not at 785 nm excitation. All permutations of
wavelength selectivity are within the scope of this disclosure.
[0041] One method of imparting wavelength selectivity to an
otherwise non-selective tag is to add a coating to a tag which
blocks light that would otherwise cause excitation. For example,
the coating of a typical SERS nanotag as described above may be
supplemented with Au nanorods that block light at 785 nm, but not
at 1064 nm. This method is more fully discussed in Examples 1-5
below.
[0042] An similar approach to tuning the wavelength selectivity of
a SERS tag in an authentication application is to overcoat a layer
of SERS nanotags with a second layer of material that blocks
absorption at a given wavelength. For example, if a SERS tag that
is responsive to 785 and 1064 nm excitation is placed into a
varnish and coated on to a piece of paper, interrogation at either
wavelength will yield a SERS spectrum. If, however, a layer of
black ink that absorbs strongly at 785 nm but transmits completely
at 1064 nm is applied over the SERS tag coating, no SERS spectrum
will be seen at 785 nm excitation but a normal spectrum will be
seen at 1064 nm excitation.
[0043] Another approach is to use a reporter that has non-zero
extinction at the excitation wavelength, giving rise to surface
enhanced Resonance Raman spectroscopy (SERRS). While it is true
that larger absorbances of the reporter molecule at the excitation
wavelength give rise to greater resonant enhancements, it is also
true that greater absorbances also lead necessarily to increased
likelihood of irreversible deactivation processes from the excited
state, which could lead to decreased tag stability.
EXAMPLE 1
Au Nanorods Associated with SERS Nanotags
[0044] Several physical mixtures of SERS nanotags and Au nanorods
were prepared. The UV-visible light extinction and SERS behavior of
the mixture at 785 and 1064 nm are plotted in FIG. 1. In
particular, the Raman spectra of SERS nanotag/Au nanorod mixtures
are illustrated with data acquired at 785 nm (chart 102) and 1064
nm (chart 104). SERS nanotag concentrations were held constant and
nanorod concentrations were varied as indicated on charts 102 and
104. UV-visible extinction spectra of the samples are also shown in
chart 106 as well as a plot of SERS response versus nanorod
concentration in chart 108. A nearly complete suppression of signal
at 785 nm may be noted, while the signal at 1064 nm is relatively
unaffected. It may also be noted that the sample containing the
most nanorods could not be measured by UV-visible because its
extinction was too high for the instrument to read.
EXAMPLE 2
Au Nanorods Electrostaticly Associated with SERS Nanotags
[0045] While the results obtained in Example 1 demonstrate that the
first disclosed method of imparting wavelength selectivity is
conceptually sound, the adsorption of an adequate amount of Au
nanorods to the nanotags is challenging. Compelling progress has
been made toward overcoming the adsorption challenge by using
electrostatic methods to bind nanorods to the glass-encapsulated
nanotags. Generally the enhanced adsorption technique involves
associating a charged coating with the nanorods and an oppositely
charged coating with the SERS nanotags. For example, as initially
produced, the nanorods used in Example 1 may be stabilized by a
positively-charged bilayer of CTAB (cetyltrimethylammonium
bromide). However, removal of excess CTAB (which hinders
adsorption) can destabilize the rods and cause aggregation. Coating
the nanorods with negatively charged polymers, allows more complete
cleaning. To fully implement this method, the SERS nanotags must be
coated with a positively charged polymer, as well.
[0046] In addition, electrostatic combination methods may be
enhanced by association of the nanorods with another molecule. In
Example 2, the nanorods were mixed with a small amount of a
resonant SERS reporter, identified as SERS-817. Subsequently, the
nanorods were stabilized by a negatively charged polymer and
cleaned extensively. A physical mixture was prepared with SERS
nanotags that had previously been coated with a positively charged
polymer, promoting some adsorption of rods to SERS particles. After
a sufficient incubation period, the mixture was stabilized by
addition of an excess of negatively charged polymer
(`encapsulating` the nanotag/nanorod assemblies and allowing them
to be more easily cleaned). The assemblies were briefly cleaned to
remove the majority of unbound nanorods and excess polymers, after
which they were encapsulated in glass. The resulting particle
assemblies are shown in the TEM images of FIG. 2. The particles are
observed to be quite clumpy and do not exhibit a particularly
strong SERS signal at 1064 nm. As shown in FIG. 3, these particles
do however have distinct and unique signatures at 785 (graph trace
302) and 1064 nm (graph trace 304), with the 1064 nm signature
corresponding to the BPE reporter on the SERS nanotags and with the
785 spectrum corresponding to the SERS spectrum of the reporter
SERS-817 which was added to the nanorods in an initial step. Thus,
this result, as illustrated in FIG. 3 demonstrates that at 785 nm,
photons are not reaching the inner core or inner reporter molecule.
If 785 nm excitation light were reaching the core of the SERS
nanotags, an intense spectrum of the BPE reporter would be
present.
EXAMPLE 3
Au Nanorods as Plasmon Absorbers
[0047] The adsorption characteristics of nanorods associated with
SERS nanotags may be improved to enhance the wavelength selectivity
of the resulting particles. The TEM images of FIG. 4 are of a
nanotag sample that was coated with nanorods (via electrostatic
adsorption, as previously described). This sample however, utilized
nanorods that because of the nanorod shape, size or aspect ratio
are inherently better suited to blocking 785 nm excitation energy.
Accordingly, as shown in FIG. 5, the SERS nanotags of Example 3
display significantly lower SERS response at 785 nm than the
original tags (See graph trace 502). All data in FIG. 5 was
acquired at a gold concentration of 12.5 .mu.g/mL. The observed
reduction in signal is about ten times less than the unmodified
tags. However, the nanorod extinction appears to have broadened,
likely due to aggregation, causing the signal at 1064 nm to be
significantly impacted (graph trace 504). This result is further
evidence that plasmon absorbers can be effectively used to dampen
the SERS response at a given wavelength, and thus create wavelength
selective particles.
EXAMPLE 4
Glass-Coated Au Nanorods as Plasmon Absorbers
[0048] The plasmonic properties of nanorods associated with the
SERS nanotags may be stabilized prior to association with the SERS
nanotags to prevent changes in the plasmonic properties caused by
nanorod-nanorod interactions. In this example, gold nanorods were
first coated with a thin glass shell. This glass shell prevents
plasmonic changes caused by aggregation or coalescence of the
nanorods before or during their adsorption to the SERS nanotags.
Thus, the optical properties of the gold nanorods are preserved and
a much more specific wavelength response is observed. As previously
described, the glass-coated nanorods can then be readily adsorbed
directly to the SERS nanotags using electrostatic methods. FIG. 6
shows Raman spectra of SERS nanotags before and after treatment
with silica-coated nanorods. The SERS intensity at 785 nm versus
1064 nm is reduced by approximately 8-fold after the treatment.
FIG. 7 shows an SEM of the nanorod-nanotag composite particles.
Example 5
Plasmonic Shells as Plasmon Absorbers
[0049] Core-shell structures with dielectric cores surrounded by
nanoscale metallic shells can be engineered to have plasmon
resonances in the near-IR. See for example the Absorbance spectrum
of a silica-AG core shell particle of FIG. 8. In particular, the
relative dimensions of the core and shell can be designed to yield
a plasmon resonance around 785 nm. Such a structure would attenuate
the SERS response of a SERS nanotag embedded within the structure
since the plasmon resonance of the shell would prevent light from
the excitation laser to reach the nanotag, and also prevent Raman
scattered light from escaping. Since the plasmon resonance can be
designed to absorb minimally at 1064 nm, the particle geometry can
be adjusted to minimally impact the SERS signal of the nanotag at
1064 nm.
Alternative Methods of Creating Wavelength-Selective SERS
Particles
[0050] A. Molecular Absorbers
[0051] Molecular absorbers may be utilized to block a selected
wavelength, for example either the 785 nm (or other wavelength)
excitation source, or the resultant SERS emission. However, the
cross section of typical chemical absorbers will be much smaller
than that of Au nanorods, thus requiring significantly more of the
molecule to be present. This may, however, be advantageous as many
of these molecular absorbers exhibit weak fluorescence. At high
concentrations, this fluorescence can be quenched, resulting in a
particle with minimal, featureless emission.
[0052] One method that may provide for high doping levels is to
create a porous glass shell that has a very high surface area. If
near IR absorbers can be physically adsorbed to the glass, the
entire particle could be capped with an additional silica layer.
The presence of surfactants in the glass growth process can lead to
mesoporous coatings, with very high surface areas. Moreover,
pseudomorphic transformation methods may allow already prepared
SERS nanotags to be converted into tags with mesoporous shells. The
pores may then, optionally, be capped to prevent the escape of the
dye or blocking molecule.
[0053] Alternatively, an absorber can be covalently linked to the
silica surface of a SERS Nanotag via a silane reagent such as
3-aminopropytrimethoxysilane (APTMS) or any other coupling agent.
In this manner, the molecules can be incorporated throughout the
silica as thicker glass shells are formed.
[0054] Any materials that absorb light at a wavelength of interest
can potentially be used for a molecular absorber application. For
example, tags may be incorporation into an ink that absorbs at the
desired wavelength.
EXAMPLE 6
SERS Nanotags Surrounded by Molecular Absorbers
[0055] The data represented in FIG. 9 demonstrates that molecular
absorbers can be used to mask the signal from a SERS Nanotag using
785 nm excitation, while leaving the signal from 1064 nm excitation
unaltered. For Example 6, SERS Nanotags were suspended in aqueous
solutions containing no molecular absorber, and 10 and 100 .mu.g/mL
of a molecular absorber identified as IRA-800. The concentration of
SERS Nanotags was the same in all cases. At 10 .mu.g/mL of the
molecular absorber, the SERS signal at 785 nm from the SERS Nanotag
is not readily apparent, although weak fluorescence from the
molecular absorber is observed. However, at an absorber
concentration of 100 .mu.g/mL, not only is the SERS signal
completely masked, the fluorescence from the molecular absorber is
also quenched, resulting in weak, featureless emission at 785. In
contrast, the SERS response at 1064 nm is virtually unchanged in
these solutions.
EXAMPLE 7
SERS Nanotags with Mesoporous Encapsulant
[0056] The particles of Example 7 feature an additional glass
coating done in the presence of a surfactant, CTAB, to prepare a
mesoporous encapsulant as described above. Although it is difficult
to determine if the glass is truly porous, as shown in FIG. 10 the
coating definitely appears different than the smooth coatings that
are obtained from typical SERS nanotag encapsulating processes.
These pores are expected to be <5 nm in size.
[0057] B. Tuning of surface plasmon
[0058] An alternative method to impart wavelength selectivity to a
SERS nanotag is to produce enhancing tags with inherently better
response at 1064 nm than at 785 nm (for example). This tuning may
be accomplished by judicious choice of tag material, shape, size or
degree of aggregation.
[0059] C. Use of Resonant Reporters
[0060] Molecules with absorption features near 1064 nm can provide
resonance enhancement. For example the dye IR-1048 (sigma-aldrich)
has strong molecular absorption centered at 1048 nm while the dye
IR-27 has a maximum absorbance at 988 nm.
[0061] D. Charge-transfer resonance
[0062] Other classes of molecules that give enhanced response at
1064 nm versus other wavelengths include azopyridine, various
AZP/benzocinnoline (specifically molecules better at 1064 nm than
785 nm), Fluorophores/metal complexes, Photochromic/thermochromic
molecules (spiropyrans) and others.
[0063] E. Masking SERS Signal
[0064] Certain examples detailed above impart wavelength
selectivity to a SERS nanotag by blocking the incidence of an
excitation wavelength or blocking the emission of a SERS spectrum
caused by excitation at the selected wavelength. Alternatively, the
SERS signal of a SERS nanotag may be generated, but effectively
masked prior to detection. For example, a molecule or material may
be associated with an encapsulant which is strongly fluorescent
using 785 nm excitation. SERS detection may then occur with 1064 nm
excitation.
EXAMPLE 8
SERS Signal Masked by Fluorescence
[0065] FIG. 11 shows two spectra obtained from a mixture containing
the dye IR-140 (100 nM) and a sample of SERS tags. When excited at
785 nm a strong fluorescence emission spectrum 1102 is observed due
to IR-140 and the presence of the SERS tag cannot be detected. The
fluorescence effectively masks the fact that a Raman label is
present. When excited at 1064 nm the Raman spectrum from the SERS
tag 1104 is detected. This result was obtained by physical mixing
of the two substances. Alternatively, a fluorescent material could
be incorporated into the structure of the SERS tag.
[0066] Note that the SERS at 785 nm is completely obscured by
fluorescence, but there is no fluorescence when excited at 1064 nm.
The amount of dye added to the particles corresponds to much less
than monolayer coverage, implying that very few fluorophores would
need to be incorporated into the SERS tag for an effective
wavelength selective tag.
[0067] F. Alternative read-out methods
[0068] Alternate read-out methods may be used to impart wavelength
selectivity to SERS nanotags. Typically Raman scattering occurs on
the picosecond time scale while fluorescence occurs at the fastest
occurs in the nanosecond regime and other luminescent processes can
be much slower. Because of this difference in temporal behavior it
is possible to detect Raman scattering even when luminescence is
occurring at the same wavelengths. Time resolved detection can be
used by exciting both Raman scattering and luminescence with pulses
of light which are much shorter than the luminescent lifetime.
Time-gated detection can then be used to measure the Raman
scattering while rejecting most of the luminescence. Alternatively,
in the frequency domain, the amplitude of the excitation source may
be modulated at high frequency. In this fashion, processes with
rapid response (i.e. Raman scattering) follow the modulation
frequency and can be detected with a frequency and phase sensitive
detector. The signal from processes with slower response may be
rejected by the frequency sensitive detector. Thus, material that
possesses both spectrally unresolved fluorescence and Raman
scattering may be used as a Raman tag.
[0069] G. Transient photobleaching
[0070] It is possible to use strong pulses of light which cause the
absorption of a molecule to saturate. This happens when the rate at
which photons are absorbed exceeds the rate at which the excited
state can be depopulated. At that point the incoming photons would
be free to excite Raman scattering and SERS. An appropriate readout
system would require a pulsed light source and fast detection
systems.
[0071] Alternative embodiments include methods of manufacturing a
wavelength selective SERS nanotag as described above.
[0072] Alternative methods also include using a wavelength
selective SERS nanotag to mark or tag an item, substance, document
or article, such that the tag may be detected at fewer
interrogation frequencies than would be expected based upon the
nature of the reporter molecule used with the SERS nanotag. The
tagging methods comprise providing a SERS active particle as
described above and associating the particle with a material or
object of interest. The method of tagging may further include
obtaining a SERS spectrum and other identification information from
the particle in association with the material of interest and
thereby identifying the marked object or substance. Supplemental
identification information can be associated with the tag or the
object, as described herein.
[0073] The small, robust, non-toxic, and easily-attachable nature
of the particles disclosed herein allows their use for tagging
virtually any desired object. The tagged object can be made of
solid, liquid, or gas phase material or any combination of phases.
The material can be a discrete solid object, such as a container,
pill, or piece of jewelry, or a continuous or granular material,
such as paint, ink, fuel, or extended piece of, e.g., textile,
paper, or plastic, in which case the particles are typically
distributed throughout the material.
[0074] Examples of specific materials or objects that can be tagged
with the particles disclosed herein, or into which the particles
can be incorporated include, but are not limited to: [0075]
Packaging, including adhesives, paper, plastics, labels, and seals
[0076] Agrochemicals, seeds, and crops [0077] Artwork [0078]
Computer chips [0079] Cosmetics and perfumes [0080] Compact disks
(CDs), digital video disks (DVDs), and videotapes [0081] Documents,
money, and other paper products (e.g., labels, passports, stock
certificates) [0082] Inks, paints, varnishes, lacquers, overcoats,
topcoats, and dyes [0083] Electronic devices [0084] Explosives and
weapons [0085] Food and beverages, tobacco [0086] Textiles,
clothing, footwear, designer products, and apparel labels [0087]
Polymers [0088] Insects, birds, reptiles, and mammals [0089]
Powders [0090] Luxury goods [0091] Other anti-counterfeiting
substances or materials, such as holograms, optically variable
devices, color-shifting inks, threads, and optically-active
particles [0092] Hazardous waste [0093] Movie props and
memorabilia, sports memorabilia and apparel [0094] Manufacturing
parts, automobile parts, aircraft parts, truck parts [0095]
Petroleum, fuel, lubricants, gasoline, crude oil, diesel fuel, fuel
additive packages, crude oil [0096] Pharmaceuticals, prescription
drugs, over-the-counter medicines, and vaccines
[0097] The particles disclosed herein can be associated with the
material in any way that maintains their association, at least
until the particles are read. Depending upon the material to be
tagged, the particles can be incorporated during production or
associated with a finished product. Because they are so small, the
particles are unlikely to have a detrimental effect on either the
manufacturing process or the finished product. The particles can be
associated with or attached to the material via any chemical or
physical means that does not inherently interfere with particle
functionality. For example, particles can be mixed with and
distributed throughout a liquid-based substance such as paint, oil,
or ink and then applied to a surface. They can be wound within
fibers of a textile, paper, or other fibrous or woven product, or
trapped between layers of a multi-layer label. The particles can be
incorporated during production of a polymeric or slurried material
and bound during polymerization or drying of the material.
Additionally, the surfaces of the particles can be chemically
derivatized with functional groups of any desired characteristic,
for covalent or non-covalent attachment to the material. When the
particles are applied to a finished product, they can be applied
manually by, e.g., a pipette, or automatically by a pipette, spray
nozzle, or the like. Particles can be applied in solution in a
suitable solvent (e.g., ethanol), which then evaporates.
[0098] The particles disclosed herein have a number of inherent
properties that are advantageous for tagging, tracking and
identifying applications. They offer a very large number of
possible codes. For example, if a panel of particles is constructed
with 20 distinguishable Raman spectra, and an object is labeled
with two particles, there are 20*19/2=190 different codes. If the
number of particles per object is increased to 5, there are 15,504
possible codes. Ten particles per object yields 1.1.times.10.sup.6
different codes. A more sophisticated monochromator increases the
number of distinguishable spectra to, e.g., 50, greatly increasing
the number of possible codes. Alternatively, different amounts of
particles can be used to generate an exponentially-increased number
of possible codes. For example, with just four different particle
types (N=4), present at three different intensity levels (e.g.
High, Medium, Low) (L=3), chosen three at a time (P=3), can
generate 58 different codes. With N=10, P=3, L =1, the number of
codes is 175. With N=50, P=5, L=4, over a billion codes are
possible.
[0099] In some embodiments, the particles may be applied to a
document or other item in an ink or other marking material. Inks
include, but are not limited to flexographic ink, lithographic ink,
silkscreen ink, gravure ink, bleeding ink, coin reactive ink,
erasable ink, pen reactive ink, heat reactive ink, visible infrared
ink, optically variable ink, and penetrating ink. photochromic ink,
solvent/chemical reactive ink, thermochromic ink, and water
fugitive ink. A particle may also be applied in electrophotographic
and ink jet printing machines and other systems including offset
lithography, letterpress, gravure, heliogravure, xerography,
photography, silk-screening systems, systems for imagewise
deposition of discrete quantities of a marking material on a
substrate surface, such as paint, chemical, and film deposition
systems; and systems for integration of colorant materials in an
exposed surface of a fibrous substrate, such as textile printing
systems.
[0100] It should be noted that additional security features may be
included or utilized along with the disclosed tags for a particular
item or documents. One such additional security feature may be a
separate security ink, such as bleeding ink, coin reactive ink,
erasable ink, pen reactive ink, heat reactive ink, visible infrared
ink, optically variable ink, penetrating ink. photochromic ink,
solvent/chemical reactive ink, thermochromic ink or water fugitive
ink. The tags may be applied as part of the ink, or in a separate
step. Other non-ink based security features which may be utilized
in addition to the disclosed tags for document or item marking
include the use of an ascending serial number (horizontal and/or
vertical format), bar code and numerals, colored fibers, embedded
security thread, face-back optical registration design (transparent
register), foil imprints, holograms, latent impressions, micro
printing, optical variable devices (OVD), planchettes, raised
marks, segmented security threads, and watermarks.
[0101] The disclosed particles may be applied by coating an image,
including but not limited to a hologram image, made with toner or
ink compositions known in the art, as with an overcoat varnish, or
a starch overcoat.
[0102] In the case of documents with other security features, such
as those including polymer threads or metal foils, the particles
may be applied to additional feature, such as the thread or the
foil. Single tags may be considered to represent a bit of data that
may be changeable according to the methods described herein. Thus
groups of distinguishable particles disclosed herein may be applied
to constitute an "alphabet" and combined as words or encoded
information, which may be selectively variable, or variable over
time.
[0103] The particles disclosed herein can be identified using a
conventional spectrometer, for example a Raman spectrometer. In
fact, one benefit of using SERS particles is the versatility of
excitation sources and detection instrumentation that can be
employed for Raman spectroscopy. Visible or near-IR lasers of
varying sizes and configurations can be used to generate Raman
spectra. Portable, handheld, and briefcase-sized instruments are
commonplace. At the same time, more sophisticated monochromators
with greater spectral resolving power allow an increase in the
number of unique taggants that can be employed within a given
spectral region. For example, the capability to distinguish between
two Raman peaks whose maxima differ by only 3 cm.sup.-1 is
routine.
[0104] Typically, if a suitable waveguide (e.g., optical fiber) is
provided for transmitting light to and from the object, the
excitation source and detector can be physically remote from the
object being verified. This allows the disclosed particles to be
used in locations in which it is difficult to place conventional
light sources or detectors. The nature of Raman scattering and
laser-based monochromatic excitation is such that it is not
necessary to place the excitation source in close proximity to the
Raman-active species. Moreover, the particles disclosed herein are
amenable for use with all known forms of Raman spectrometers,
including some more recent implementations, including spatially
offset Raman, Raman absorption spectrometers, instruments to
measure Raman optical activity, and so forth.
[0105] Another characteristic of the disclosed particles is that
the measurement of their spectra does not need to be strictly
confined to "line of sight" detection, as with, e.g., fluorescent
tags. Thus their spectrum can be acquired without removing the
particles from the tagged object, provided that the material is
partially transparent to both the excitation wavelength and the
Raman photon. For example, water has negligible Raman activity and
does not absorb visible radiation, allowing the particles disclosed
herein in water to be detected. The particles can also be detected
when embedded in, e.g., clear plastic, paper, or certain inks.
[0106] The disclosed particles also allow for quantitative
verification, because the signal intensity is an approximately
linear function of the number of analyte molecules. For
standardized particles (uniform analyte distribution), the measured
signal intensity reflects the number or density of particles. If
the particles are added at a known concentration, the measured
signal intensity can be used to detect undesired dilution of liquid
or granular materials.
[0107] In another embodiment, SERS particles in tagged items are
detected with an instrument capable of measuring inelastically
scattered light and determining the identity of the SERS particles
and by extension the tagged item. In one embodiment, the instrument
requires an excitation source that illuminates the tagged item. The
inelastically scattered light from the SERS particles is collected.
The spectrum of scattered light is analyzed and the identity of the
particles, and hence the item, is determined The reader may be a
Raman Spectrometer. The instrument to collect and analyze the Raman
spectrum (the reader) can be as small as 1 cubic millimeter and as
large as 1000 cubic meters.
[0108] The light source used to excite the particles may be a
monochromatic light from a laser operating in the solid state, in
gas or in liquid. The laser can be continuous or pulsed. A
continuous laser can have powers from 01. femtowatt up to 1
megawatt. A pulsed laser can have similar total power with pulses
as short as less than 1 femtosecond, and with a pulse repetition
rate up to 1 terahertz. Alternatively, multiple light sources can
be used. In one embodiment, multiple separate excitation
wavelengths are used to determine the presence or absence of
wavelength selective particles as described above or to compensate
for detectors that have low photon-to-electron conversion
efficiencies in certain spectral regions, using one excitation
wavelength to cover a certain portion of the Raman shift window
(e.g. 100-1800 cm.sup.-1), and the second to cover another (e.g.
1801-3600 cm.sup.-1).
[0109] In addition to lasers, the light can come from an
electroluminescent material such as a light emitting diode.
Alternatively, the excitation light can come from an incandescent
or fluorescent light source. In all embodiments the excitation
wavelength range can be from 100 nm to 100 microns. The excitation
light can be spectrally filtered with discrete filters or spatially
dispersing elements.
[0110] In one embodiment, the monochromatic light spectral width is
less than 0.5 nm. In other embodiments, the spectral width is from
0.01 nm bandwidth to 100 nm bandwidth. The excitation and collected
light may be steered to and from the item under interrogation with
lenses, mirrors, light pipes, gratings, waveguides, optical fiber
or any other component. All optical and mechanical elements can,
but need not be, integrated into a single platform.
[0111] In one embodiment the excitation source and collection
system are connected to the sample delivery optics with light pipes
or optical fibers. In other embodiments, discrete optical elements
connect the excitation source and detection element. The discrete
optics include lenses, mirrors or other waveguides. In other
embodiments the excitation source, the collection spectrometer or
all items are made using micro-manufacturing techniques such as
LIGA, molding, etching, MEMS, NEMS, lithography, photolithography,
or other monolithic methods. The illuminated spot from the
excitation source may be larger than 100 microns in diameter. In
other embodiments, the illuminated spot may be as small as 100
square nanometers and as large as 1 square meter.
[0112] In one embodiment the collected light is analyzed by a
spectrometer. The spectrometer uses a grating to disperse the
collected light onto an area array detector, preferably a Charge
Coupled Device (CCD). The CCD divides the spectrum into bins, with
each bin corresponding to a given wavelength range. The number of
bins used can range from 1 bin to many thousands of bins. In one
embodiment, the number of bins is more than 20.
[0113] The optics of the spectrometer typically has a specific
spectral resolution. For example, the resolution may be less than
10 nm or between 1 nm to 4 nm. In other embodiments, the resolution
is from 0.01 nm to 5000 nm. The selected resolution can be 0.01
cm.sup.-1 to 40000 cm.sup.-1 expressed as wave numbers.
[0114] In one embodiment, the method of optically separating light
into bins uses any form of light dispersion with a prism, grating
or any spatially dispersing element. In other embodiments, a
digital micro mirror array is used to spatially disperse light.
Other tunable spectral filters are used including acousto-optic
tunable filters, electro-optics tunable filters, liquid crystal
tunable filters. Any form of scanning spectral analysis can be used
as well such as Fourier Transform correlation spectroscopy. In
another embodiment, a single detection element or an array of
detection elements may is used. The spectrum is analyzed with
discrete optical filters or with the other aforementioned spectral
filtering methods
[0115] In one embodiment, the detector element is a CCD or
photodiode array made from silicon, InGAs, or any other
semiconductor. Recently, detectors made from organic materials
(e.g. conducting polymers) and from carbon-based composites have
been described. In other embodiments, the detection element is any
element that converts electromagnetic energy, i.e. photons into
electrons or other electrical energy or thermal energy or sound
energy.
[0116] The converted electrical energy is analyzed by an electrical
circuit. The circuit will typically, if required convert the analog
signal from the detector to a digital signal that is stored in or
analyzed by a computer. The digital signal can be analyzed to
determine the presence of the tag. The digital signal can be a
discrete signal level or a stream of signal levels corresponding to
a spectrum. In other embodiments, the circuit can use analog logic
elements to determine the signal level of the tag and whether the
item is tagged or not.
[0117] In one embodiment, the acquired spectrum is analyzed by a
computer to determine the presence of the SERS particles after
accounting for the presence of other materials contributing to the
spectrum, i.e other inks, materials soiling etc. For example, the
SERS particles with a commercially available Raman Spectrometer,
such as the Delta Nu Reporter. The Raman spectrometer may be
controlled by a small computer in a phone or other personal data
assistant. The small computer may communicate with the Raman
Spectrometer over a wireless connection, either blue tooth or wi-fi
or other wireless protocol. In this embodiment, the small computer
may receive the acquired spectrum from the Raman Spectrometer,
analyzes the spectrum and identifies the item.
[0118] In another embodiment the reader system is part of another
machine. The reader uses a signal from the machine to start
detection of the tag and perform classification all in real time.
The machine contains a central processor that identifies the tagged
item and makes a decision on the item whether it is real or not and
or whether the tag is correct. The machine can be one used in the
processing, issuing, sorting, counting, screening, tracking, or
authentication of banknotes or currency, or for any other
industrial security application, and where the tagged items could
be pills, bullets, items of clothing, machine parts, software,
food, beverages, or any other item to which SERS particles are
applied.
[0119] In other embodiments, the machine is a currency or stamp or
document printing press or inkjet printer or digital printer or any
other type of printing instrumentation where the reader is used for
process monitoring. In other embodiments, the machine is part of a
final packaging or labeling line where the taggants are checked as
a final step.
[0120] In addition to Raman spectral analysis, the instrumentation
or reader can perform other functions. For example, the instrument
can measure both elastic and inelastic light scattering.
Alternatively, the instrument can acquire an optical image of an
item as well as a spectral signature. Likewise, the instrument can
measure a fluorescence spectrum in one spectral window and a Raman
spectrum in another spectral window.
[0121] The spectrum can be analyzed for spectral peaks, widths,
heights, and positions, numbers of peaks, ratios of peaks, or
combinations thereof The spectrum can be analyzed by any number of
mathematical methods, including but not limited to wavelet
analysis, principal component analysis, linear and non-linear
regression, or combinations thereof In addition Fourier transform,
Laplace transforms, Hildebrand transforms, Hadamard transforms or
any other mathematical method, i.e. first to higher order
derivatives, first or higher order integrals or any other analysis,
can be used to manipulate the spectral information. All of the
above methods can be used to remove any interfering or extraneous
or unwanted signals, including but not limited to (a) standard
interferences, including but not limited to daylight, impurities,
paper, ink, thread, fiber, metal, liquids, solids, solvents,
moisture, (b) use-related signals, including that from dirt, stains
(e.g. coffee, beer, skin fluids), dust, charcoal, trace drugs (e.g.
cocaine), and (c) interfering optical signals, including but not
limited to fluorescence, luminescence, absorbance, scattering,
phosphorescence, and chemiluminescence.
[0122] In one embodiment wavelength selective SERS particles are
used on their own or in combinations to make codes. Tag and their
combinations are organized in a database which can be correlated to
products, lot numbers or other attributes. Libraries of know tag
spectra can be used to find the wanted tag spectra. Libraries can
include all other compounds, spoofs or any other anticipated
material. Backgrounds and other components can be separated using
the same methods. Backgrounds and other contaminants can be modeled
synthetically by using a polynomial or other mathematical function,
rolling circle subtraction and spectral filtering
[0123] The database information can be stored on the detection
device or stored on a remote computer. The remote computer could be
part of a cellular phone or other mobile device that is linked to a
single or multiple instruments. The remote computer could be a
personal computer, laptop, or central computing cloud that
communicates with a range of instruments, from 1 to 2 million, over
the internet connection or other communication protocol. The
instruments and computers can be linked through a wireless
network
[0124] Multiple attributes of the SERS particles can be used to
determine the identity of a marked item. These attributes include
the amount of material and the quality of the spectrum, the amount
of the material relative to another material, the spectra relative
to other spectra.
[0125] The classification of a code or combination of SERS
particles can be performed using statistical methods, such as
Bayesian methods. These methods can be used to assign probabilities
that the sample contains the code. In other methods a threshold is
set for an attribute.
[0126] While the aforementioned examples are directed toward
wavelength selectivity in SERS tags, those skilled in the art will
recognize that incorporation of wavelength selective features can
be built into particles designed for other optical detection
methods, including but not limited to fluorescence, luminescence,
phosphorescence, elastic (Rayleigh) light scattering, upconversion,
downconversion, and multi-photon processes. Unless otherwise
indicated, all numbers expressing quantities of ingredients,
dimensions reaction conditions and so forth used in the
specification and claims are to be understood as being modified in
all instances by the term "about".
[0127] In this application and the claims, the use of the singular
includes the plural unless specifically stated otherwise. In
addition, use of "or" means "and/or" unless stated otherwise.
Moreover, the use of the term "including", as well as other forms,
such as "includes" and "included", is not limiting. Also, terms
such as "element" or "component" encompass both elements and
components comprising one unit and elements and components that
comprise more than one unit unless specifically stated
otherwise.
[0128] Various embodiments of the disclosure could also include
permutations of the various elements recited in the claims as if
each dependent claim was a multiple dependent claim incorporating
the limitations of each of the preceding dependent claims as well
as the independent claims. Such permutations are expressly within
the scope of this disclosure.
[0129] While the embodiments have been particularly shown and
described with reference to a number of examples, it would be
understood by those skilled in the art that changes in the form and
details may be made to the various embodiments disclosed herein
without departing from the spirit and scope of the invention and
that the various embodiments disclosed herein are not intended to
act as limitations on the scope of the claims. All references cited
herein are incorporated in their entirety by reference.
[0130] The description has been presented for purposes of
illustration and description, but is not intended to be exhaustive
or limiting of the invention to the form disclosed. The scope of
the present invention is limited only by the scope of the following
claims. Many modifications and variations will be apparent to those
of ordinary skill in the art. The embodiment described and shown in
the figures was chosen and described in order to best explain the
principles of the invention, the practical application, and to
enable others of ordinary skill in the art to understand the
invention for various embodiments with various modifications as are
suited to the particular use contemplated.
* * * * *