U.S. patent application number 14/104712 was filed with the patent office on 2017-12-14 for liquid core photonic crystal fiber biosensors using surface enhanced raman scattering and methods for their use.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. The applicant listed for this patent is The Regents of the University of California. Invention is credited to Claire Gu, Leo Saballos, Chao Shi, Jin Z. Zhang, Yi Zhang.
Application Number | 20170356850 14/104712 |
Document ID | / |
Family ID | 40429467 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170356850 |
Kind Code |
A1 |
Gu; Claire ; et al. |
December 14, 2017 |
LIQUID CORE PHOTONIC CRYSTAL FIBER BIOSENSORS USING SURFACE
ENHANCED RAMAN SCATTERING AND METHODS FOR THEIR USE
Abstract
The invention is drawn to a photonic crystal fiber that can be
used with nanoparticles to detect and quantify components in a test
sample. The invention further relates to methods of using the
photonic crystal fiber for detecting chemical and biological
analytes, and in use in optical communications.
Inventors: |
Gu; Claire; (Santa Cruz,
CA) ; Zhang; Yi; (Santa Cruz, CA) ; Shi;
Chao; (Santa Cruz, CA) ; Zhang; Jin Z.; (Santa
Cruz, CA) ; Saballos; Leo; (Santa Cruz, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of California |
Oakland |
CA |
US |
|
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
CALIFORNIA
Oakland
CA
|
Family ID: |
40429467 |
Appl. No.: |
14/104712 |
Filed: |
December 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12733492 |
Jan 19, 2011 |
8717558 |
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PCT/IB2008/002872 |
Oct 29, 2008 |
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14104712 |
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60967555 |
Sep 4, 2007 |
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61192632 |
Sep 19, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/656 20130101;
G02B 6/02385 20130101; B82Y 20/00 20130101; G01N 21/658
20130101 |
International
Class: |
G01N 21/65 20060101
G01N021/65; G02B 6/02 20060101 G02B006/02; B82Y 20/00 20110101
B82Y020/00 |
Goverment Interests
[0002] This invention was made partly using funds from the United
States' National Science Foundation grant number ECS-0401206 and
ARP/UARC grant number NAS2-03144-TO.030.3MM.DGU-06. The Federal
Government has certain rights to this invention.
Claims
1. A photonic crystal fiber, the fiber comprising a proximal end
and a distal end, the ends defining a first lumen through the
fiber, the fiber further comprising an outer surface, the first
lumen comprising an inner surface, a plurality of second lumens,
wherein both ends of the fiber comprises a plurality of sealed
apertures of each second lumen, the inner surface further
comprising, in part, a first metallic nanoparticle composition.
2. The photonic crystal fiber of claim 1, the inner surface further
comprising, in part, a second metallic nanoparticle
composition.
3. The photonic crystal fiber of claim 1, the outer surface further
comprising, in part, a metallic nanoparticle composition.
4. The photonic crystal fiber of claim 1, wherein the lumen further
comprises a solid composition.
5. The photonic crystal fiber of claim 1 wherein the photonic
crystal fiber has a cylindrical shape and having an approximately
circular cross-section.
6. The photonic crystal fiber of claim 1 wherein the photonic
crystal fiber is flexible.
7. The photonic crystal fiber of claim 1 wherein the lumen further
comprises a composition, the composition selected from the group
consisting of a liquid, a plasma, and a gas.
8. The photonic crystal fiber of claim 1, wherein the first
metallic nanoparticle composition comprises a double substrate
sandwich structure.
9. The photonic crystal fiber of claim 1, wherein the first
metallic nanoparticle composition comprises a single layer.
10. The photonic crystal fiber of claim 1, wherein the first
metallic nanoparticle composition comprises a plurality of
layers.
11. The photonic crystal fiber of claim 1, wherein the metallic
nanoparticle composition comprises a metal selected from the group
consisting of gold, silver, platinum, copper, aluminum, palladium,
cadmium, iridium, and rhodium.
12. The photonic crystal fiber of claim 11 wherein the metal is
silver.
13. The photonic crystal fiber of claim 1 wherein the first
metallic nanoparticle composition comprises silver citrate.
14. The photonic crystal fiber of claim 1 wherein the cross-section
of the photonic crystal fiber has dimensions selected from the
group consisting of about between 0.1 .mu.m, 0.2 .mu.m, 0.3 .mu.m,
0.4 .mu.m, 0.5 .mu.m, 0.6 .mu.m, 0.7 .mu.m, 0.8 .mu.m, 0.9 .mu.m, 1
.mu.m, 2 .mu.m, 3 .mu.m, 4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m, 8
.mu.m, 9 .mu.m, 10 .mu.m, 12 .mu.m, 13 .mu.m, 14 .mu.m, 15 .mu.m,
16 .mu.m, 17 .mu.m, 18 .mu.m, 19 .mu.m, 20 .mu.m, 25 .mu.m, 30
.mu.m, 35 .mu.m, 40 .mu.m, 45 .mu.m, 50 .mu.m, 55 .mu.m, 60 .mu.m,
65 .mu.m, 70 .mu.m, 75 .mu.m, 80 .mu.m, 85 .mu.m, 90 .mu.m, 95
.mu.m, and 100 .mu.m.
15. The photonic crystal fiber of claim 1 wherein the length of the
photonic crystal fiber has dimensions of about between 0.5 cm, 0.6
cm, 0.7 cm, 0.8 cm, 0.9 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7
cm, 8 cm, 9 cm, 10 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18
cm, 19 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 cm, 55 cm,
60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 85 cm, 90 cm, 95 cm, and 100
cm
16. The photonic crystal fiber of claim 1 wherein the cross-section
of the lumen of the photonic crystal fiber has dimensions of about
between 0.1 .mu.m, 0.2 .mu.m, 0.3 .mu.m, 0.4 .mu.m, 0.5 .mu.m, 0.6
.mu.m, 0.7 .mu.m, 0.8 .mu.m, 0.9 .mu.m, 1 .mu.m, 2 .mu.m, 3 .mu.m,
4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m, 8 .mu.m, 9 .mu.m, 10 .mu.m, 12
.mu.m, 13 .mu.m, 14 .mu.m, 15 .mu.m, 16 .mu.m, 17 .mu.m, 18 .mu.m,
19 .mu.m, 20 .mu.m, 25 .mu.m, 30 .mu.m, 35 .mu.m, 40 .mu.m, 45
.mu.m, 50 .mu.m, 55 .mu.m, 60 .mu.m, 65 .mu.m, 70 .mu.m, 75 .mu.m,
80 .mu.m, 85 .mu.m, 90 .mu.m, 95 .mu.m, and 100 .mu.m.
17. The photonic crystal fiber of claim 3, wherein the metallic
nanoparticle composition comprises a double substrate sandwich
structure.
18. The photonic crystal fiber of claim 3, wherein the metallic
nanoparticle composition comprises a single layer.
19. The photonic crystal fiber of claim 3, wherein the metallic
nanoparticle composition comprises a plurality of layers.
20. The photonic crystal fiber of claim 3, wherein the metallic
nanoparticle composition comprises a metal selected from the group
consisting of gold, silver, platinum, copper, aluminum, palladium,
cadmium, iridium, and rhodium.
21. The photonic crystal fiber of claim 20 wherein the metal is
silver.
22. The photonic crystal fiber of claim 3 wherein the metallic
nanoparticle composition comprises silver citrate.
23. A method for sensing an analyte in a test sample, the method
comprising the steps of: (i) providing the photonic crystal fiber
of claim 1; (ii) providing a test sample; (iii) immersing the
photonic crystal fiber in the test sample; (iv) irradiating the
photonic crystal fiber and the test sample with an excitation
light, the excitation light having a wavelength in the visible to
the near infra-red (near-IR) portion of the spectrum; (v) measuring
the Raman spectrum of a photonic crystal fiber of claim 1 and a
control sample, thereby determining the background Raman spectrum;
(vi) detecting the surface enhanced Raman scattering (SERS) signal
emitted from the photonic crystal fiber and the test sample; (vii)
measuring the Raman spectrum of the photonic crystal fiber and the
test sample, thereby determining the analyte Raman spectrum;
subtracting the background Raman spectrum from the analyte Raman
spectrum, thereby sensing the analyte in the sample; (viii)
determining the enhancement factor of the SERS signal from the
control sample; (ix) determining the enhancement factor of the SERS
signal from the test sample; wherein the enhancement factor of the
SERS signal from the test sample is at least 100-fold compared with
a SERS signal from the control sample, the method resulting in
sensing the analyte.
24. The method of claim 23, wherein the analyte is a biological
composition.
25. The method of claim 24, wherein the biological composition is
selected from the group consisting of a protein, a peptide, a
polyketide, an antibody, an antigen, a nucleic acid, a peptide
nucleic acid, a sugar, a lipid, a glycophosphoinositol, and a
lipopolysaccharide.
26. The method of claim 23 wherein the analyte is selected from the
group consisting of an explosive, a chemical warfare agent, a
biological warfare agent, a toxin, a virus particle, and a
biological cell.
27. A method for measuring the quantity of an analyte in a test
sample, the method comprising the steps of: (i) providing the
photonic crystal fiber of claim 1; (ii) providing a test sample;
(iii) immersing the photonic crystal fiber in the test sample; (iv)
irradiating the photonic crystal fiber and the test sample with an
excitation light, the excitation light having a wavelength in the
visible to the near infra-red (near-IR) portion of the spectrum;
(v) measuring the Raman spectrum of a photonic crystal fiber of
claim 1 and a control sample, thereby determining the background
Raman spectrum; (vi) detecting the surface enhanced Raman
scattering (SERS) signal emitted from the photonic crystal fiber
and the test sample; (vii) measuring the Raman spectrum of the
photonic crystal fiber and the test sample, thereby determining the
analyte Raman spectrum; subtracting the background Raman spectrum
from the analyte Raman spectrum, thereby determining the quantity
of the analyte in the sample; (viii) determining the enhancement
factor of the SERS signal from the control sample; (ix) determining
the enhancement factor of the SERS signal from the test sample;
wherein the enhancement factor of the SERS signal from the test
sample is at least 100-fold compared with a SERS signal from the
control sample, the method resulting in measuring the quantity of
the analyte.
28. The method of claim 27, wherein the analyte is a biological
composition.
29. The method of claim 28, wherein the biological composition is
selected from the group consisting of a protein, a peptide, a
polyketide, an antibody, an antigen, a nucleic acid, a peptide
nucleic acid, a sugar, a lipid, a glycophosphoinositol, and a
lipopolysaccharide.
30. The method of claim 27 wherein the analyte is selected from the
group consisting of an explosive, a chemical warfare agent, a
biological warfare agent, a toxin, a virus particle, and a
biological cell.
Description
[0001] This application is a continuation of co-pending U.S.
application Ser. No. 12/733,492, filed on 19 Jan. 2011, which in
turn was a national phase application filed under 35 U.S.C.
.sctn.371 of International Patent Application Number
PCT/IB2008/002872, filed on 29 Oct. 2008; the International Patent
Application claimed priority to U.S. Provisional Patent Application
Ser. No. 60/967,555 entitled "Liquid Core Photonic Crystal Fiber
Biosensors Using Surface Enhanced Raman Scattering And Methods For
Their Use", filed Sep. 4, 2007, and U.S. Provisional Patent
Application Ser. No. 61/192,632 entitled "Liquid Core Photonic
Crystal Fiber Biosensors Using Surface Enhanced Raman Scattering
And Methods For Their Use", filed Sep. 19, 2008, which are all
herein incorporated by reference in their entirety for all
purposes.
TECHNICAL FIELD
[0003] The present invention relates to crystal fibers having a
coating of particles comprising metallic nanoparticles having
useful properties. The invention further relates to methods of
using the crystal fibers for detecting chemical and biological
analytes, and in use in optical communications.
BACKGROUND ART
[0004] During the 1980s Raman Scattering in fibers was demonstrated
by Lin, Stolen, and other co-workers of AT&T Bell Laboratories
in Holmdel, N.J. using Raman lasers operating between 0.3 to 2.0
.mu.m. In the early years of the Raman fiber before extensive work
had begun, no one perceived that a Raman fiber could be pumped by a
practical semiconductor laser-based source or that an efficient
CW-pumped Raman Fiber Laser was possible. However, with the
development of Cladding-pumped Fiber Lasers and Fiber Bragg
Gratings, diode-laser-based CW Raman Fiber Lasers have been made
efficient, emitting at various wavelengths throughout the infrared
spectrum a reality. (See van Gisbergen et al. (1996) Chem. Phys.
Lett. 259: 599-604.)
[0005] Raman spectroscopy is a powerful optical technique for
detecting and analyzing molecules. Its principle is based on
detecting light scattered off a molecule that is shifted in energy
with respect to the incident light. The shift, called Raman shift,
is characteristic of individual molecules, reflecting their
vibrational frequencies that are like fingerprints of molecules. As
a result, the key advantage of Raman spectroscopy is its molecular
specificity while its main limitation is the small signal due to
low quantum yield of Raman scattering. One way to enhance the Raman
signal is to tune the excitation wavelength to be on resonance with
an electronic transition, so called resonance Raman scattering.
This can usually produce an enhancement on the order of
10.sup.2-10.sup.3 fold.
[0006] Another technique to enhance Raman scattering is surface
enhancement by roughened metal surfaces, notably silver and gold,
that provides an enhancement factor on the order of
10.sup.6-10.sup.8. This is termed surface enhanced Raman scattering
(SERS). Similar or somewhat larger enhancement factors
(.about.10.sup.8-10.sup.10) have been observed for metal, mostly
silver or gold, nanoparticles.
[0007] In the last few years, it has been shown that an even larger
enhancement (.about.10.sup.10-10.sup.15) is possible for aggregates
of metal nanoparticles (MNPs), silver and gold. The largest
enhancement factor of 10.sup.14-10.sup.15 has been reported for
rhodamine 6G (R6G) on single silver nanoparticle aggregates. This
huge enhancement is thought to be mainly due to significant
enhancement of the local electromagnetic field of the nanoparticle
aggregate that strongly absorbs the incident excitation light for
the Raman scattering process. With such large enhancement, many
important molecules that are difficult to detect with Raman
normally can now be easily detected. This opens many interesting
and new opportunities for detecting and analyzing molecules using
SERS with extremely high sensitivity and molecular specificity.
[0008] SERS can also be developed into a molecular imaging
technique for biomedical and other applications. Existing Raman
imaging equipment should be usable for SERS imaging. SERS will
provide a much-enhanced signal and thereby significantly shortened
data acquisition time, making the technique practically useful for
medical or other commercial and industrial applications including
chip inspection or chemical monitoring. SERS is also useful for
detecting other cancer biomarkers that can interact or bind to the
MNP surface. For example, Sutphen et al. have recently shown that
lysophospholipids (LPL) are potential biomarkers of ovarian cancer
(Sutphen et al. (2004) Cancer Epidemiol. Biomarker Prev. 13:
1185-1191).
[0009] Photonic crystal fibers have been developed that can detect,
identify, and quantify ultra small quantities of analytes in air
and aqueous samples. In one example of the prior art, Du and
Sukhishvili disclose a sensor comprising a photonic crystal fiber
having an air hole cladding with functionalized air holes (Du and
Sukhishvili, US Publication Number US 2007/0020144 A1, published 25
Jan. 2007). The photonic crystal fiber disclosed by Du and
Sukhishvili comprises a solid core photonic crystal fiber; of note,
Du and Sukhishvili described that "(c)omparison of FIG. 18 with
FIG. 16 shows that the Ag nanoparticles 82 are present at a much
lower density than the Ag nanoparticles 74 of the previous
experiment. It is also apparent that the Ag nanoparticles 82 are
much larger than the nanoparticles 74, and would, therefore, be
less suitable for enhancement of SERS spectra" and that "(t)he
moderate signals detected from adsorbed Rh6G (rhodamine 6G) in no
salt aqueous solution were highly prone to fast photodegradation,
and in a typical experiment, a SERS signal was not detectable after
a 1 minute exposure of the substrate to 532 nm 10 mW laser
radiation" (Du and Sukhishvili, paragraphs 59 and 52,
respectively).
[0010] Others have also disclosed photonic crystal fibers, for
example Konorov et al. (2005, Optics Express, 13: 3454-3459) and
Konorov et al. (2006, Optics Lett., 31: 1911-1913). Konorov et al.
(2005) disclose multicore hollow photonic crystal fibers of fused
silica or soft glasses having inner diameters of the hollow core of
about 2.5 m and 3 m or about 3 .mu.m and 3.5 .mu.m, respectively.
Konorov et al. (2006) disclose hollow photonic crystal fibers with
inner diameters of between about 8.6 .mu.m and 9.5 .mu.m and an
outer diameter of 84 .mu.m. Yan et al. also disclosed a novel
hollow core photonic crystal fiber surface-enhanced Raman probe in
Yan et al., (2006) (Yan et al. (2006) Appl. Phys. Lett.
89:204101).
[0011] The original single multimode SERS fiber probe was
demonstrated in 1991 by Mullen et al. (Mullen and Carron (1991)
Anal. Chem. 63: 2196). In the following years, studies involving
different kinds of fiber tips were tested, such as flat, angled and
tapered fibers (Viets and W. Hill (2000) J. Raman Spec. 31: 625;
Viets and Hill (2001) J. Phys. Chem. B 105: 6330; and Viets and
Hill (1998) Sens. Actuators B-Chem. 51: 92). Although they were
easy to implement, the small number of SERS substrate particles in
the active region limited the sensitivity of these sensors. In
order to involve more particles in the SERS activity, hollow core
photonic crystal fiber (HCPCF) and liquid core photonic crystal
fiber (LCPCF) were tested recently (see Zhu et al. (2006) Opt. Exp.
14: 3541; Yan et al. (2006) Appl. Phys. Lett. 89: 204101; and Zhang
et al. (2007) Appl. Phys. Lett. 90, 193504. High sensitivity, and
low fiber SERS background show a promising future of PCF sensors.
However, the wavelength sensitive nature of HCPCFs limits the
application of a HCPCF to a single excitation wavelength and the
cost of PCFs is still high. While normal fibers are lower in cost,
their sensitivities are somewhat limited, often due to the
background Raman scattering from the fiber itself. Therefore, it is
highly desired to improve the detection sensitivity of SERS sensors
based on conventional fibers. Fiber SERS sensors with high
sensitivity, remote sensing capability, and low cost will find
potential applications in medical, environmental, food detection,
and toxin identification.
[0012] For many practical applications, for example SERS and
optical fibers, it is highly desirable to narrow the distribution
of size/shape of nanoparticle aggregates. For SERS in particular,
the incident light has to be on resonance with the substrate
absorption. Only those nanoparticle aggregates that have resonance
absorption of the incident light are expected to be SERS active. It
is thus extremely beneficial to have a narrow size/shape
distribution and thereby narrow optical absorption.
[0013] Fluorescent nanoparticles (quantum dots (QDs) such as
semiconductor quantum dots, SQDs) have been used recently as
fluorescent biological markers and have been found to be extremely
effective. They offer advantages including higher stability,
stronger fluorescence, tunability of color, and possibility of
optical encoding based on different sized or colored SQDs.
[0014] Metal nanoparticles have been recognized for their unique
optical properties that could be exploited in optoelectronic
devices. Nanoparticle systems composed of gold, for example, have
distinct optical properties that make them amenable to study by
Raman scattering. The Raman spectrum of the adsorbed species is
significantly enhanced by 10 to 15 orders of magnitude when the
metal nanoparticles have aggregated, leading to enhanced
electromagnetic field effects near the surface that increases the
Raman scattering intensity. The greater sensitivity found in the
surface enhanced Raman scattering (SERS) of metal nanoparticle
aggregates facilitates the detection and analysis of a whole host
of molecules that were previously difficult to study.
[0015] Wang et al. disclose a method of using SQDs (dye-conjugated
CdTe nanoparticles, CT-NPs) to detect interactive binding between
Ag-CT-NPs and Ab-CT-NPs (Wang et al. (2002) NanoLett. 2: 817-822).
The interactions were determined by differential quenching or
enhancement fluorescence activity of two different sized SQDs (red
or green) measured during the analysis.
[0016] The chemical methods used historically for the production of
gold nanoparticle aggregates (GNAs) results in a wide distribution
of aggregate size. This distribution leads to a broadened
absorption spectrum. Accordingly, researchers have attempted to
narrow the lineshape of the spectral peak due to the aggregates by
homogenizing the size of the GNAs after they have been produced. By
eliminating certain ranges of aggregate size, absorption spectrum
peaks should narrow appreciably and concomitantly increase in
intensity, resulting in more sensitive detection. Previous attempts
to select for a narrow size range of aggregates have employed
mechanical techniques such as passing a solution of aggregates
through a filter. For example, Emory & Nie have employed
size-selective fractionation using membrane filters to select for
optically active silver nanoparticles (Emory and Nie, (1997) J.
Phys. Chem. B, 102: 493-497).
[0017] The use of SERS for analyte detection of biomolecules has
been previously studied. U.S. Pat. No. 6,699,724 to West et al.
describes a chemical sensing device and method (nanoshell-modified
ELISA technique) based on the enzyme-linked immunoadsorbant assay
(ELISA). The chemical sensing device can comprise a core comprising
gold sulfide and a surface capable of inducing surface enhanced
Raman scattering (SERS). In much of the patent disclosure, the
nanoparticle is disclosed as having a silica core and a gold shell.
The patent discloses that an enhancement of 600,000-fold
(6.times.10.sup.5) in the Raman signal using conjugated
mercaptoaniline was observed.
[0018] In the nanoshell-modified ELISA technique, antibodies are
directly bound to the metal nanoshells. Raman spectra are taken of
the antibody-nanoshell conjugates before and after the addition of
a sample containing a possible antigen, and binding of antigen to
antibody is expected to cause a detectable shift in the
spectra.
[0019] The conjugation of quantum dots to antibodies used for
ultrasensitive nonisotopic detection for use in biological assays
has also been studied. U.S. Pat. No. 6,468,808 B1 to Nie et al.
disclosed an antibody is conjugated to a water-soluble quantum dot.
The binding of the quantum dot-antibody conjugate to a targeted
protein will result in agglutination, which can be detected using
an epi-fluorescence microscope. In addition, Nie et al. described a
system in which a quantum dot is attached to one end of an
oligonucleotide and a quenching moiety is attached to the other.
The preferred quenching moiety in the Nie patent is a
nonfluorescent organic chromophore such as
4-[4'-dimethylaminophenylazo]benzoic acid (DABCYL).
[0020] Raman amplifiers are also expected to be used globally as a
key device in next-generation optical communications, for example,
in wavelength-division-multiplexing (WDM) transmission systems.
Raman scattering occurs when an atom absorbs a photon and another
photon of a different energy is released. The energy difference
excites the atom and causes it to release a photon with low energy;
therefore, more light energy is transferred to the photons in the
light path.
[0021] There is therefore a need in the art for use in the
biomedical analytical industries and the optical communications
industries to provide more sensitive compositions and devices that
are inexpensive to manufacture and easy to use.
DISCLOSURE OF THE INVENTION
[0022] The invention provides a photonic crystal fiber, methods for
manufacture and/or fabrication of said a photonic crystal fiber,
and methods for using the photonic crystal fiber. The photonic
crystal fiber is used as a sensor for any analyte and is many times
more sensitive than sensors in current use, an unexpected property.
The photonic crystal fiber is used to measure the surface enhanced
Raman scattering (SERS) resulting from interactions between the
components of the photonic crystal fiber and the analyte of
interest.
[0023] In one embodiment, the invention provides a photonic crystal
fiber having improved sensitivity for detecting and/or sending a
chemical, the fiber comprising a proximal end, a distal end, the
ends defining a lumen, an outer surface, and an inner surface. In
one embodiment, the inner surface further comprises, in part, a
metallic nanoparticle composition. In an alternative embodiment,
the outer surface further comprises, in part, a metallic
nanoparticle composition. In one preferred embodiment the photonic
crystal fiber has a cylindrical shape and an approximately circular
cross-section. In another preferred embodiment the photonic crystal
fiber is flexible. In one preferred embodiment the lumen of the
fiber further comprises a liquid and/or a gas. In another preferred
embodiment the lumen of the fiber comprises a solid composition. In
one embodiment of the photonic crystal fiber, the metallic
nanoparticle composition comprises a double substrate sandwich
structure. In an alternative embodiment, the metallic nanoparticle
composition comprises a single layer. In another alternative
embodiment, the metallic nanoparticle composition comprises a
plurality of layers.
[0024] In one embodiment the sensitivity is enhanced by at least 10
times. In another embodiment, the sensitivity is enhanced by at
least 25 times. In another embodiment the sensitivity is enhanced
by at least 50 times. In another embodiment, the sensitivity is
enhanced by at least 75 times. In another embodiment the
sensitivity is enhanced by at least 100 times. In another
embodiment, the sensitivity is enhanced by at least 200 times. The
sensitivity can be enhanced by, for example, up to 10 times, up to
15 times, up to 20 times, up to 25 times, up to 30 times, up to 35
times, up to 40 times, up to 45 times, up to 50 times, up to 55
times, up to 60 times, up to 65 times, up to 70 times, up to 75
times, up to 80 times, up to 85 times, up to 90 times, up to 95
times, up to 100 times, up to 150 times, up to 200 times, up to 250
times, up to 300 times, up to 350 times or more, or any similar
level thereabouts.
[0025] In an alternative embodiment, the photonic crystal fiber
further comprises a plurality of lumens and wherein each end of the
fiber comprises a plurality of apertures to each lumen.
[0026] In one alternative preferred embodiment the photonic crystal
fiber is solid.
[0027] In another embodiment, the metallic nanoparticle composition
comprises a metal, wherein the metal is selected from the group
consisting of can be gold, silver, platinum, copper, aluminum,
palladium, cadmium, iridium, and rhodium. In a more preferred
embodiment the metal is silver. In a most preferred embodiment, the
metallic nanoparticle composition comprises silver citrate.
[0028] In one embodiment, the cross-section of the photonic crystal
fiber has dimensions of about between 0.1 .mu.m and 100 .mu.m. For
example, the cross-section of the photonic crystal fiber can be
about 0.1 .mu.m, 0.2 .mu.m, 0.3 .mu.m, 0.4 .mu.m, 0.5 .mu.m, 0.6
.mu.m, 0.7 .mu.m, 0.8 .mu.m, 0.9 .mu.m, 1 .mu.m, 2 .mu.m, 3 .mu.m,
4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m, 8 .mu.m, 9 .mu.m, 10 .mu.m, 12
.mu.m, 13 .mu.m, 14 .mu.m, 15 .mu.m, 16 .mu.m, 17 .mu.m, 18 .mu.m,
19 .mu.m, 20 .mu.m, 25 .mu.m, 30 .mu.m, 35 .mu.m, 40 .mu.m, 45
.mu.m, 50 .mu.m, 55 .mu.m, 60 .mu.m, 65 .mu.m, 70 .mu.m, 75 .mu.m,
80 .mu.m, 85 .mu.m, 90 .mu.m, 95 .mu.m, 100 .mu.m, or any dimension
therebetween. In another embodiment, the length of the photonic
crystal fiber has dimensions of about between 0.5 cm and 100 cm.
For example, the length of the photonic crystal fiber can be about,
0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, 0.9 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5
cm, 6 cm, 7 cm, 8 cm, 9 cm, 10 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16
cm, 17 cm, 18 cm, 19 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm,
50 cm, 55 cm, 60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 85 cm, 90 cm, 95
cm, 100 cm, or any dimension therebetween. In another embodiment,
the cross-section of the lumen of the photonic crystal fiber has
dimensions of about between 0.1 .mu.m and 100 .mu.m. For example,
the cross-section of the lumen of the photonic crystal fiber can be
about 0.1 .mu.m, 0.2 .mu.m, 0.3 .mu.m, 0.4 .mu.m, 0.5 .mu.m, 0.6
.mu.m, 0.7 .mu.m, 0.8 .mu.m, 0.9 .mu.m, 1 .mu.m, 2 .mu.m, 3 .mu.m,
4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m, 8 .mu.m, 9 .mu.m, 10 .mu.m, 12
.mu.m, 13 .mu.m, 14 .mu.m, 15 .mu.m, 16 .mu.m, 17 .mu.m, 18 .mu.m,
19 .mu.m, 20 .mu.m, 25 .mu.m, 30 .mu.m, 35 .mu.m, 40 .mu.m, 45
.mu.m, 50 .mu.m, 55 .mu.m, 60 .mu.m, 65 .mu.m, 70 .mu.m, 75 .mu.m,
80 .mu.m, 85 .mu.m, 90 .mu.m, 95 .mu.m, 100 .mu.m, or any dimension
therebetween.
[0029] The photonic crystal fiber is particularly useful for
sensing and measuring the quantities of an analyte. The photonic
crystal fiber disclosed herein is an improvement over the prior art
in that the presence of a fluid or liquid detection in the lumen of
the photonic crystal fiber results in an unexpectedly superior
enhancement factor of the SERS signal from the photonic crystal
fiber and a test sample comprising the analyte of interest. In a
preferred embodiment the analyte is a biological composition. The
biological composition can be, for example, a protein, a peptide, a
polyketide, an antibody, an antigen, a nucleic acid, a peptide
nucleic acid, a sugar, a lipid, a glycophosphoinositol, and a
lipopolysaccharide. In another alternative embodiment the analyte
can be an explosive, a chemical and/or biological warfare agent, a
toxin, a virus particle, and a biological cell.
[0030] In yet a further embodiment, the photonic crystal fiber
comprises a support. In a preferred embodiment, the support
comprises a medium that is permeable to an analyte of interest. In
one embodiment the support can be a gel, a solid, or a liquid. The
support can comprise a synthetic composition, such as, but not
limited to a polymer, a block copolymer, a random copolymer, a
carbon composite material, a metal composite material, or the like.
Alternatively, the support can comprise a biological compound, such
as, but not limited to, a starch composition, a cellulose
composition, a collagen composition, a latex composition, a
protein, a polypeptide, a carbohydrate, a sugar, a mixture thereof,
or the like. In another alternative, the support can be a liquid or
a gel-phase composition, such as, but not limited to, an aqueous
composition, an alcohol composition, a hydrogel, a mixture thereof,
or the like. The support can be in the form of a matrix, a
crystalline structure, a cross-linked polymer, a porous
composition, or the like. Such structures, materials, and
compositions are well known to those of skill in the art.
[0031] In another preferred embodiment, the photonic crystal fiber
has a surface wherein the surface can induce surface enhanced Raman
scattering (SERS).
[0032] In still another preferred embodiment, the photonic crystal
fiber further comprises at least one detecting molecule, wherein
the detecting molecule is bound to the surface or support. In a
more preferred embodiment the detecting molecule is selected from
the group consisting of proteins, peptides, antibodies, antigens,
nucleic acids, peptide nucleic acids, sugars, lipids,
glycophosphoinositols, and lipopolysaccharides.
[0033] In a yet more preferred embodiment the detecting molecule is
an antibody. In another preferred embodiment, the detecting
molecule is an antigen.
[0034] In another embodiment, the invention provides a photonic
crystal fiber further comprising at least one semiconductor quantum
dot. In a preferred embodiment the semiconductor quantum dot
further comprises a linker molecule, the linker molecule selected
from the group consisting of a thiol group, a sulfide group, a
phosphate group, a sulfate group, a cyano group, a piperidine
group, an Fmoc group, and a Boc group.
[0035] In a still further embodiment, the invention provides a
photonic crystal fiber comprising at least one semiconductor
quantum dot wherein the semiconductor quantum dot further comprises
a detecting molecule, wherein the detecting molecule is bound to
the semiconductor quantum dot. In a more preferred embodiment, the
detecting molecule is selected from the group consisting of
proteins, peptides, antibodies, antigens, nucleic acids, peptide
nucleic acids, sugars, lipids, glycophosphoinositols, and
lipopolysaccharides.
[0036] In a more preferred embodiment, the detecting molecule is an
antibody. In the alternative, a more preferred embodiment comprises
a chemical sensing device wherein the detecting molecule is an
antigen.
[0037] The invention further provides a method for sensing an
analyte in a test sample, the method comprising the steps of: (i)
providing the photonic crystal fiber disclosed herein; (ii)
providing a test sample; (iii) immersing the photonic crystal fiber
in the test sample; (iv) irradiating the photonic crystal fiber and
the test sample with an excitation light, the excitation light
having a wavelength in the visible to near infra-red (near-IR)
portion of the spectrum, such as, for example, from between about
600 nm to about 1,400 nm, from between about 620 to about 1,000 nm,
from between about 650 to about 950 nm, from between about 700 nm
to about 900 nm, from between about 750 nm to about 880 nm, or from
between about 770 nm to about 800 nm; (v) measuring the Raman
spectrum of a photonic crystal fiber and a control sample, thereby
determining the background Raman spectrum; (vi) detecting the
surface enhanced Raman scattering (SERS) signal emitted from the
photonic crystal fiber and the test sample; (vii) measuring the
Raman spectrum of the photonic crystal fiber and the test sample,
thereby determining the analyte Raman spectrum; subtracting the
background Raman spectrum from the analyte Raman spectrum, thereby
determining the quantity of the analyte in the sample; (viii)
determining the enhancement factor of the SERS signal from the
control sample; (ix) determining the enhancement factor of the SERS
signal from the test sample; wherein the enhancement factor of the
SERS signal from the test sample is at least 100-fold compared with
a SERS signal from the control sample, the method resulting in
sensing the analyte. In a preferred embodiment, the analyte is a
biological composition. In a more preferred embodiment, the
biological composition is selected from the group consisting of a
protein, a peptide, a polyketide, an antibody, an antigen, a
nucleic acid, a peptide nucleic acid, a sugar, a lipid, a
glycophosphoinositol, and a lipopolysaccharide. In an alternative
more preferred embodiment, the analyte is selected from the group
consisting of an explosive, a chemical warfare agent, a biological
warfare agent, a toxin, a virus particle, and a biological
cell.
[0038] The invention further provides a method for measuring the
quantity of an analyte in a test sample, the method comprising the
steps of: (i) providing the photonic crystal fiber disclosed
herein; (ii) providing a test sample; (iii) immersing the photonic
crystal fiber in the test sample; (iv) irradiating the photonic
crystal fiber and the test sample with an excitation light, the
excitation light having a wavelength in the visible to near
infra-red (near-IR) portion of the spectrum, such as, for example,
from between about 600 nm to about 1,400 nm, from between about 620
to about 1,000 nm, from between about 650 to about 950 nm, from
between about 700 nm to about 900 nm, from between about 750 nm to
about 880 nm, or from between about 770 nm to about 800 nm; (v)
measuring the Raman spectrum of a photonic crystal fiber and a
control sample, thereby determining the background Raman spectrum;
(vi) detecting the surface enhanced Raman scattering (SERS) signal
emitted from the photonic crystal fiber and the test sample; (vii)
measuring the Raman spectrum of the photonic crystal fiber and the
test sample, thereby determining the analyte Raman spectrum;
subtracting the background Raman spectrum from the analyte Raman
spectrum, thereby determining the quantity of the analyte in the
sample; (viii) determining the enhancement factor of the SERS
signal from the control sample; (ix) determining the enhancement
factor of the SERS signal from the test sample; wherein the
enhancement factor of the SERS signal from the test sample is at
least 100-fold compared with a SERS signal from the control sample,
the method resulting in measuring the quantity of the analyte. In a
preferred embodiment, the analyte is a biological composition. In a
more preferred embodiment, the biological composition is selected
from the group consisting of a protein, a peptide, a polyketide, an
antibody, an antigen, a nucleic acid, a peptide nucleic acid, a
sugar, a lipid, a glycophosphoinositol, and a lipopolysaccharide.
In an alternative more preferred embodiment, the analyte is
selected from the group consisting of an explosive, a chemical
warfare agent, a biological warfare agent, a toxin, a virus
particle, and a biological cell. In one preferred embodiment the
wavelength of the excitation light is about 633 nm. In another
alternative preferred embodiment the wavelength of the excitation
light is about 785 nm.
[0039] Another embodiment of the invention provides a method for
detecting an analyte in a sample using a photonic crystal fiber,
the method comprising the steps of: i) providing a sample; ii)
providing a semiconductor quantum dot comprising a linker molecule
(LM-SQD); iii) conjugating the analyte in the sample with the
LM-SQD thereby producing an analyte-LM-SQD conjugate; iv) providing
a photonic crystal fiber comprising a plurality of particles, each
particle comprising: a shell having at least one surface and a
lumen and wherein the shell comprises a sulfur-oxygen molecular
species, and the shell surface further comprising a detecting
molecule; v) incubating the analyte-LM-SQD conjugate with the
photonic crystal fiber for a predetermined time period; and vi)
measuring the extent of binding between the analyte-LM-SQD
conjugate and the photonic crystal fiber; thereby detecting the
analyte in the sample.
[0040] In a yet additional embodiment, the invention provides an
optical communications device comprising a photonic crystal fiber,
a plurality of particles, each particle comprising: a shell having
at least one surface and a lumen.
[0041] In a more preferred embodiment the optical communications
device comprises a fiber, wherein the fiber is selected from the
group consisting of ceramics, glasses, polymers, and metal-polymer
composites. In another preferred embodiment the chemical sensor is
disposed upon a surface of the fiber.
[0042] The invention also provides a process for fabricating a
photonic crystal fiber, the method comprising the steps of (i)
mixing AgNO.sub.3 with ethanol; (ii) stirring the AgNO.sub.3 in
ethanol until the AgNO.sub.3 is dissolved in the ethanol; (iii)
adding three molar equivalents of hexanethiol to the solution; (iv)
adding toluene to the solution; (v) reducing the solution using a
ten-fold molar excess of NaBH.sub.4 dissolved in nanopure water;
(vi) washing the solution at least three times with nanopure water
thereby removing inorganic impurities; (vii) collecting the toluene
phase; (viii) evaporating the toluene phase, thereby causing
metallic nanoparticles to come out of solution; (ix) collecting the
metallic nanoparticles; (x) dissolving the metallic nanoparticles
in methanol; (xi) evaporating the methanol; (xii) collecting the
metallic nanoparticles; re-dissolving the metallic nanoparticles in
methanol; (xiii) providing a crystal fiber, the crystal fiber
having a proximal end and a distal end; (xiv) dipping the distal
end of the crystal fiber into the metallic nanoparticle solution;
(xv) removing the distal end of the fiber from the metallic
nanoparticle solution; (xvi) washing the distal end of the crystal
fiber with ethanol; (xvi) drying the distal end of the crystal
fiber using a gas; (xvii) irradiating the crystal fiber with
ultra-violet radiation; (xviii) repeating steps (xiv) through
(xvii) at least once; the process thereby fabricating a photonic
crystal fiber. In one preferred embodiment the metallic
nanoparticles are hexanethiolate-protected silver (AgC6)
nanoparticles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1(a) shows the transmission spectrum of the Air-6-800
photonic crystal fiber.
[0044] FIG. 1(b) shows a micrograph of the cross section of a
hollow core photonic crystal fiber (HCPCF).
[0045] FIG. 1(c) shows the probing tip of a HCPCF after
post-fabrication processing.
[0046] FIG. 1(d) is an enlarged view of FIG. 1(c).
[0047] FIG. 2 is a schematic of a liquid core photonic crystal
fiber (LCPCF) SERS sensor and its cross-sectional view. The
spectrometer above the surface contains a CCD detector, a
monochromator, and electronics for data collection.
[0048] FIGS. 3a, 3b, and 3c show representative spectra of a hollow
core photonic crystal fiber.
[0049] FIG. 3a, curve A: Background Raman spectrum of the HCPCF.
Curve B: rhodamine 6G (R6G) Raman spectrum obtained using a HCPCF
SERS probe without the post-fabrication processing; the HCPCF was
dipped into the nanoparticle/R6G solution, Curve C: Subtraction of
curve A from curve B showing the net R6G Raman signal.
[0050] FIG. 3b shows a human insulin SERS spectrum obtained using a
LCPCF SERS probe after the post-fabrication processing. The fiber
background has been subtracted from the observed spectrum.
[0051] FIG. 3c is a comparison of SERS intensities between
tryptophan obtained from the post-processed LCPCF SERS probe and
that obtained directly from a dried nanoparticle/analyte film.
[0052] FIG. 4 shows some of the confined modes of a photonic
crystal fiber (PCF) when the hollow core is empty (upper plate) or
filled with liquid (lower plate).
[0053] FIG. 5 is a schematic of the tip coated multimode fiber
sensor.
[0054] FIG. 6 is a TEM micrograph of Ag-C6SH nanoparticles. The
inset shows a size histogram, illustrating an average core size for
the fiber of 4.9.+-.2.1 nm.
[0055] FIG. 7 shows SERS spectra of R6G molecules at various
concentrations using different detection methods (TCMMF, MMF in
sample solution, and direct detection). The concentrations of the
R6G molecules are as follows: FIG. 7(a), 10.sup.-5 M; 7(b),
10.sup.-6 M; 7(c), 10.sup.-7 M; 7(d), 10.sup.-8 M; and 7(e),
10.sup.-9 M.
[0056] FIG. 7(f) illustrates data from FIGS. 7(a)-(e) showing a
plot of SERS intensity versus R6G concentration using the peak
1514.3 cm.sup.-1 as an example for three detection methods (TCMMF,
MMF in sample solution, and direct detection).
MODE(S) FOR CARRYING OUT THE INVENTION
[0057] The embodiments disclosed in this document are illustrative
and exemplary and are not meant to limit the invention. Other
embodiments can be utilized and structural changes can be made
without departing from the scope of the claims of the present
invention.
[0058] As used herein and in the appended claims, the singular
forms "a," "an," and "the" include plural reference unless the
context clearly dictates otherwise. Thus, for example, a reference
to "a particle" includes a plurality of such particles, and a
reference to "a surface" is a reference to one or more surfaces and
equivalents thereof, and so forth.
[0059] The invention provides a photonic crystal fiber and methods
for fabricating a hollow photonic crystal fiber (HCPCF) and a
liquid core photonic crystal fiber (LCPCF) and demonstrates using
the SERS sensor for in vitro molecular detection.
[0060] In another embodiment the invention provides a crystal fiber
having a configuration based on a double-substrate "sandwich"
structure (DSSS) that is designed to enhance the SERS activity
using two substrates simultaneously.
Liquid Core Photonic Crystal Fiber Sensor Based on Surface Enhanced
Raman Scattering
[0061] Surface enhanced Raman scattering (SERS) sensors based on
optical fibers have attracted significant interest in molecule
sensing. On one hand, SERS offers rich molecular information while
amplifying the signal by orders of magnitude (.about.10.sup.9). On
the other hand, the flexibility of optical fibers makes it an ideal
SERS platform for practical applications. Previously, fibers with
different configurations such as a flat, angled, or tapered tip
were tested as SERS platforms. The main limitation has been the
small number of SERS substrate particles on the active fiber
region, requiring high laser intensities and/or long integration
times to attain reasonable SERS spectra.
[0062] To overcome this hurdle, several types of photonic crystal
fibers were suggested and tested. Previously, SERS was reported
with the gold nanoparticles and analyte coated (dried) on the inner
surface of the air holes of a hollow core photonic crystal fiber
(HCPCF) with the excitation light coupled into the opposite end.
Although the active sensing area was significantly increased, the
HCPCF SERS sensor performed well when the nanoparticles/analyte
dried along the light path. If the HCPCF were dipped directly into
the sample solution, the central hole, along with the surrounding
cladding holes, would all be filled with solution, leading to a
reduction of the refractive index contrast inside and outside the
holes, therefore, losing the photonic bandgap. This would in turn
result in the loss of light confinement and limit in vivo and in
vitro applications of as a HCPCF SERS sensor. The cladding holes of
the HCPCF (model Air-6-800 or model HC-633-01 fibers, for example;
other suitable fibers may also be used) were alternatively sealed
using a fusion splicer. Heat from the two electric tips of the
fusion splicer sealed the cladding holes leaving the central core
of the fiber open.
[0063] The invention provides methods, system, and apparatus to
fabricate an ultrasensitive chemical and biological sensor based on
surface enhanced Raman scattering and a novel liquid core photonic
crystal fiber (LCPCF). Surface enhanced Raman scattering provides
the fingerprint of the analyte molecules and enlarges or amplifies
the signal by up to at least 10.sup.15 times that of regular Raman
signals. The sensor can be used for in vivo and in vitro detection
and sensing if a flexible LCPCF probe is used. With this novel
fiber architecture, LCPCF achieved a much greater interaction
volume compared with a regular solid core multimode fiber, due, in
part, to both the photonic bandgap guiding and the index guiding
mechanisms; hence, a highly improved sensitivity with an additional
enhancement of at least one hundred times.
A Double Substrate "Sandwich" Structure for Fiber Surface Enhanced
Raman Scattering Detection
[0064] The invention provides methods, systems, and apparatus to
fabricate an ultrasensitive chemical and biological sensor based on
a novel liquid core photonic crystal fiber (LCPCF) with silver
nanoparticles (SNPs) coated on the inner wall of the fiber core and
surface enhanced Raman scattering (SERS). Surface enhanced Raman
scattering provides the fingerprint of the analyte molecules and
enlarges its signals by up to 10.sup.15 times that of regular Raman
signals and the flexible LCPCF probe makes the sensor applicable
for in vivo and in vitro detection. At the same time, the SNPs on
the inner wall can induce extra stronger electromagnetic field
enhancement due to the "sandwich" structure, which can result in
higher sensitivity. The analyte molecules are sandwiched between
two SNPs. One is coated on the inner wall and another is in the
solution with the molecules absorbed on it. As the simulation
shows, the electromagnetic field can be stronger between two
closely placed SNPs, thereby indicating that the stronger
electromagnetic field can result in higher SERS signal. This novel
fiber architecture comprising an inner wall coated LCPCF achieved a
much greater sensitivity up to at least ten times better than the
uncoated LCPCF model (regular solid core multimode fiber).
[0065] In one embodiment, a configuration based on a
double-substrate "sandwich" structure (DSSS) was designed to
enhance the SERS activity using two substrates simultaneously. One
simple approach to achieve this was to coat one SERS substrate, for
example, silver nanoparticles (SNPs), on the tip of a multimode
fiber (MMF) and mix second substrate in solution with the target
analyte molecules. Upon dipping the coated fiber probe into the
solution, randomly formed structures of the two substrates sandwich
the analyte molecules in between. While this approach does not
generate controllable sandwich structures, it is easy to implement.
Perfect "sandwich" structures would be expected to show stronger
enhancement than such random structures.
[0066] As shown in Xu and Kall's simulation (Xu and Kall, 2002),
the electromagnetic field between two closely spaced silver
nanoparticles was substantially enhanced by an order of 1011 in hot
nanojunctions. (See Xu and Kall (2002) Phys. Rev. Lett. 89: 246802;
Xu et al. (2000) Phys. Rev. E 62: 4138). Based on this huge
enhancement, "sandwich" structures have the potential to reach
greatly improved SERS sensitivity when the analyte molecules are
placed between two metal substrate nanostructures.
[0067] There are different approaches to implement such a
"sandwich" structure. One simple scheme is shown in FIG. 5 based on
a tip coated multimode fiber (TCMMF). The excitation light for SERS
is focused into the MMF from one end and well confined in the fiber
during the propagation to the far end of the fiber where most light
will be absorbed by the SERS substrate, SNPs, coated onto the fiber
tip and form a strong field around the tip. The sample solution is
a mixture of the analyte molecules, for example, R6G, and SNPs with
the molecules adsorbed on the nanoparticle surface. When the coated
tip dips into the solution, the SNPs and analyte molecules in the
solution interact and bind to the SNPs coated on the fiber tip.
Statistically, some of the molecules are sandwiched in the junction
between the two SNPs substrates, where the electromagnetic field is
further enhanced leading to stronger SERS signals. The SERS signal
from the sample propagates back from the MMF and photons are
detected by the Raman spectrometer.
[0068] SERS can also be developed into a molecular imaging
technique for biomedical and other applications. Exciting Raman
imaging equipment may be usable for SERS imaging. SERS can provide
an enhanced signal and thereby significantly shortened data
acquisition time, making the technique practically useful for
medical or other commercial and industrial applications including,
but not limited to, chip inspection or chemical monitoring.
SERS for Raman Amplifier in Optical Communications
[0069] Raman amplifiers have been used to amplify signal in optical
communications. SERS can provide more amplification than normal
Raman amplifiers. By coating nanoparticle compositions onto or into
glass or polymer fibers, Raman scattering from the glass or polymer
matrix can be used to amplify optical signal with the proper
wavelength.
Detection of Specific Compounds Using Fibers
[0070] The nanoparticle compositions can be used to detect specific
compounds that may be at very low levels in a sample. Such a sample
can be blood, urine, saliva, lung lavage, gastric fluid, lymphatic
fluid, any other body fluid, or the like. In addition, the sample
can be a sample of water or other aqueous medium, such as water
from a spring, a stream, a river, a pond, a lake, a sea, or an
ocean. The sample can be a geological sample such as from a
geothermal spring, a lava evaporate or exudate, a hydrocarbon, or
from an abyssal trench; a plant sample such as from the xylem or
phloem of a stalk or trunk; a sample from a fluid in a man-made
structure such as concrete, cement, aggregate, or the like; a
sample of fluid from a piece of machinery such as an engine, motor,
compressor, or the like.
[0071] The nanoparticle composition can be conjugated with
antibody, the antibody having been synthesized to bind a specific
compound. Such a specific compound can be a protein, a fatty acid,
a carbohydrate, an organic compound based upon a benzene ring
structure, an organic compound based upon a short chain
hydrocarbon, a medium chain hydrocarbon or a long chain
hydrocarbon. The specific compound can be modified with a reactive
group. Such reactive groups are well known to those of skill in the
art and can include phosphate groups, methyl groups, hydroxyl
groups, sulphate groups, acetyl groups, or the like.
[0072] The resulting substrate surface can have a surface area that
is up to at least about 8,000-fold larger than the distal end
surface of the original fiber. The diameter of the fiber can be
from between about 0.01 .mu.m to about 10 .mu.m. In one
alternative, the diameter is from between about 0.1 m to about 1
.mu.m. In another alternative, the diameter is between about 0.2
.mu.m to about 8 .mu.m.
[0073] The nanoparticle composition coating is applied and
incorporated onto the substrate surface and light is directed
longitudinally through the fiber. The light can be coherent and/or
non-coherent. The light interacts with the nanoparticle
aggregate-antibody conjugate complex and a resulting SERS profile
can be compared with a SERS profile from the nanoparticle
aggregate-antibody conjugate complex that is bound with a known
amount of specific compound. The SERS radiation is detected using a
photon detector suitably disposed to detect the SERS radiation. The
detector can be disposed at or near the substrate surface of the
fiber at the distal end or distal section of the fiber, at or near
the proximal end or proximal section of the fiber, or at another
position as disclosed herein.
[0074] The fiber can have one or more such substrate surfaces. In
the case of two substrate surfaces, the second substrate surface
can reflect the SERS signal from the first substrate surface to the
detector longitudinally along the length of the fiber, resulting in
a markedly improved amplification of the SERS signal. Similarly,
the first substrate surface can reflect a SERS signal from the
second substrate surface to the detector.
[0075] In another alternative, at least one additional fiber can be
positioned in proximity to the distal end or distal section of the
fiber. The end of the additional fiber can have the same shape as
the shape of the distal end or distal section of the fiber, such
that SERS radiation emitted from the fiber is conducted through the
additional fiber to a detector. Two additional fibers can be used
in parallel where there are two new substrate surfaces on the
fiber.
[0076] The fiber can additionally have a non-uniform diameter, for
example, the distal end having a cross-section perpendicular to the
longitudinal plane that is larger in magnitude than a cross-section
of the proximal end. Such a shape can further increase the amount
of SERS radiation produced by a photon source.
[0077] The fiber can be made using glass, ceramics, or the like; or
a polymeric compound such as cyclic olefin polymer (COP),
polysulfone (for example, UDEL and RADEL resins), fluorinated
terpolymers (such as those synthesized from tertafluoroethylene,
hexafluoropropylene, and vinylidene fluoride), polycarbonate,
polyacrylate, polystryrene, or the like.
[0078] The SERS radiation can be further enhanced approximately
4-5-fold if an electrical field of a few Volts per centimeter
(V/cm) is applied across the fiber, approximately perpendicular to
the substrate surface. The potential difference can be maintained
through an electrically conducting solution. The electrically
conducting solution can be aqueous or non-aqueous but should not
quench SERS radiation to the extent that the SERS enhancement due
to the electrical field is quenched by the electrically conducting
solution.
[0079] In one embodiment, a method to fabricate the LCPCF has been
developed. The LCPCF sensor based on SERS has been demonstrated in
the detection of molecules including R6G, human insulin, and
tryptophan. With all the holes in a HCPCF filled with liquid
samples, only the R6G SERS signal could be detected. However, using
the LCPCF with only the hollow core filled with liquid samples,
both human insulin and tryptophan SERS signals were easily detected
besides R6G. This is attributed to confinement of both light and
sample in the central core of the LCPCF and thereby increased
interaction volume. Comparison between SERS signals measured with
an LCPCF and by directly focusing the excitation light on a sample
dried on a crystal substrate has indicated an enhancement factor of
100 for LCPCF. Theoretical analysis has verified the light
confinement in an LCPCF.
[0080] In another embodiment, a unique double substrate sandwich
structure based on TCMMF has been developed as a highly sensitive
SERS probe. This probe is tested using R6G molecules and the
sensitivity has been found to be 10 times better than that using a
single SNPs substrate in solution. Concentration as low as
10.sup.-9 M can be readily detected using this probe, which is not
possible using one of the two single substrates alone. The
improvement of SERS sensitivity is attributed to the extremely
large electromagnetic enhancement between SNPs. These experiments
demonstrate the potential of using such a "sandwich" configuration
for chemical and biological sensing and detection applications.
EXAMPLES
[0081] The invention will be more readily understood by reference
to the following examples, which are included merely for purposes
of illustration of certain aspects and embodiments of the present
invention and not as limitations.
Example I: Synthesis of Liquid Core Photonic Crystal Fiber
Sensor
[0082] Here we describe an exemplary method developed to fabricate
a liquid core photonic crystal fiber (LCPCF) and demonstrate the
potential of using the LCPCF SERS sensor for in vitro molecular
detection. The LCPCF was fabricated by sealing the cladding holes
of a hollow core photonic crystal fiber (HCPCF) while leaving the
central core channel open to the outside, then dipping the
processed tip into a solution of silver nanoparticles/analyte to
fill the core by the capillary action. The HCPCF was purchased from
Newport (Photonic Crystal Fiber, Model Air-6-800) (Newport
Corporation, Irvine, Calif.). The fiber possessed a good band gap
for the excitation wavelength (785 nm) that made it suitable for
biomolecular sensing applications (see FIG. 1(a)). The HCPCF was
cut into segments of .about.10 cm in length, with both ends cleaved
carefully (FIG. 1(b)). The cladding holes were sealed by exposing
2-3 mm of one tip of the well cleaved HCPCF into a high temperature
flare (.about.1000.degree. C.) for 3-5 seconds. For a piece of well
processed HCPCF, one could see that only the surrounding cladding
holes were closed and the central hollow core was still left open,
as desired (FIG. 1(c)). After annealing, the processed fiber tip
(probing tip) was cooled down for about 5 min then dipped into the
solution containing both the SERS substrate and the analyte for 5
seconds to allow the solution to fill the hollow cores by .about.1
cm via capillary action, therefore, only the central hole is filled
with the liquid sample making it a LCPCF. The fiber was then lifted
out and mounted on the microscope with the measuring tip under the
objective focus.
[0083] As shown in FIG. 2, the excitation light was coupled in from
the unprocessed end (measuring tip) of the LCPCF and was well
confined in the core during the propagation. After interacting with
the nanoparticles/analytes solution, the SERS signal from the
sample propagated back to the measuring tip and was then collected
through the objective lens into the Raman spectrometer. Sample
measurements were obtained using a 785 nm diode laser coupled into
the fiber through a Renishaw micro-Raman spectrometer with a Leica
microscope and 50.times. objective lens. Ideally, the excitation
beam should propagate in the core of the fiber. However, the beam's
elliptical shape and size of .about.200 m.sup.2 was much larger
than the radius of the fiber core (a=3 .mu.m).
[0084] Before using the HCPCF for measuring SERS spectrum of
molecules, its Raman spectrum was obtained and presented as the
inset in FIG. 3a, curve A. The spectrum is the same as that of a
conventional silica fiber with solid core.
[0085] Silver nanoparticles, used as the SERS substrate, were
synthesized using a citrate reducing agent. The UV-Vis of the
nanoparticles has broad plasmon band in the 420 nm region indicates
the presence of mainly individual silver nanoparticle that have a
broad size/shape distribution and the TEM images verified that the
size of the nanoparticle varies between 40 and 60 nm. Silver
nitrate and sodium citrate were both purchased from Fisher
Scientific. R6G, human insulin and tryptophan solutions
(Sigma-Aldrich, St Louis, Mo.) were prepared and then mixed with
the nanoparticles to test the LCPCF SERS probe's sensitivity. The
final concentrations of the samples were .about.10.sup.-4-10.sup.-5
M. Samples with similar concentration has been detected before by
other researchers, however, difference types of SERS substrate,
laser excitation wavelength and power were used, which makes the
quantitative comparison more difficult and unavailable.
[0086] Before the post-fabrication processing, a sample of R6G
solution was used to test the HCPCF SERS sensor's performance. The
observed SERS of R6G is shown in FIG. 3a, Curve B. As shown on FIG.
3a, curve C is a difference spectrum of curve B and curve A
obtained by using the subtraction function provided by Renishaw
(Renishaw PLC, Wotton-under-Edge, Gloucestershire, United Kingdom),
showing the net R6G Raman signal. Similar experiments were
conducted for human insulin and tryptophan solutions using the
unprocessed HCPCFs. However, no SERS signals were detected through
the probe, even at higher concentrations. This is because with both
the hollow core and the cladding holes were filled with solution,
the photonic bandgap disappeared at the excitation laser wavelength
due to the reduced refractive index contrast inside and outside the
holes.
[0087] With a processed LCPCF, SERS measurements were conducted for
human insulin and tryptophan again. The SERS signals presented in
FIGS. 3b and 3c were collected with the 785 nm laser at 3 mW and a
scanning period of 20 s. The insulin SERS signal measured through
the LCPCF, FIG. 3b, matches almost all characteristic peaks of the
reference signal reported in literature.
[0088] The SERS signal of the silver nanoparticles/tryptophan
solution measured through LCPCF is shown in FIG. 3c, curve B. For
comparison, a SERS signal from a 100 .mu.l drop of the same
solution dried on a crystal substrate was obtained. The effective
size of the dried film was about 2000 .mu.m.sup.2, however, the
laser spot size was around 200 m.sup.2, meaning only 1/10 of the
molecules in the dried film were involved in the detection.
However, in the PCF, the volume of center core was about 0.3 .mu.l
(r=3 .mu.m and 1 cm of the central core is filled with solution).
Therefore, were the molecules in the probed dry film area was 30
times that in the fiber. The Raman signal of the dried silver
nanoparticles/tryptophan film is also shown in FIG. 3c, curve A.
Clearly all the characteristic peaks match well. It is worth
noticing that the magnitude of the SERS signal from the film sample
is only 3 times that of the solution sample, obtained by using the
curve fitting software provided by Renishaw, even though it was
exposed to a laser power 10 times as strong and contained 30 times
as many molecules. This gives an estimated enhancement factor
.about.100, introduced by the LCPCF. This enhancement is believed
to result from better light confinement in the fiber core and large
interaction volume between the analytes and light.
[0089] To ensure that a LCPCF can guide the laser light inside the
fiber core, we studied the modes of a PCF with its hollow core
filled with liquid. A theoretical analysis of the fiber modes was
carried out for the HCPCF used in our experiments using the MIT
photonic-bands (MPB) code. The PCF core had a diameter of 6 .mu.m,
and the cladding air holes, which were arranged in a triangular
lattice with a 1.6 m pitch, had an average diameter of 1.5 .mu.m.
FIG. 4 shows some of the confined modes when the hollow core is
empty or filled with liquid, respectively. The results show that
when the hollow core is filled with liquid, the confinement
actually becomes better, due to both the index guiding and the
photonic bandgap guiding. Therefore, the theoretical simulation
suggests that a LCPCF can improve the performance of the HCPCF SERS
probe making it an ideal probe for sensing liquid samples.
[0090] In conclusion, a method to fabricate the LCPCF has been
developed. The LCPCF sensor based on SERS has been demonstrated in
the detection of molecules including R6G, human insulin, and
tryptophan. With all the holes in a HCPCF filled with liquid
samples, only the R6G SERS signal could be detected. However, using
the LCPCF with only the hollow core filled with liquid samples,
both human insulin and tryptophan SERS signals were easily detected
besides R6G. This is attributed to confinement of both light and
sample in the central core of the LCPCF and thereby increased
interaction volume. Comparison between SERS signals measured with
an LCPCF and by directly focusing the excitation light on a sample
dried on a crystal substrate has indicated an enhancement factor of
100 for LCPCF. Theoretical analysis has verified the light
confinement in an LCPCF.
Example II: Synthesis of Double Substrate "Sandwich" Structure for
Substrate and/or Fiber
[0091] The light source was a 633 nm diode laser inside the
Renishaw micro-Raman spectrometer with a Leica microscope and
50.times. objective. The multi-mode fiber (MMF) used as a SERS
probe was purchased from Newport (Model F-MLD-500) (Newport
Corporation, Irvine, Calif.). The SNPs coated on the tip passivated
with hexanethiol were prepared by using a modified Brust method
(Brust et al. (1994) J. Chem. Soc.-Chem. Comm. 801: 1994).
Typically, 170 mg of AgNO.sub.3 was dissolved in 5 ml of ethanol
and kept under constant magnetic stirring. To that mixture, 3 molar
equivalents of hexanethiol was added dropwise followed by an
addition of 80 ml of toluene. The solution was subsequently reduced
with a ten-fold molar excess of NaBH.sub.4 in 10 ml of nanopure
water. The reduction was allowed to proceed overnight. Afterward,
the solution was washed several times with nanopure water to remove
any inorganic impurities and the toluene phase was collected and
was placed under rotary evaporation. The particles were further
purified with methanol and the resulting purified
hexanethiolate-protected silver (AgC6) nanoparticles were collected
on a glass frit. In order to determine the core size of the
particles, transmission electron microscopy was used (National
Center for Electron Microscopy, Lawrence Berkeley National Labs).
The samples were (.about.1 mg/ml) dropcast onto a 200 mesh carbon
grid. FIG. 6a shows a TEM micrograph of the Ag-C6SH. The average
core diameter is 4.9.+-.2.1 nm. UV-visible spectroscopic
measurements of the resulting particles in tetrahydrofuran solvent
exhibited an intense absorption peak at 425 nm, characteristic of
the surface plasmon resonance of SNPs.
[0092] The coating of the fibers was based on a simple dipping
procedure. A concentrated solution of the silver nanoparticles (10
mg/ml) was prepared. The end of the fiber, with its protection
jacket removed, was then dipped into the solution and left in the
solution for 5 minutes. After dipping, the end of the fiber coated
with the silver particles was washed with copious amounts of
ethanol and then dried with a gentle stream of ultra-high purity
nitrogen. The fiber was then placed in a UVO chamber for ten
minutes to remove the organic component from the particles. The
dipping procedure was repeated to form a multilayer of particles on
the surface of the fiber optic fiber.
[0093] The SNPs used in the solution were prepared by using a
different synthetic protocol from Lee and Meisel (Lee and Meisel
(1982) J. Phys. Chem. 86: 3391). Briefly, silver nitrate was used
as the metal precursor and sodium citrate as the reducing agent.
The formation of the SNPs was monitored by UV-vis spectroscopy
using a HP 8452A spectrometer with 2 nm resolution, and the
corresponding surface plasmon absorption in the aqueous solution
was observed at 406 nm. The core diameter of these SNPs was found
to be 25 nm by observation under a transmission electron microscope
(TEM, Model JEOL JEM 1200EX). Compared to the AgC6 particles
organic solvent, nanoparticles made by the Lee and Meisel method in
aqueous solution have larger average diameter but show a blue shift
in the plasmon peak. The reason for this seemingly contradictory
data is that the peak position depends not only on particle size
but also on the media or the solvent. The larger refractive index
of dielectric constant of the organic solvent causes a substantial
red-shift of the plamson peak compared to that of water.
[0094] The sample solution in this study was prepared for various
concentrations of R6G molecules (10.sup.-5 M.about.10.sup.-9 M) and
sodium chloride (NaCl, 10 mM) was added to induce aggregate
formation. Starting with aqueous R6G solution (10.sup.-4M), SNPs
was added to dilute the R6G solutions. 30 .mu.l of the R6G solution
and 270 .mu.l of the SNPs colloid were mixed and therefore we
obtained 300 .mu.l sample with a concentration of 10.sup.-5 M of
R6G molecules. Then 30 .mu.l of the resulting solution was added to
270 .mu.l of the SNPs colloid again to obtain a sample solution
with an R6G concentration of 10.sup.-6 M. Solutions of various
concentrations from 10.sup.-7 M to 10.sup.-9 M, respectively, were
prepared using the similar method. The solutions were incubated for
about 10 minutes at room temperature and then activated with 15
.mu.l NaCl solution. Raman tests were performed about 20 minutes
after the introduction of salt.
[0095] Four different configurations were tested to compare the
performance of the TCMMF sensors with other approaches, for various
concentrations: 1) detection with the TCMMF probe dipped in the
mixed sample solution; 2) direct detection of the SERS signal in
the sample solution; 3) detection with an uncoated MMF as the probe
dipped in the mixed sample solution; 4) detection with the TCMMF
probe dipped in the aqueous R6G solution.
[0096] The lowest detectable concentration with the fourth
configuration was around 10.sup.-3 M.about.10.sup.-4 M, which was
much higher than the other three methods, therefore, was not
included in the following comparison.
[0097] FIG. 7(a), 7(b), 7(c), 7(d), and 7(e) compare results
obtained with the first three methods for various concentrations.
For each concentration, the output power from the laser diode was
3.2 mW, and at the far end of an ordinary MMF, the power was around
3.0 mW, indicating a 93.75% coupling efficiency. Whereas at the far
end of a TCMMF, the power was 1.0 mW, indicating that most of the
light was absorbed by the SNPs coated at the tip and the field was
confined well around the tip. The lowest detectable concentration
with the last approach was around 10.sup.-3 M.about.10.sup.-4 M,
which was much higher than the other three methods and did not
considered in this comparison. Taking the peak at 1514.3 cm.sup.-1
as an example, the SERS intensity versus R6G concentration was
shown in FIG. 7(f).
[0098] Based on quantitative comparison of the SERS results, the
lowest detectable concentration using the MMF probe, direct
solution detection, and the TCMMF probe were 10.sup.-6 M, 10.sup.-8
M and 10.sup.-9 M, respectively. For the same concentration of R6G,
the signal intensity from the TCMMF probe was consistently much
higher than that from the MMF probe or direct solution detection,
as well as the simple sum of the signals from MMF plus the direct
solution detection. This indicates stronger SERS activity with the
TCMMF due most likely to stronger electromagnetic enhancement as a
result of the unique "sandwich" structure. Such sandwich structures
formed by SNPs on the fiber probe with SNPs in solution are
expected to exhibit stronger SERS due to stronger electromagnetic
enhancement as compared to each substrate alone since some of the
R6G analyte molecules are at junctions of SNPs. Under the same
given conditions, the TCMMF experimental setup can be easily
reproducible as for the practical usage. These results show that
sandwich structures are indeed promising for improving SERS
detection.
[0099] In conclusion, a unique double substrate sandwich structure
based on TCMMF has been developed as a highly sensitive SERS probe.
This probe is tested using R6G molecules and the sensitivity has
been found to be 10 times better than that using a single SNPs
substrate in solution. Concentration as low as 10.sup.-9 M can be
readily detected using this probe, which is not possible using one
of the two single substrates alone. The improvement of SERS
sensitivity is attributed to the extremely large electromagnetic
enhancement between SNPs. These experiments demonstrate the
potential of using such a "sandwich" configuration for chemical and
biological sensing and detection applications.
[0100] Those skilled in the art will appreciate that various
adaptations and modifications of the just-described embodiments can
be configured without departing from the scope and spirit of the
invention. Other suitable techniques and methods known in the art
can be applied in numerous specific modalities by one skilled in
the art and in light of the description of the present invention
described herein. Therefore, it is to be understood that the
invention can be practiced other than as specifically described
herein. The above description is intended to be illustrative, and
not restrictive. Many other embodiments will be apparent to those
of skill in the art upon reviewing the above description. The scope
of the invention should, therefore, be determined with reference to
the appended claims, along with the full scope of equivalents to
which such claims are entitled.
* * * * *