SERS-based Biosensors
James Krier, Lalitha Muthusubramaniam
Kevin Wang, Douglas Detert
Final Presentation
EE235: Nanofabrication
May 12, 2009
Overview
•
Technology Landscape: Optical techniques for
biosensing
•
Surfaced-enhanced Raman scattering (SERS)
•
•
Technical background
•
SERS-based biosensors
Financial and market considerations of SERS
Vast Technology Landscape
Diverse Applications
Total internal reflectance
fluorescence (TIRF) biosensor
TIR
Evanescent wave
http://www.microscopyu.com/articles/fluorescence/tirf/tirfintro.html
Typical TIRF Sensogram
Epifluorescence
TIRF
Advantages
High Signal to noise ratio (very little secondary emission from bulk solution)
Highly robust, low cost, portable
Drawbacks
Need for labels
High cross-reactivity (hence not easy to multiplex)
http://www.tirftechnologies.com/principles.php
Molecularly Imprinted Polymers as Optical
Sensors
Schematic representation of molecular imprinting
Distribution of binding affinities in MIP vs. Ab
Chemical Reviews, Chem. Rev.,100 2495 (2000)
3 methods to monitor binding in
MIPs
•
Direct monitoring of analyte
in solution; Incorporation of
spectroscopically
responsive monomers into
the matrix;Competition
assays using labeled
ligands
Polymer International, Vol 56( (4), pp. 482-488
Reflectometric interference
spectroscopy (RIFS)
•
The reflected beams
superimpose and change
optical thickness of the
transducer by binding events
onto the surface. Shift in
characteristic interference
spectrum is transformed into
a signal curve.
J. Immunological Methods Vol 292, Issues 1-2, September 2004, pp.35-42
Reflectometric interference
spectroscopy (RIFS)
Protein concentration determined
spectrophotometrically and active
antibody concentration determined
by biosensor and ELISA for 9
sequentially eluted fractions.
J. Immunological Methods Vol 292, Issues 1-2, September 2004, pp.35-42
The SERS Solution
Adsorption
Excitation
Detection
Raman Spectroscopy
C.V. Raman
http://www.kamat.com/database/content/pen_ink_portraits/c_v_raman.htm
Adapted from http://upload.wikimedia.org/wikipedia/commons/8/87/Raman_energy_levels.jpg
Raman Spectroscopy
•
Selection rules
Based on symmetry elements of
polarizability tensor
•
Provides rich info. about structural data!
adenine
Vibrational fingerprint
cytosine
Comprised of narrow
spectral features
•
Robust mechanism
Not subject to photobleaching
•
guanine
Weak Signal
thymine
uracil
Compared to Rayleigh
scattering / fluorescence
Gelder, et al., J. Raman Spectrosc., 38 1133 (2007)
A. Campion et al., Chem. Soc. Rev., 27 241 (1998)
Surface-Enhanced Raman
Scattering
1928
C.V. Raman discovers “Raman Effect” of inelastic
scattering
1974
Discovery of enhanced Raman signals (105-106)
from molecules adsorbed on roughed Ag surfaces.
Mechanism is attributed to enhanced surface area
for adsorption.
1977
Debate begins over the exact mechanism of signal
enhancement.
M. Fleischmann, et al., Chem. Phys. Lett., 26 163 (1974)
D.L. Jeanmaire, R.P. Van Duyne, J. Electroanal. Chem., 84
1 (1977)
M.G. Albrecht, J. A. Creighton, J. Am. Chem. Soc., 99 15
(1977)
S. Schultz, et al., Surface Science, 104 419 (1981)
M. Moskovits, , Reviews of Modern Physics, 57 3 (1985)
K. Kneipp, et al., Chem. Rev., 99 2957 (1999)
SERS Enhancement
•
Chemical Enhancement
Based on metal-molecule chargetransfer effects
•
Tunable resonances: Shape- and Size-effects
Electromagnetic enhancement
Coupled to surface plasmon excitation
of metal nanostructures
Away from plasmon
resonance
At plasmon
resonance
A.J. Haes, et al., Anal. Bioannal. Chem., 379 920 (2004)
S. A. Maier, et al., Adv. Mater., 13 1501 (2001)
SERS Enhancement
•
Plasmon resonance leads to local field
enhancement near the surface
Enhancing SERS
substrates
Adsorbed molecules see increased field
•
Raman signal enhancement (up to 1015)
Depends on local geometry of adsorption site
10-250 nm
K. Kneipp, et al., Chem. Rev., 99 2957 (1999)
J. Aizpurua, et al., Phys. Rev. Lett., 90 057401-1 (2003)
The SERS Advantage
•
Molecular fingerprinting
Unique vibrational spectra distinguishes molecules
•
Tagless biosensing
Fluorescent dyes are not needed
•
Multiplexed sensing
Plasmon resonances allow for sensor tunability
•
In vivo applicability
1500 cm-1
1532cm-1
1600cm-1
1635cm-1
Near-IR excitation and biocompatability allow
•
Femtomolar and beyond
Single molecule spectroscopy is possible
S.M. Nie, et al., Science, 275 1102 (1997)
http://www.oxonica.com/diagnostics/diagnostics_sers_imaging_applications.php
Single Molecule Detection
PRL 78, 1667 (1997)
TERS
nanowerk.com
TERS
Faraday Discuss., 132, 9 (2006)
TOPOGRAPHY + SPECTROSCOPY
PRL 100, 236101 (2008)
In-vivo glucose sensing
Faraday Discuss., 132, 9 (2006)
Other Options
PRL 62, 2535 (1989).
More Moerner et al.
Nature 402, 491 (2000).
stanford.edu/group/moerner/sms_movies.html
NSOM
JPC 100, 13103 (1996)
SERS Market
• Consumables
$50 to $750 per analysis
$1 million market annually
• Instrumentation
$10,000 - $180,000
Image source: http://senseable.mit.edu/nyte/visuals.html (New York Talk Exchange)
Numbers: http://www.thefreelibrary.com/Market+profile:+SERS-a0137966471
SERS Companies
• Bruker Optics
• D3 Technologies (Mesophotonics)
• Oxonica
• Renishaw
• Real Time Analyzers
http://www.brukeroptics.com/raman.html
SERS Vials
• Real Time Analyzers
• Sol-gel of Au or Ag
nanoparticles
• 106 signal
enhancement
www.rta.biz
Portable Raman
• Real Time Analyzers RamanID
• DeltaNu Inspector Raman
Diesel Fuel Spectrum
SPR Companies
• Biacore (GE)
• Biosensing Instrument
• FujiFilms
• GWC Technologies
• Ibis
• Sensiq
SPR Analyzer
• Biosensing Instrument BI2000
• Cost: $39k
• Liquid/Gas Detection
• 10-4 degree sensitivity
Cost Comparison
Method
Equipment
Consumables
SERS
Spectrometer, $10kHe/Ne
Laser, $760Optics,
$100Microflow Cell,
$300Total = $11.1k
Au Nanoparticles ($3/mL)
TERS (AFM+ SERS)
AFM ($90k - $150k)Total =
$111k - $161k
AFM tips ($10)
SPR
Full Setup, $39k - $60k
Au Nanoparticles ($3/mL)
NSOM
Full Setup, $100k - $250k
NSOM tip ($100)
Conclusion: SERS
•
Even simple (diatomic) molecules can have complex and
reproducible vibrational fingerprints
•
The most practical option for sensing near the single-molecule
level for a variety of analytes in solution or air, lending to an
array of applications ranging from trace gas detection to
automated protein identification
•
Easy to couple with other supplementary techniques (e.g.,
AFM)
•
Provides an economically feasible sensing mechanism for
portable devices in atmospheric conditions