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 Evanescent wave TIR - propagating light encounters a boundary to a medium of lower refractive index, at angle greater than “critical angle” reflected light generates a highly restricted electromagnetic field adjacent to the interface in the lower ref. index medium ev. Wave is identical in frequency to the incident light, and decays exponentially in intensity with distance from the interface (high S/N) possible to do single molecule fluoresence http://www.microscopyu.com/articles/fluorescence/tirf/tirfintro.html

Typical TIRF Sensogram Epifluorescence http://www.tirftechnologies.com/principles.php http://www.microscopyu.com/articles/fluorescence/tirf/tirfintro.html http://www3.interscience.wiley.com/cgi-bin/fulltext/118806996/HTMLSTART 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 This is a process where functional and cross-linking monomers are copolymerized in the presence of a target analyte (the imprint molecule), which acts as a molecular template. The functional monomers initially form a complex with the imprint molecule, and following polymerization, their functional groups are held in position by the highly cross-linked polymeric structure. Subsequent removal of the imprint molecule reveals binding sites that are complementary in size and shape to the analyte. In that way, a molecular memory is introduced into the polymer, which is now capable of selectively rebinding the analyte Despite the conceptual similarities between MIPs and antibodies, they display very different types of recognition properties. The most significant difference is that MIPs contain a heterogeneous distribution of binding sites, whereas monoclonal antibodies are homogeneous and have a single type of binding site. The concentration-dependant binding properties can be exploited at low analyte concentrations. 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 Challenges in developing fluorescent and UV-visible monitored MIP sesnors: (1) low selectivities and high cross-reactivities of MIPs; (2) lack of an inherent signaling mechanism in MIPs; (3) poor optical and material properties of MIPs. http://www3.interscience.wiley.com/cgi-bin/fulltext/114082177/HTMLSTART http://pubs.acs.org/doi/full/10.1021/cr990099w http://www.rsc.org/delivery/_ArticleLinking/ArticleLinking.cfm?JournalCode=AN&Year=2001&ManuscriptID=b102799a&Iss=6 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

Provides rich info. about structural data! Raman Spectroscopy Selection rules Based on symmetry elements of polarizability tensor Vibrational fingerprint Comprised of narrow spectral features Robust mechanism Not subject to photobleaching Weak Signal Compared to Rayleigh scattering / fluorescence Provides rich info. about structural data! adenine cytosine guanine thymine uracil 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)

Away from plasmon resonance SERS Enhancement Chemical Enhancement Based on metal-molecule charge- transfer effects Electromagnetic enhancement Coupled to surface plasmon excitation of metal nanostructures Tunable resonances: Shape- and Size-effects 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 Adsorbed molecules see increased field Raman signal enhancement (up to 1015) Depends on local geometry of adsorption site Enhancing SERS substrates 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 Near-IR excitation and biocompatability allow Femtomolar and beyond Single molecule spectroscopy is possible 1500 cm-1 1532cm-1 1600cm-1 1635cm-1 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 Image source: http://senseable.mit.edu/nyte/visuals.html (New York Talk Exchange) Numbers: http://www.thefreelibrary.com/Market+profile:+SERS-a0137966471

SERS Companies Renishaw Real Time Analyzers Bruker Optics D3 Technologies (Mesophotonics) Oxonica Renishaw Real Time Analyzers Source: http://www.brukeroptics.com/raman.html http://www.brukeroptics.com/raman.html

SERS Vials Real Time Analyzers Sol-gel of Au or Ag nanoparticles 106 signal enhancement Source: RTA 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 BI- 2000 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 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