Rapid and Sensitive Detection of Respiratory Virus Molecular Signatures Using a Silver Nanorod Array SERS Substrate Saratchandra Shanmukh, ² Les Jones, § Jeremy Driskell, ² Yiping Zhao, ‡ Richard Dluhy, ² and Ralph A. Tripp* ,§ Department of Chemistry, Physics and Astronomy and Center for Disease InterVention, Department of Infectious Diseases, UniVersity of Georgia, Athens, Georgia 30602 Received July 19, 2006; Revised Manuscript Received September 12, 2006 ABSTRACT A spectroscopic assay based on surface enhanced Raman scattering (SERS) using silver nanorod array substrates has been developed that allows for rapid detection of trace levels of viruses with a high degree of sensitivity and specificity. This novel SERS assay can detect spectral differences between viruses, viral strains, and viruses with gene deletions in biological media. The method provides rapid diagnostics for detection and characterization of viruses generating reproducible spectra without viral manipulation. Introduction. Rapid and sensitive pathogen detection is central to human health care, required for proper therapeutic treatment, and required for prevention and control of pandemics or bioterrorism. The majority of existing viral detection assays employ antibody-based methods that include enzyme-linked immunosorbant assays (ELISA), 1 fluorescent antibody assays, 2 or serologic testing. 17 These methodologies lack the sensitivity and specificity required for low level virus detection, therefore more costly and laborious polymerase chain reaction (PCR) assays are often necessary to enhance virus detection. 8 Since these diagnostic methods are generally cumbersome and often have limited sensitivity, a variety of new virus detection methods, including microcantilevers, 9 evanescent wave biosensors, 4 immunosorbant electron mi- croscopy, 31 and atomic force microscopy, 12 have been investigated to overcome these limitations. However, these new techniques are unable to discriminate between virus species with reasonable sample throughput, thus there is an unmet need for a rapid, reproducible, and sensitive means of detecting viruses that may inflict substantial burdens on human and animal health. Raman spectroscopy has previously been used to charac- terize virus structure; 27 however, normal, un-enhanced Raman spectroscopy has an extremely small scattering cross section, which limits its use as a low level bioanalytical sensor. Surface-enhanced Raman spectroscopy (SERS) is a variation of Raman in which the incoming laser beam interacts with electrons in plasmon oscillations in metallic nanostructures to enhance, by orders of magnitude, the vibrational spectra of molecules adsorbed to the surface. 15 The morphology of the metallic nanostructures is a primary factor determining the magnitude of signal enhancement and sensitivity of detection. 25 Since SERS is useful for determining molecular structural information, and because SERS provides ultra- sensitive detection limits including single molecule sensitiv- ity, 11,29 it has been used to detect bacteria 21 and viruses using direct spectroscopic characterization 1 or reporter molecule sandwich assemblies. 5 However this remarkable analytical sensitivity has, for the most part, not translated into the development of practical in-situ diagnostic SERS probes. 15 This is due in large part to the difficulty in easily preparing robust, metal-coated substrates of the correct surface mor- phology that provide maximum SERS enhancements. We recently showed that a silver (Ag) nanorod SERS array fabricated using the oblique angle deposition (OAD) method acts as an extremely sensitive SERS substrate with enhance- ment factors of greater than 10 8 . 3,30 The nanofabrication technique (OAD) offers a flexible, easy, and inexpensive method for fabrication of integrated nanoprobes for high sensitivity SERS applications. The SERS substrates produced by OAD have the advantages of large area, uniform, reproducibility. These novel substrates allow us to develop SERS-based biosensors rapidly, accurately, and cost-ef- fectively to detect extremely low levels of viruses, thus bridging a critical need for a rapid, sensitive, and reliable * Corresponding author. ² Department of Chemistry. ‡ Department of Physics and Astronomy. § Department of Infectious Diseases. NANO LETTERS 2006 Vol. 6, No. 11 2630-2636 10.1021/nl061666f CCC: $33.50 © 2006 American Chemical Society Published on Web 09/30/2006