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.

Substrates consisting of silver nanorod arrays with an irregular surface lattice ͑i.e., random nucleation sites͒ and with varying rod lengths were fabricated by an oblique angle vapor deposition method. These arrays were evaluated as potential surface-enhanced Raman spectroscopy ͑SERS͒ substrates using trans-1,2-bis͑4-pyridyl͒ethene as a reported molecule. SERS activity was shown to depend upon the length of the nanorods. The Ag nanorods with average lengths of 508.29± 44.86 nm, and having aspect ratios of 5.69± 1.49 exhibited the maximum SERS enhancement factors of greater than 10 8. Theoretical calculations indicate that this large SERS enhancement may be partially explained by the shape, density, and lateral arrangement of the Ag nanorod arrays.

Aligned Ag nanorod arrays have been fabricated on glass substrates using an oblique angle vapor deposition (OAD) method. The surface morphology and structure of the Ag rods were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Individual nanorods were found to be primarily cylindrical, albeit with irregularly shaped surface protrusions of the rods. The surface enhanced Raman scattering (SERS) response as a function of nanorod length was investigated using trans-1,2-bis(4pyridyl)ethene as a probe molecule at an excitation wavelength of 785 nm. The enhancement factors reached a maximum of ∼5 × 10 8 as the nanorod length approached 868 nm and then decreased to ∼3 × 10 6 as the nanorod length increased further to 1900 nm. For the 868 nm nanorod array, signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 10%, while an RSD of 15% was measured in signals collected from different substrates. When stored in a food vacuum bag, the substrates are stable with respect to SERS intensity for greater than 2 months. This study demonstrates that the OAD Ag nanorod arrays are highly sensitive, uniform, and stable SERS substrates that are suitable for a variety of surface chemical analysis applications.

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