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  • Surface-enhanced Raman spectroscopy detects viruses

Dec 2006
David Shenkenberg

To enable better management of viral outbreaks, diagnostic technology needs to become more rapid, sensitive and reliable. Enzyme-linked immunosorbent assays and fluorescent antibody assays cannot detect low virus levels, and atomic force microscopy and immunosorbent electron microscopy cannot discriminate among viral strains or work rapidly enough to handle significant patient loads.

Ralph A. Tripp and colleagues at the University of Georgia in Athens hypothesized that surface-enhanced Raman spectroscopy using a silver nanorod array substrate could enable improved detection because they had already observed enhancement factors of greater than 100 million for the array. Therefore, they tested the device’s ability to differentiate among a variety of viruses, viral strains and viruses with gene deletions in biological media.

In their experiments, the researchers employed a near-IR confocal Raman microscope system, a fiber optic interfaced 785-nm near-IR diode laser and an f/1.8-near-IR spectrograph, all from Kaiser Optical Systems of Ann Arbor, Mich. The spectrograph was equipped with an LN2-cooled CCD camera from PI/Acton of Trenton, N.J. They used a relatively low laser power of 10 to 15 mW that minimized photodamage and a collection time of 30 to 50 s, conveniently rapid for clinical use.

As reported in the Oct. 21 online publication of Nano Letters, the investigators detected distinct spectral bands for adenovirus, rhinovirus and a tropical strain of HIV, demonstrating that various viral species could be detected using their assay. They performed tests with respiratory syncytial virus that showed that the growth medium did not confound their results. They tested a mixture of strains of influenza and differentiated among them, demonstrating that even related viral strains could be distinguished within a complex mixture. They also showed that different strains of respiratory syncytial virus, including an artificial strain with a gene deletion, could be detected reproducibly.

As a result of these experiments, Tripp said, “I strongly believe that our technology represents the advent of the next generation of pathogen detection.”

Tripp may create a spin-off company based on his patent-pending assay. His lab is currently testing the ability of the device to detect bacteria and a wider range of viral species.

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