Surface-enhanced Raman spectroscopy detects viruses
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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