Detecting Different Strains Of A Single Virus Type

In addition to the capacity to differentiate between different virus types, SERS can also be used to distinguish strains of a single virus type. One example is the detection of RSV strains (fig 7), although we have also shown that SERS can readily distinguish influenza A strains. Using SERS, the RSV viruses A/Long, A2 and ΔG (belonging to the RSV A strain), as well as the RSV strain B1, have been analyzed and their corresponding baseline corrected spectra (1400 cm^-1–600 cm^-1) are shown in fig 7.

Fig. 7. Summed SERS spectra of individual RSV strains (a) strain A/Long, (b) strain B1, (c), strain A2 with a G gene deletion (ΔG), and (d) strain A2.

The SERS spectrum of A/Long (fig 7a) differs from the other RSV spectra in that the prominent C–N stretch occurs at 1055 cm^-1, compared with 1042–1045 cm^-1 for the other RSV viruses. Bands unique to A/Long are also observed at 877 cm^-1 and 663 cm^-1, while the band at 528 cm^-1 (present in the other spectra) is absent. It is likely that the different spectrum observed for A/Long relates to a different composition of nucleic acids and viral envelope proteins. As predicted, there are also differences in the SERS spectra between the A and B1 strains. The differences that distinguished the A strain from the B strain SERS spectra include the relative intensities of the nucleic acid bands compared with the other bands in the spectrum. Significantly, we have also been able to show that the intrinsic SERS spectra are capable of detecting gene deletions in viruses. This is shown by the SERS spectra comparing the parental A2 strain (fig 7d) to the RSV G protein gene deletion mutant from which it was derived, ΔG (fig 7c). Comparison of the spectra reveals subtle yet real differences in peak intensities of the Raman spectra between 700 –900 cm^-1.