Determination of lentiviral titer by surface enhanced Raman scattering

Lentiviruses are commonly used to deliver genetic code into host cells for biomedical applications, such as gene therapy, pharmaceuticals, and vaccine development. Knowing the infectious titer of these virus particles is critical for development in these areas. Current methods of determining viral titer often require cell culture, where a cell is infected and the inserted genetic code is expressed in a known number of cells, which can require days or weeks to prepare and analyze samples. To provide a more rapid method of determining viral titer, the use of surface enhanced Raman spectroscopy (SERS) was explored. SERS provides both chemical and structural information by using plasmonic metallic nanostructures to amplify the Raman signal. Two different lentiviruses, one with a vector encoding a GFP gene and the same virus without the GFP gene included, were analyzed by SERS in viral production media at various concentrations. The SERS response was demonstrated to be sensitive to the incorporation of the GFP gene into the viral vector. Chemometric analysis using multivariate curve resolution (MCR) was able to identify a component in the observed SERS spectra that correlated with the concentration of GFP containing virus particles. Using the MCR model and the SERS response, the viral titer of lentivirus encoding for GFP was determined. The viral titer determined by SERS agreed well with expression of the GFP in infected cells. The SERS response using different metals and excitation wavelengths was also explored. Overall, this work demonstrates the utility of SERS for rapid determination of lentiviral titer.