Surface-enhanced Raman scattering (SERS) detection of multiple viral antigens using magnetic capture of SERS-active nanoparticles.

A highly sensitive immunoassay based on surface-enhanced Raman scattering (SERS) spectroscopy has been developed for multiplex detection of surface envelope and capsid antigens of the viral zoonotic pathogens West Nile virus (WNV) and Rift Valley fever virus (RVFV). Detection was mediated by antibody recognition using Raman reporter-coated Au nanoparticles (GNPs) and paramagnetic nanoparticles (PMPs) conjugated with polyclonal antibodies specific for each antigen target, followed by 785nm laser excitation of magnetically concentrated GNP/antigen/PMP complexes. The discrimination of WNV and RVFV antigen detection in mixed Raman spectra was achieved by SERS enhancement of Raman spectra specific for the Raman reporter dyes Infrared 792 (IR-792) and Nile Blue (NB), respectively. Assay reactions containing dilutions of both target antigens yielded a reduction in the intensification of IR-792 and NB signature spectrum peaks and provided a conservative limit of detection of ∼5fg/ml for assays conducted in phosphate buffered saline buffer (PBS) and ∼25pg/ml for assays containing PBS spiked with fetal bovine serum. Based on the inherent simplicity of the assay, magnetic capture-based SERS assays afford promise as a biosensor platform that provides high-level multiplex detection sensitivity and can be adapted for portable diagnostic applications in limited resource settings.