Clinical validation of surface-enhanced Raman scattering-based immunoassays in the early diagnosis of rheumatoid arthritis

We assessed the clinical feasibility of conducting immunoassays based on surface-enhanced Raman scattering (SERS) in the early diagnosis of rheumatoid arthritis (RA). An autoantibody against citrullinated peptide (anti-CCP) was used as a biomarker, magnetic beads conjugated with CCP were used as substrates, and the SERS nanotags were comprised of anti-human IgG-conjugated hollow gold nanospheres (HGNs). We were able to determine the anti-CCP serum levels successfully by observing the distinctive Raman intensities corresponding to the SERS nanotags. At high concentrations of anti-CCP (> 25 U/mL), the results obtained from the SERS assay confirmed those obtained via an ELISA-based assay. Nevertheless, quantitation via our SERS-based assay is significantly more accurate at low concentrations (< 25 U/mL). In this study, we compared the results of an anti-CCP assay of 74 clinical blood samples obtained from the SERS-based assay to that of a commercial ELISA kit. The results of the anti-CCP-positive group (n = 31, > 25 U/mL) revealed a good correlation between the ELISA and SERS-based assays. However, in the anti-CCP-negative group (n = 43, < 25 U/mL), the SERS-based assay was shown to be more reproducible. Accordingly, we suggest that SERS-based assays are novel and potentially useful tools in the early diagnosis of RA.