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Abstract

A quick and reproducible surface-enhanced Raman scattering (SERS)-based immunoassay technique, using hollow gold nanospheres (HGNs) and magnetic beads, has been developed. Here, HGNs show strong enhancement effects from individual particles because hot spots can be localized on the pinholes in the hollow particle structure. Thus, HGNs can be used for highly reproducible immunoanalysis of cancer markers. Magnetic beads were used as supporting substrates for the formation of the immunocomplex. This SERS-based immunoassay technique overcomes the problem of slow immunoreaction caused by the diffusion-limited kinetics on a solid substrate because all of the reactions occur in solution. For the validation of our SERS immunoassay, a well-known lung cancer marker, carcinoembryonic antigen (CEA), was used as a target marker. According to our experimental results, the limit of detection (LOD) was determined to be 1-10 pg/mL, this value being about 100-1000 times more sensitive than the LOD of enzyme-linked immunosorbent assay, the assay time took less than 1 h, including washing and optical detection steps. In addition, a microfluidic platform allows the integration of solenoids for low-volume immunoassay. Using the gradients generation channel, four different concentrations of analytes were obtained and chaotic mixer was adopted for complete mixing. A whole SERS-based sandwich immunoassay procedure has been performed on chip in an automatic manner from analyte dilution to detection. Anti-rabbit immunoglobulin G antibodies were quantified with 4 ng/mL, all performed within 25 min.