SERS-based wash-free immunoassay of prostate specific antigen using microdroplet sensor

We report a novel magnetic immunoassay technique using a SERS-based microdroplet sensor. The proposed method provides a rapid and sensitive assay applicable to PSA cancer markers in serum. The sensor used in this study consisted of four distinct compartments that function that act to generate microdroplets, separate immunocomplexes and supernatant solution, isolate magnetic immunocomplex droplets, and collect unbound SERS nano tag droplets for Raman detection. The technique allows for a convenient immunoassay of the PSA marker without any washing, since the magnetic immunocomplexes can be easily isolated by splitting droplets into two smaller parts via the application of a magnetic bar. Raman signals of the remaining SERS nano tags in the large droplet (supernatant solution) could then be used for quantitative evaluation of PSA marker [1].