Accelerated surface-enhanced Raman spectroscopy (SERS)-based immunoassay on a gold-plated membrane.

A rapid and simple SERS-based immunoassay has been developed to overcome diffusion-limited binding kinetics that often impedes rapid analysis in conventional heterogeneous immunoassays. This paper describes the development of an antibody-modified membrane as a flow-through capture substrate for a nanoparticle-enabled SERS immunoassay to enhance antibody-antigen binding kinetics. A thin layer of gold is plated onto polycarbonate track-etched nanoporous membranes via electroless deposition. Capture antibody is immobilized onto the surface of a gold-plated membrane via thiolate coupling chemistry to serve as a capture substrate. A syringe is then used to actively transport the analyte and extrinsic Raman labels to the capture substrate. The fabrication of the gold-plated membrane is thoroughly investigated and established as a viable capture substrate for a SERS-based immunoassay in the absence of sample/SERS label flow. A syringe pump is used to systematically investigate the effect of flow rate on antibody-antigen binding kinetics and demonstrate that active transport to the capture membrane surface expedites antibody-antigen binding. Mouse IgG and goat anti-mouse IgG are selected as a model antigen-antibody system to establish proof of principle. It is demonstrated that the assay for mouse IgG is reduced from 24 h to 10 min and a 10-fold improvement in detection limit is achieved with the flow assay developed herein relative to the passive, i.e., no flow, assay. Moreover, mouse serum is directly analyzed and IgG level is determined using the flow assay.