A Novel Interference-Based Supercritical Angle Fluorescence Biosensor

Supercritical angle fluorescence (SAF) is a near-field collection technique used to create surface-sensitive optical transducers. While SAF biosensors require simpler excitation optics compared with total internal reflection fluorescence (TIRF)-based systems, they rely on complex fluorescence collection setups involving large, expensive microscopes to achieve similar sensitivities. In this article, we present a novel interference-based SAF transducer that leverages complementary metal oxide semiconductor (CMOS)-compatible technologies to significantly simplify and miniaturize the collection scheme without compromising sensitivity. The transducer incorporates an interference filter designed to block both excitation light and undercritical angle fluorescence (UAF) while transmitting SAF. We validated its performance using a protein A immunoassay and compared the results to those of the same assay performed on fluorescence well plates. Our SAF transducer achieved a limit of detection (LoD) of 1 pM, compared to 10 pM for the well plates. Furthermore, the transducer enables a washless assay format, significantly reducing the time to result. Its CMOS-compatible materials also support scalable, cost-effective manufacturing by using standard semiconductor fabrication processes.