A universal ultrasensitive platform for enzyme-linked immunoassay based on responsive surface-enhanced Raman scattering

Abstract

Enzyme-linked immunosorbent assay (ELISA) is the current gold standard assay for biomarkers. However, its detection sensitivity is greatly limited by the colorimetric readout. Herein, we developed a high-performance immunoassay through the combination of traditional ELISA and ultrasensitive surface-enhanced Raman scattering (SERS) assay using a responsive SERS probe. The probe is a Au nanoplate constituted cabbage-like microparticle functionalized with synthesized phenol-responsive Raman reporter 4, 4’-dithiodibenzyldiazonium (DTDBD). The new SERS probe can detect trace amount of phenol with a limit of detection (LOD) of 0.4 nM, and alkaline phosphatase (LOD of 0.04 mU/L) with phenol as an enzymatic product. More important, the ultrasensitive detection of cholera toxin (CT) in real serum samples indicates such ELISA-SERS assay promising for practical applications using alkaline phosphatase as an enzyme labeling and SERS probe as a signal readout. We envision that this new method can be employed as a universal platform for the profiling of any antigen using alkaline phosphatase as the enzymatic label to its corresponding antibody.