A silver auto-catalyzed plasmonic enzyme-linked immunosorbent assay for colorimetric and fluorescent detection of neutrophil gelatinase associated lipocalin (NGAL)

The conventional ELISA lacked sufficient sensitivity and accuracy for analyzing neutrophil gelatinase associated lipocalin (NGAL), a potential biomarker of ulcerative colitis. Here, we developed a dual-readout plasmonic ELISA with cascade amplification of alkaline phosphatase hydrolysis and O-phenylenediamine oxidation. In this novel plasmonic ELISA, alkaline phosphatase-conjugated antibodies capture NGAL from samples, alkaline phosphatase hydrolyzes 2-phospho-L-ascorbic acid into ascorbic acid, and then ascorbic acid blocks silver-catalyzed O-phenylenediamine oxidation by turning silver ions into silver microwires. Therefore, NGAL concentration is proportional to the decrease in chromogenic and fluorescent response. This novel plasmonic ELISA exhibited a linear range of 0.5–80 ng/mL, and the LOD was as low as 0.5 ng/mL. The sensitivity was superior to that of conventional ELISA and previous studies. The plasmonic ELISA exhibited favorable selectivity because of the specific antibody-antigen interaction and the robust cascade amplification. Besides, the dual-readout feature endowed the plasmonic ELISA with advantages in terms of convenience and compatibility. In summary, our study provided a novel and sensitive plasmonic ELISA for the diagnosis of ulcerative colitis.