Plasmonic ELISA for naked-eye detection of ochratoxin A based on the tyramine-H2O2 amplification system

A novel direct competitive plasmonic enzyme-linked immunosorbent assay (dc-pELISA) was applied to detect ochratoxin A (OTA) with naked eyes. In this assay, horseradish peroxidase (HRP) + hydrogen peroxide (H 2 O 2 ) + tyramine (TYR)-induced gold nanoparticle (AuNP) aggregation was considered as a signal output; AuNP aggregation could be triggered through the phenol polymerization of TYR , which was induced by hydroxyl radicals from HRP-catalyzed H 2 O 2 ; OTA-labeled catalase (CAT) was used as a competing antigen to consume H 2 O 2 . Owing to the combined advantages of ultrahigh CAT catalytic activity for H 2 O 2 and dual-color responses (red and blue) generated through AuNP aggregation, the proposed method was highly sensitive and thus could be employed with naked eyes to detect OTA qualitatively with a cut-off limit of 150 pg/mL. Our method also demonstrated a good dynamic linear range (12.5–150 pg/mL) for quantitative OTA determination with a reliable correlation coefficient of R 2  = 0.992, a half-maximal inhibitory concentration of 84.75 pg/mL, and a detection limit of 17.8 pg/mL. In brief, this newly-designed technique is considerably suitable for high-throughput screening detection or point-of-care diagnostics in resource-constrained regions because of the easy readout of results by naked eyes without the use of advanced detection equipment.