Effective multicolor visual biosensor for ochratoxin A detection enabled by DNAzyme catalysis and gold nanorod etching

A novel detection technique is introduced that offers sensitive and reliable ochratoxin A (OTA) detection. The method leverages the etching of gold nanorods (AuNRs) stabilized by hexadecyl trimethyl ammonium bromide (CTAB) using the oxidized form of 3,3 ',5,5 '-tetramethyl benzidine sulfate (TMB2+), creating a susceptible multicolor visual detection system for OTA. The visual detection is enabled by Mg2+-assisted DNAzyme catalysis combined with the catalytic hairpin assembly (CHA) signal amplification strategy. The presence of OTA triggers CHA and signaling responses along with the formation of G-quadruplex-hemin DNAzyme, which promotes the oxidation of TMB with H2O2, leading to the etching of AuNRs and a reduction in their aspect ratio. AuNRs experienced a blue shift in the longitudinal localized surface plasmon resonance peak, resulting in a color change. The technique has been shown to detect OTA with a low detection limit of 0.309 pg/mL, demonstrating high sensitivity and specificity. The detection technique offers versatility by enabling the detection of other pollutants through a simple replacement of the aptamer, expanding the range of detection platforms available for pollutant determinations.