Mesostructured Silica Xerogel-Encapsulated Gold Nanoclusters as an Electrochemiluminescence Emitter Combined with a DNA Walker Amplification Strategy for Detection of Ochratoxin A

Gold nanoclusters (AuNCs) exhibit unique optical properties and satisfactory biocompatibility, enabling them as highly promising electrochemiluminescence (ECL) emitters. However, the low ECL efficiency, resulting from the free movement of ligands, significantly hinders the development of AuNCs in the sensing field. In this work, polyelectrolytes were utilized to encapsulate AuNCs within the mesostructured silica xerogel, forming mesostructured silica xerogel-encapsulated gold nanoclusters (AuNCs@MSX). The space-confinement effect of the MSX and the uniform spatial distribution of encapsulated AuNCs reduced energy loss and the self-quenching effect. Compared with the aggregated AuNCs, the ECL efficiency of AuNCs@MSX increases by more than 2-fold. Meanwhile, the quantum yield can reach 16.98%. Furthermore, based on the ECL-resonance energy transfer (ECL-RET), an "on-off" ECL biosensor was designed. By the integration of a DNA walker cyclic amplification strategy, the exonuclease III (Exo III)-assisted biosensor enabled precise detection of ochratoxin A (OTA). As expected, the ECL biosensor exhibited an ideal linear ranging from 0.001 to 100 ng/mL, achieving a low detection limit of 0.31 pg/mL. The results confirm that encapsulating AuNCs in MSX to enhance ECL efficiency is a viable approach for preparing emitters in trace biomarker detection.