A novel colorimetric sensor using aptamers to enhance peroxidase-like property of gold nanoclusters for detection of Escherichia coli O157:H7 in milk

Abstract

Escherichia coli O157:H7 is a pathogenic foodborne bacterium of public health concern. A simple, rapid, and environmentally friendly method was developed to synthesise papain-modified gold nanoclusters (papain@AuNCs). Following this, aptamers-modified papain@AuNCs (aptamers@papain@AuNCs) were constructed by reacting Au–S covalent bonds between thiolated aptamers and the papain@AuNCs, enhancing the peroxidase activity. E. coli O157:H7 could be captured through the aptamer@papain@AuNCs, significantly improving the catalytic activity toward the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine, and the blue products could be generated. Papain was used for the first time as a template for the synthesis of AuNCs of peroxidase-like activity for detection. The quantitative detection for E. coli O157:H7 was 39 cfu mL−1 in pure culture. The detection limit of E. coli O157:H7 was 5.6 × 102, 5 × 102 and 4.9 × 102 cfu mL−1 in ultra-high temperature sterilised, pasteurised, and raw milk samples, respectively, after 2 h pre-incubation, indicating that the developed sensor has potential for pathogen detection in foods.