A colorimetric assay method for invA gene of Salmonella using DNAzyme probe self-assembled gold nanoparticles as single tag

• This work provided a novel and simple colorimetric sensing strategy for Salmonella detection.
• DNAzyme probes self-assembled gold nanoparticles were used for signal amplification effectively.
• The color change of target DNA could be easily observed by naked eye.
• This method was successfully applied to detect Salmonella sample in water.

A simple colorimetric sensing method was developed for detection of invA gene of Salmonella by combining DNAzyme probe self-assembled gold nanoparticles and polymerase chain reaction (PCR) technique. Amino-modified capture probe was covalently immobilized on the surface of DNA–BIND plate, and further hybridized with target sequence and DNAzyme probe self-assembled gold nanoparticles to form a sandwich-type hybridization structure. In the presence of hemin, the DNAzyme probe could form a G-quadruplex/hemin complex, which catalyzed the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine dihydrochloride hydrate (TMB) to cause a dramatic color change. The invA gene was isolated from Salmonella and amplified using a polymerase chain reaction technique, and signal was further enhanced by DNAzyme probe self-assembled gold nanoparticles. Under optimal conditions, the absorbance value was linear with the logarithm of target sequence concentrations in the range of 0.5–50 nM, with a limit of detection of 0.44 nM for target sequence. In addition, the designed method allowed the quantitative Salmonella detection in water from 3 × 103 to 3 × 106 CFU mL−1. This strategy exhibited good stability, sensitivity and simplicity and might be a potential tool for the practical Salmonella detection in clinical diagnosis, food safety and environmental monitoring.

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