Construction of cytosine-rich ssDNA for ultralow detection of Salmonella Typhimurium by enhancing the peroxidase-like activity of Fe3O4@Au nanoparticles

Recently, aptamer-enhanced nanozyme activity sensing platforms have gained considerable attention in the bioanalytical and diagnostic fields due to their simplified operations, rapid speed of analysis and visual observation convenience. However, the ability of an aptamer to enhance nanozyme activity has thus far been restricted by oligonucleotide type and length, in turn resulting in the typically high limit of detection (LOD) of aptamer-enhanced nanozyme activity sensing platforms. In this study, a novel cytosine-rich single-stranded DNA (C-rich ssDNA) was designed to overcome these drawbacks and, thereby, significantly enhance the peroxidase-like activity of Fe3O4@Au nanoparticles (NPs). The ability of this C-rich ssDNA to enhance the peroxidase-like activity of Fe3O4@Au NPs was shown to be 30% more effective than aptamers. To verify this outstanding performance, a C-rich ssDNA-enhanced Fe3O4@Au NPs activity sensing platform was developed for the detection of Salmonella Typhimurium (S. Typhimurium). Under optimum conditions, the novel colorimetric method realized quantitative S. Typhimurium determination ranging from 2.8 × 101 to 2.8 × 106 CFU/mL, with an ultralow detection limit of 1.8 CFU/mL. Additionally, the feasibility of the proposed colorimetric method was validated in spiked lettuce and milk, with LODs of 2.7 and 3.2 CFU/mL, respectively. These results indicate the significant potential of this novel colorimetric method for effective S. Typhimurium detection in food samples.