G-Quadruplex-Enhanced DNA Silver Nanoclusters Enable CRISPR/Cas12a System for Ultrasensitive Detection of <i>Salmonella typhimurium</i>

DNA-templated silver nanoclusters (tDNA-AgNCs) show considerable promise as fluorescence reporters for the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system because of their ease of synthesis, strong resistance to photobleaching, and large Stokes shift. However, the weak luminous intensity and low cleavage efficiency of tDNA-AgNCs limit the sensitivity of CRISPR assays. In this study, we developed a novel approach by introducing activator DNA (aDNA) with a G-quadruplex structure to enhance the luminous intensity of the tDNA-AgNCs. As a result of the high cleavage efficiency of free aDNA by activated CRISPR/Cas12a, the G-quadruplex-enhanced tDNA-AgNCs (GED-AgNCs) were integrated into recombinase polymerase amplification and CRISPR/Cas12a system for the ultrasensitive detection of <i>Salmonella typhimurium</i>. By optimizing the synthesis of tDNA-AgNCs and GED-AgNCs, our developed G-quadruplex-enhanced DNA-AgNC CRISPR assay (G-DACA) platform enabled the sensitive determination of <i>S. typhimurium</i> with a detection limit as low as 1 CFU/mL and a wide dynamic range of 10-10⁸ CFU/mL. Moreover, our proposed method demonstrated good accuracy and reliability for the quantitative analysis of <i>S. typhimurium</i> in real pasteurized milk samples, with recovery rates ranging from 81.06% to 102.33% and relative standard deviations between 7.17% and 14.84%. Overall, our innovative G-DACA platform offers an economical and versatile solution for food safety and clinical diagnostics.