Smartphone-Based Fluorescence/Colorimetric Dual-Mode Aptasensor for the Detection of Salmonella Using Multivalent Aptamer and CHA Amplification

Foodborne diseases attributed to Salmonella represent a substantial public health concern, necessitating the development of rapid and sensitive detection methodologies. In this study, we constructed a dual-mode fluorescent/colorimetric aptasensor, leveraging multivalent aptamer competitive assays and catalytic hairpin assembly (CHA), and integrated it with a smartphone-based portable device to expedite the detection of Salmonella. In this detection system, the tetrahedral DNA nanostructure-based multivalent aptamer competitive probe was designed to achieve primary signal amplification by recognizing target bacteria with high binding avidity and releasing a substantial amount of cDNA. The released cDNA subsequently triggers fluorescent and colorimetric signal readout through CHA-mediated secondary signal amplification, facilitating sensitive detection with self-referenced correction in both signal modes. The concentration of bacteria can be captured and analyzed using a smartphone-based portable device. Consequently, this method enables the quantitative detection of Salmonella within a linear range of 10 to 10⁷ CFU/mL, with detection limits of 28 CFU/mL for colorimetric detection and 10 CFU/mL for fluorescent detection. Additionally, the methods demonstrated high specificity in milk, egg, cod, and chicken samples, demonstrating its practical applicability. The inherent versatility of aptamers additionally permits the potential detection of other bacterial pathogens, rendering this platform a valuable tool for food safety monitoring and clinical diagnostics.