Conformational change-based fluorometric aptasensor for sensitive cadmium(II) detection in fruits and vegetables

Cadmium (Cd²⁺) is a highly toxic heavy metal that can accumulate in the human body through contaminated food and water, posing great health risks. In this study, a label-free fluorescent aptasensor based on SYBR Green I (SGI) for the rapid and sensitive detection of Cd²⁺ in food samples was designed. The aptasensor utilizes a Cd²⁺-specific aptamer (Cd-(21)) and its complementary strand (CS_Cd-(21)) to form a double-stranded DNA (dsDNA) structure in the absence of Cd²⁺. SGI intercalates into the dsDNA, resulting in a strong fluorescence signal. In the presence of Cd²⁺, the aptamer undergoes a conformational change, preventing the formation of dsDNA and leading to a decrease in fluorescence intensity. Under optimized conditions, the aptasensor exhibited a linear response to Cd²⁺ concentrations ranging from 0.11 to 157.37 ng mL^-1, with a limit of detection (LOD) of 0.07 ng mL^-1. The aptasensor demonstrated high specificity and was successfully applied to detect Cd²⁺ in fruits and vegetables, with satisfactory recovery rates (95-111%). The proposed aptasensor provides a promising tool for the rapid and sensitive detection of Cd²⁺ in food.