Tag-Free Fluorometric Aptasensor for Rapid Detection of Chromium (Vi) in Fruits and Vegetables Based on Sybr Green I Signal Amplification and Aptamer Structure Transition

In response to growing concerns about heavy metal contamination in food, particularly chromium (VI) contamination, this study presents a rapid, sensitive, and practical method for chromium (VI) detection. A magnetic separation-based capture-exponential enrichment ligand system evolution (SELEX) method was utilized to identify and characterize DNA aptamers with high affinity for chromium (VI). An aptamer, Cr-15, with a dissociation constant (Kd) of 4.42 ± 0.44 μM was obtained after only eight rounds of selection. Further innovative methods combining molecular docking, dynamic simulation, and thermodynamic analysis revealed that CrO42- could bind to the 19th and 20th guanine bases of Cr-15 through hydrogen bonds. Crucially, a label-free fluorometric sensor based on SYBR Green 1 was successfully constructed for detecting CrO42-, achieving a linear detection range of 60-300 nM with a lower limit of detection (LOD) of 44.31 nM. Additionally, this aptasensor was able to quantitatively detect CrO42- in grapes and broccoli within 40 min, with spike recovery rates ranging from 91.91% to 108.24%. The designed fluorometric aptasensor exhibited high selectivity and could detect CrO42- in real samples without any sample processing or target pre-enrichment. The aptasensor demonstrates its potential as a reliable tool for monitoring chromium (VI) contamination in fruit and vegetable products.