Enzyme‐Free Ratiometric Electrochemical Aptasensor for Ultrasensitive Detection of Bisphenol A Based on Dual‐Amplification of Highly Conductive AuNPs@2D Ni/Co‐MOF and Hybridization Chain Reaction

ABSTRACT An ultrasensitive ratiometric electrochemical aptasensor with dual‐signal amplification strategy was developed for the detection of bisphenol A (BPA). The sensing signal was amplified by the gold nanoparticles/two‐dimensional (2D) Ni/Co‐metal–organic framework nanosheets (AuNPs@2D Ni/Co‐MOF composite) and enzyme‐free isothermal amplification technology. The introduction of metal–organic frameworks (MOF) allowed for supporting a large number of anchor sites for the immobilization of aptamer; meanwhile, AuNPs compensated for its relatively weak conductivity. SH‐DNA hybridized with a ferrocene‐labeled BPA aptamer (Fc‐apt) was decorated on the composite, and in the presence of BPA, the Fc‐apt detached from the electrode surface. Hybridization chain reaction was triggered and resulted in the formation of long double‐stranded DNA (dsDNA), during which methylene blue (MB) was intercalated. Fc and MB acted as ratiometric signaling tags, and the aptasensor demonstrated a wider linear response range from 1 × 10 −17 to 1 × 10 −11 M, and an extremely low detection limit of 9.25 × 10 −18 M was achieved under optimal experimental conditions. Furthermore, the aptasensor showed excellent selectivity and reproducibility. The aptasensor was proved to be effective in quantitatively detecting BPA in real‐world samples and yielded satisfactory recoveries from 93.28% to 117.50% with relative standard deviations (RSDs) of 1.3%–8.8%, indicating its potential for application in food safety monitoring. This study provides new approaches and sets the groundwork for constructing ratiometric electrochemical aptasensor with high sensitivity and selectivity.