Ferrocene-functionalized ZIF-8@Pt nanoparticles-engineered dual-mode aptasensor: Ratiometric electrochemical/impedimetric detection of chlorpyrifos with high reliability

The rapid and reliable detection of pesticide residues play a pivotal role in safeguarding food safety. By integrating ratiometric electrochemical (EC) and electrochemical impedance spectroscopy (EIS) strategies, this work develops an all-in-one dual-mode aptasensor based on ferrocene-functionalized zeolitic imidazolate framework decorated with platinum nanoparticles (ZIF-8@Fc@PtNPs) for reliable detection of chlorpyrifos (CPS). ZIF-8@Fc@PtNPs were synthesized via a facile self-assembly approach, functioning as a dual-functional substrate to yield a reference signal (I_Fc) and amplify response signals. Complementary DNA (cDNA) was then immobilized via Pt-N bond, providing specific binding sites for assembling methylene blue-labelled CPS aptamer@Au nanoparticles (MB-CPS Apt@AuNPs). In the presence of CPS, specific bindings triggered the detachment of MB-CPS Apt@AuNPs, leading to measurable changes in the I_Fc/I_MB and electron transfer resistance (R_et). This dual-mode platform, by integrating ratiometric EC (based on I_Fc/I_MB) and EIS (based on R_et) strategies, allows for reciprocal validation of results derived from both modes, ensuring enhanced accuracy and reliability. The approach achieved high detection sensitivity for CPS within 30 pg mL⁻¹-30 ng mL⁻¹ (ratiometric EC mode) and 10 pg mL⁻¹-30 ng mL⁻¹ (EIS mode), coupled with good selectivity, reproducibility, and stability. Successful application in vegetable samples demonstrates its great potential for practical pesticide residue monitoring.