A microfluidic ratiometric electrochemical aptasensor for highly sensitive and selective detection of 3,3′,4,4′-tetrachlorobiphenyl

Abstract

This study proposes a strategy using a microfluidic ratiometric electrochemical aptasensor to detect PCB77 with excellent sensitivity and specificity. This sensing platform combines a microfluidic chip, a wireless integrated circuit system for aptamer-based electrochemical detection, and a mobile phone control terminal for parameter configuration, identification, observation, and wireless data transfer. The sensing method utilizes a cDNA (MB–COOH–cDNA–SH) that is labelled with the redox probe Methylene Blue (MB) at the 5′ end and has a thiol group at the 3′ end. Additionally, it utilizes a single strand PCB aptamer that has been modified with ferrocenes at the 3′ end (aptamer–Fc). Through gold–thiol binding, the labelled probe of MB–COOH–cDNA–SH was self-assembled onto the surface of an Au/Nb₂CT_x/GO modified electrode. On exposure to aptamer–Fc, it will hybridize with MB–COOH–cDNA–SH to form a stable double-stranded structure on the electrode surface. When PCB77 is present, aptamer–Fc binds specifically to the target, enabling the double-stranded DNA to unwind. Such variation caused changes in the differential pulse voltammetry (DPV) peak currents of both MB and Fc. A substantial improvement is observed in the ratio between the two DPV peaks. Under the optimum experimental conditions, this assay has a response that covers the 0.0001 to 1000 ng mL⁻¹ PCB77 concentration range, and the detection limit is 1.56 × 10⁻⁵ ng mL⁻¹. The integration of a ratiometric electrochemical aptasensor with designed microfluidic and integrated devices in this work is an innovative and promising approach that offers an efficient platform for on-site applications.