A near-infrared light photoelectrochemical immunosensor based on a Au-paper electrode and naphthalocyanine sensitized ZnO nanorods

Abstract

A label-free photoelectrochemical (PEC) immunosensor is introduced into a microfluidic paper-based analytical device using tetra-carboxyl naphthalocyanine zinc (ZnNc-COOH) sensitized ZnO nanorods (NRs) as photoactive materials. Firstly, ZnO NRs are grown on a Au nanoparticles modified paper working electrode (Au-PWE) via a simple and low temperature hydrothermal method. With the aid of 4-aminothiophenol (PATP), ZnNc-COOH can be attached onto the ZnO NRs surface due to the formation of a strong bond (Zn–S) between the thiol end of the PATP molecule and the ZnO NRs, and the remaining amino group forms an acrylamide bond with ZnNc-COOH. To perform the immunoassay, carcinoembryonic antigen (CEA) antibodies are conjugated onto the ZnNc-COOH sensitized electrode by using the classic 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) coupling reactions between COOH groups on the surfaces of the ZnNc-COOH and NH₂ groups of the antibodies. The concentrations of CEA are measured through the decrease in photocurrent intensity resulting from the increase in steric hindrance due to the formation of the immunocomplex. Under the optimized experimental conditions, the paper-based PEC immunosensor exhibits excellent analytical performance for detection of CEA, ranging from 0.005–100 ng mL⁻¹ with a low detection limit of 1.6 pg mL⁻¹. The PEC immunosensor shows high sensitivity, stability, and reproducibility. The proposed method provides a new strategy for a sensitive, low-cost, specific, and multiplex assay.