Ultrasensitive determination of cadherin-like protein 22 with a label-free electrochemical immunosensor using brush type poly(thiophene-g-glycidylmethacrylate) modified disposable ITO electrode

Abstract

A label-free immunosensor for the determination of Cadherin-like protein 22 (CDH 22) was successfully developed by using poly(thiophene-g-glycidyl methacrylate) (PT-GMA) brush type polymer modified disposable ITO electrode. This immunosensor was fabricated by immobilizing of anti-CDH 22 antibodies on epoxy functional groups of brush type polymer. Brush type polymer was coated on the disposable ITO electrode by utilizing the spin-coating method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses were employed for monitoring of electrochemical properties of the immunosensor. Single frequency impedance (SFI) analysis was utilized to investigate the specific recognition interaction between anti-CDH22 antibody and CDH22 antigen. Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to prove the attachment of anti-CDH 22 antibodies on the electrode surface. Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) analyses were carried out to indicate the changes formed on the sensing interface during the immobilization process. The electrochemical signals in response to different concentrations of CDH 22 antigens were evaluated with EIS measurements under the optimal experimental conditions. With the increase of concentrations of CDH 22 antigens, a thick protein layer was obtained on the electrode surface, resulting in higher electrochemical signals. The variations in impedance values were proportional to the CDH22 concentrations, with a wide linear detection range of 0.01-3 pg/mL, and a low detection limit of 3.2 fg/mL. The suggested immunosensor was an easy and low-cost label-free detection technique and provided a simple way for determination of cancer biomarkers such as CDH 22.