A label-free electrochemical immunosensor for bladder tumor marker NMP22 using AuNPs@OMC and Thi@Gr-COOH nanocomposites.

A highly sensitive and selective label-free electrochemical immunosensor was developed to detect nuclear matrix protein 22 (NMP22), a bladder cancer marker, in urine. A screen-printed carbon electrode (SPCE) was modified with carboxylate graphene-supported thionine (Thi@Gr-COOH) as a redox probe, and a unique structure of ordered mesoporous carbon decorated with gold nanoparticles (AuNPs@OMC). The large active site and uniform porosity of OMC facilitated the deposition of AuNPs, significantly increasing the antibody coverage. NMP22 concentration was determined based on changes in the peak current of Thi reduction measured by differential pulse voltammetry before and after the formation of the immunocomplex. In the optimal condition, the proposed immunosensor demonstrated linearity of 1.0 × 10^-7 to 1.0 × 10^-1 ng mL^-1 with detection limit of 2.96 × 10^-8 ng mL^-1. Furthermore, the proposed sensor demonstrated good reproducibility, stability for over 20 days, reusability up to 5 cycles of binding and regeneration, and good selectivity. The developed electrochemical immunosensor effectively detected NMP22 in human urine samples, achieving good recoveries and results that matched the NMP22™ Bladderchek™ TEST, proving it can be used effectively.