Hollow porous AuNPs decorated on Pty and MB-coated rGO-COOH for a highly sensitive label-free electrochemical cystatin-C immunosensor for chronic kidney disease assessment

A label-free electrochemical immunosensor for cystatin-C (Cys-C) was developed by integrating hollow porous gold nanoparticles (HPAuNPs), polytyramine (Pty), methylene blue (MB), and carboxylated reduced graphene oxide (rGO-COOH) to modify a screen-printed carbon electrode (SPCE). rGO-COOH was employed to support the MB redox indicator and enhance the conductivity and surface area of the electrode. Pty was employed to prevent material detachment from the surface electrode and to support the attachment of HPAuNPs. The outstanding conductivity and extensive surface area of HPAuNPs improved immunosensor performance. Differential pulse voltammetry was used to determine Cys-C by measuring the oxidation current change of MB resulting from the immunoreaction between Cys-C and cystatin-C antibody (anti-Cys-C). The immunosensor for Cys-C detection exhibited a linear response range from 1.0 ×$$10⁻⁸ to 1.0 × 10¹ ng mL⁻¹, with a limit of detection of 3.67 ×$$10⁻⁹ ng mL⁻¹. Additionally, good reproducibility, storage stability, reusability, and excellent selectivity were obtained. The proposed label-free immunosensor for detecting Cys-C in human plasma shows results consistent with immunoturbidimetric assay (P>0.05), indicating its reliability and accuracy.