A Microfluidic Electrochemical Immunosensor for Point-of-Care Testing of Cystatin C in Human Serum

Chronic kidney disease (CKD) is a progressive disorder characterized by structural and functional alterations in the kidneys arising from various etiologies. Cystatin C (Cys C) is regarded as a superior endogenous biomarker because it is less affected by confounding factors such as age and gender. In this work, an electrochemical immunosensor was developed for Cys C detection by electropolymerizing o-phenylenediamine (OPD) on the electrode surface via cyclic voltammetry (CV) to form poly(o-phenylenediamine) (PoPD). The PoPD layer not only accelerated electron-transfer kinetics but also provided a favorable matrix for antibody immobilization. The immunosensor achieved a limit of detection (LOD) of 186.88 ng mL −1 and a linear range of 500–6000 ng mL −1 , while exhibiting satisfactory reproducibility, specificity, and operational stability. Spike recovery studies and direct analysis of human serum samples verified the practical performance of the proposed sensor. A low-cost, portable microfluidic electrochemical device was developed for serum Cys C quantification. The integration of electrochemical sensing with the microfluidic platform offers low sample consumption, simplified operation, fast detection, and promising potential for POCT. Graphical A label-free microfluidic electrochemical immunosensor with a PoPD-modified interface enables rapid Cys C detection across a wide clinically relevant range, covering serum levels from normal to elevated pathological concentrations. This broad detection window, together with low sample consumption, supports practical quantitative analysis in real serum samples and POCT kidney injury screening.