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.