Label-Free Electrochemical Immunosensor Toward IGFBP-7 Biomarker for Early Monitoring of Acute Kidney Injury

Insulin-like growth factor-binding protein 7 (IGFBP-7) is a potential biomarker for early diagnosis of acute kidney injury (AKI). Herein, we have developed a novel label-free electrochemical immunosensor based on the self-assembly of 6-(ferrocenyl)hexanethiol (Fc) and antibody-coupled L-cysteine on the gold nanoparticle-modified electrode (Ab/Fc-Au/SPCE) for sensitive detection of IGFBP-7 in urine. Fc was directly embedded on the electrode surface to serve as an intrinsic redox signal for the IGFBP-7 immunosensor. The binding of IGFBP-7 target to the immobilized antibody resulted in a decrease in the peak current of the differential pulse voltammetry (DPV) measurement. The Ab/Fc-Au/SPCE exhibited a good linear DPV response to IGFBP-7 concentrations ranging from 0.0001 to 100.0 pg mL-1, with a limit of detection (LOD) of 0.07 pg mL-1. Validation using spiked artificial urines showed recovery rates in a range of 79.8 to 109.3%. The proposed immunosensor demonstrated good specificity and long-term stability, which are crucial properties for biosensor implementation. Importantly, the electrochemical IGFBP-7 immunosensor can function without the need for external redox agents, requiring only simple steps of sample incubation and subsequent PBS buffer rinsing. Our findings demonstrate a promising potential of Ab/Fc-Au/SPCE immunosensor as a Point-of-Care Testing (POCT) device for rapid detection of IGFBP-7 in early AKI diagnosis.