Ultrasensitive and label-free electrochemical immunosensor using gold nanoparticles deposited on a carbon electrode for the quantification of osteopontin: A serum-based oncomarker.

Early detection of cancer biomarkers is crucial for effective diagnosis and treatment, prompting the development of an ultrasensitive label-free electrochemical immunosensor. In this study, we fabricated an ultrasensitive label-free electrochemical immunosensor using a glassy carbon electrode/gold nanoparticles (GCE/AuNPs) modification for quantification of osteopontin (OPN), an oncomarker. The surface features of the modified electrodes were confirmed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The electrochemical behavior of the bare and modified electrode was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The quantification of the OPN antigen was achieved through the differential pulse voltammetry (DPV) method. The fabricated immunosensor demonstrated excellent detection capabilities in both commercial serum samples and phosphate-buffered saline (PBS). It showed sensitive quantification of OPN in the range of 0.001 to 1000 ng/mL with a limit of detection (LOD) of 0.005 ng/mL in PBS. Furthermore, the immunosensor retained approximately 89.3 % of its initial signal after storage for up to 8 weeks. The results were validated by detecting OPN-spiked commercial serum samples with a satisfactory recovery rate. The potential of this immunosensor makes it suitable for assaying OPN in real cancer patient's serum samples with minimal interference from complex sample matrices.