An electrochemically charged nanoengineered bioelectronic immunosensing device for osteopontin detection in serum samples

Osteopontin (OPN) is a crucial biomarker for osteosarcoma, an aggressive bone cancer. Elevated levels of OPN are found in osteosarcoma tissues and blood samples, associated with tumor growth, metastasis, and poor prognosis. The present electrochemical voltammetric detection methods are mainly assisted by redox couple/chemical mediators in a measuring solution. However, in resource-confined settings, such a detection strategy undermines the potential for the development of precise and easy-to-use point-of-care bioelectronic devices. To simplify the detection method, herein, we present a reliable and straightforward clinically deployable immunosensor <i>via</i> engineering an electrochemically charged surface that does not require mediators in the solution phase. Such an electroactive surface offers a simplistic label-free detection of the protein OPN, requiring only the use of a buffer solution to obtain the signals. The electroactive immunosensor probe was engineered using electrodeposited gold, bimetallic FeGdHCF redox nanoparticles, and oxidized graphene nanoplatelets for immobilizing the OPN antibodies. Since the detection is precisely dependent on the redox-active electrode surface for obtaining analytical signals, this strategy was further designed into a miniaturized device cascade for the direct and on-site detection of OPN. The immunosensor probe showed a low LOD of 0.437 (±0.002) (RSD < 4.09%, <i>n</i> = 5) pg mL^-1 and a wide LDR of 5 × 10² to 2 × 10⁶ pg mL^-1. It was applied to detect OPN in serum samples and was also evaluated for its selectivity against various molecules coexisting in real clinical samples and was found to be stable for a period of six weeks.