Self-signal generating bioelectronic sensor surface using gadolinium hexacyanoferrate nanocomposite for oral cancer diagnosis

External redox reagents and chemical mediators in measuring solutions are extensively used to monitor the analytical signals in electrochemical immunosensors. These mediators add more steps and complications to the sensing procedures which are aggravated when testing the target molecule in real samples. Thus, it is important to resolve such issues by fabricating and engineering sensitive electroactive surfaces without the requirement of mediators in the solution phase. In this work, we report a self-reporting electrochemical biosensor for cyfra-21–1 detection in saliva samples without using any external mediator molecules in solution phase. To fabricate an electrochemically active surface, a redox active Gadolinium hexacyanoferrate (GdHCF) nanoparticles have been synthesized and deposited onto the electrode surface for label-free detection of cyfra-21–1 in combination with gold nanoparticles (AuNP) and graphene oxide (GO). The sensor probe was thoroughly characterized using X-ray diffraction (XRD), UV–vis spectroscopy, transmission electron microscopy (TEM), Raman Spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). An alternation in the protein biomarker concentrations led to a change in the current response of the electrode surface. differential pulse voltammetry (DPV) was used to establish the analytical performance of the fabricated biosensor. The sensor achieved a clinically relevant range as well as a wide linear dynamic range (LDR) of 2–50 ng/mL of cyfra-21–1 and a detection limit (DL) of 0.039 ( ± 0.01) ng/mL ((RSD < 4.12%, 95% confidence level, n = 3), with negligible interferences effect due to various co-existing molecules. This is the first-ever report where a redox-active surface has been fabricated comprising GdHCF for direct detection of cyfra-21–1 in human saliva samples without using any redox mediator in the solution phase.