Detection of specific antibodies against SARS-CoV-2 spike protein via ultra-sensitive bio-functionalized carbonnitride-reduced graphene oxide electrochemical immunosensing platform in real samples

Abstract

In this work, we fabricate a facile de novo synthesis route to prepare bio-functionalized carbon nitride-reduced graphene oxide with chitosan (Chi) nanocomposite (C₃N₄/RGO/Chi). The nitrogen-rich C₃N₄ has been synthesized through facile and low-cost thermal oxidation and offers a metal-free and highly active surface for synergistic modification with RGO and Chi. Moreover, the synergistically incorporated C₃N₄/RGO and biopolymer improve the electrocatalytic activity, provide surface functionalities, and enhance electroconductivity for immunosensing applications. Consequently, the bio-functionalized C₃N₄/RGO nanocomposite provides a suitable substrate for the immobilization of SARS-CoV-2 RBD spike protein. The immunosensor detects SARS-CoV-2 antibodies in a wide detection range from 10 zg mL⁻¹ (10 × 10⁻²¹ g mL⁻¹) to 100 ng mL⁻¹ with an ultra-low detection limit (LOD) of 3.31 zg mL⁻¹. The validation of the immunosensor was also carried out on spiked serum samples, which show a linear detection range of 100 ag mL⁻¹ to 100 ng mL⁻¹ and a LOD of 1.73 ag mL⁻¹. Nevertheless, the clinical diagnostic application of the immunosensor is validated through the examination of real serum samples from COVID-19 patients. The results suggest that the immunosensor can be efficiently used as a screening platform to distinguish between positive and negative samples with high accuracy. The findings of the work have the potential to translate the immunosensing strategy into next-generation point-of-care testing (POCT) of various infectious diseases.