Surface Functionalization of Carbon-based Electrodes for Enhancing Biosensing Applications

Enhancing the signal of a label-free immunosensing platform significantly improves the sensitivity and reliability of electrochemical sensors for detecting disease biomarkers at low concentration levels. This advancement has major implications for point-of-care diagnostics, simplifying assays and creating a more user-friendly and cost-effective platform. Current approaches rely on complex electrode fabrication techniques and functionalization methods, which often suffer from poor control, non-specific adsorption, and high detection limits. Therefore, there is a need for simple electrode fabrication techniques that maintain integrity, along with straightforward functionalization methods that are efficiently controlled, minimize non-specific adsorption, and aid in signal amplification. To address this need, I demonstrate a multifunctional platform on thermoplastic electrodes (TPEs) and laser induced graphene (LIG) electrodes, utilizing varying lengths of polyethylene glycol (PEG) chains, terminated with either ferrocene to facilitate electron transfer or biotin for antibody immobilization. The multifunctional monolayer was formed using the highly efficient diazonium salt grafting technique to functionalize the electrode surface with alkyne groups, enabling “click chemistry” to occur with the mixture of PEG chains. PEG was employed to minimize non-specific adsorption by the hydration of its hydrophilic polyether backbone and providing dense surface coverage of the electrode. Characterization with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) confirmed successful functionalization efforts on TPEs and LIG. In a proof-of-concept study, label-free detection of the SARS-CoV-2 nucleocapsid protein on TPEs achieved a limit of detection of below 60 PFU/mL, exceeding the current capabilities of available point-of-care biosensors for SARS-CoV-2, though further optimizations are required.