Graphene Quantum Dots vs Graphene Oxide as Nanoplatforms for Electrochemical Immunosensors: A Comparative Study

This study systematically evaluates the use of graphene quantum dots (GQDs) as alternative for graphene oxide (GO) as signal-enhancing materials for label-free electrochemical immunosensors. For this, screen-printed electrodes (SPEs) were functionalized with GO or GQDs, followed by anti-RBD antibody immobilization targeting the SARS-CoV-2 receptor-binding domain (RBD). A label-free electrochemical detection strategy was implemented, relying on signal suppression due to immunocomplex formation (anti-RBD/RBD) at the electrode surface, which hinders the redox probe signal. GQD-based sensors demonstrated a remarkable enhancement in analytical performance, showing ∼87% higher sensitivity in DPV (18.65 vs 10.00%Ip/log ng·mL–1) and ∼71% higher sensitivity in EIS (74.01 vs 43.29%Rct/log ng·mL–1) compared to GO-modified electrodes. Both platforms exhibited a linear response from 10 to 1000 ng·mL–1 and achieved ∼80% accuracy in fortified saliva and nasal swab samples. Notably, GQD-based immunosensors also offered 25% improved operational stability (35 vs 28 days) and superior discrimination in saliva matrices. Importantly, GQDs were synthesized via a one-step, low-energy citric acid pyrolysis, a greener and more sustainable approach compared to the multistep Hummers’ oxidation used for GO, which involves strong oxidants and generates hazardous waste. Combining superior sensitivity, lower detection limits, extended stability, and eco-friendly synthesis, GQDs emerge as the optimal nanomaterial for next-generation electrochemical immunosensors, offering high analytical performance with reduced environmental impact.