Biofunctionalized Graphene Quantum Dots Based Fluorescent Biosensor toward Efficient Detection of Small Cell Lung Cancer

Quantitative detection of cancer biomarkers with higher accuracy and sensitivity provides an effective platform for screening, monitoring, early diagnosis, and disease surveillance. The present work demonstrates the fabrication and application of fluorescent turn-on biosensor for ultrasensitive detection of small cell lung cancer biomarker utilizing biofunctionalized graphene quantum dots as the energy donor and gold nanoparticles (AuNPs) as the energy acceptor. One-pot and the bottom-up hydrothermal route have been employed for the synthesis of in situ amine-functionalized and nitrogen-doped graphene quantum dots (amine-N-GQDs) and further characterized experimentally by different analytical techniques. The molecular simulation studies were performed using the Material Studio software for optimizing the possible chemical structure of synthesized amine-N-GQDs, a comprehensive analysis of experimental results to validate the presence of potential N-doping and amine functionalization sites. Then monoclonal neuron-specific enolase antibodies (anti-NSE) were covalently immobilized to amine-N-GQDs to provide the biofunctionalized GQDs (anti-NSE/amine-N-GQDs). A label-free and efficient fluorescent biosensor based on nanosurface energy transfer (NSET) between anti-NSE/amine-N-GQDs and AuNPs has been developed for neuron-specific enolase (NSE) detection. The fluorescence response studies of anti-NSE/amine-N-GQDs@AuNPs nanoprobe conducted as a function of NSE antigen exhibited fast response time (16 min), broader linear detection range (0.1 pg mL^-1 to 1000 ng mL^-1), and remarkably low detection limit (0.09 pg mL^-1). Additionally, the fluorescent biosensor exhibited excellent performance in real samples, with an average recovery value of 94.69%.