Fe³⁺-Doped Graphene Quantum Dots-Based Nanozyme for H₂O₂ Detection in Cellular Metabolic Distress

Nanozymes are nanomaterials that mimic enzymatic functions, catalyzing reactions that enable them to play key roles in applications such as biosensing and biodetection. Traditional methods for detecting H 2 O 2 in solutions or in biological systems often take at least 5 min of reaction time with a high limit of detection, especially in basic pH. Herein, we report a graphene quantum dots (GQDs)-based nanozyme that displays catalytic properties, enabling rapid, ultrasensitive detection and quantification within seconds in neutral solutions. This is based on the advantageous properties of these GQDs that include small size, high surface area-to-volume ratio, and biocompatibility, making the GQDs suitable for target molecule detection. The GQDs described herein, denoted as GQDs-Fe, were synthesized using a nitrogen-rich, hydrophilic polyethylenimine (PEI) precursor and doped with Fe(III) ions, leveraging the Fenton reaction catalysis for H 2 O 2 detection. The GQDs-Fe displayed characteristic optical properties; however, they produced a remarkable quantum yield of 67%, 1.2 times higher than the quinine sulfate control. The nanozyme demonstrated a limit of detection of 20 nM and a linear range of detection of 0–10 μM in neutral solution, establishing it as an ultrasensitive platform for biodetection. Biocompatibility and cellular uptake studies in mouse-brain-derived microvascular endothelial cells (BMVECs) confirmed the suitability of GQDs-Fe for use in normal and metabolically distressed conditions, opening pathways for advanced biomedical research and diagnostics. This system shows strong potential for targeted applications in detecting oxidative stress, which is essential for research in neurovascular health and metabolic diseases.