In this work we have targeted two aspects of GQDs, Size and ROS to reduce their cytotoxicity. Small size can damage cell organelles and production of ROS (reactive oxygen species) can hamper cell machinery in multiple ways. We have shown that cytotoxicity can be significantly reduced by embedding GQDs inside the PEG matrix rather than creating a thin shell around each GQD. Thin PEG shell around GQD can control ROS production but cannot circumvent the toxicity due to small size. Thus it was essential to solve both the issues. We have used a simple electrochemical method (12 h at room temperature) for synthesizing GQDs and embedded them in PEG matrix via a simple one step hydrothermal reaction (24 h at 160° C.) involving only GQDs, PEG, and deionized water. The P-GQDs formed after hydrothermal reaction show nanoparticles of diameter of ˜80-100 nm containing GQDs entrapped in PEG matrix. MTT assay showed significant 60% cells viability at a very high concentration of 5.5 mg/mL of P-GQDs compared to 10-15% viability for C-GQD and H-GQD. ROS production by P-GQDs was least compared to C-GQD and H-GQD in cell free and intracellular ROS assay suggesting involvement of ROS in cytotoxicity. In this work we have solved the issue of cytotoxicity due to ‘small size’ and ‘ROS generation’ without compromising with fluorescence properties of GQDs. P-GQDs was used for bioimaging and drug delivery in HeLa cells. In short we can obtain biocompatible P-GQDs in very short span of time with minimal use of hazardous chemicals and simple methodology.
