Carbon quantum dots (CQDs), assemi-conductor nanocrystals, are the preferred bioimaging agents thanks to their lower cytotoxicity, higher chemical stability and photostability compared to inorganic-based quantum dots. Polyethylene glycol (PEG) is a biocompatible and hydrophilic polymer that, when used as a coating (PEGylation), alters the physicochemical properties, as well as the cytotoxicity and intercellular uptake, of inorganic and organic materials.

CQDs were synthesized using the hot bubble synthesis (HBBBS) method that was developed by our group. PEGylation of CQDs was performed in a noncovalent manner using PEG polymers of different molecular weights (PEG-2, PEG-4, PEG-6, and PEG-10). For CQD PEGylation, PEGs of different molecular weights were dissolved in either acetone or distilled water at concentrations of 0.01M or 0.001M and PEGylation was performed at different stirring speeds (300, 600, and 900 rpm). The physical and optical characterization of the PEGylated CQDs was conducted using DLS, Zeta potential, and UV-Vis spectrophotometry instruments, and visualized using fluorescence microscopy (excitation: 385 nm).

The PEGylated CQDs had more homogenous distribution and were smaller in size when prepared with concentrations at 600 rpm and 0.001M PEG, regardless of the solvent and PEG molecular weight. Therefore, water was selected as the solvent to avoid cytotoxicity. PEGylated CQDs with 0.001M PEG (in distilled water) will be further characterized in future research using FTIR, SEM, EDS analysis, and TEM. Additionally, to evaluate their biocompatibility, these samples will be tested on HEK293 cells for cell viability using the CCK-8 kit, and the cellular localization of the nanoparticles will be visualized utilizing fluorescence microscopy.