Efficient synthesis of rice based graphene quantum dots and their fluorescent properties

We present a facile green approach to synthesize monodisperse graphene quantum dots (GQDs) of sizes 2-6.5 nm using rice grains as a carbon source. As the size of the GQDs increases from 2-6.5 nm, a red shift (blue to cyan) in the photoluminescence emission spectra is observed due to quantum confinement effect. The colloidal solution of as synthesized GQDs is highly luminescent under 336 nm illumination. The quantum yield (QY) of the as-prepared GQDs in water is size dependent and increases from 16 to 24% with the decrease in size from 6.5 to 2 nm. The potential of these GQDs as biomarkers for cell imaging is explored further. The cytoxicity study with different concentrations of the GQDs confirms the excellent biocompatibility of the GQDs.