Quantum dots are semiconductor nanocrystals which can be organic- (carbon-based) or inorganic-based and have unique properties such as good chemical and photostability and fluorescence. Carbon quantum dots (CQDs) possess the attributes of photoluminescence, easy functionalization, biocompatibility, and adjustable size properties. CQDs are used in bioimaging (in vitro and in vivo), biosensors, drug delivery, and cancer diagnostics fields.

In this experiment, the microwave-assisted pyrolysis technique is used to synthesize CQDs from Turkish coffee ground waste, which remains at the bottom of the cup. Turkish coffee is one of the most consumed beverages in Turkey and differs from other coffees in its brewing and preparation method. The aim of this study is to recycle Turkish coffee ground waste as the main carbon source and use it for the green synthesis of CQDs.

In the study, collected Turkish coffee ground waste was dried in an oven at 80°C. The dried Turkish coffee ground waste was then roasted at different levels, at 250 °C for 0, 5, 10, 15 minutes, to observe the effect of the roasting level of the waste on the properties of the CQDs. The most optimized CQD synthesis conditions were then selectedin terms of time (30–120 minutes) and the four different ethanol concentrations at 220 °C at 600 rpm. The synthesized CQDs were then characterized using FTIR, DLS, TEM, SEM, EDS, and UV-Vis instruments and Zeta Potential analysis was conducted after purification using a dialysis membrane, and the optimal synthesis parameters were selected for each roasting level accordingly. The effect of the CQDs on the cell viability was tested on HepG2, MCF-7, and HEK293 cell lines uisng the CCK-8 assay, and the cellular localization of the CQDs was assessed utilizing a fluorescent microscope.