Rational design and in vivo toxicity assessment of multichannel fluorescent carbon dots derived from Withania coagulans in Drosophila melanogaster.

In vivo imaging with biocompatible fluorescent agents such as carbon dots (C-Dots) is becoming increasingly popular in theranostics. This study investigates the efficacy and safety of fluorescent C-Dots derived from Withania coagulans (WC) flowers, as well as their modified version, through in vitro and in vivo experiments. A hydrothermal method was used to synthesize three types of C-Dots, i.e. WC-CD, WC-Cys-CD, and WC-FA-CD, using WC flowers alone and with cysteamine (Cys) and folic acid (FA) respectively. We observed that the surface-modified carbon dots exhibited higher fluorescence quantum yields of 2.13 and 7.27% for WC-Cys-CD and WC-FA-CD compared with unmodified ones (WC-CD; 0.68%). The surface analysis and optical profile confirm the formation of CDs having the crystalline core composed of sp and sp carbons with the average size of 5.4 ± 1.2 nm, 5.0 ± 1.5 nm, and 5.2 ± 1.3 nm for WC-CD, WC-Cys-CD, and WC-FA-CD, respectively, and negative zeta potential values. A detailed structural analysis via XPS and FT-IR shows how modifying agents can lead to distinct surface functionalities. All three C-Dots exhibited excellent cytocompatibility in MCF-7 cells, even at concentrations up to 500 μg/mL, along with no significant inhibition of cell growth. However, in vivo studies revealed that cysteamine-modified C-Dots exhibited higher toxicity compared to unmodified and folic acid-modified C-Dots. The higher toxicity of cysteamine-modified C-Dots is attributed to oxidised sulphur species that disrupt cellular redox balance and induce oxidative stress.