Chiral carbon dot as a fluorescent stain with enantiomer-dependent cell imaging

Chiral carbon dots (CDs) are gaining significant interest because of their potential uses in the biological fields. The biological effects of these nanoparticles are highly influenced by their chiral structure. The influence of CD's chirality on cell imaging with red emission, particularly in both fixed and live cell states, has not been studied yet. Here, red emissive chiral CDs (LCD and DCD) were prepared through a simple and one-step method by tyrosine (L and D) and phenylenediamine (ortho). The LCD and DCD share very identical properties, including optical absorption, fluorescence emission, functional groups, size, and zeta potential, with the only difference being their chirality. Red emission minimizes tissue auto-fluorescence interference and enhances tissue penetration depth, making these CDs ideal for cell imaging. As staining agents, LCDs effectively enter cells and predominantly localize in the cytoplasm and nucleolus but the brightness of DCD is lower than LCDs and is not able to identify nucleoli. In addition, both LCDs and DCDs are highly biocompatible, but LCDs exhibit much lower toxicity. DCDs show significant toxicity from 20 µg.mL^-1, while LCDs show this effect from 150 µg.mL^-1. The different performance between isomers is due to their spatial structure, which affects their interaction with biomolecules and cellular uptake. These factors affect their ability to penetrate cells, localize within specific regions, exhibit cytotoxicity, and generate imaging signals. Chiral CDs are expected to lead the development of smart materials with enhanced efficiency for various biological applications.