Biogenic carbon dots derived from the microwave carbonization of amino acid mixture: cellular biocompatible, biomolecular probes, and live cell imaging agents

Developing highly fluorescent biogenic carbon dots (CDs) as molecular probes and cellular imaging agents with excellent cellular biocompatibility and water dispersibility can advance the scope of CDs in various biomedical applications. The present work aims to produce CDs from biological precursors such as natural amino acids. Due to their molecular recognition properties, the resultant CDs exhibit biocompatibility, polar functional groups, and selective molecule sensing. Microwave (MW)-assisted carbonization of L-tryptophan, L-glutamic acid, and their mixture led to the formation of CDs. However, the CDs derived from the mix of amino acids exhibited strong emission at 450 nm, with a quantum yield of 31.3%, and showed excellent stability under wide pH conditions. These CDs have a crystalline graphitic core, predominantly derived from the carbonization of the aromatic moiety intrinsic to L-tryptophan amino acid, while the partial carbonization of L-glutamic acid led to anchor polar functional groups on the CDs surface. These CDs were established as molecular probes for sensing the biomolecule cysteamine with enhanced sensitivity and remarkable cross-selectivity among the interfering metal ions, anions, and other thiols. To demonstrate these materials' cellular biocompatibility, the cell viability of MCF-7 and fibroblast cells was studied following their exposure to CDs. The studies revealed that the fluorescent CDs did not elicit cytotoxic effects on the cells at elevated concentrations. The CDs from the mixture of amino acids were efficiently internalized by MCF-7 cells, enabling efficient imaging of live cells. Overall, this study developed biogenic and cellular biocompatible CDs with robust luminescent properties and demonstrated their applications in biomolecular sensing, cellular uptake, and imaging.