pH-sensitive fluorescent carbon nanoparticles for monitoring bacterial metabolic activity

The influence of precursor composition, solvent, and hydrothermal synthesis temperature on the chemical nature, thermal stability, and photoluminescent properties of carbon nanoparticles (CNPs) was investigated. TPD-MS and thermogravimetric analysis revealed that the CNPs consist of aliphatic and unsaturated fragments with carboxyl and hydroxyl groups. Increasing the synthesis temperature from 170 to 200 °C and using citric acid promotes the formation of more carbonized nanoparticles with higher contribution of conjugated carbon domains. CNPs exhibit pH-sensitive emission (pH 3–6), are nontoxic toward E. coli, providing a proof-of-concept fluorescent monitoring approach for bacterial metabolic activity and the effectiveness of antimicrobial action.