Investigação das propriedades fotoluminescentes de pontos quânticos de carbono : aplicações como sensores físico-químicos, atividade antimicrobiana e bioimageamento

Abstract

Carbon quantum dots (CQDs) is a general term used to refer to zero-dimensional carbon nanoparticles with a core-shell structure rich in π-conjugated domains and functional groups on the surface. Their remarkable optical properties make them suitable for various applications, such as nanosensors, biomarkers, and antimicrobial agents. In this research, we utilized two CQDs: CD-MR, derived from the azo dye Methyl Red, and CD-ANS, derived from 5-amino-2-naphthalenesulfonic acid (CD-5ANS2). The optical characteris#tics of CD-MR were explored in microbiology, making it a potential antimicrobial agent and photosensitizer for Antimicrobial Photodynamic Therapy (aPDT). The emergence of drug-resistant pathogenic microorganisms has become a public health concern, creating a demand for strategies to suppress their proliferation in healthcare facilities. The possibility of using CD-MR to generate reactive oxygen species (ROS) was analyzed, and a high quantum eficiency for singlet oxygen generation was observed. Additionally, the antimicrobial activity of CD-MR was assessed against the pathogenic microorganisms Staphylococcus aureus, Escherichia coli, Candida albicans, and Cryptococcus neoformans. Kirby-Bauer tests showed that CD-MR exhibits antimicrobial activity only after photo excitation at 532 nm. The thermal and pH e#ects on the photoluminescence of CD-ANS were investigated, as well as its sensitivity to doping with metal ions, methanol, and the agricultural pesticide Methomyl. The results indicate a significant contribution of a thermally activated mechanism to the fluorescence of CD-5ANS2. Sensitivity to variations in pH, metal ions, methanol, and the pesticide was measured, and the variation in photoluminescence is likely related to the surface states of the nanoparticle. The doping e#ect of CD-ANS with nitrogen and sulfur was verified, revealing that the addition of these heteroatoms afects the optical properties of CD-ANS without causing significant structural modifications. Finally, both CQDs studied here also demonstrated potential as biomarkers, successfully penetrating the cell wall of the yeasts Candida albicans and Cryptococcus neoformans and exhibiting excellent photoluminescence in the intracellular environment.