Filme fluorescente a base de carbon dots derivados do extrato de limão aplicado em termometria

Abstract

Luminescent nanomaterials have been actively involved in the development of thermometers with high sensitivity, non-invasive measurement, and a wide detection range. In this study, we aimed to develop luminescent carbon nanoparticles (Carbon Dots/CDs) and create a fluorescent film based on CDs to assess their potential as a thermal sensor and antioxidant agent. To achieve this, the NPs were synthesized from the aqueous extract of lemon pomace using a simple and rapid microwaveassisted method, and the polymeric film was produced by incorporating the CDs in PVA (Polyvinyl alcohol). The resulting Carbon Dots (CD-L) were characterized using HRMET, FTIR, UV-VIS, and PL techniques. HRTEM images demonstrated that CD-L exhibited a spherical shape with a size of less than 10 nm, showing an average distribution of 2.47 ± 0.47 nm. FTIR analysis indicated the presence of O-H, C-H, C=O, C=C, and C-N groups on the surface of CD-L, which are characteristic of the groups present in the lemon's composition. The UV-Vis spectrum revealed absorption peaks associated with the electronic transitions π - π * (C=C) and n - π *(C=O/C-N) of the graphitic core and surface groups of CD-L. PL analysis demonstrated strong fluorescence of CD-L in the blue region (446 nm), regardless of the excitation source. The material's photostability was also evaluated by continuous UV excitation at 330 nm for 60 minutes, and the emission intensity remained almost unchanged. The quantum yield of CD-L was calculated using quinine sulfate as a reference and was found to be RQ= 10%. The antioxidant activity of CD-L was assessed using HOCl and O2●˗, revealing a higher elimination potential in HOCl tests, indicating its efficiency in capturing reactive oxygen species of biological significance. When tested on non-tumor human skin fibroblast cells (HFF-1), CD-L demonstrated low cytotoxicity, with cell viability maintained above 85% for concentration up to 1000 µg/ml. Additionally, the produced fluorescent film (Film-L) effectively retained the luminescent properties of CD-L and exhibited potential for use as a thermal sensor, displaying a maximum relative thermal sensitivity of 2.69% K -1 at 333 K and stability for multiple cycles.