Caracterização termo-óptica de corante natural e pontos de carbono (CDs) fluorescentes para bioaplicações.

Abstract

In this work, the extraction process of natural dye from the leaves of Tradescantia pallida purpurea in an aqueous solution was enhanced. The dye was characterized using various spectroscopic techniques, including absorption, fluorescence, time-resolved fluorescence (TRFL), Fourier-transform infrared spectroscopy (FTIR), and high-performance liquid chromatography. This characterization enabled the identification of the main components of the dye and the detection of anthocyanin at different pH levels, ranging from 3.96 to 8.02. Furthermore, the thermo-optical properties of the dye were investigated, including the thermo-optic coefficient (dn/dT) and fluorescence quantum efficiency (η). This was accomplished using a Mach-Zehnder interferometer and the Conical Diffraction technique, which detects rings in the far-field resulting from thermally induced spatial self-phase modulation at the laser wavefront. The study also explored two practical applications of the dye. Initially, its potential as a probe for milk was assessed at different pH values, simulating food adulterations through pH-associated colorimetric and fluorometric variations. Subsequently, the dye was tested as a fungicidal agent against Fusarium solani, Sclerotinia sclerotiorum, and Colletotrichum gloeosporioides fungi. The results indicated promising fungicidal potential, with significant reductions of approximately 25% for Fusarium and 50% for Colletotrichum when exposed to varying concentrations of anthocyanin, ranging from 0.1% to 50%. Additionally, the natural dye extracted from Tradescantia leaves served as a precursor in the synthesis of carbon dots (CDs), both in the presence and absence of urea, using simple carbonization methods such as hydrothermal and pyrolysis. The synthesized Cdts were characterized using various analytical techniques, including absorption, fluorescence, and Raman spectroscopy, atomic force microscopy, FTIR, and TRFL. Thermal lens measurements were employed to calculate the η of the synthesized Cdts. The η values ranged from 10% to 50% due to variations in synthesis and doping conditions. These results were compared with CDs synthesized from natural carbon sources, such as corn stalks, banana peels, anthocyanin, Catharanthus roseus leaves, and soybeans.