Nanopartículas fluorescentes de carbono a partir da goma do cajueiro (Anacardium occidentale)

Abstract

Since its discovery in 2004, carbon quantum dots or carbon dots (CD) have attracted much attention from the scientific community for its unique luminescent properties that expand its application in bio-imaging techniques, sensors, drug carriers, among others. CD are an alternative to inorganic quantum dots (QD) usually based on cadmium (CdSe) whose toxicity limits its use in biological applications. Several routes have been proposed for CD production from carbohydrate. This work proposes the production of fluorescent carbon nanoparticles from the raw cashew gum (RCG) by microwave heating. RCG 5% solution was heated for 10, 20, 40 and 60 min. The dried material after heating showed variation in color from yellow to brown indicating that the formation of fluorophores groups gives up the polysaccharide caramelization. The material was dissolved in water and centrifuged (NP10, NP20, NP40 and NP60) and part of it was precipitated with acetone (NP10P, NP20P, NP40P and NP60P). Precipitation decreased the nanoparticles diameter and polydispersity index was twice lower and zeta potential (Pζ), always negative, increased in module. The quantum yield did not change after precipitation and peak molar mass decreased. Higher heating time formed particles with higher quantum yield (0.45%-1.04%), smaller size (282 nm-111 nm) and higher zeta potential (-14 mV and -24 mV), molar mass also decreased with the heating time (104 to 103 g/mol). Excitation-wavelength dependent fluorescence characteristic of CD was observed. The infrared spectra showed ester band which increased with heating time and glycosidic linkage were broken and pyranosidic ring was opened, indicating depolymerization to produce fluorophores by caramelization. Samples from 40 minutes heating presented the best features from the data presented, besides their non-toxicity and antioxidant activity. NP40 presented a reducing and stabilizing power on silver nanoparticles synthesis, by green synthesis in mild conditions of neutral medium, being promising to biological applications in bioimagem, drug carrier or sensors