Carbon dots on paper for determination of Cu2+ in sugar cane spirits samples for fluorescence digital image-based method

In the present work, we proposed for the first time a simple and low-cost fluorometric method based on digital image using a UV-LED chamber and a 3D platform made of biodegradable polyacid lactic (PLA) and carbon dots (CDs) obtained from rice functionalized with cuprizone for the determination of Cu2+ in sugar cane spirits, using a paper-based device. The synthesized CDs were characterized by the techniques of UV-Vis spectrophotometry, spectrofluorometry, dynamic light scattering, scanning electron microscopy, zeta potential. The CDs obtained using a green hydrothermal method from biomass proved to be selective for the determination of Cu2+ when functionalized with bis (cyclohexanone) oxaldihidrazone (CPZ). The mechanism of detection was based on the quenching of fluorescence emitted by the CDs due to the Cu2+. For excitation of the CDs/CPZ, a chamber was built with four UV-LED as radiation source with maximum emission at 370 nm. An opening at the top allows the smartphone to detect the fluorescence emitted by the CDs. The captured image was decomposed to red (R), green (G) and blue (B) values. The determination of Cu2+ in the sugar cane spirits samples was obtained in a linear range from 2.00 to 7.22 mg L-1 with LD of 0.23 mg L-1 for B channel with R-2 = 0.9993. Based on the recovery data from 87.60% to 112.4% the matrix effect was not found. Samples of sugar cane spirits were analyzed by the fluorescence digital image method and the atomic absorption spectrophotometry, and there are no significant differences for 95% confidence of the data obtained, and thus, the method developed was accurace for Cu2+ detection.