Aplicações de quantum dots na eletroquímica: desenvolvimento de sensor e microdispositivo

Abstract

In electrochemical analyzes with the use of sensors, innovation is sought for the development of self-assembled layers, since the objective of modifying the surface of an electrode is to increase its physical-chemical stability, interaction, selectivity and sensitivity with a specific analyte. The use of quantum dots in electrochemistry has increased considerably, in view of its optical and electronic properties. Quantum dots are extensively studied for their optical properties, however, their electrical properties are deficient in elaborate literature when compared to the volume and quality of the existing literature on optical properties. Based on this, we sought to give an electrochemical application with the development of electrochemical sensor and electrochemical detection microdevice, since the search for increasingly faster/practical analyzes to be carried out has increased in recent years. Such microdevices have emerged as a powerful and reliable analysis methodology as they present several clear advantages such as greater portability, reduced cost, less waste generation, more suitable disposability. In the present study, an electrochemical sensor was developed using the gold electrode modified with β-cyclodextrin (β-CD) and the quantum dot of shell core structure, cadmium selenide/cadmium sulfide (CdSe/CdS). This system was characterized against the electrochemical properties using the cyclic voltammetry techniques, the composites were quantified against the cyclic voltammetry and differential pulse voltammetry techniques. An electrochemical sensor was developed, with a self-organized monolayer on the surface of a gold electrode, aminothiol / 11-MUA / CdSe / CdS / β-CDSH called system 1 and another sensor with a self-organized monolayer on the surface of a gold electrode, aminothiol / CdSe / CdS / β-CDSH called system 2. System 1 always presented higher peak currents, so it proved to be more suitable. For the evaluation of its optical properties, UV-Vis spectroscopy was used. Electrochemical detection of uric acid and dopamine was achieved by cyclic voltammetry and differential pulse voltammetry. Using UV-Vis spectroscopy, there was a shift in the absorption bands. For electrochemical and spectroscopic experiments, phosphate buffer at pH 6.96 was used, electrochemical measurements were performed at a speed of 50 mVs-1, the reference electrode was Ag / AgCl. Subsequently, a microdevice made of paper was developed through a simple and inexpensive way coupled with carbon electrodes, the microdevices produced were used as electrochemical cells for the experiments. The working electrode used in the analyzes was made of carbon modified with the quantum dot of CdSe/CdS shell core structure. The modification of the working electrode was developed, characterized and optimized. The CdSe/CdS deposited on the working electrode showed excellent electrochemical and analytical performance. The microdevice showed good stability, since the values obtained for the relative standard deviation for the anodic peak currents was 2.85% and for the anodic peak potentials it was 2.46% for repeatability; for reproducibility, the electrochemical responses showed a variation of the relative standard deviation of 9.03% for the anodic peak and 4.29% for the anodic peak potentials.