Navegando por Palavras-chave "Electrochemical Impedance Spectroscopy"

Agora exibindo 1 - 2 de 2
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Eletrodos de ouro modificados com monocamadas auto-organizadas aplicados à determinação eletroanalítica de hormônios
    (Universidade Federal de São Paulo (UNIFESP), 2020-06-04) Batista, Fabio Henrique Ferreira [UNIFESP]; Oliveira, Lucia Codognoto de [UNIFESP]; Universidade Federal de São Paulo
    In this work, characterization studies of gold electrodes modified with self-organized monolayers of 3-mercaptopropionic acid (AuMPA) and 2-mercapto-5-methyl-benzimidazole (AuMMB) and their applications in the determination of hormones are presented. The characterization by cyclic voltammetry indicated the immobilization of the monolayer of the MPA thiol on the surface of the gold electrode; the characterization by electrochemical impedance spectroscopy (EIS) showed the increase in charge transfer resistance due to the presence of the monolayer and made it possible to estimate the electrode coverage of the modified electrodes AuMPA and AuMMB in 74.4 e 65.4%, respectively; in the characterization by Raman spectroscopy, the presence of several shifts attributed to the MPA and MMB species was observed, thus showing that the modification of the electrodes was in fact performed. The potential of the modified electrodes was evaluated in the electrochemical study of the hormonal endocrine disruptors estradiol and estrone; pH studies indicated the 1: 1 proton: electron ratio and potential sweep rate studies denoted an electrochemical diffusion-controlled process for both. In the voltammetric study of signal stability, greater peak current stability for hormones was obtained when using the AuMMB electrode after 10 successive voltammograms. After the optimization of the square wave voltammetry parameters, analytical curves for estrone over Au and AuMMB electrodes were obtained, with limits of detection (LOD) and quantification (LOQ) of 1.07x10-6 mol L-1 and 3.57x10-6 mol L-1 (Au); and 1.17x10-6 mol L-1 and 3.90x10-6 mol L-1 (AuMMB) in ultrapure water and limits of detection (LOD) and quantification (LOQ) of 7.53x10-7 mol L-1 and 2.51x10 -6 mol L-1 (Au); and 6.94x10-7 mol L-1 and 2.31x10-6 mol L-1 (AuMMB) in water collected in the Billings dam, respectively. From partition studies in the water/n-octanol system for estrone, logD values ​​were estimated at 1.02 and 1.08 (pH 10.0), and 2.10 and 1.35 (pH 12.0 ) in ultrapure water and water sample from Billings Dam, respectively. Thus, the presence of other organic compounds in the matrix influences the partitioning process and suggests the accumulation of this species in sediments when inserted in quiescent water bodies.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Impedance sensing of DNA hybridization onto nanostructured phthalocyanine-modified electrodes
    (Pergamon-Elsevier Science Ltd, 2016) Manzanares-Palenzuela, C. L.; Fernandes, Edson Giuliani Ramos [UNIFESP]; Lobo-Castanon, M. J.; Lopez-Ruiz, B.; Zucolotto, V.
    DNA detection is still undergoing major innovations in pursuit of low-cost and simple approaches for decentralized applications. Label-free sensing of DNA hybridization via impedance measurements is a popular strategy to fulfil the goals of cost-efficiency and simplicity. Several materials are often reported for electrode modification to improve the sensitivity of impedance-based sensors. Herein we evaluate the electronic properties of copper phthalocyanine tetrasulfonate (CuPcTs) in Layer-by-Layer (LbL) films for impedimetric sensing of DNA hybridization using silanized Fluorine-doped Tin Oxide (FTO) electrodes. 1 to 5 bilayers were prepared by alternate immersion of the substrate in CuPcTs and poly(allylamine hydrochloride) (PAH). DNA probe immobilization was carried out electrostatically onto the last PAH layer, followed by hybridization with the target sequence leading to the formation of a partial double stranded (pds) structure onto the films. Impedance decreased after hybridization proportionally with the concentration of the target sequence at picomolar levels. Not only are these findings useful as a potential biosensing strategy, but also leave an open question about the electronic and synergistic properties of DNA interacting with different materials and surfaces. (C) 2016 Elsevier Ltd. All rights reserved.