An electrochemical sensor for H2O2 determination was prepared by electrodepositing copper oxide nanoparticles on the activated pencil graphite electrodes. At first, a study has been made of the optimum conditions for chemical activation of the pencil graphite electrodes (APGE) and then the activated pencil graphite electrode was modified with copper oxide nanoparticles (CuO/APGE) and used as a non-enzymatic hydrogen peroxide sensor. The morphology of the modified electrode surface was investigated by scanning electron microscopy (SEM). Upon the addition of H2O2, the modified electrode (CuO/APGE) exhibits significant oxidation of H2O2 with starting potential around +0.05 V (vs. Ag/AgCl) which dramatically decreases the overpotential of H2O2 oxidation. Under the optimal experiment conditions, the electrocatalytic response current of this sensor was proportional to the H2O2 concentration in the range of 5.0 × 10-6 to 1.6 × 10-3 mol L-1 with a detection limit down to 0.21 µmol L-1 (signal/noise = 3). The sensitivity was calculated to be 4.75 µAL mmol-1. The electrochemical active surface area and the catalytic rate constant of hydrogen peroxide electro-oxidation were calculated. The H2O2 sensor exhibited a low detection limit, a good signal reproducibility (relative standard deviation (RSD), n = 4) 2.36% and the accurate measurements in milk as the real sample.

A preparação e aplicação de poli-(2,6-diaminopiridina) sobre a superfície de um eletrodo de carbono vítreo (GCE) modificado com nanotubos de carbono de paredes múltiplas (CNTs) são descritas. Voltametria cíclica foi usada na síntese eletroquímica e na caracterização dos polímeros depositados sobre GCE. O eletrodo modificado mostra um efeito sinérgico das propriedades eletrocatalíticas e a elevada superfície ativa de ambos, polímero condutor e nanotubos de carbono, dando origem a uma melhora notável da oxidação eletrocatalítica de ácido ascórbico (AA), dopamina (DA) e ácido úrico (UA) com respeito a eletrodos modificados com polímero e eletrodos modificados com CNTs. Este tipo de eletrodo modificado mostra uma excelente atividade eletrocatalítica para a oxidação de AA, DA e UA dentro de um intervalo linear de 2,70 × 10-5-1,83 × 10-3, 8,33 × 10-7-1,00 × 10-5 e 4,16 × 10-6-2,25 × 10-4 mol L-1, respectivamente, em pH 8.0 (solução padrão de fosfato). A mistura ternária que contém AA, DA e UA pode ser muito bem separada uma da outra a uma velocidade de varredura de 100 mV s-1 com uma diferença de potencial de 184, 147 e 321 mV em voltametria de pulso diferencial (DPV) entre AA e DA, DA e UA, e AA e UA, respectivamente. Esta abordagem é tão fácil que pode ser usada para detectar seletivamente DA, AA e UA na presença uma das outras e também em algumas amostras reais

The preparation and application of poly-(2,6-diaminopyridine) on the surface of a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (CNTs) are reported. Cyclic voltammetry was used for both the electrochemical synthesis and characterization of the polymers deposited on GCE. The modified electrode shows a synergic effect of the electrocatalytic properties and high active surface area of both the conducting polymer and carbon nanotubes, giving rise to a remarkable improvement of electrocatalytic oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA) with respect to polymer-modified electrodes and CNTs‑modified electrodes. This kind of modified electrode shows and excellent electrocatalytic activity towards the oxidation of AA, DA and UA within the linear range of 2.70 × 10-5-1.83 × 10-3, 8.33 × 10-7-1.00 × 10-5 and 4.16 × 10-6-2.25 × 10-4 mol L-1, respectively, in pH 8.0 (phosphate buffer solution). The ternary mixture, which contains AA, DA and UA, can be well separated from each other at a scan rate of 100 mV s-1 with a potential difference of 184, 147 and 321 mV in differential pulse voltammetry (DPV) between AA and DA, DA and UA, and AA and UA, respectively. This approach is so simple and easy that can be used to selectively detect DA, AA and UA in the presence of each other and also in some real samples.