A nanosensor was developed for hydrogen peroxide determination based on nafion/graphene oxide/silver nanoparticles/tertiary butylhydroquinone (TBHQ) modified glassy carbon electrode (N-GO/AgNPs/TBHQ/GCE). Cyclic voltammetry was used to investigate the electrochemical behavior of this modified electrode and differential pulse voltammetry was used for the reduction of H2O2. The limit of detection was 0.46 µmol L-1 and three linear calibration ranges were obtained for H2O2 determination from 1.52-9.79 µmol L-1 for first linear segment, 9.79-231.0 µmol L-1 for second linear segment and 231.0-8330.0 µmol L-1 for third linear segment. Finally, the reliability of the nanosensor was confirmed in the real sample analysis in different beverages with satisfactory results.

A trifunctional electrochemical sensor was fabricated for simultaneous determination of ascorbic acid (AA), levodopa (LD), and insulin. This was done by modifying a glassy carbon electrode (GCE) with multi-walled carbon nanotubes and reactive blue 19 (RB-MWCNT-GCE). Cyclic voltammetry was used to investigate the redox properties of this modified electrode. The electro-catalytic activity of the modified electrode was studied for the oxidation of AA, LD, and insulin. By differential pulse voltammetry (DPV), the detection limits of AA, LD, and insulin were estimated to be 0.45 µmol L -1, 0.37 µmol L-1, and 0.25 µmol L-1, respectively. In DPV measurements, the RB-MWCNT-GCE could separate the oxidation peak potentials of AA, LD, uric acid (UA), insulin, and acetylsalicylic acid (ASA) in a mixture. The practical utility of this modified electrode was demonstrated by detecting AA, LD, UA, insulin, and ASA in real samples.

O presente estudo descreve as características eletroquímicas de um derivado de oxadiazol eletrodepositado sobre um eletrodo de carbono vítreo modificado por nanotubos de carbono de paredes múltiplas (OMWCNT-GCE) e seu papel como sensor eletroquímico altamente sensível para oxidação eletrocatalítica de dopamina (DA). A constante da taxa de transferência de carga da superfície (k s) e o coeficiente de transferência de carga (α) para a transferência de elétrons entre GCE e oxadiazol eletrodepositado foram calculados. OMWCNT-GCE exibiu propriedades eletrocatalíticas apropriadas para a oxidação de DA em solução tampão de fosfato (pH 7,0). O eletrodo modificado exibiu baixo limite de detecção (0,12 µmol L-1) para DA. Em medidas de voltametria de pulso diferencial (DPV), OMWCNT-GCE pode separar os potenciais de pico de oxidação de DA, acetaminofeno (AC) e triptofano (Trp) presentes na mesma solução, enquanto a GCE forneceu duas respostas amplas. O desempenho analítico deste sensor foi avaliado para determinar DA e AC em amostras reais.

The present study describes the electrochemical characteristics of an electrodeposited oxadiazole derivative on multi-walled carbon nanotubes glassy carbon electrode (OMWCNT-GCE) and its role as highly sensitive electrochemical sensor for the electrocatalytic oxidation of dopamine (DA). The surface charge transfer rate constant (k s) and the charge transfer coefficient (α) for the electron transfer between GCE and electrodeposited oxadiazole were calculated. OMWCNT-GCE exhibited suitable electrocatalytic properties for DA oxidation in a phosphate buffer (pH 7.0) solution. The modified electrode exhibited low limit of detection (0.12 µmol L-1) for DA. In differential pulse voltammetry (DPV) measurements, OMWCNT-GCE could separate the oxidation peak potentials of DA, acetaminophen (AC) e tryptophan (Trp) present in the same solution, while the bare GCE gave two broad responses. The analytical performance of this sensor was evaluated to determine DA and AC in real samples.