The sensitive determination of hydrogen peroxide has broad analytical applications. In this work, a novel non-enzymatic hydrogen peroxide sensor based on Pt nanoparticles (PtNPs) electrochemically deposited on previously modified and activated screen-printed carbon electrodes (aSPCEs) was constructed. The pretreatment consisted of subjecting the electrodes to a surface activation treatment with hydrogen peroxide followed by the electrodeposition of poly(azure A) films (PAA) in a sodium dodecyl sulfate micellar aqueous solution. The PtNPs/PAA/aSPCEs were characterized by scanning electron microscope, X-Ray photoelectron spectrometry, linear scan voltammetry and electrochemical impedance spectroscopy. Linear sweep voltammograms showed that the oxidation peak potential of H2O2 shifts from ~1 V at SPCEs to ~0.1 V at PtNPs/PAA/aSPCEs. The fabricated electrodes showed excellent electrocatalytic activity towards H2O2 oxidation, making its detection possible at 0.1 V. The detection limit was 51.6 nM, which is significantly lower than other modified electrodes found in the literature, and the linear range ranging from 0 to 300 µM. The proposed electrode was successfully applied to the determination of H2O2 in real samples in different areas. Additional experiments against common interfering agents (ascorbic acid, dehydroascorbic acid, glucose, salicylic acid, among other compounds) showed no increase in the current signal and only in the case of ascorbic acid a small interference, not greater than 10% is observed, which indicates high specificity of the sensor. These electrodes open up alternative avenues for the development of highly sensitive, robust and low cost electrochemical H2O2 sensors for field tests.

Herein, a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on a surface containing platinum nanoparticles (PtNPs) electrodeposited on poly(Azure A) (PAA) previously electropolymerized on activated screen-printed carbon electrodes (GOx-PtNPs-PAA-aSPCEs) is reported. The resulting electrochemical biosensor was validated towards glucose oxidation in real samples and further electrochemical measurement associated with the generated H2O2. The electrochemical biosensor showed an excellent sensitivity (42.7 μA mM−1 cm−2), limit of detection (7.6 μM), linear range (20 μM–2.3 mM), and good selectivity towards glucose determination. Furthermore, and most importantly, the detection of glucose was performed at a low potential (0.2 V vs. Ag). The high performance of the electrochemical biosensor was explained through surface exploration using field emission SEM, XPS, and impedance measurements. The electrochemical biosensor was successfully applied to glucose quantification in several real samples (commercial juices and a plant cell culture medium), exhibiting a high accuracy when compared with a classical spectrophotometric method. This electrochemical biosensor can be easily prepared and opens up a good alternative in the development of new sensitive glucose sensors.

14Soil has been utilized in criminal investigations for some time because of its prevalence and 15 transferability. It is usually the physical characteristics that are studied, however the research

Abstract.Gamma Hydroxybutyric Acid (GHB), when studied in a platinum electrode using cyclic voltammetry, presented three oxidation peaks in acid solutions that correspond to the oxidation of the alcohol group to the corresponding aldehyde and carboxylic acid (succinic acid). An anodic scan of GHB yielded two characteristic waves, which indicates an oxidation process dependent on the chemical environment on the surface of the electrode. The cathodic scan presented an inverted oxidation peak with an onset partially overlapping with the tail of the cathodic peak for the reduction of the platinum oxide formed initially during the anodic scan. This inverted peak can be observed at a potential close to +0.2V (vs Ag/AgCl at pH 2) and separated 0.4 and 0.8 V from the two other oxidation peaks obtained during the anodic scan and in such conditions that the surface is particularly activated to favour this electrochemical process. The response obtained in the electronic current for the different peaks when GHB concentration and scan rate were changed allows inferring that these are the result of a potential dependent mechanism.

No abstract

Abstract.The electro-oxidation of gamma-hydroxybutyric acid (GHB) on a polycrystalline platinum electrode in acidic medium has been studied using chronoamperometry. The study has been performed in a wide interval of potentials and at different concentrations.It was found that at longer times the density currents reached stationary values at more anodic potentials, whereas it is zero at lower potentials. These characteristics in the j-t curves suggest a different mechanism for the electro-oxidation of GHB, potential dependent, with a catalytic process at high potentials and an adsorption process controlled by mass transport at low potential.The change in the stationary current obtained at +0.9 V with variable GHB concentrations also suggests an oxidation mechanism catalysed by the platinum surface with platinum hydroxides acting as reaction intermediates to make the final oxidation product for GHB. The results obtained using chronoamperometry are in good agreement with those obtained using cyclic voltammetry where the alcohol group is oxidised at different potentials.In situ Surface Enhanced Raman Scattering (SERS) spectra corresponding to GHB intermediates and water adsorbed species being formed/consumed at the potentialdependent adsorption processes have been analyzed using spectro-electrochemistry. A peak at 1590 cm -1 , corresponding to the asymmetric stretching of carboxylic group in a bridge configuration, increases with the potential. This supports the hypothesis of a mechanism of formation of the succinic acid on the platinum surface as reaction product under the experimental conditions studied.2

Coumaphos is an organophosphorus compound used as insecticide and frequently used by beekeepers for the management of parasitic mites. The most important metabolite, chlorferron (CFN), has been identified in biological samples and foodstuff. The need to quickly identify the presence of typical metabolites, as an indication of interaction with coumaphos has driven the need to produce a highly sensitive electrochemical method for chlorferron analysis, based on molecularly imprinting polymers (MIP) technology. It showed irreversible behaviour with mixed diffusion/adsorption-controlled reactions at the electrode surface. A monoelectronic mechanism of reaction for oxidation has also been suggested. The linear range observed was from 0.158 to 75 µM. Median precision in terms of %RSD around 3% was also observed. For DPV, the limit of detection (LOD) and the limit of quantitation (LOQ) for the CFN-MIP were 0.158 µM and 0.48 µM, respectively. The obtained median % recovery was around 98%. The results were also validated to reference values obtained using GC-MS. Urine and human synthetic plasma spiked with CFN were used to demonstrate the usability of the method in biological samples, showing the potential for biomonitoring. The developed imprinted sensor showed maximum signal change less than 16.8% when related metabolites or pesticide were added to the mix, suggesting high selectivity of the MIP sensor toward CFN molecules. The results from in vitro metabolism of CMP analysed also demonstrates the potential for detection and quantification of CFN in environmental samples. The newly developed CFN-MIP sensor offers similar LoDs than chromatographic methods with shorter analysis time.

No abstract