High enzymatic activity preservation of malate dehydrogenase immobilized in a Langmuir-Blodgett film and its electrochemical biosensor application for malic acid detection

In this study, malate dehydrogenase (MDH) enzyme was immobilized on a cation octadecylamine (ODA+) monolayer at the air-water interface. Pressure-area (?-A) isotherm studies confirmed that the ODA-MDH system formed a stable monolayer at the air-water interface. The as-prepared MDH-ODA monolayer was transferred onto an indium tin oxide coated glass substrate (ITO) by the Langmuir-Blodgett (LB) method as an MDH-ODA/ITO LB film and characterized using FT-IR, SEM and UV-Vis absorption spectroscopy. The catalytic activity of the enzyme immobilized electrode (MDH-ODA/ITO) was assayed by sensing malic acid (MA) in the range of 10.0-50.0 mM. The high and preserved enzymatic activity of MDH in in vitro media was explored by following the absorbance (A340 nm) of nicotinamide adenine dinucleotide (NADH). Moreover, the highly sensitive electrochemical biosensor behavior of the MDA-ODA/ITO electrode for MA detection was displayed by cyclic voltammetry studies. The electrochemical studies revealed that a voltammetric current from the MDA-ODA/ITO electrode was obtained, while the ODA/ITO electrode did not show this current response. The MDA-ODA/ITO demonstrated sensitive electrochemical sensor ability for quantification of MA in both standard solutions and real samples. © 2016 The Royal Society of Chemistry

Underpotential deposition of Te monolayers on Au surfaces from perchloric acid solution studied by chronocoulometry and EQCM

We report a study of the underpotential deposition (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry. We find that tellurium(IV) oxide (as TeO32-, TeO2 or HTeO2+) is adsorbed onto Au at potentials positive, of the UPD region. EQCM experiments, in which an An electrode poised at +0.7 V in pure, HClO4 electrolyte was monitored as a function of time before and after the addition of TeO2, showed a slow ad sorption of a submonolayer of TeO2. Energy-dispersive X-ray (EDX) measurements confirm the presence of a Te-containing species on the surface. Two distinct reductive UPD features at approximately +0.400 V and -0.100 V vs Ag\AgCl were observed by cyclic voltammetry. EQCM measurements indicate that there is a small, reproducible mass decrease accompanying the first UPD wave, consistent with the loss of H2O from the surface as an adsorbed layer of HTeO2+ is reduced to a submonolayer of Te atoms. Chronocoulometry indicates a charge density of 160 muC/cm(2) for the first UPD wave, which, when taken together with the mass change data, is consistent with the four-electron reduction of adsorbed HTeO2+ to Te. In addition, analysis of the current-time data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41. The second UPD peak results in the formation of a dense monolayer by reduction of HTeO2+ from solution. This process also appears to occur by a direct four-electron reduction and exhibits simple Langmuir adsorption behavior as evidenced by exponentially decaying current-time transients. The saturation coverage is approximately 0.9

Selenium electrochemistry in choline chloride–urea deep eutectic electrolyte

info:eu-repo/semantics/publishe