Graphene oxide (GO) in water was reduced heterogeneously by decamethylferrocene (DMFc) or ferrocene (Fc) in 1,2-dichloroethane (DCE), which could then act as a catalyst for an interfacial oxygen reduction reaction (ORR) and production of hydrogen peroxide (H 2 O 2 ). The reduced graphene oxide (RGO) produced at the liquid/liquid interface was characterized by using electron microscopy, spectroscopy (Raman, infrared, and electron energy loss), and electrochemical techniques.The oxygenated functional groups at the edge/defects of the RGO surface activate O 2 adsorption, forming superoxidelike adducts that can be protonated at the liquid/liquid interface and reduced by DMFc or Fc. This process is facilitated by the higher electrical conductivity of the RGO sheets. The key feature of this catalytic reaction is the in situ partial-reduction of GO at the liquid/liquid interface, forming an efficient and inexpensive catalyst for the production of H 2 O 2 .Electrochemistry at polarized interfaces between two immiscible electrolyte solutions (ITIES) has developed over the past 30 years, in which charge-transfer (electron-and ion-transfer) reactions have found applications in areas such as phase-transfer catalysis, solvent-extraction processes, chemical sensing, solar-energy-conversion systems, drug release and delivery, and in mimicking the function of biological membranes. [1] Liquid/liquid interfaces provide a unique platform at which to study ORRs, at which aqueous protons react with organic solubilized electron donors in the absence or presence of adsorbed catalysts, usually through a proton-coupled electron-transfer (PCET) reaction. [2] The molecular catalysts studied include cobalt, [3] free-base porphyrins, [4] and in situ-deposited platinum particles. [5] The ORR proceeds either by a 4 e À /4 H + pathway to produce water or a 2 e À /2 H + route to yield H 2 O 2 , which is considered a green oxidant.H 2 O 2 is widely used in many industrial areas, particularly in the chemical industry or for environmental protection, and is currently produced on an industrial scale through the biphasic anthrahydroquinone oxidation (AO) process (representing ca. 95 % of the world's H 2 O 2 production). [6] Generally, anthrahydroquinone is oxidized by O 2 to produce H 2 O 2 and anthraquinone and, subsequently, the formed anthraquinone is reduced back to the anthrahydroquinone by using H 2 in the presence of a metal catalyst. Both reactions occur in the organic phase, and H 2 O 2 is recovered by extraction to the aqueous phase. [6] The advantage of the AO process is the very high yield of H 2 O 2 generated per cycle. Conversely, side reactions generating organic byproducts need to be dealt with by regenerating the solution and by using separation techniques to eliminate such impurities. Conceptually, following the AO process, the reduction of O 2 was investigated at quinone-modified carbon surfaces. O 2 reduction to H 2 O 2 was mediated by surface-bound quinone groups via superoxide anion intermediates, [7] and such modified elec...

We report on the Prussian Blue based lactate biosensor with the remarkably increased upper detection limit suitable for analysis of undiluted sweat. Engineering of the enzyme lactate oxidase has been carried out upon its immobilization from water-isopropanol mixtures with the high (90%) content of organic solvent. To decrease the enzyme binding constant, we propose to shield the substrate binding sites in its active center with negatively charged polyelectrolyte. The biosensor made from the optimal mixture (3% γ- aminopropyltriethoxysilane and 5% perfluorosulfonated ionomer) is characterized by the calibration graph, which even in batch mode is shifted for 2 orders of magnitude toward high analyte concentrations as compared to it of lactate sensitive electrode made without Nafion analogue. In flow-injection mode, the biosensor allows lactate detection up to 0.5 M. The biosensor displays stable response for 4 h of continuous operation. The achieved analytical performance characteristics allow the monitoring of lactate content in undiluted sweat. A successful validation of the elaborated flow-through monitor with the integrated biosensor opens new horizons for noninvasive diagnostics of hypoxia-related conditions.

a b s t r a c tWe report the mapping of biocatalytically active surfaces, particularly on an express search for optimal immobilization conditions of the enzyme lactate oxidase by means of scanning electrochemical microscopy (SECM). With this aim, soft stylus SECM probes containing a carbon paste ultramicroelectrode were modified with Prussian Blue yielding reproducible hydrogen peroxide (H 2 O 2 ) sensors with a sensitivity of 1.6 ± 0.5 A M À1 cm À2 for screening applications. The ultramicroelectrode response was stable under harsh conditions of 1 mM H 2 O 2 during the first hour, while the response decay during the second hour was less than 4% providing sensor suitability for long-term experiments. SECM imaging in contact mode of different lactate oxidase spots containing membranes allowed for a straightforward optimization of the enzyme immobilization conditions on rough screen-printed carbon paste substrates. The resulting lactate biosensor was characterized by improved analytical performance characteristics: a four times enhanced sensitivity (up to 0.3 A M À1 cm À2) in comparison to previous reports and a remarkably increased operational stability.