TEMPO as a Promising Electrocatalyst for the Electrochemical Oxidation of Hydrogen Peroxide in Bioelectronic Applications

Abstract

A number of bioelectronic applications work with oxidase enzymes and many of them can operate with small molecule or polymer redox mediators. However, for some oxidases, there are no known redox mediators able to mediate electron transfer. Therefore, electron transfer must occur through peroxide production and oxidation at the electrode surface. Organic redox catalysts such as oxoammonium cations, are able to oxidize H 2 O 2 to form nitroxyl radicals, which can be electro-oxidized and regenerate the oxoammonium cation form. In this study, we investigate the ability to use TEMPO as a platform for the electrocatalytic oxidation of H 2 O 2 at different pHs. The results have shown that TEMPO can be used to monitor H 2 O 2 in broad pH range (≥4) at 530 mV (vs SCE). Combining TEMPO with cholesterol oxidase, we have shown the possibility to monitor the cholesterol oxidation with a linear range between 20 μM and 2.5 mM with a sensitivity of 54.86 mA cm −2 M −1 . Furthermore, we have studied the electrocatalytic oxidation of oxalate by oxalate oxidase for biofuel cell applications. These combined results demonstrate TEMPO as a promising electrocatalyst applied for the development of electrochemical biosensors or enzymatic biofuel cells. Hydrogen peroxide (H 2 O 2 ) is an enzymatic product of oxygen (O 2 ) reduction, which can be catalyzed by an exhaustive list of oxidase enzymes including glucose oxidase, alcohol oxidase, lactate oxidase, urate oxidase, cholesterol oxidase, D-amino acid oxidase, glutamate oxidase, lysine oxidase, and oxalate oxidase. Hydrogen peroxide is the smallest and simplest peroxide and is of great interest in multiple fields as a disinfectant, as a propellant in the aerospace industry, and as a biomarker for biological decomposition in the food industry.1 It also applied in the defense system of some insects, 2 the immune system, 3 and regulation of cellular processes. 4 Development of enzymatic biosensors presents a significant utility for the detection and quantification of the large number of oxidase substrates for fundamental studies as well as diagnostic and industry applications. Different techniques for the detection of oxidase substrates that have been described in the literature include spectrophotometry, 5 fluorimetry, 6 chemiluminescence, 7 and fluorescence, 8 but most of them are costly and time consuming. Hydrogen peroxide can be oxidized electrochemically, and thus electrochemical techniques have also been used as detection methods. Electrochemistry is commonly described as a simpler, cheaper, faster, and more sensitive detection technique for the development of oxidase substrate biosensors and enzymatic biofuel cells. 9,10The direct electrochemical oxidation and reduction of H 2 O 2 require high overpotentials (>+0.65 V for oxidation and >−1.7 V for reduction versus NHE). These high potentials limit analytical applications involving the oxidation or reduction of H 2 O 2 in complex media, because media electrolysis causes interference and can foul the electrode surface. In order to d...

Facile Synthesis of a Nickel Sulfide (NiS) Hierarchical Flower for the Electrochemical Oxidation of H2O2and the Methanol Oxidation Reaction (MOR)

“…24,25 Due to its key role, the determination of H 2 O 2 have arisen a great interest, hence many approaches have been developed, such as optical, titration-based, and electrochemical methods. [26][27][28] Among these methods, electrochemical analysis is particularly promising due to its many advantages such as low cost, easy to manipulate and fast analysis.…”

TEMPO-Functionalized Nanoporous Au Nanocomposite for the Electrochemical Detection of H2O2

“…To ascertain the synergistic peroxidase-like activity between the TEMPO and np-AuNPs, we compared the net current strengths (ΔI) of TEMPO-np-AuNPs and np-AuNPs, where the ΔI refers to the difference strength value within H 2 O 2 in and without it. The nitroxide mediator can improve the free diffuse state, which is adjacent to the electrode surface [ 22 , 23 ]. The ΔI of np-AuNPs sharply rose to 403 μ A after it was modified with the TEMPO.…”

“…Particularly, nanoporous gold nanoparticles (np-AuNPs), one of the most important nanoscale hollow materials, combining their high surface areas with tunable surface plasmon resonance (SPR) features, can serve larger immobilized surface and excellent catalytic sites in chemical reactions and also provide a substrate material to manufacture functionalized nanocomposite [ 12 , 15 ]. Meanwhile, TEMPO plays a key role in chemistry and biology as an organic redox catalyst for alcohol, aldehydes, and ketones [ 16 – 21 ] and has shown its catalytic oxidation potential to H 2 O 2 due to the electrochemical oxidation of stable nitroxyl radical [ 22 , 23 ]. Recently, the nitroxyl radical of TEMPO has been reported to attach to solid surfaces by chemical routes to form supramolecular assemblies with high coverage of catalytic radicals [ 24 , 25 ].…”

Integrating Hydrogen Production with Aqueous Selective Semi‐Dehydrogenation of Tetrahydroisoquinolines over a Ni2P Bifunctional Electrode

“…Therefore,N i II /Ni III ,o nt he surface of electrode,w orks as an efficient redox active species to promote the conversion of 1a into 2a,s imilar to the reported organic electrooxidation processes driven by TEMPO mediator. [10] In addition, the radical process is possibly involved in the electrocatalytic selective semi-dehydrogenation of 1a to 2a (Figure 3e and Figure S9). [6a, 11] TheC Vw as also carried out in acetonitrile with glassy carbon (GC) as the working electrode to analyze the electrooxidative behavior of organic substrate (for details see the Supporting Information).…”