Direct voltammetry and catalysis of hemoenzymes in methyl cellulose film

Horseradish Peroxidase Immobilization on Amine Functionalized Carbon Nano Tubes: Direct Electrochemistry and Bioelectrocatalysis

Horseradish peroxidase (HRP) was successfully immobilized on amine functionalized TiO2-coated multiwalled carbon nanotubes (NH2 TiO2 CNTs) by a convenient and efficient method. Electrochemical impedance spectroscopy, cyclic voltammetry and amperometry were applied to characterize the HRP/NH2- TiO2 - CNT nano-composite. These techniques showed that the NH2 TiO2CNTs greatly enhance the electron transfer between HRP and the modified electrode. Owing to the redox reaction of the electroactive centre of HRP, the HRP/NH2-TiO2-CNTs modified electrode exhibited a pair of quasi-reversible peaks with a peak-to-peak separation (Δ Ep) of 70.6 m V and a formal potential ( E°’) of - 367.65 m V (versus Ag/AgCl) in phosphate buffer solution. The charge transfer coefficient (a) and the apparent charge transfer rate constant (ks) were found to be 0.34 and 2.08 s-1 respectively. The prepared biosensor responded to H2O2 with a linear range, detection limit, sensitivity and response time of 1.0 × 10−9 to 1.0 × 10 −7 M, 0.786nM, 28.4 μA A nM−1 and 3 s, respectively.

Recent advances in electrochemical sensing for hydrogen peroxide: a review

Due to the significance of hydrogen peroxide (H(2)O(2)) in biological systems and its practical applications, the development of efficient electrochemical H(2)O(2) sensors holds a special attraction for researchers. Various materials such as Prussian blue (PB), heme proteins, carbon nanotubes (CNTs) and transition metals have been applied to the construction of H(2)O(2) sensors. In this article, the electrocatalytic H(2)O(2) determinations are mainly focused on because they can provide a superior sensing performance over non-electrocatalytic ones. The synergetic effect between nanotechnology and electrochemical H(2)O(2) determination is also highlighted in various aspects. In addition, some recent progress for in vivo H(2)O(2) measurements is also presented. Finally, the future prospects for more efficient H(2)O(2) sensing are discussed.

A review on direct electrochemistry of catalase for electrochemical sensors

Catalase (CAT) is a heme enzyme with a Fe^(III/II) prosthetic group at its redox centre. CAT is present in almost all aerobic living organisms, where it catalyzes the disproportionation of H₂O₂ into oxygen and water without forming free radicals. In order to study this catalytic mechanism in detail, the direct electrochemistry of CAT has been investigated at various modified electrode surfaces with and without nanomaterials. The results show that CAT immobilized on nanomaterial modified electrodes shows excellent catalytic activity, high sensitivity and the lowest detection limit for H₂O₂ determination. In the presence of nanomaterials, the direct electron transfer between the heme group of the enzyme and the electrode surface improved significantly. Moreover, the immobilized CAT is highly biocompatible and remains extremely stable within the nanomaterial matrices. This review discusses about the versatile approaches carried out in CAT immobilization for direct electrochemistry and electrochemical sensor development aimed as efficient H₂O₂ determination. The benefits of immobilizing CAT in nanomaterial matrices have also been highlighted.

Direct electrochemistry of catalase at multiwalled carbon nanotubes-nafion in presence of needle shaped DDAB for H2O2 sensor

The direct electrochemistry of catalase (CAT) at didodecyldimethylammonium bromide (DDAB) present on nafion dispersed multiwalled carbon nanotubes (MWCNTs-NF) modified glassy carbon electrode (GCE) has been reported. The presence of DDAB in MWCNTs-NF-CAT film enhances the surface coverage concentration of CAT (Fe(III/II)) to 48%. Similarly, in presence of DDAB, there is a 57% enhancement in electron transfer rate (ks) with 66% increase in CAT stability. (Fe(III/II)) redox couple exhibits linear dependence with the pH variation (-51 mV pH(-1)). The UV-vis absorption spectroscopy study reveals the entrapped CAT in DDAB film retains its native structure at MWCNTs-NF modified electrodes. Similarly, electrochemical impedance spectroscopy results confirm the co-existence of CAT and DDAB in the modified film. Further, scanning electron microscopy results reveal the structural morphological difference between various components in MWCNTs-NF-(DDAB/CAT) film. The cyclic voltammetry (CV) and amperometry (i-t curve) have been used for the measurement of electroanalytical properties of H2O2 by means of various film modified GCEs. The sensitivity values of MWCNTs-NF-(DDAB/CAT) film for H2O2 using CV (35.62 microA mM(-1)cm2) are higher than the values which are obtained for MWCNTs-NF-CAT film (2.74 mmicroA mM(-1)cm2). Similarly, the sensitivity values using i-t curve are 101.74 microA mM(-1)cm2 for MWCNTs-NF-(DDAB/CAT) and 74.69 microA mM(-1)cm2 for MWCNTs-NF-CAT film. Finally, the diffusion coefficient of H2O2 at MWCNTs-NF-(DDAB/CAT) film (3.4 x 10(-10) cm2 s(-1)) has been calculated using rotating disc electrode studies.

Preliminary electrochemical studies of the flavohaemoprotein from Ralstonia eutropha entrapped in a film of methyl cellulose: Activation of the reduction of dioxygen

A flavohaemoprotein (FHP) from Ralstonia eutropha, obtained in a pure and active form, has been entrapped in a film of methyl cellulose on the electrode surface and gives a stable and reproducible electrochemical response at pH 7.00 when subject to cyclic voltammetry using a glassy carbon electrode. To our knowledge, no previous direct electrochemistry had been achieved with a bacterial flavohaemoglobin, which possess both a FAD and a haem. A single couple is observed which is assigned to the haem moiety of the protein, since the same result is obtained with a semi-apo form of the protein deprived of FAD (semi-apo FHP). The data collected were further confirmed by potentiometry with a platinum electrode, and the homogeneous electron transfer rate estimated by double potential step chronocoulometry at a bare glassy carbon electrode in the presence of methyl viologen (MV). The presence of FAD in the holoprotein is easily confirmed by UV-Vis spectrophotometry, but its expected electron relay role remains elusive. The protein activates the reduction of dioxygen by about 400 mV, the reduction current being proportional to the concentration of dioxygen up to 10% in volume in the gas mixture.

Zirconia nanoparticles enhanced grafted collagen tri-helix scaffold for unmediated biosensing of hydrogen peroxide

A novel, biocompatible, thermally steady, and nontoxic zirconia enhanced grafted collagen tri-helix scaffold was prepared on a graphite electrode. This scaffold provided a microenvironment for loading biomolecules and helped to retain their natural structure. UV-vis spectroscopy and scanning electron microscopy were used to characterize the scaffold and the structure of immobilized biomolecules. Using horseradish peroxidase (HRP) as an example, this scaffold accelerated its electron transfer and led to its direct electrochemical behavior with a good thermal stability up to 80 degrees C. The surface electron-transfer rate constant of the immobilized HRP was (5.55 +/- 0.43) s(-)(1) in 0.1 M pH 7.0 PBS at 18 degrees C. The immobilized HRP showed an electrocatalytic activity to the reduction of hydrogen peroxide (H(2)O(2)) without aid of an electron mediator. The linear response range of the biosensor for H(2)O(2) was from 1.0 to 73.0 microM with a correlation coefficient of 0.999 (n = 14), a limit of detection down to 0.25 microM and an apparent Michaelis-Menten constant of (0.28 +/- 0.02) mM. The biosensor exhibited high sensitivity, acceptable stability, and reproducibility. The ZrO(2) grafted collagen provided an excellent matrix for protein immobilization and biosensor preparation.

Preliminary Investigations on a New Disposable Potentiometric Biosensor for Uric Acid

In this paper, uricase, catalase, and electron mediator were coimmobilized on the surface of the tin oxide (SnO2)/indium tin oxide (ITO) glass, to develop a disposable potentiometric uric acid biosensor. The SnO2/ITO glass was employed as a pH sensor, fabricated by sputtering SnO2 thin films on the ITO glass. 3-Glycidyloxypropyltrimethoxysilane (GPTS) was utilized to immobilize uricase, catalase and the electron mediator (ferrocenecarboxylic acid, FcA) on the sensing window. The experimental results reveal that the optimal weight ratio of uricase, FcA to catalase (CAT) is 4:1:2. The sensor responds linearly between 2 mg/dl and 7 mg/dl at pH 7.5, in 20 mM of test solution, with a correlation coefficient of 0.99213. Accordingly, no significant interference was observed when interfering substances, glucose, urea and ascorbic acid, were added to the uric acid solution. Moreover, the recorded voltage was relatively constant during the first 28 days of measurement. Consequently, a potentiometric uric acid biosensor was realized with the advantages of low cost and simple fabrication.