Hemoglobin/colloidal silver nanoparticles immobilized in titania sol–gel film on glassy carbon electrode: Direct electrochemistry and electrocatalysis

Revisiting the nitrite reductase activity of hemoglobin with differential pulse voltammetry

Nitric oxide (NO) is an omnipresent signalling molecule in all vertebrates. NO modulates blood flow and neural activity. Nitrite anion is one of the most important sources of NO. Nitrite is reduced to NO by various physiological mechanisms including reduction by hemoglobin in vascular system. In this study, nitrite reductase activity (NRA) of hemoglobin is reported using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in a wide potential window from +0.3 V to -1.3 V (vs. Ag/AgCl). To the best of our knowledge, a detailed look into NRA of hemoglobin is proposed here for the first time. Our results indicated two different regimes for reduction of nitrite by hemoglobin in its Fe(II) and Fe(I) states. Both reactions showed a reversible behaviour in the time scale of the experiments. The first reduction displayed a normal redox behaviour, while the latter one had the characteristics of a catalytic electro-reduction/oxidation. The reduction in Fe(II) state was selected as a tool for comparing the NRA of hemoglobin (Hb) and hemoglobin-S (Hb-S) under native-like conditions in a didodecyldimethyl ammonium bromide (DDAB) liquid crystal film. These investigations lay the prospects and guidelines for understanding the direct electrochemistry of hemoglobin utilizing a simplified mediator-free platform.

Superior non-enzymatic glucose sensing properties of Ag-/Au-NiCo2O4 nanosheets with insight from electronic structure simulations

Ag-/Au-NiCo₂O₄ nanosheets were synthesized by a facile electrodeposition approach on conducting Ni foam, and their non-enzymatic glucose sensing performance was investigated.

Nitrite biosensing via selective enzymes--a long but promising route

The last decades have witnessed a steady increase of the social and political awareness for the need of monitoring and controlling environmental and industrial processes. In the case of nitrite ion, due to its potential toxicity for human health, the European Union has recently implemented a number of rules to restrict its level in drinking waters and food products. Although several analytical protocols have been proposed for nitrite quantification, none of them enable a reliable and quick analysis of complex samples. An alternative approach relies on the construction of biosensing devices using stable enzymes, with both high activity and specificity for nitrite. In this paper we review the current state-of-the-art in the field of electrochemical and optical biosensors using nitrite reducing enzymes as biorecognition elements and discuss the opportunities and challenges in this emerging market.

Synthesis of phthalocyanine stabilized rhodium nanoparticles and their application in biosensing of cytochrome c

A single step synthesis route is described for the preparation of rhodium nanoparticles using a cobalt aminophthalocyanine macrocyclic complex as a stabilizer. The results of nanoparticles characterization using electronic absorption, Raman and X-ray spectroscopes as well as transmission electron microscopy are reported. Rhodium nanoparticle modified electrode behavior as examined by cyclic and differential pulse voltammetry is also provided. The nanoparticles were found to be well dispersed and stabilized throughout the macromolecular matrix. TEM studies showed that they have an average diameter of 3 to 5 nm with spherical shape. The colloidal rhodium was then used for electrochemical sensing of cytochrome c using glassy carbon electrode. The results showed that the colloidal rhodium nanoparticles enhanced the electron transfer process between cytochrome c and the electrode. Differential pulse voltammetric measurements of cytochrome c at the colloidal rhodium nanoparticles modified glassy carbon electrode showed a linear relationship with the oxidation peak currents in the concentration range of 100 nM to 3 microM of cytochrome c.

A novel nitrite biosensor based on the direct electron transfer of hemoglobin immobilized on CdS hollow nanospheres

A novel nitrite biosensor based on the direct electron transfer of hemoglobin (Hb) immobilized on CdS hollow nanospheres (HS-CdS) modified glassy carbon electrode was constructed. The direct electron transfer of Hb showed a pair of redox peaks with a formal potential of -286 mV (vs. SCE) in 0.1M pH 7.0 phosphate buffer solution. It was a surface-controlled electrode process involving a single proton transfer coupled with a reversible one-electron transfer for each heme group of Hb. HS-CdS had a large specific surface area and good biocompatibility and had a better electrochemical response than that of solid spherical CdS. The immobilized Hb on HS-CdS displayed an excellent response to NO(2)(-) with one irreversible electrode process for NO reduction. Under optimal conditions, the biosensor could be used for the determination of NO(2)(-) with a linear range from 0.3 to 182 microM and a detection limit of 0.08 microM at 3 sigma based on the irreversible reduction of NO. HS-CdS provided a good matrix for protein immobilization and had a promising application in constructing sensors.