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Hemoglobin (Hb) has been demonstrated to endow electrochemical sensors with pH-switchable response because of the presence of carboxyl and amino groups. Hb was deposited in a chitosan matrix on a glassy carbon electrode (GCE) that was previously coated with clustered gold nanoparticles (Au-NPs) by electrodeposition. The switching behavior is active ('on') to the negatively charged probe [Fe(CN)] at pH 4.0, but inactive ('off') to the probe at pH 8.0. This switch is fully reversible by simply changing the pH value of the solution and can be applied for pH-controlled reversible electrochemical reduction of HO catalyzed by Hb. The modified electrode was tested for its response to the different electroactive probes. The response to these species strongly depends on pH which was cycled between 4 and 8. The effect is also attributed to the presence of pH dependent charges on the surface of the electrode which resulted in either electrostatic attraction or repulsion of the electroactive probes. The presence of Hb, in turn, enhances the pH-controllable response, and the electrodeposited Au-NPs improve the capability of switching. This study reveals the potential of protein based pH-switchable materials and also provides a simple and effective strategy for fabrication of switchable chemical sensors as exemplified in a pH-controllable electrode for hydrogen peroxide. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel reagentless NO biosensor based on hemoglobin (Hb) immobilized on nanometer-sized gold colloid particles associated with a cysteamine monolayer on gold electrode surface was presented. The experimental optimization was studied in detail. The immobilized Hb displayed an excellent electrocatalytic response to NO. The electrocatalytic currents were proportional to the NO concentration from 1.2 × 10[sup -8] to 5.0 × 10[sup -6] M and the detection limit was as low as 4.0 × 10[sup -9] M (S/N = 3) with good stability. Arginine, ascorbate, nitrite, uric acid, epinephrine and cystine didn't interfere with the determination of NO. The Michaelis-Menten constant (K[sub m]) was determined to be 0.19 mM. This resulting biosensor has been applied to the direct determination of trace NO in raw blood. [ABSTRACT FROM AUTHOR]

In the current work, a highly sensitive and stable amperometric biosensing interface for the rapid detection of 1-pyrene butyric acid (1-PBA) was constructed based on the functions of alginate-polylysine microencapsulated hemoglobin (AP@Hb) and Au nanoparticles (AuNPs). AP@Hb was simply prepared by a two-step template method. The morphology and size were characterized by scanning electron microscopy. AuNPs were employed to facilitate the electron transfer between the electrode and Hb. Through the electron tunneling effect of AuNPs and the catalysis of Hb, the resultant biosensor achieved rapid electron transfer and high sensitivity toward 1-PBA with a quantification limit as low as 23.5 fM. Thus, this biosensor is promising for the quantitative detection of 1-PBA in real samples and might provide assistance to public health agencies for the control and prevention of certain diseases caused by 1-PBA. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents both electrochemical and electrochemiluminescence (ECL) detections based on the layer-by-layer (LBL) films fabricated with hemoglobin (Hb) and the optimal nanocomposite containing multiwall carbon nanotubes (MWCNTs) and CdS quantum dots (QDs). Hb and the MWCNT–CdS nanocomposite were electrostatically assembled on the chitosan (CS) modified glassy carbon electrode (GCE) forming with up to six bilayer films. Our results on cyclic voltammograms (CVs) revealed that the redox peak currents of Hb at the six-bilayer film ({MWCNT–CdS/Hb}6) modified GCE were the largest. Hydrogen peroxide (H2O2) could be stably detected using the six bilayer films modified GCE with a wide linear range from 0.125μM to 1.20mM. Nitrite (NO2 −) could also be determined through CdS QDs of the multilayer films based on stable ECL intensities with a linear range from 0.60μM to 0.80mM. [Copyright &y& Elsevier]

Abstract: A novel platform, which hemoglobin (Hb) was immobilized on core–shell structurally Fe3O4/Au nanoparticles (simplified as Fe3O4@Au NPs) modified glassy carbon electrode (GCE), has been developed for fabricating the third biosensors. Fe3O4@Au NPs, characterized using transmission electron microscope (TEM), scanning electron microscope (SEM) and energy dispersive spectra (EDS), were coated onto GCE mediated by chitosan so as to provide larger surface area for anchoring Hb. The thermodynamics, dynamics and catalysis properties of Hb immobilized on Fe3O4@Au NPs were discussed by UV–visible spectrum (UV–vis), electrochemical impedance spectroscopy (EIS), electrochemical quartz crystal microbalance technique (EQCM) and cyclic voltammetry (CV). The electrochemical parameters of Hb on Fe3O4@Au NPs modified GCE were further carefully calculated with the results of the effective working area as 3.61cm2, the surface coverage concentration (Γ) as 1.07×10−12 molcm−2, the electron-transfer rate constant (K s ) as 1.03s−1, the number of electron transferred (n) as 1.20 and the standard entropy of the immobilized Hb (ΔS 0′) as calculated to be −104.1Jmol−1 K−1. The electrocatalytic behaviors of the immobilized Hb on Fe3O4@Au NPs were applied for the determination of hydrogen peroxide (H2O2), oxygen (O2) and trichloroacetic acid (TCA). The possible functions of Fe3O4 core and Au shell as a novel platform for achieving Hb direct electrochemistry were discussed, respectively. [Copyright &y& Elsevier]