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Most clinical tests for biomarker detection require the support of a laboratory, and the results are usually slow, less sensitive, and lack the possibility for Point-of-Care (PoC) testing. Further, with the increasing demand for sensitive, portable, rapid, and low-cost devices for clinical PoC applications, innovative methods are crucial. Thus, we report on utilizing nanostructured gold-platinum (Au-Pt) hybrid electrodes as a PoC device for highly sensitive and selective PTH detection in human serum samples. The method employs the immobilization of 3-mercaptopropionic acid to Au and subsequent activation of the carboxyl groups to enable anti-PTH antibody immobilization. Serum PTH was detected by monitoring the changes in electrochemical properties (ΔR ct and Δi) of the sensor using electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) against a standard hexacyanoferrate (II/III) probe. Changes in relative response percentage (RR%) in electrochemical properties due to increased PTH concentrations in serum were observed with EIS and DPV. The biosensor exhibited a low detection limit of 0.36 pg.mL -1 (EIS) and 0.59 pg.mL -1 (DPV) in serum with a linear range of 1 to 100,000 pg.mL -1 . Further, to validate the accuracy of the proposed method, clinical samples (n = 20) were examined using the EIS method and compared to an established commercial test., (Copyright © 2019. Published by Elsevier B.V.)

A protein based electrochemical sensor for the detection of hydrogen peroxide based on Myoglobin immobilized on gold nano structures patterned on Indium tin oxide electrode was developed. A uniformly distributed nanometer sized Au-array on ITO electrode surface was obtained by optimizing electro deposition conditions. The morphology of Mb molecules and Au-nanostructures on ITO was investigated by scanning electron microscopy. A Cyclic voltammetry technique was employed to study electrochemical behavior of immobilized Mb on Au/ITO electrode. From CV, a pair of quasi-reversible redox peaks of Mb obtained in 10 mM PBS buffer solution at 0.28 and 0.11 V respectively. From the electrochemical experiments, it is observed that Mb/Au/ITO electrode provides a facile electron transfer between Mb and modified ITO electrode and it also catalyzes the reduction of H2O2. A linear increase in amperometric current with increase in H2O2 concentration was also observed. The stability, reusability and selectivity of the biosensor were also evaluated. The proposed biosensor exhibits an effective and fast catalytic response to reduction of H2O2 which can be used in future biosensor applications.

We developed a nanoscale memory device consisting of signal-responsive biomaterial, which is capable of switching physical properties (such as electrical/electrochemical, optical, and magnetic) upon application of appropriate electrical signals to perform memory switching. Here, we propose a highly robust surface-confined switch composed of an electroactive cysteine-modified azurin immobilized on an Au hexagonal pattern formed on indium tin oxide (ITO) substrates that can be controlled electrochemically and reversibly converted between its redox states. The memory effect is based on conductance switching, which leads to the occurrence of bistable states and behaves as an extremely robust redox switch in which an electrochemical input is transduced into optical and magnetic outputs under ambient conditions. The fact that this molecular surface switch, operating at very low voltages, can be patterned and addressed locally, and also has good stability and excellent reversibility, makes it a promising platform for nonvolatile memory devices., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Here, we describe the formation of a hybrid biointerface consisting of gold nanoparticle (AuNP) and cytochrome c (cyt c) on indium tin oxide (ITO) electrodes using a two-step immobilization procedure. The Au nanoparticles were attached to the ITO electrodes by 3-mercaptopropyl trimethoxysilane (3-MPTMS). The electrode was then incubated with 11-mercapundecanoic acid (11-MUA) and the nanoparticles were activated to allow for coupling to cyt c. This process resulted in the formation of the AuNP/cyt c hybrid on the ITO electrode. The ITO/AuNP/cyt c substrate surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction analysis (XRD), and cyclic voltammetry (CV) techniques. Further analysis regarding the surface roughness properties of ITO, ITO/AuNP and ITO/AuNP/cyt c were also performed. The ITO/AuNP/cyt c immobilized ITO electrode displayed a pair of well-defined redox peaks (E(pa) at 0.09 V and E(pc) at 0.02 V) at pH 7.0 in HEPES buffer solution. Differential pulse voltammetry (DPV) and amperometric i-t measurements on the modified electrode showed a linear response after the addition of hydrogen peroxide (H(2)O(2)). The developed electrode sensor had an electron transfer rate constant (k(s)) of 0.69 s(-1) with a detection limit of 0.5 μM. The results of this study suggest that the hybrid layers were well fabricated on the ITO surface and the developed ITO/AuNP/cyt c electrode displayed an excellent electrocatalytic response for the detection of H(2)O(2)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Here, we developed a method for the formation of redox metalloprotein azurin (Az) and gold nanoparticle (Au-NP) hybrid and evaluated its electrical and electrochemical properties using a combination of scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). A cysteine residue was introduced in Az to directly coordinate with the Au surface without the use of any additional linkers, followed by the binding of Au-NP to Az. Electrochemical experiments were performed to determine the redox behavior of the Az-Au-NP hybrid system, which showed a pair of voltammetric peaks at 150 and 50 mV for oxidation and reduction respectively. The hybrid system showed an enhanced reduction current when compared with its individual components. The tunneling current-voltage (I-V) characteristics and their derivative (dI/dV-V) curves exhibited a clear gap and peak structure around the gap, with limited fluctuations in the I-V curves, which were statistically characterized. The hybrid system was found to exhibit semiconducting behavior with a band gap that varied from 1.4 to 2.0 eV. From the observed results, the Au/Az-Au-NP hybrid system based on the combined STM/STS technique can be used in the development of future nanobiodevices., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A protein-based electrochemical sensor for hydrogen peroxide (H(2)O(2)) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe-2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)(6)(3-/4-) redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10mM, pH 7.0 Tris-HCl buffer solution at -170 and -120mV respectively. One electron reduction of the [2Fe-2S](2+) cluster occurs at one of the iron atoms to give the reduced [2Fe-2S](+). The formal reduction potential of Fdx ca. -150mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, k(s), for electron transfer between the Au electrode and Fdx was estimated to be 0.12s(-1). From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H(2)O(2). The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H(2)O(2).The sensor calibration plot was linear with r(2)=0.998 with sensitivity approximately 68.24μAm M(-1)cm(-2). Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H(2)O(2). Finally, the addition of H(2)O(2) on MUA/Au electrode was observed which has no effect on amperometric current., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Abstract: A bioelectronic device composed of self-assembled mutant azurin thin films with memory function has been developed for molecular electronics. Azurin was recombined with a cysteine residue to enhance the stability of self-assembled protein on gold surface. The thin films of protein on gold substrate were investigated by surface plasmon resonance spectroscopy, scanning tunneling microscopy and Raman spectroscopy, respectively. The memory characteristics, including the “read”, “write” and “erase” functions of self-assembled azurin layer, were obtained with three distinct electrical states of azurin layers by cyclic voltammetry. These results show the proposed biomemory device as a step towards the protein based nanobiochip. [Copyright &y& Elsevier]

Abstract: Highly dense and uniform protein dot arrays on Au-nanodots using size controllable method were fabricated on indium tin oxide (ITO) substrate in order to develop an electrochemical nanobiochip. Cysteine modified azurin was directly immobilized on the fabricated Au-nanodots without any linker materials. Atomic force microscopy was used for characterizing Au-dots formed on ITO substrate. Electrochemical scanning tunneling microscopy (ECSTM) revealed the monolayer formation with an in situ cyclic voltammetry to observe redox behaviour of both bare Au-dots and protein immobilized Au-dots. I–V characteristics were obtained on both bare Au-dots and protein immobilized Au-dots structured on ITO conductive electrodes. [Copyright &y& Elsevier]