Ajay Kumar Yagati

Electrochemical performance of gold nanoparticle-cytochrome c hybrid interface for H2O2 detection.

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).

An enzymatic biosensor for hydrogen peroxide based on CeO2 nanostructure electrodeposited on ITO surface

In this study, an enzymatic biosensor for amperometric detection of hydrogen peroxide was developed based on the direct electrochemistry of myoglobin (Mb) on a porous cerium dioxide (CeO2) nanostructured film. The developed film accomplished with large surface area was electrodeposited on an indium tin oxide (ITO) substrate. Surface morphological studies revealed that the formed CeO2 film has a large specific surface area with a unique nanostructure on the ITO surface. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to demonstrate the electrochemical behavior of Mb immobilized on the fabricated film, which exhibited facile, direct electrochemistry and good electrocatalytic performance without any electron mediator. The electrode displayed a pair of quasi-reversible reduction-oxidation peaks at -0.3 and -0.2V, respectively, due to the Mb [Fe(3+)/Fe(2+)] redox couple, which is a surface-controlled electrochemical process with one electron transfer. This reagent-less biosensor showed good stability and high sensitivity for detecting H2O2 without any influence of intermediate compounds. This protein-based biosensor was capable of detecting H2O2 as low as 0.6μM with linearity up to 3mM and a response time of ~8s, compared to those of other modified electrodes. Hence, porous CeO2 is a possible candidate material for fabricating enzymatic sensors or devices.

Silver nanoflower-reduced graphene oxide composite based micro-disk electrode for insulin detection in serum.

Sensitive and selective determination of protein biomarkers remains a significant challenge due to the existence of various biomarkers in human body at a low concentration level. Therefore, new technologies were incessantly steered to detect tiny biomarkers at a low concentration level, yet, it is difficult to develop reliable, stable and sensitive detection methods for disease diagnostics. Therefore, the present study demonstrates a methodology to detect insulin in serum at low levels based on Ag nanoflower (AgNF) decorated reduced graphene oxide (rGO) modified micro-disk electrode arrays (MDEAs). The morphology of AgNF-rGO composite was characterized by scanning electron microscopy, the structure was analyzed using X-ray diffraction patterns and Raman spectra. The hybrid interface exhibited enhanced electrical conductivity when compared with its individual elements and had improved capturing ability for antibody-antigen binding towards insulin detection. In order to measure quantitatively the insulin concentration in PBS and human serum, the change in impedance (ΔZ) from electrochemical impedance spectroscopy was analyzed for various concentrations of insulin in [Fe(CN)6](3-/4-) redox couple. The electrode with adsorbed antibodies showed an increase in ΔZ for the addition of antigen concentrations over a working range of 1-1000 ng mL(-1). The detection limits were 50 and 70 pg mL(-1) in PBS and human serum, respectively.

Amperometric sensor for hydrogen peroxide based on direct electron transfer of spinach ferredoxin on Au electrode

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.

Label-free and direct detection of C-reactive protein using reduced graphene oxide-nanoparticle hybrid impedimetric sensor

For label-free and direct detection of C-reactive protein (CRP), an impedimetric sensor based on an indium tin oxide (ITO) electrode array functionalized with reduced graphene oxide-nanoparticle (rGO-NP) hybrid was fabricated and evaluated. Analytical measurements were performed to examine the properties of rGO-NP-modified ITO microelectrodes and to determine the influence upon sensory performance of using nanostructures modified for antibody immobilization and for recognition of CRP binding events. Impedimetric measurements in the presence of the redox couple [Fe(CN)6](3-/4-) showed significant changes in charge transfer resistance upon binding of CRP. The impedance measurements were highly target specific, linear with logarithmic CRP concentrations in PBS and human serum across a 1 ng mL(-1) and 1000 ng mL(-1) range and associated with a detection limits of 0.06 and 0.08 ng mL(-1) respectively.

Multi-bit biomemory consisting of recombinant protein variants, azurin

In this study a protein-based multi-bit biomemory device consisting of recombinant azurin with its cysteine residue modified by site-directed mutagenesis method has been developed. The recombinant azurin was directly immobilized on four different gold (Au) electrodes patterned on a single silicon substrate. Using cyclic voltammetry (CV), chronoamperometry (CA) and open circuit potential amperometry (OCPA) methods the memory function of the fabricated biodevice was validated. The charge transfer occurs between protein molecules and Au electrode enables a bi-stable electrical conductivity allowing the system to be used as a digital memory device. Data storage is achieved by applying redox potentials which are within the range of 200mV. Oxidation and open circuit potentials with current sensing were used for writing and reading operations respectively. Applying oxidation potentials in different combinations to each Au electrodes, multi-bit information was stored in to the azurin molecules. Finally, the switching robustness and reliability of the proposed device has been examined. The results suggest that the proposed device has a function of memory and can be used for the construction of nano-scale multi-bit information storage device.

A robust nanoscale biomemory device composed of recombinant azurin on hexagonally packed Au-nano array

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.

Construction of RNA–Quantum Dot Chimera for Nanoscale Resistive Biomemory Application

RNA nanotechnology offers advantages to construct thermally and chemically stable nanoparticles with well-defined shape and structure. Here we report the development of an RNA-QD (quantum dot) chimera for resistive biomolecular memory application. Each QD holds two copies of the pRNA three-way junction (pRNA-3WJ) of the bacteriophage phi29 DNA packaging motor. The fixed quantity of two RNAs per QD was achieved by immobilizing the pRNA-3WJ with a Sephadex aptamer for resin binding. Two thiolated pRNA-3WJ serve as two feet of the chimera that stand on the gold plate. The RNA nanostructure served as both an insulator and a mediator to provide defined distance between the QD and gold. Immobilization of the chimera nanoparticle was confirmed with scanning tunneling microscopy. As revealed by scanning tunneling spectroscopy, the conjugated pRNA-3WJ-QD chimera exhibited an excellent electrical bistability signal for biomolecular memory function, demonstrating great potential for the development of resistive biomolecular memory and a nano-bio-inspired electronic device for information processing and computing.

STM and cyclic voltammetric investigation of recombinant azurin-gold nanoparticle hybrids.

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.

Electrochemical cell chip to detect environmental toxicants based on cell cycle arrest technique

A cell-based chip was recently developed and shown to be an effective in vitro tool for analyzing effect of environmental toxin on target cells. However, common cell chips are inappropriate for the detection of multiple environmental toxins. Here, we fabricated a neural cell chip to detect different cellular responses induced by BPA (bisphenol-A) and PCB (poly chlorinated biphenyl). This approach was based on an electrochemical method using a cell cycle-arrest technique. Neural cells were synchronized at the synthesis phase by treatment with thymidine, which results in a sharp reduction peak when compared to unsynchronized cells. The fabricated chip containing 50% G1/S and 50% G2/M phase cells was used to determine the effects of environmental toxins on neural cancer cells. At the end, the cell-chips could be used to assess both BPA and PCB toxicity that the cells were completely synchronized at the G1/S and G2/M phase. The proposed neural cell chip can be a useful tool for biosensors to evaluate easily and sensitively multiple effects of environmental toxicants on target cells.