Electrochemical immunosensor for highly sensitive and quantitative detection of tumor necrosis factor-α in human serum

Yagati, Ajay Kumar,Lee, Min-Ho,Min, Junhong Elsevier 2018 Bioelectrochemistry Vol.122 No.-

<P><B>Abstract</B></P> <P>Highly sensitive and selective biosensors for accurate determination of specific protein biomarkers at low levels in serum are a prerequisite for the present healthcare systems. Therefore, here we developed a label-free impedimetric method for tumor necrosis factor-alpha (TNF-α) detection using reduced graphene oxide (RGO) with gold nanoparticles (AuNP) on an indium tin oxide (ITO) microdisk electrodes. The detection mechanism relies on resistance change occurs due to [Fe(CN)<SUB>6</SUB>]<SUP>3−/4−</SUP> redox probe movement towards the conductive channels of the AuNP-RGO films gated by the recognition of the target biomarker by its anti-TNF-α antibody. The conductivity of the AuNP-RGO structures enhanced by 10-fold in comparison with bare electrode chips. The observed resistance changes at 2Hz (ΔR <SUB>at 2Hz</SUB>) enabled the quantification of various concentrations of TNF-α in human serum (C<SUB>HS-TNF-α</SUB>). The antibody-adsorbed electrode showed a good increment of resistance change (ΔR) with additions of antigen concentration. The sensor possesses a linear range of 1–1000pg/ml had a detection limit of 0.67pg/ml (38.51fM) and 0.78pg/ml (44.83fM) in PBS and human serum, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> AuNP-RGO electrodes showed 10-fold increment in conductivity compared to ITO. </LI> <LI> Hybrid electrodes have smallest R<SUB>CT</SUB> (1845Ω) and high C<SUB>dl</SUB> (121.42nF). </LI> <LI> Sensor exhibited EC<SUB>50</SUB> of 61.7pg/ml and 150pg/ml in PBS and serum respectively. </LI> <LI> AuNP-RGO based TNF-α biosensor has LOD: 0.78pg/mL and linear range: 1–1000pg/ml. </LI> </UL> </P>

Ferredoxin molecular thin film with intrinsic switching mechanism for biomemory application.

Yagati, Ajay Kumar,Kim, Sang-Uk,Min, Junhong,Choi, Jeong-Woo American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.5

<P>A biomemory device consisting of cysteine modified ferredoxin molecules which possess a memory effect via a charge transfer mechanism was developed. For achieving an efficient bioelectronic device, cysteine modified ferredoxin was developed by embodying cysteine residues in ferredoxin by site--directed mutagenesis method to directly coordinate with the gold (Au) surface without use of any additional linkers. The thin film formation of ferredoxin molecules on Au electrode is confirmed by surface plasmon resonance (SPR) spectroscopy and scanning tunneling microscope (STM). Cyclic voltammetry (CV) and open circuit potential amperometry (OCPA) methods were used to verify the memory switching characteristics of the fabricated device. The charge transfer between ferredoxin 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 voltages which are within the range of -500 mV. These results suggest that the proposed device has a function of memory and can be used for the construction of a nano-scale bioelectronic device.</P>

Multi-Bit Biomemory Consisting of Self-assembled Redox Protein

Ajay Kumar Yagati,Sang-Uk Kim,Cheol-Heon Yea,Da-Yeon Kang,Junhong Min,Jeong-Woo Choi 한국생물공학회 2008 한국생물공학회 학술대회 Vol.2008 No.4

Protein Based Electrochemical Biosensors for H₂O₂ Detection Towards Clinical Diagnostics

Yagati, Ajay Kumar,Choi, Jeong‐,Woo WILEY‐VCH Verlag 2014 Electroanalysis Vol.26 No.6

<P><B>Abstract</B></P><P>Hydrogen peroxide (H<SUB>2</SUB>O<SUB>2</SUB>) has a diverse array of physiological and pathological effects within the living cells depending on the extent, timing, and location of its production. Detection of H<SUB>2</SUB>O<SUB>2</SUB> is important in food industry, clinical diagnostics, and environmental monitoring at lowest levels. Electrochemical biosensors are efficient as they can analyze biological sample by direct conversion into an electrical signal. Electrochemical sensors based on direct electron transfer (DET) of proteins were developed to achieve fast electron transfer by avoiding free‐diffusing redox species with improved sensitivity. We summarize the prerequisites for the DET of proteins for immobilization on the electrode surfaces with recent developments in development of H<SUB>2</SUB>O<SUB>2</SUB> sensors and future prospects in this field.</P>

Impedimetric Tumor Necrosis Factor-α Sensor Based on a Reduced Graphene Oxide Nanoparticle-Modified Electrode Array

Yagati, Ajay Kumar,Lee, Ga-Yeon,Ha, Sungji,Chang, Keun-A,Pyun, Jae-Chul,Cho, Sungbo American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11

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

Yagati, Ajay Kumar,Choi, Yonghyun,Park, Jinsoo,Choi, Jeong-Woo,Jun, Hee-Sook,Cho, Sungbo Elsevier 2016 Biosensors & bioelectronics Vol.80 No.-

<P><B>Abstract</B></P> <P>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)<SUB>6</SUB>]<SUP>3−/4−</SUP> redox couple. The electrode with adsorbed antibodies showed an increase in ΔZ for the addition of antigen concentrations over a working range of 1–1000ngmL<SUP>−1</SUP>. The detection limits were 50 and 70pgmL<SUP>−1</SUP> in PBS and human serum, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Simple electrodeposition methods enabled reproducible AgNF-rGO hybrid system. </LI> <LI> AgNF and rGO hybrid layers acts as signal enhancing agents and possessed evenly distributed electric field. </LI> <LI> AgNF-rGO electrode possess smallest R<SUB>CT</SUB> (1243 Ω) and high C<SUB>DL</SUB> (333.6 nF). </LI> <LI> Sensor has working range of 1 to 1000 ng mL<SUP>−1</SUP>; LOD of 70 pg mL<SUP>−1</SUP> and EC<SUB>50</SUB> of 49.21 ng mL<SUP>−1</SUP>. </LI> </UL> </P>

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

Lee, Taek,Yagati, Ajay Kumar,Pi, Fengmei,Sharma, Ashwani,Choi, Jeong-Woo,Guo, Peixuan American Chemical Society 2015 ACS NANO Vol.9 No.7

<P>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.</P>

Electrochemical Characterization of Poly-L-Lysine Coating on Indium Tin Oxide Electrode for Enhancing Cell Adhesion

Choi, Yonghyun,Yagati, Ajay Kumar,Cho, Sungbo American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.10

An electrochemical H2O2 detection method based on direct electrochemistry of myoglobin immobilized on gold deposited ITO electrode.

Dengale, Santosh Machhindra,Yagati, Ajay Kumar,Chung, Yong-Ho,Min, Junhong,Choi, Jeong-Woo American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.9

<P>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.</P>

Charge storage investigation in self-assembled monolayer of redox-active recombinant azurin

Sang-Uk Kim,Ajay Kumar Yagati,Ravindra P. Singh,Junhong Min,최정우 한국물리학회 2009 Current Applied Physics Vol.9 No.2

Charge storage in nanoscaled monolayer of recombinant azurin by using direct self-assembly method was investigated for the construction of bioelectronic devices. Recombinant azurin having a cysteine residue was utilized to enhance the stability of the self-assembled protein on the gold surface without any chemical linker. We investigated the immobilization of protein by surface plasmon resonance and scanning tunneling microscopy. The electrochemical properties of recombinant azurin immobilized on the surface were confirmed by cyclic voltammetry. The memory device characteristics, including the ‘‘Read”, ‘‘Write”, and ‘‘Erase” functions of the self-assembled azurin layer, were obtained with three distinct electrical states of the azurin layers by cyclic voltammetry. It was concluded that the proposed device had a memory function and could be used for the construction of a nanobiochip with memory function. Charge storage in nanoscaled monolayer of recombinant azurin by using direct self-assembly method was investigated for the construction of bioelectronic devices. Recombinant azurin having a cysteine residue was utilized to enhance the stability of the self-assembled protein on the gold surface without any chemical linker. We investigated the immobilization of protein by surface plasmon resonance and scanning tunneling microscopy. The electrochemical properties of recombinant azurin immobilized on the surface were confirmed by cyclic voltammetry. The memory device characteristics, including the ‘‘Read”, ‘‘Write”, and ‘‘Erase” functions of the self-assembled azurin layer, were obtained with three distinct electrical states of the azurin layers by cyclic voltammetry. It was concluded that the proposed device had a memory function and could be used for the construction of a nanobiochip with memory function.