Hexagonal Co₃O₄ anchored reduced graphene oxide sheets for high-performance supercapacitors and non-enzymatic glucose sensing

Vilian, A. T. Ezhil,Dinesh, Bose,Rethinasabapathy, Muruganantham,Hwang, Seung-Kyu,Jin, Chang-Soo,Huh, Yun Suk,Han, Young-Kyu The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.29

<P>Reduced graphene oxide (RGO) incorporated onto metal-organic framework (MOF)-derived Co3O4 hexagons is prepared <I>via</I> a hydrothermal route for supercapacitor and glucose sensor applications. Various analysis techniques demonstrate that the Co3O4 hexagons were uniformly spread over the thin graphene sheets to assist the electron accessibility of the electrode materials. Under optimized conditions, using 0.1 M KOH electrolyte at a current density of 4 A g<SUP>−1</SUP>, a specific capacitance value of 1300 F g<SUP>−1</SUP> is obtained. The fabricated asymmetric supercapacitor cycled reversibly and exhibits high energy and power density values of 65.8 W h kg<SUP>−1</SUP> and 2048 W kg<SUP>−1</SUP>, respectively, over the voltage range of −0.1 V to 0.4 V. The asymmetric supercapacitor shows 80.5% capacitance retention even after 5000 cycles at a current density of 4 A g<SUP>−1</SUP>, which indicates its high cycling stability in view of the fact that it is binder-free. Furthermore, the RGO-Co3O4 hexagon-modified electrode was optimized to realize the reliable amperometric determination of glucose concentration with a very low detection limit and excellent sensitivity value of 0.4 μM and 1.315 mA mM<SUP>−1</SUP> cm<SUP>−2</SUP>, respectively. All of these remarkable performance indicators suggest that RGO-Co3O4 is a promising electrode material for next-generation energy storage devices and electrochemical sensors.</P>

Recent advances in molybdenum disulfide-based electrode materials for electroanalytical applications

Vilian, A. T. Ezhil,Dinesh, Bose,Kang, Sung-Min,Krishnan, Uma Maheswari,Huh, Yun Suk,Han, Young-Kyu Springer-Verlag 2019 Mikrochimica acta Vol.186 No.3

Pd nanospheres decorated reduced graphene oxide with multi-functions: Highly efficient catalytic reduction and ultrasensitive sensing of hazardous 4-nitrophenol pollutant

Vilian, A.T. Ezhil,Choe, Sang Rak,Giribabu, Krishnan,Jang, Sung-Chan,Roh, Changhyun,Huh, Yun Suk,Han, Young-Kyu Elsevier 2017 Journal of hazardous materials Vol.333 No.-

<P><B>Abstract</B></P> <P>We illustrate a facile approach for in situ synthesis of Pd-gum arabic/reduced graphene oxide (Pd-GA/RGO) using GA as the reducing agent, which favors the instantaneous reduction of both Pd ions and GO into Pd nanoparticles (NPs) and RGO. From the morphological analysis of Pd-GA/RGO, we observed highly dispersed spherical 5nm Pd NPs decorated over RGO. The as-synthesized Pd-GA/RGO composite was employed for the catalytic reduction and the electrochemical detection of 4-nitrophenol (4-NP), respectively. The catalytic reduction of 4-NP was highly pronounced for Pd-GA/RGO (5min) when compared to Pd NPs (140min) and Pd/RGO (36min). This enhanced catalytic activity was attributed to the synergistic effect of Pd NPs and the presence of various functional groups of GA. Significantly, the fabricated sensor offered a low detection limit (9fM) with a wider linear range (2–80 pM) and long-term stability. The simple construction technique, high sensitivity, and long-term stability with acceptable accuracy in wastewater samples were the main advantages of the developed sensor. The results indicated that the as-prepared Pd-GA/RGO exhibited better sensing ability than the other graphene-based modified electrodes. Therefore, the proposed sensor can be employed as a more convenient sensing platform for environmental and industrial pollutants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pd-GA/RGO catalysts were successfully synthesized by a simple chemical reduction method. </LI> <LI> Pd-GA/RGO catalysts show excellent fast catalytic activity (5min) towards the reduction of 4-NP to 4-AP. </LI> <LI> The developed sensor showed a wide linear range of 2–80pM with a low detection limit of 9fM. </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication of Palladium Nanoparticles on Porous Aromatic Frameworks as a Sensing Platform to Detect Vanillin

Vilian, A. T. Ezhil,Puthiaraj, Pillaiyar,Kwak, Cheol Hwan,Hwang, Seung-Kyu,Huh, Yun Suk,Ahn, Wha-Seung,Han, Young-Kyu American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.20

<P>Here, we report the fabrication of palladium nanoparticles on porous aromatic frameworks (Pd/PAF-6) using a facile chemical approach, which was characterized by various spectro- and electrochemical techniques. The differential pulse voltammetry (DPV) response of Pd/PAF-6 toward the vanillin (VA) sensor shows a linear relationship over concentrations (10-820 pM) and a low detection limit (2 pM). Pd/PAF-6 also exhibited good anti -interference performance toward 2 -fold excess of ascorbic acid, nitrophenol, glutathione, glucose, uric acid, dopamine, ascorbic acid, 4-nitrophenol, glutathione, glucose, uric acid, dopamine, and 100 -fold excess of Na4, Mg2+, and r during the detection of VA. The developed electrochemical sensor based on Pd/PAF-6 had good reproducibility, as well as high selectivity and stability. The established sensor revealed that Pd/PAF-6 could be used to detect VA in biscuit and ice cream samples with satisfactory results.</P>

Pt-Au bimetallic nanoparticles decorated on reduced graphene oxide as an excellent electrocatalysts for methanol oxidation

Vilian, A.T. Ezhil,Hwang, Seung-Kyu,Kwak, Cheol Hwan,Oh, Seo Yeong,Kim, Chang-Yeon,Lee, Go-woon,Lee, Jin Bae,Huh, Yun Suk,Han, Young-Kyu Elsevier Sequoia 2016 Synthetic metals Vol.219 No.-

<P><B>Abstract</B></P> <P>In this study, we report a general and simple strategy for the synthesis of platinum nanoparticles (PtNPs), highly dispersed on reduced graphene oxide (RGO) substrate with Au nanoparticles. The electrochemically active surface area (ECSA) of the Pt-Au-RGO electrocatalyst is found to be higher than the Pt-RGO electrocatalyst, which is more comparable to a commercial Pt/C catalyst. The obtained ratio of the voltammetric forward peak current to the reverse peak current for the Pt-Au-RGO electrocatalyst (<I>I</I> <SUB>f</SUB>/<I>I</I> <SUB>b</SUB> =2.33) is much higher than that of the Pt-RGO electrocatalyst (<I>I</I> <SUB>f</SUB>/<I>I</I> <SUB>b</SUB> =1.16). This phenomenon is attributed to the synergistic effects of the Au and the RGO substrate, which help to enhance the electrochemical activity of Pt nanoparticles for methanol oxidation and carbonaceous poisoning resistance. The reported methanol oxidation is found to exhibit excellent electrocatalytic performance, reliability, and stability, surpassing that of several reported modified electrodes that can also be used for platinum-based catalysts in fuel cell applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We prepared an efficient Pt-Au-RGO architecture using an effective strategy to enhancing loading of Au nanoparticles into RGO. </LI> <LI> The electrochemically active surface area (ECSA) of the Pt-Au-RGO heterogeneous electrocatalyst is found to be higher than the Pt-RGO and Pt/C electrocatalysts. </LI> <LI> The Pt-Au-RGO electrocatalyst demonstrated better electrocatalytic activity and stability than the Pt-RGO or Pt/C black for methanol oxidation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Salt-templated three-dimensional porous carbon for electrochemical determination of gallic acid

Vilian, A.T.Ezhil,Song, Ji Yoon,Lee, Yun Sung,Hwang, Seung-Kyu,Kim, Hae Jin,Jun, Young-Si,Huh, Yun Suk,Han, Young-Kyu Elsevier 2018 Biosensors & bioelectronics Vol.117 No.-

<P><B>Abstract</B></P> <P>We report an electrochemical sensor based on three-dimensional porous amorphous carbon (3DPAC) for the sensitive and selective determination of gallic acid (GA). The tailor-made carbon was prepared via salt-templating in which the organic molecular precursor, i.e., glucose, was simply ground and carbonized with a eutectic mixture of LiBr and KBr at 800 °C in an inert atmosphere. Salt removal from the carbon-salt mixture with water yielded 3DPAC with a hierarchical porous structure and oxygen-containing functional groups. When employed as an electrochemical sensor, 3DPAC exhibited remarkable sensitivity (0.1045 µA pM<SUP>−1</SUP> cm<SUP>−2</SUP>) with a lower detection limit of 0.434 pM at a signal-to-noise ratio of 3 and a linear response up to 1–150 pM for determination of GA. Under optimized test conditions, 3DPAC showed a superior peak current response for GA as compared to the glassy carbon electrode. In addition, ascorbic, uric, and caffeic acids did not interfere with the voltammetric detection of GA in terms of selectivity, stability, and repeatability. We envision that 3DPAC can provide a promising platform for the development of electrochemical sensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of 3DPAC using glucose as a carbon source and a eutectic mixture of LiBr and KBr as salt-template. </LI> <LI> A wide linear range of 1–150 pM, LOD of 0.434 pM, and sensitivity of 0.1045 µA pM<SUP>−1</SUP> cm<SUP>−2</SUP> towards GA oxidation. </LI> <LI> Rapid response time, excellent stability, repeatability and reproducibility in GA detection. </LI> <LI> Quantitative analysis of GA in human serum and urine samples with satisfactory results. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Efficient electron-mediated electrochemical biosensor of gold wire for the rapid detection of C-reactive protein: A predictive strategy for heart failure

Vilian, A.T. Ezhil,Kim, Wonyoung,Park, Bumjun,Oh, Seo Yeong,Kim, TaeYoung,Huh, Yun Suk,Hwangbo, Chang Kwon,Han, Young-Kyu Elsevier 2019 Biosensors & bioelectronics Vol.142 No.-

<P><B>Abstract</B></P> <P>C-reactive protein (CRP) is considered a promising biomarker for the rapid and high-throughput real-time monitoring of cardiovascular disease and inflammation in unprocessed clinical samples. Implementation of this monitoring would enable various transformative biomedical applications. We have fabricated a highly specific sensor chip to detect CRP with a detection limit of 2.25 fg/mL. The protein was immobilized on top of a gold (Au) wire/polycarbonate (PC) substrate using 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide hydrochloride/N-hydroxy succinimide-activated 3-mercaptoproponic acid (MPA) as a self-assembled monolayer agent and bovine serum albumin (BSA) as a blocking agent. In contrast to the bare PC substrate, the CRP/BSA/anti-CRP/MPA/Au substrate exhibited a considerably high electrochemical signal toward CRP. The influence of the experimental parameters on CRP detection was assessed via various analysis methods, and these parameters were then optimized. The linear dynamic range of the CRP was 5–220 fg/mL for voltammetric and impedance analysis. Morever, the strategy exhibited high selectivity against various potential interfering species and was capable of directly probing trace amounts of the target CRP in human serum with excellent selectivity. The analytical assay based on the CRP/BSA/anti-CRP/MPA/Au substrate could be exploited as a potentially useful tool for detecting CRP in clinical samples.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The sensor utilizes Au wires to attaching antibodies for specific binding of CRP for heart failure diagnostics. </LI> <LI> A low detection limit of 2.25 fg/mL with linear concentrations of 5–220 fg/mL for CRP was measured. </LI> <LI> The advanced sensor has excellent stability, reproducibility and selective sensing for CRP. </LI> <LI> The offered sensor is used to detect CRP in human serum and saliva with a good recovery. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication of 3D honeycomb-like porous polyurethane-functionalized reduced graphene oxide for detection of dopamine

Vilian, A.T. Ezhil,An, Suyeong,Choe, Sang Rak,Kwak, Cheol Hwan,Huh, Yun Suk,Lee, Jonghwi,Han, Young-Kyu Elsevier 2016 Biosensors & bioelectronics Vol.86 No.-

<P><B>Abstract</B></P> <P>A three dimensional reduced graphene oxide/polyurethane (RGO-PU) porous material with connected pores was prepared by physical adsorption of RGO onto the surface of porous PU. The porous PU was prepared by directional melt crystallization of a solvent, which produced high pores with controlled orientation. The prepared RGO-PU was characterized by scanning electron microscopy, spectroscopy and electro-chemical methods. The RGO-PU porous material revealed better electrochemical performance, which might be attributed to the robust structure, superior conductivity, large surface area, and good flexibility. Differential pulse voltammetry (DPV) analysis of DA using the RGO-PU exhibited a linear response range over a wide DA concentration of 100–1150pM, with the detection limit of 1pM. This sensor exhibited outstanding anti-interference ability towards co-existing molecules with good stability, sensitivity, and reproducibility. Furthermore, the fabricated sensor was successfully applied for the quantitative analysis of DA in human serum and urine samples with acceptable recovery, which indicates its feasibility for practical application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> RGO-PU sensor was constructed for DA detection. </LI> <LI> The developed method exhibited wide linear range and low detection limit. </LI> <LI> The fabricated RGO-PU sensor exhibits good selectivity, reproducibility and excellent anti-interference property. </LI> <LI> The prepared sensor was applied to detect DA in real sample with satisfactory results. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile synthesis of MnO2/carbon nanotubes decorated with a nanocomposite of Pt nanoparticles as a new platform for the electrochemical detection of catechin in red wine and green tea samples

Ezhil Vilian, A. T.,Madhu, Rajesh,Chen, Shen-Ming,Veeramani, Vediyappan,Sivakumar, Mani,Huh, Yun Suk,Han, Young-Kyu The Royal Society of Chemistry 2015 Journal of materials chemistry. B, Materials for b Vol.3 No.30

<P>Herein, we report a simple and facile synthesis strategy of MnO2/carbon nanotubes decorated with a nanocomposite of Pt nanoparticles using a simple electrodeposition method. The Pt/MnO2/f-MWCNT modified electrode were characterized by several analytical and spectroscopy techniques and were adopted as a composite for a novel catechin sensor. The as-prepared Pt/MnO2/f-MWCNT modified glassy carbon electrode (GCE) exhibited a smaller peak potential separation (Δ<I>E</I>p), and electron transfer kinetics during the oxidation reaction of catechin. This can be attributed to the larger effective surface area, greater porosity, and more reactive sites on the Pt/MnO2/f-MWCNT-modified GCE. Notably, we achieved a very low detection limit (under optimized conditions) of catechin <I>ca.</I> 0.02 μM (S/N = 3); the linear range is 2-950 μM with excellent sensitivity. The real time application of catechin in red wine, black tea, and green tea samples with excellent performance. The proposed sensor was successfully developed and the advantages of low cost, ease of preparation, long-term stability, and good reproducibility were demonstrated which are superior to recently reported modified electrodes, thereby enabling practical industrial applications.</P>

A spick-and-span approach to the immobilization of horseradish peroxidase on Au nanospheres incorporated with a methionine/graphene biomatrix for the determination of endocrine disruptor bisphenol A

Vilian, A.T. Ezhil,Giribabu, Krishnan,Choe, Sang Rak,Muruganantham, Rethinasabapathy,Lee, Hoomin,Roh, Changhyun,Huh, Yun Suk,Han, Young-Kyu Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.251 No.-

<P><B>Abstract</B></P> <P>In the present study, we employ a straightforward, benign strategy to prepare thiol-functionalized reduced graphene oxide (S-RGO) using methionine as the sulphur source and reducing agent. The immobilization of horseradish peroxidase (HRP) over the AuNPs/S-RGO was developed by incorporating AuNPs on the S-RGO surface. The fabricated HRP/AuNPs/S-RGO electrode exhibits a remarkable decrease in the overpotential and a significantly increased oxidation peak current of bisphenol A (BPA) compared with the bare glassy carbon electrode (GCE) and AuNPs/S-RGO electrode. The biosensor shows an excellent amperometric analytical performance with a low detection limit of 2.6×10<SUP>−12</SUP> M and a linear range from 2.0×10<SUP>−11</SUP> to 1.18×10<SUP>−9</SUP> M, with the response time <2s for BPA. From the results, the apparent Michaelis-Menten constant was calculated as 8.14nM. The HRP/AuNPs/S-RGO biosensor exhibited faster response, adequate storage stability, inexpensive, simple fabrication with disposability, satisfactory reproducibility and repeatability, and outstanding selectivity. Finally, the constructed biosensor was utilized successfully for detecting BPA in tomato juice and milk samples with acceptable results.</P> <P><B>Highlights</B></P> <P> <UL> <LI> HRP/AuNPs/S-RGO biocomposite has been prepared to determine bisphenol A. </LI> <LI> The AuNPs/S-RGO is a promising platform for HRP immobilization. </LI> <LI> The biosensor exhibits excellent stability, reproducibility and high selectivity. </LI> <LI> It exhibits LOD of 2.6×10<SUP>−12</SUP> in a wide linear range from 2.0×10<SUP>−11</SUP> to 1.18×10<SUP>−9</SUP> M. </LI> <LI> It detects bisphenol A in real samples such as tomato juice and milk. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>