Browsing by Author "Singh, Pragya"

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A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors
(2019-01-01)
Krishnan, Siva Kumar
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Singh, Eric
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Singh, Pragya
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Meyyappan, Meyya
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Nalwa, Hari Singh
Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters. Over the last decade, different nanomaterials have been exploited to design highly efficient biosensors for the detection of analyte biomolecules. The discovery of graphene has spectacularly accelerated research on fabricating low-cost electrode materials because of its unique physical properties, including high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency. Graphene and its oxygenated derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the field of biosensors. The presence of oxygenated functional groups makes GO nanosheets strongly hydrophilic, facilitating chemical functionalization. Graphene, GO and rGO nanosheets can be easily combined with various types of inorganic nanoparticles, including metals, metal oxides, semiconducting nanoparticles, quantum dots, organic polymers and biomolecules, to create a diverse range of graphene-based nanocomposites with enhanced sensitivity for biosensor applications. This review summarizes the advances in two-dimensional (2D) and three-dimensional (3D) graphene-based nanocomposites as emerging electrochemical and fluorescent biosensing platforms for the detection of a wide range of biomolecules with enhanced sensitivity, selectivity and a low limit of detection. The biofunctionalization and nanocomposite formation processes of graphene-based materials and their unique properties, surface functionalization, enzyme immobilization strategies, covalent immobilization, physical adsorption, biointeractions and direct electron transfer (DET) processes are discussed in connection with the design and fabrication of biosensors. The enzymatic and nonenzymatic reactions on graphene-based nanocomposite surfaces for glucose- and cholesterol-related electrochemical biosensors are analyzed. This review covers a very broad range of graphene-based electrochemical and fluorescent biosensors for the detection of glucose, cholesterol, hydrogen peroxide (H2O2), nucleic acids (DNA/RNA), genes, enzymes, cofactors nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP), dopamine (DA), ascorbic acid (AA), uric acid (UA), cancer biomarkers, pathogenic microorganisms, food toxins, toxic heavy metal ions, mycotoxins, and pesticides. The sensitivity and selectivity of graphene-based electrochemical and fluorescent biosensors are also examined with respect to interfering analytes present in biological systems. Finally, the future outlook for the development of graphene based biosensing technology is outlined.
Electrophoretic Deposition of Nitrogen-Boron Co-Doped Graphene as High Performance Electrode for Next Generation Supercapacitors
(2018-01-01)
Kumar, Amit
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Kumar, Nagesh
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Singh, Pragya
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Leu, Jihperng
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Tseng, Tseung-Yuen
In this study, we report the electrophoretic deposition (EPD) of nitrogen-boron co-doped graphene (NBG) synthesized via simple hydrothermal method and subsequent annealing at 750 degrees C in reducing environment. The structural, chemical-compositional and morphological investigations of the as synthesized NBG have been investigated using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electrochemical properties of the samples have been studied via cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) cycling and electrochemical impedance spectroscopy (EIS) in a conventional three-electrode system using 6M KOH aqueous electrolyte. The EPD grown binder free NBG electrode exhibits high specific capacitance of 217 Fg(-1) at the scan rate of 5 mVs(-1) which is about 1.2 times higher than the specific capacitance (180 Fg(-1) at 5 mVs(-1)) of pristine reduced graphene oxide synthesized via similar approach. Furthermore, this sample exhibits excellent rate capability, and similar to 103% retention after 8800 successive charge-discharge cycles at 1 Ag-1.
Flexible Molybdenum Disulfide (MoS2) Atomic Layers for Wearable Electronics and Optoelectronics
(2019-03-27)
Singh, Eric
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Singh, Pragya
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Kim, Ki Seok
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Yeom, Geun Young
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Nalwa, Hari Singh
Flexible, stretchable, and bendable materials, including inorganic semiconductors, organic polymers, graphene, and transition metal dichalcogenides (TMDs), are attracting great attention in such areas as wearable electronics, biomedical technologies, foldable displays, and wearable point-of-care biosensors for healthcare. Among a broad range of layered TMDs, atomically thin layered molybdenum disulfide (MoS2) has been of particular interest, due to its exceptional electronic properties, including tunable bandgap and charge carrier mobility. MoS2 atomic layers can be used as a channel or a gate dielectric for fabricating atomically thin field-effect transistors (FETs) for electronic and optoelectronic devices. This review briefly introduces the processing and spectroscopic characterization of large-area MoS2 atomically thin layers. The review summarizes the different strategies in enhancing the charge carrier mobility and switching speed of MoS2 FETs by integrating high-K dielectrics, encapsulating layers, and other 2D van der Waals layered materials into flexible MoS2 device structures. The photoluminescence (PL) of MoS2 atomic layers has, after chemical treatment, been dramatically improved to near-unity quantum yield. Ultraflexible and wearable active-matrix organic light-emitting diode (AM-OLED) displays and wafer-scale flexible resistive random-access memory (RRAM) arrays have been assembled using flexible MoS2 transistors. The review discusses the overall recent progress made in developing MoS2 based flexible FETs, OLED displays, nonvolatile memory (NVM) devices, piezoelectric nanogenerators (PNGs), and sensors for wearable electronic and optoelectronic devices. Finally, it outlines the perspectives and tremendous opportunities offered by a large family of atomically thin-layered TMDs.
Highly sensitive nitric oxide gas sensor based on ZnO-nanorods vertical resistor operated at room temperature
(2019-03-01)
Singh, Pragya
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Hu, Li-Lun
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Zan, Hsiao-Wen
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
We successfully demonstrated a simple and low-cost nitric oxide (NO) gas sensor to deliver parts-per-billion (ppb) regime detection at room temperature operation. A vertical-channel ZnO nanorods resistor is fabricated by putting silver nanowire electrode onto the hydrothermal ZnO nanorods film. With suitable process condition, the nanorods film exhibits a uniform morphology to enable the formation of gas-permeable nanowire top electrode while also the nanorods provide good surface-to-volume ratio to deliver strong reaction with NO gas. A detection limit to 10 ppb NO is observed while the sensing dynamic range from 10 ppb to 100 ppb is obtained. The sensor is reversible and the real-time sensing response is within 30 s. The results benefit the NO breath detection for patients with chronic inflammatory airway disease, such as asthma.
Resistive switching behavior of Ga doped ZnO-nanorods film conductive bridge random access memory
(2018-08-30)
Singh, Pragya
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Simanjuntak, Firman Mangasa
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Kumar, Amit
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The influence of Ga dopant on resistive switching behavior of ZnO-nanorods film conducting bridge random access memory was investigated. Using a hydrothermal process, we grew vertically well-aligned and uniform Ga doped ZnO (GZO)-NRs films on transparent glass substrates to fabricate Cu/TiW/GZO-NRs/Indium Tin Oxide/Glass devices. The GZO-NRs film provides a diffusion path for the Cu ions to form a conducting bridge; thus, reducing the formation of a branched filament. The Ga dopant induces a significant improvement in switching distribution of high resistance states (HRS) and low resistance states (LRS). The 1.5 mol% Ga doped device exhibits good retention up to 10(4) s and high HRS/LRS ratio of 30 times. Therefore, our proposed device structure may be a good candidate for future conductive-bridge resistive random access memory application.
Role of nanorods insertion layer in ZnO-based electrochemical metallization memory cell
(2017-12-01)
Simanjuntak, Firman Mangasa
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Singh, Pragya
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Chandrasekaran, Sridhar
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Lumbantoruan, Franky Juanda
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Yang, Chih-Chieh
An engineering nanorod array in a ZnO-based electrochemical metallization device for nonvolatile memory applications was investigated. A hydrothermally synthesized nanorod layer was inserted into a Cu/ZnO/ITO device structure. Another device was fabricated without nanorods for comparison, and this device demonstrated a diode-like behavior with no switching behavior at a low current compliance (CC). The switching became clear only when the CC was increased to 75 mA. The insertion of a nanorods layer induced switching characteristics at a low operation current and improve the endurance and retention performances. The morphology of the nanorods may control the switching characteristics. A forming-free electrochemical metallization memory device having long switching cycles (> 10(4) cycles) with a sufficient memory window (10(3) times) for data storage application, good switching stability and sufficient retention was successfully fabricated by adjusting the morphology and defect concentration of the inserted nanorod layer. The nanorod layer not only contributed to inducing resistive switching characteristics but also acted as both a switching layer and a cation diffusion control layer.
Sensing performance of gas sensors fabricated from controllably grown ZnO-based nanorods on seed layers
(2020-07-01)
Singh, Pragya
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Simanjuntak, Firman Mangasa
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Wu, Yi-Chu
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Kumar, Amit
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Zan, Hsiao-Wen
ZnO nanorods (NRs) grown on different ZnO seed layers deposited at various Ar-O-2 ambient conditions, and the morphologies of the seed layers that affect their response to nitric oxide (NO) gas were investigated. The sensing performance of the devices fabricated with the seed layers deposited under an O-2-rich condition tends to deteriorate. We believe that the surface roughness, grain size, and defect concentration of the seed layer are responsible for this phenomenon. Despite the response to the gas was found to be less dependent on NR length, the gas sensing response is significantly dependent on the oxygen vacancy concentration and the exposure of the NR structure to the NO gas ambient surface. Excellent gas response (57.5% at 1 ppm and 7.1% at 100 ppb of NO gas) was achieved at room temperature-superior to the response presented by other proposed methods. This study not only proposes the potential of ZnO-NRs for high-performance NO gas sensor devices but also offers a simple and low-cost method to optimize the response without using any catalyst and additional treatment.