Browsing by Author "Bharath, G."

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    Facile synthesis of Au@α-Fe2O3@RGO ternary nanocomposites for enhanced electrochemical sensing of caffeic acid toward biomedical applications
    (2018) Bharath, G.; Alhseinat, E.; Madhu, R.; Mugo, Samuel; Alwasel, S.; Harrath, A. H.
    Demonstrated herewith is a novel eco-friendly Au@α-Fe2O3@RGO ternary nanocomposites using chlorophyll as reductants and stabilizers. Systematic characterizations studies confirm Au and α-Fe2O3 nanoparticles are uniformly decorated on the surfaces of reduced graphene oxide (RGO) nanosheets. As a proof-of-concept, the developed Au@α-Fe2O3@RGO ternary nanocomposites were coated on a glass carbon electrode (GCE) and evaluated for electrochemical detection of caffeic acid. The electrochemical mechanism involves the synergistic electrocatalytic activity of Au and α-Fe2O3 towards caffeic acid oxidation, with the RGO serving as an efficient electron shuttling mediator–enhancing the sensor performance. The Au@α-Fe2O3@RGO modified GCE caffeic acid sensor exhibited a wide linear response range of 19–1869 μM, sensitivity of 315 μA μM−1 cm-2, and a detection limit of 0.098 μM at very low potential of 0.21 V. This ternary nanocomposite provides high catalytic performance as well as excellent selectivity toward caffeic acid. To demonstrate real life application of the Fe2O3@RGO modified GCE caffeic acid sensor, caffeic acid in a coffee sample was measured. The α-Fe2O3, Au-NPs, and conductive graphene sheets composites, result in a highly catalytic and stable electrode system, with no pulverization problems. As such, it is demonstrated herewith that the Fe2O3@RGO ternary nanocomposite electrode is rapid, highly stable, and sensitive, with promised for utilization in fabrication of other multifarious biosensors.
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    Integrated microcentrifuge carbon entrapped glucose oxidase poly (N-isopropylacrylamide) (pNIPAm) microgels for glucose amperometric detection
    (2018) Mugo, Samuel; Berg, Darren; Bharath, G.
    This study demonstrates a miniaturized integrated glucose biosensor based on a carbon microbeads entrapped by glucose oxidase (GOx) immobilized on poly (N-isopropylacrylamide) (pNIPAm) microgels. Determined by the Lowry protein assay, the pNIPAm microgel possesses a high enzyme loading capacity of 31 mg/g. The pNIPAm GOx loaded on the microgel was found to maintain a high activity of approximately 0.140 U determined using the 4-aminoantipyrine colorimetric method. The integrated microelectrochemical cell was constructed using a microcentrifuge vial housing packed with (1:1, w/w) carbon entrapped by pNIPAm GOx microgels, which played the dual role of the microbioreactor and the working electrode. The microcentrifuge vial cover was used as a miniaturized reference electrode and an auxiliary electrode holder. The device can work as biosensor, effectively converting glucose to H2O2, with subsequent amperometric detection at an applied potential of −0.4 V. The microelectrochemical biosensor was used to detect glucose in wide linear range from 30 µM to 8.0 mM, a low detection limit of 10 µM, a good linear regression coefficient (R2) of 0.994, and a calibration sensitivity of 0.0388 µA/mM. The surface coverage of active GOx, electron transfer rate constant (ks), and Michaelis-Menten constant (KMapp) of the immobilized GOx were 4.0 × 10−11 mol/cm2, 5.4 s−1, and 0.086 mM, respectively. To demonstrate the applicability and robustness of the biosensor for analysis of high sample matrix environment, glucose was analyzed in root beer. The microelectrochemical device was demonstrated for analysis of small sample (<50 µL), while affording high precision and fast signal measurement (≤5 s).