Browsing by Author "Berg, Darren"

Now showing 1 - 5 of 5
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    An integrated carbon entrapped molecularly imprinted polymer (MIP) electrode for voltammetric detection of resveratrol in wine
    (2015) Mugo, Samuel; Edmunds, Benjamin; Berg, Darren; Gill, Navpreet
    A carbon entrapped molecularly imprinted polymer (CEMIP) electrode has been demonstrated as a sensitive and selective voltammetric sensor for the in situ detection of resveratrol in red wine. Using differential pulse voltammetry (DPV), the CEMIP was compared to the carbon entrapped non-imprinted polymer (CENIP), with the resveratrol imprinted format found to be 12 times more sensitive for the detection of resveratrol. The CEMIP and CENIP had a detection limit of 20 and ∼100 μg L−1, respectively, with both electrodes giving good linear standard addition calibrations with R2 ≥ 0.99 for concentrations between 0.1 and 5 mg L−1, which is the usual occurrence range of resveratrol in wine. Compared to the conventional carbon MIP composite (CMIPC), the CEMIP platform was 2.7 orders of magnitude more sensitive, which is attributed to the better electron transfer and unhindered access of the analyte to the responsive sites within the imprinted polymer. The CMIPC was only ∼2.5 times more sensitive than the CNIPC. The %RSD for CEMIP and CMIPC for ∼5.0 mg L−1 of resveratrol in spiked wine was determined to be 3.2% and 5.1%, respectively.
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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).
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    Lipase-modified pH-responsive microgel-based optical device for triglyceride sensing
    (2015) Zhang, Qiang; Berg, Darren; Mugo, Samuel; Serpe, Michael
    Lipase-modified pH-responsive poly(N-isopropylacrylamide)-based microgels were synthesized. An optical device was subsequently fabricated by sandwiching the enzyme loaded responsive microgels between two thin Au layers, and their response to triolein, a model triglyceride, was investigated. The device's response depended on the triglyceride concentration, demonstrating its potential application as a triglyceride biosensor.
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    Molecularly imprinted carbon based electrodes for tetrahydrocannabinol sensing
    (2019) Zhang, Qiang; Berg, Darren; Mugo, Samuel
    Tetrahydrocannabinol (THC) sensors were fabricated using carbon nanotubes (CNT) or carbon beads and poly(methyl acrylic acid-co- ethylene glycol dimethacrylate) (poly(MAA-Co-EGDMA)) with molecularly imprinting technology in micropipette tubes. The carbon materials allow the electrode high sensitivity due to high surface area, and the cavities of THC temples will enhance selectivity of the electrode toward THC because of molecular recognition of THC cavities. These electrodes exhibit high THC detection selectivity over caffeine and acetaminophen. The limit of THC detection for CNT-MIP electrodes is as low as 0.18 ± 0.02 ng/mL, which is much lower than that of electrodes with nonimprinted polymers (NIP) which is 12.5 ± 0.5 ng/mL. The morphology was characterized using scanning electron microscope (SEM), which exhibited the presence of polymers on the surface of carbon materials in the electrodes. The thermal stability of polymers was also tested using thermogravimetric analysis (TGA).
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    Optical devices constructed from ferrocene-modified microgels for H2O2 sensing
    (2016) Zhang, Qiang Matthew; Berg, Darren; Duan, Jiaqi; Mugo, Samuel; Serpe, Michael
    Ferrocene-modified poly(N-isopropylacrylamide)-based microgels were synthesized, characterized, and used to construct optical devices (etalons). The response of the microgels and etalons to H2O2 was investigated, and we show that both the microgel diameter and the optical properties of the etalons depend on the solution concentration of H2O2 from 0.6 to 35 mM. This behavior is a direct result of the oxidation of ferrocene, which influences the microgel diameter. This was also demonstrated by electrochemical-mediated oxidation/reduction of ferrocene using cyclic voltammetry. We go on to show that these materials could be used to monitor H2O2 that is generated from enzymatic reactions. Specifically, we show that the H2O2 generated from the oxidation of glucose catalyzed by glucose oxidase could be quantified. Finally, the devices can be reused multiple times via a regeneration process. This investigation illustrates the versatility of the etalon system to detect species of broad relevance and how they could potentially be used to quantify products of biological reactions.