Kwang-Pill Lee

Development of a stable cholesterol biosensor based on multi-walled carbon nanotubes–gold nanoparticles composite covered with a layer of chitosan–room-temperature ionic liquid network

A novel amperometric biosensor was fabricated based on the immobilization of cholesterol oxidase (ChOx) into a cross-linked matrix of chitosan (Chi)-room-temperature ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate). Initially, the surface of bare electrode (indium tin oxide coated glass) was modified with the electrodeposition of Au particles onto thiol (-SH) functionalized multi-walled carbon nanotubes (MWNTs). The biosensor electrode is designated as MWNT(SH)-Au/Chi-IL/ChOx. Scanning electron microscopy image of MWNT(SH)-Au/Chi-IL/ChOx reveals that Chi-IL exists as the interconnected wires covering the Au particles on the surface of MWNT(SH)-Au. Cyclic voltammetry and chronoamperometry were used for the electrochemical determination of cholesterol at the biosensor electrode, MWNT(SH)-Au/Chi-IL/ChOx. The presence of Au particles in the matrix of CNTs provides an environment for the enhanced electrocatalytic activities. The MWNT(SH)-Au/Chi-IL/ChOx biosensor exhibited a linear response to cholesterol in the concentration range of 0.5-5mM with a correlation coefficient of 0.998, good sensitivity (200 microAM(-1)), a low response time ( approximately 7s), repeatability (R.S.D value of 1.9%) and long term stability (20 days with a decrease of 5% response). The synergistic influence of MWNT(SH), Au particles, Chi and IL contributes to the excellent performance for the biosensor.

Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4-aminothiophenol) modified electrode

A modified electrode is fabricated by embedding gold nanoparticles into a layer of electroactive polymer, poly(4-aminothiophenol) (PAT) on the surface of glassy carbon (GC) electrode. Cyclic voltammetry (CV) is performed to deposit PAT and concomitantly deposit Au nanoparticles. Field emission transmission electron microscopic image of the modified electrode, PAT-Au(nano)-ME, indicates the presence of uniformly distributed Au nanoparticles having the sizes of 8-10nm. Electrochemical behavior of the PAT-Au(nano)-ME towards detection of ascorbic acid (AA) and dopamine (DA) is studied using CV. Electrocatalytic determination of DA in the presence of fixed concentration of AA and vice versa, are studied using differential pulse voltammetry (DPV). PAT-Au(nano)-ME exhibits two well defined anodic peaks at the potential of 75 and 400mV for the oxidation of AA and DA, respectively with a potential difference of 325mV. Further, the simultaneous determination of AA and DA is studied by varying the concentration of AA and DA. PAT-Au(nano)-ME exhibits selectivity and sensitivity for the simultaneous determination of AA and DA without fouling by the oxidation products of AA or DA. PAT and Au nanoparticles provide synergic influence on the accurate electrochemical determination of AA or DA from a mixture having any one of the component (AA or DA) in excess. The practical analytical utilities of the PAT-Au(nano)-ME are demonstrated by the determination of DA and AA in dopamine hydrochloride injection and human blood serum samples.

Electrocatalytic oxidation of NADH at gold nanoparticles loaded poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) film modified electrode and integration of alcohol dehydrogenase for alcohol sensing.

A new modified electrode is fabricated by dispersing gold nanoparticles onto the matrix of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), PEDOT-PSS. The electrocatalytic activity of the PEDOT-PSS-Au(nano) electrode towards the oxidation of beta-nicotinamide adenine dinucleotide (NADH) is investigated. A substantial decrease in the overpotential (>0.7 V) has been observed for the oxidation of NADH at the PEDOT-PSS-Au(nano) electrode in comparison to the potential at PEDOT-PSS electrode. The Au nanoparticles dispersed in the PEDOT-PSS matrix prevents the fouling of electrode surface by the oxidation products of NADH and augments the oxidation of NADH at a less positive potential (+0.04V vs. SCE). The electrode shows high sensitivity to the electrocatalytic oxidation of NADH. Further, the presence of ascorbic acid and uric acid does not interfere during the detection of NADH. Important practical advantages such as stability of the electrode (retains approximately 95% of its original activity after 20 days), reproducibility of the measurements (R.S.D.: 2.8%; n=5), selectivity and wide linear dynamic range (1-80 microM; R(2)=0.996) are achieved at PEDOT-PSS-Au(nano) electrode. The ability of PEDOT-PSS-Au(nano) electrode to promote the electron transfer between NADH and the electrode makes us to fabricate a biocompatible dehydrogenase-based biosensor for the measurement of ethanol. The biosensor showed high sensitivity to ethanol with rapid detection, good reproducibility and excellent stability.

Interaction between the surface of the silver nanoparticles prepared by γ-irradiation and organic molecules containing thiol group

The colloidal silver nanoparticles were prepared by the γ-irradiation of silver nitrate (AgNO3) in a mixture solution of water and 2-propanol in the presence of poly(vinylpyrrolidone) as a colloidal stabilizer. The Ag colloids obtained by γ-irradiation were characterized by use of XRD and TEM. The surface of the Ag colloids were modified by use of mercaptosuccinic acid (MSA), (d)-cysteine (Cys), and (l)-Cys, respectively. The MSA and (l)-Cys-capped Ag colloids were aggregated because of hydrogen bonding of the carboxylic acid and amino acid group, respectively. From the analysis by CD spectroscopy, it was shown that chiral-enhanced phenomena were obtained in (l)- and (d)-Cys-capped Ag colloids.

Fabrication of enzymatic glucose biosensor based on palladium nanoparticles dispersed onto poly(3,4-ethylenedioxythiophene) nanofibers.

A new methodology involving the combination of a soft template (surfactant) and an ionic liquid (co-surfactant) is used to electrodeposit poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers. Electrochemical deposition of palladium nanoparticles and glucose oxidase (GOx) immobilization are done sequentially into nanofibrous PEDOT to fabricate the modified electrode (ME) (denoted as PEDOT-Pd/GOx-ME). The PEDOT-Pd/GOx-ME displays excellent performances for glucose at +0.4 V (vs. Ag/AgCl) with a high sensitivity (1.6 mA M(-)(1) cm(-2)) in a wider linear concentration range, 0.5 to 30 mM (correlation coefficient of 0.9985). Further, the electrode is insusceptible to the electroactive interfering species.

Fabrication of a novel layer-by-layer film based glucose biosensor with compact arrangement of multi-components and glucose oxidase

Layer-by-layer (LbL) film based glucose biosensor was fabricated with alternative layers of a nanocomposite (comprising of multiwalled carbon nanotubes (MWNTs), Au nanoparticles (Au NPs) and thiol functionalized polyaniline (PANI(SH)) and glucose oxidase (GOx). The successful formation of multilayers was confirmed by UV-visible spectroscopy. The components in the nanocomposite provide adequate electron transfer path between GOx and the electrode. A high value for the rate constant of electron transfer process (27.84 s(-1)) was observed at [GOx/Au-(SH)PANI-g-MWNT](n)/ITO electrode. The [GOx/Au-(SH)PANI-g-MWNT](n) biosensor exhibited high sensitivity (3.97 microA/mM) for the detection of glucose over a concentration range of 1-9 mM with a low detection limit of 0.06 microM.

Adsorption of uranium ions by resins with amidoxime and amidoxime/carboxyl group prepared by radiation-induced polymerization

Abstract In order to recover uranium ions from seawater, chelate-type resins with amidoxime and amidoxime/carboxylic acid groups were prepared by radiation-induced polymerization of acrylonitrile (AN) and AN/acrylic acid and by subsequent amidoximation of cyano group of poly(AN), respectively. The resins were characterized by FT–IR, FT–Raman, solid-state 13 C-NMR, SEM, and elemental analysis, respectively. The adsorption rate of uranium ion by resins with the amidoxime/carboxylic acid group were higher than that of resins with the amidoxime group. The adsorption of uranium ions in artificial seawater to chelate-type resins was also examined.

Development of a novel cyano group containing electrochemically deposited polymer film for ultrasensitive simultaneous detection of trace level cadmium and lead.

Poly(diphenylamine-co-2-aminobenzonitrile) (P(DPA-co-2ABN)), a cyano group containing conducting polyaniline derivative, has been electrodeposited developed as the new material and utilized for the simultaneous electrochemical determination of trace levels of cadmium (Cd(2+)) and lead (Pb(2+)). P(DPA-co-2ABN) film preconcentrates effectively through cyano chelation and electrochemically strips the heavy metal ions with well separated potentials, which are beneficially utilized for ppb level simultaneous detection of Cd(2+) and Pb(2+). Differential pulse voltammetry studies revealed that Cd(2+) and Pb(2+) ions were simultaneously stripped with well-defined, separated and sharp peaks for Cd(2+) and Pb(2+). The influence of various operational parameters such as pulse amplitude, pulse time, scan rate, initial potential, end potential, accumulation potential and accumulation time on the electrochemical stripping of heavy metals were investigated in details. Under the optimal conditions, good linear correlations were obtained from 1.26 to 907.8 ppm for Cd(2+) and 0.26 to 58.73 ppm for Pb(2+), respectively. Low detection limits for Cd(2+) and Pb(2+), 0.255 ppm and 0.165 ppm, respectively, were observed. The practical utility of the new procedure was demonstrated in real samples.

Bioelectrocatalytic determination of nitrite ions based on polyaniline grafted nanodiamond

Polyaniline chains were grafted onto nanodiamond (PANI-g-ND) through electrochemical polymerization of aniline in the presence of amine functionalized ND. A robust and effective composite film comprising PANI-g-ND/gold particles was subsequently prepared. Cytochrome c was successfully immobilized onto PANI-g-ND/Au film. Field emission scanning electron microscope (FESEM) image of PANI-g-ND/Au reveals the presence of fibrous PANI embedded into ND galleries with uniformly distributed Au clusters (∼1 μm). Direct electrochemistry and electrocatalysis of cyt c were investigated. PANI-g-ND/Au film showed an obvious direct electron transfer between cyt c and the underlying electrode. Cyclic voltammograms revealed that PANI-g-ND/Au/cyt c exhibited an excellent electrocatalysis towards the detection of nitrite ions. Differential pulse voltammetry of PANI-g-ND/Au/cyt c revealed a wide linear concentration range (0.5 μM-3 mM) for current responses, sensitivity (88.2 μA/mM) and low detection limit (0.16 μM) towards the electrochemical detection of nitrite ions.

Efficient visible-light-driven photocatalytic degradation of nitrophenol by using graphene-encapsulated TiO2 nanowires

In this work, a new hybrid nanocatalyst, namely titanium dioxide (TiO2) composite nanowires, encapsulated with graphene (G) and palladium nanoparticles (Pd NPs) (designated as G-Pd@TiO2-CNWs), was prepared. In preparing the nanowires, a combination of electrospinning and hydrothermal approaches was employed. The visible-light-driven photocatalytic performance of G-Pd@TiO2-CNWs was investigated using the reduction of 4-nitrophenol (4-NP) as a model reaction. The results showed that G-Pd@TiO2-CNWs converted nearly 100% of 4-NP under visible light irradiation. The reaction kinetics of the photocatalytic reduction of 4-NP was studied by UV-vis spectrophotometry and the apparent rate constant was determined and compared with those for other supported TiO2 catalysts. Furthermore, the spent G-Pd@TiO2-CNWs could be recovered by simple centrifugation and reused. The work is expected to shed new light on the development of G-incorporated hybrid nanostructures for harvesting light energy and on the development of new photocatalysts for the removal of environmental pollutants.