Martin Choi - Academia.edu (original) (raw)

Papers by Martin Choi

Research paper thumbnail of Synthesis of 1.4 nm alpha-Cyclodextrin-Protected Gold Nanoparticles for Luminescence Sensing of Mercury(II) with Picomolar Detection Limit

Journal of Physical Chemistry C, 2010

Research paper thumbnail of Probing Histidine-Stabilized Gold Nanoclusters Product by High-Performance Liquid Chromatography and Mass Spectrometry

The Journal of Physical Chemistry C, 2013

Research paper thumbnail of Development of a galactose biosensor with galactose oxidase-immobilized epidermis of Solanum lycopersicum: Potential point-of-care testing for citrin deficiency in high-prevalence areas

Research paper thumbnail of Microcalorimetric Investigation of the Toxic Effect of Iron Species on Escherichia coli

ABSTRACT A microcalorimetric technique based on bacterial heat output was explored to evaluate th... more ABSTRACT A microcalorimetric technique based on bacterial heat output was explored to evaluate the toxic effect of iron species on Escherichia coli. Power-time curves of the growth metabolism of E. coli and the effect of different iron species on it were studied using the TAM III multichannel microcalorimetric system, isothermal mode, at 37 degrees C. The differences in shape of the power-time curves and the thermodynamic and kinetic characteristics of E. coli growth have been compared. The thermodynamic parameters, that is, growth rate constant (k), inhibitory ratio (I), half-inhibitory concentration (IC(50)), P(max), and Q(total), have been calculated. The experimental results reveal that the sequence of antibiotic activity of the different iron species (three forms) on E. coli growth is Fe(3+) (ferric citrate) > Fe(2+) (ferrous chloride) > Fe(3+) (ferric chloride). These results are important to further studies of the physiology and pharmacology of iron species as antibacterial agents.

Research paper thumbnail of Classical interacting particles in confinement

Solid State Communications, 1997

The lowest energy configurations of systems with N classical particles interacting repulsively an... more The lowest energy configurations of systems with N classical particles interacting repulsively and confined in a parabolic potential are studied using a molecular dynamics method. Three different types of interacting potentials, namely 1r, 1r2 and −lnr, where r is the particle separation, are considered. The lowest energy configurations show a shell structure for these interactions. Results are given for up

Research paper thumbnail of Microwave activation of the mutarotation of ?-D-glucose: An example of an interinsic microwave effect

Journal of Physical Organic Chemistry, 1993

Research paper thumbnail of Electro-Oxidation of Methane on Roughened Palladium Electrode in Acidic Electrolytes at Ambient Temperatures

Http Dx Doi Org 10 1080 00032710903492508, Mar 11, 2010

ABSTRACT The aim of this research is to investigate the electro-oxidation of methane on roughened... more ABSTRACT The aim of this research is to investigate the electro-oxidation of methane on roughened Pd electrode (RP) in acidic media. The results showed that RP electrode has large surface-to-volume ratio, good reversibility, and facile electron transfer kinetics. Electro-oxidation of methane on RP electrode was studied by cyclic voltammetry and differential pulse voltammetry. Higher electro-catalytic activity and shorter response time for methane oxidation were found on the RP electrode in acidic media at ambient temperatures than those found on the smooth Pd electrode. Differential pulse voltammetry was employed to study the response of RP electrode to various concentrations of methane. The increase in peak current was monitored and related to the methane concentration. The mechanisms for electro-oxidation of methane on RP electrode were also discussed.

Research paper thumbnail of Detection of Ag(+) using graphite carbon nitride nanosheets based on fluorescence quenching

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 17, 2016

The graphite carbon nitride (g-C3N4) nanosheets were synthesized and applied for the detection of... more The graphite carbon nitride (g-C3N4) nanosheets were synthesized and applied for the detection of Ag(+) ion in aqueous solutions. Transmission electron microscopy, Fourier infrared spectroscopy, x-ray diffraction, ultraviolet/visible and photoluminescence spectroscopy were used for characterization of g-C3N4 nanosheets. The fluorescence intensity of g-C3N4 nanosheets decreases with the increase in the concentration of Ag(+). The fluorescence probe can be applied for detection of Ag(+). The results show that it has high selectivity to Ag(+) and exhibits a good linearity over the concentration range 0.020-2.0μM with a detection limit of 27nM. Most cations do not have any interference on the detection of Ag(+). The quenching process is assessed and discussed. Finally, the g-C3N4 nanosheets have been successfully used for the detection of Ag(+) in real water samples. The recoveries of spiked water samples are >97%.

Research paper thumbnail of Elucidating the structure of carbon nanoparticles by ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight tandem mass spectrometry

Analytica chimica acta, Jan 10, 2016

A fast and accurate ultra-performance liquid chromatography coupled with electrospray ionisation ... more A fast and accurate ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) method was developed for the separation and structural elucidation of fluorescent carbon nanoparticles (CNP). The CNP was synthesised from microwave-assisted pyrolysis of citric acid (CA) and 1,2-ethylenediamine (EDA). By using UPLC separation, the CNP product was well separated into ten fractions within 4.0 min. Based on high-accuracy MS and MS/MS analyses, the CNP species were revealed to display six kinds of chemical formulas, including (C10H20N4O5)n, (C8H12N2O5)n, (C16H22N4O9)n, (C6H8O7)n, (C14H18N2O11)n, and (C14H16N2O10)n. In particular, our study revealed for the first time that the CNP species exist as supramolecular clusters with their individual monomers units linked together through non-covalent bonding forces. These findings clearly indicated the usefulness of UPLC-ESI-Q-TOF-MS/MS in identifying the che...

Research paper thumbnail of SPE/HPLC/UV studies on acrylamide in deep-fried flour-based indigenous Chinese foods

Microchemical Journal, Aug 31, 2008

Research paper thumbnail of Immobilization of beef liver catalase on eggshell membrane for fabrication of hydrogen peroxide biosensor

Enzyme and Microbial Technology, 2004

A simple and low-cost hydrogen peroxide biosensor was fabricated using a beef liver catalase-immo... more A simple and low-cost hydrogen peroxide biosensor was fabricated using a beef liver catalase-immobilized eggshell membrane and an oxygen electrode. Catalase from beef liver extract was covalently immobilized on an eggshell membrane and subsequently covered the surface of an oxygen electrode. The detection scheme was based on the increase in dissolved oxygen content upon exposure to hydrogen peroxide solution. The

Research paper thumbnail of Application of capillary zone electrophoresis for separation of water-soluble gold monolayer-protected clusters

Electrophoresis, Jun 1, 2008

An effective capillary electrophoretic technique for separating samples of negatively charged, po... more An effective capillary electrophoretic technique for separating samples of negatively charged, polydisperse, water-soluble gold monolayer-protected cluster (Au MPC) protected by monolayers of N-acetyl-L-cysteine has been developed. The separation mechanisms of the Au MPC in CZE suggest that the larger core sizes Au MPC emerge first from the capillary. The electrophoretic separation depends on pH, buffer concentration, and organic modifiers. The addition of aliphatic alcohols to the run buffer can improve the separation of Au MPC by reducing the EOF and changing the selectivity between the Au MPCs. The enhancement of resolution is attributed to the more significant difference in the charge-to-size ratio between the Au MPCs. The run buffer containing 20 v/v % ethanol provides the best separation for water-soluble Au MPC. Our proposed CE method provides a powerful tool to evaluate and separate the water-soluble Au MPC products.

Research paper thumbnail of Synthesis and Characterization of High-Quality Water-Soluble Near-Infrared-Emitting CdTe/CdS Quantum Dots Capped by N -Acetyl- l -cysteine Via Hydrothermal Method

Research paper thumbnail of Capillary electrophoretic study of thiolated α-cyclodextrin-capped gold nanoparticles with tetraalkylammonium ions

Journal of Chromatography a, Nov 27, 2009

Research paper thumbnail of High-performance liquid chromatographic analysis of as-synthesised N,N′-dimethylformamide-stabilised gold nanoclusters product

Research paper thumbnail of Symmetrical electrochemical cell for determination of coextraction constants of metal salts for ion-selective polymeric membranes

Analytica Chimica Acta, Jun 6, 2003

Research paper thumbnail of Near-infrared luminescence quenching method for the detection of phenolic compounds using N-acetyl- l-cysteine-protected gold nanoparticles–tyrosinase hybrid material

Biosensors and Bioelectronics, Jan 15, 2010

Research paper thumbnail of Assemblies of brilliant cresyl violet to DNA in the presence of ?-cyclodextrin

Talanta, 2010

The interactions of brilliant cresyl violet (BCV) with herring sperm DNA in γ-cyclodextrin (γ-CD)... more The interactions of brilliant cresyl violet (BCV) with herring sperm DNA in γ-cyclodextrin (γ-CD) supramolecular system were studied by UV-vis absorption spectroscopy and cyclic voltammetry (CV). Both UV-vis absorption and CV data show that the interaction of BCV with DNA depends on the concentration ratio of BCV to DNA (R), the initial concentration of BCV and γ-CD. The binding constants of BCV monomer, (BCV)2 dimer and (BCV)2-γ-CD inclusion complex with DNA are 1.64 × 105, 2.56 × 104 and 2.32 × 103 M−1, respectively. It was observed that γ-CD can affect the interactive mode of BCV with DNA. If R is larger than 0.5, the (BCV)2-γ-CD inclusion complex will retain intact and bind to DNA via the electrostatic attraction forces. By contrast, when R is smaller than 0.5, the inclusion complex will be partially dissociated and the free BCV monomer is intercalated into the double-helix structure of DNA attributing to the more favorable microenvironment of DNA for the BCV monomer. Our work postulates the importance of the initial concentration of dye and host molecule on the interaction of dye with DNA in living bodies.

Research paper thumbnail of Detection of ethanol in food: A new biosensor based on bacteria

Journal of Food Engineering, Sep 1, 2013

A microbial biosensor for determination of ethanol has been developed. The microbial ethanol bios... more A microbial biosensor for determination of ethanol has been developed. The microbial ethanol biosensor comprises a Methylobacterium organophilium-immobilized eggshell membrane and an oxygen (O2) electrode. The microbial biosensor responds linearly to ethanol in the range 0.050–7.5 mM with a detection limit of 0.025 mM (S/N = 3) and the response time is 100 s. The optimal loading of bacterial cells on the biosensor membrane is 40 mg (wet weight). The optimal working conditions for the microbial biosensor are pH 7.0 phosphate buffer (50 mM) at 20–25 °C. The interference test, operational and storage stability of the biosensor are studied in detail. Finally, the biosensor is applied to determine the ethanol contents in various alcohol samples and the results are comparable to that obtained by a gas chromatographic method. Our work demonstrates that the proposed microbial biosensor is a reliable method to determine the ethanol content in wine samples.► A microbial biosensor for determination of ethanol has been developed. ► The sensor comprises bacterial-immobilized eggshell membrane and an O2 electrode. ► The biosensor responds linearly to ethanol in the range 0.050–7.5 mM. ► The detection limit of 0.025 mM (S/N = 3) and the response time is 100 s.

[Research paper thumbnail of Facile Fabrication of Porous CuS Nanotubes Using Well-Aligned [Cu(tu))Cl · 1/2H2O Nanowire Precursors as Self-Sacrificial Templates](https://a.academia-assets.com/images/blank-paper.jpg)

Crystal Growth Design, 2009

... b) Anuar, K. ; Zainal, Z. ; Hussein, MZ ; Saravanan, N. ; Haslina, I. Sol. Energy Mat. Sol. C... more ... b) Anuar, K. ; Zainal, Z. ; Hussein, MZ ; Saravanan, N. ; Haslina, I. Sol. Energy Mat. Sol. C. 2002, 73, 351– 365 ...

Research paper thumbnail of Synthesis of 1.4 nm alpha-Cyclodextrin-Protected Gold Nanoparticles for Luminescence Sensing of Mercury(II) with Picomolar Detection Limit

Journal of Physical Chemistry C, 2010

Research paper thumbnail of Probing Histidine-Stabilized Gold Nanoclusters Product by High-Performance Liquid Chromatography and Mass Spectrometry

The Journal of Physical Chemistry C, 2013

Research paper thumbnail of Development of a galactose biosensor with galactose oxidase-immobilized epidermis of Solanum lycopersicum: Potential point-of-care testing for citrin deficiency in high-prevalence areas

Research paper thumbnail of Microcalorimetric Investigation of the Toxic Effect of Iron Species on Escherichia coli

ABSTRACT A microcalorimetric technique based on bacterial heat output was explored to evaluate th... more ABSTRACT A microcalorimetric technique based on bacterial heat output was explored to evaluate the toxic effect of iron species on Escherichia coli. Power-time curves of the growth metabolism of E. coli and the effect of different iron species on it were studied using the TAM III multichannel microcalorimetric system, isothermal mode, at 37 degrees C. The differences in shape of the power-time curves and the thermodynamic and kinetic characteristics of E. coli growth have been compared. The thermodynamic parameters, that is, growth rate constant (k), inhibitory ratio (I), half-inhibitory concentration (IC(50)), P(max), and Q(total), have been calculated. The experimental results reveal that the sequence of antibiotic activity of the different iron species (three forms) on E. coli growth is Fe(3+) (ferric citrate) > Fe(2+) (ferrous chloride) > Fe(3+) (ferric chloride). These results are important to further studies of the physiology and pharmacology of iron species as antibacterial agents.

Research paper thumbnail of Classical interacting particles in confinement

Solid State Communications, 1997

The lowest energy configurations of systems with N classical particles interacting repulsively an... more The lowest energy configurations of systems with N classical particles interacting repulsively and confined in a parabolic potential are studied using a molecular dynamics method. Three different types of interacting potentials, namely 1r, 1r2 and −lnr, where r is the particle separation, are considered. The lowest energy configurations show a shell structure for these interactions. Results are given for up

Research paper thumbnail of Microwave activation of the mutarotation of ?-D-glucose: An example of an interinsic microwave effect

Journal of Physical Organic Chemistry, 1993

Research paper thumbnail of Electro-Oxidation of Methane on Roughened Palladium Electrode in Acidic Electrolytes at Ambient Temperatures

Http Dx Doi Org 10 1080 00032710903492508, Mar 11, 2010

ABSTRACT The aim of this research is to investigate the electro-oxidation of methane on roughened... more ABSTRACT The aim of this research is to investigate the electro-oxidation of methane on roughened Pd electrode (RP) in acidic media. The results showed that RP electrode has large surface-to-volume ratio, good reversibility, and facile electron transfer kinetics. Electro-oxidation of methane on RP electrode was studied by cyclic voltammetry and differential pulse voltammetry. Higher electro-catalytic activity and shorter response time for methane oxidation were found on the RP electrode in acidic media at ambient temperatures than those found on the smooth Pd electrode. Differential pulse voltammetry was employed to study the response of RP electrode to various concentrations of methane. The increase in peak current was monitored and related to the methane concentration. The mechanisms for electro-oxidation of methane on RP electrode were also discussed.

Research paper thumbnail of Detection of Ag(+) using graphite carbon nitride nanosheets based on fluorescence quenching

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 17, 2016

The graphite carbon nitride (g-C3N4) nanosheets were synthesized and applied for the detection of... more The graphite carbon nitride (g-C3N4) nanosheets were synthesized and applied for the detection of Ag(+) ion in aqueous solutions. Transmission electron microscopy, Fourier infrared spectroscopy, x-ray diffraction, ultraviolet/visible and photoluminescence spectroscopy were used for characterization of g-C3N4 nanosheets. The fluorescence intensity of g-C3N4 nanosheets decreases with the increase in the concentration of Ag(+). The fluorescence probe can be applied for detection of Ag(+). The results show that it has high selectivity to Ag(+) and exhibits a good linearity over the concentration range 0.020-2.0μM with a detection limit of 27nM. Most cations do not have any interference on the detection of Ag(+). The quenching process is assessed and discussed. Finally, the g-C3N4 nanosheets have been successfully used for the detection of Ag(+) in real water samples. The recoveries of spiked water samples are >97%.

Research paper thumbnail of Elucidating the structure of carbon nanoparticles by ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight tandem mass spectrometry

Analytica chimica acta, Jan 10, 2016

A fast and accurate ultra-performance liquid chromatography coupled with electrospray ionisation ... more A fast and accurate ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) method was developed for the separation and structural elucidation of fluorescent carbon nanoparticles (CNP). The CNP was synthesised from microwave-assisted pyrolysis of citric acid (CA) and 1,2-ethylenediamine (EDA). By using UPLC separation, the CNP product was well separated into ten fractions within 4.0 min. Based on high-accuracy MS and MS/MS analyses, the CNP species were revealed to display six kinds of chemical formulas, including (C10H20N4O5)n, (C8H12N2O5)n, (C16H22N4O9)n, (C6H8O7)n, (C14H18N2O11)n, and (C14H16N2O10)n. In particular, our study revealed for the first time that the CNP species exist as supramolecular clusters with their individual monomers units linked together through non-covalent bonding forces. These findings clearly indicated the usefulness of UPLC-ESI-Q-TOF-MS/MS in identifying the che...

Research paper thumbnail of SPE/HPLC/UV studies on acrylamide in deep-fried flour-based indigenous Chinese foods

Microchemical Journal, Aug 31, 2008

Research paper thumbnail of Immobilization of beef liver catalase on eggshell membrane for fabrication of hydrogen peroxide biosensor

Enzyme and Microbial Technology, 2004

A simple and low-cost hydrogen peroxide biosensor was fabricated using a beef liver catalase-immo... more A simple and low-cost hydrogen peroxide biosensor was fabricated using a beef liver catalase-immobilized eggshell membrane and an oxygen electrode. Catalase from beef liver extract was covalently immobilized on an eggshell membrane and subsequently covered the surface of an oxygen electrode. The detection scheme was based on the increase in dissolved oxygen content upon exposure to hydrogen peroxide solution. The

Research paper thumbnail of Application of capillary zone electrophoresis for separation of water-soluble gold monolayer-protected clusters

Electrophoresis, Jun 1, 2008

An effective capillary electrophoretic technique for separating samples of negatively charged, po... more An effective capillary electrophoretic technique for separating samples of negatively charged, polydisperse, water-soluble gold monolayer-protected cluster (Au MPC) protected by monolayers of N-acetyl-L-cysteine has been developed. The separation mechanisms of the Au MPC in CZE suggest that the larger core sizes Au MPC emerge first from the capillary. The electrophoretic separation depends on pH, buffer concentration, and organic modifiers. The addition of aliphatic alcohols to the run buffer can improve the separation of Au MPC by reducing the EOF and changing the selectivity between the Au MPCs. The enhancement of resolution is attributed to the more significant difference in the charge-to-size ratio between the Au MPCs. The run buffer containing 20 v/v % ethanol provides the best separation for water-soluble Au MPC. Our proposed CE method provides a powerful tool to evaluate and separate the water-soluble Au MPC products.

Research paper thumbnail of Synthesis and Characterization of High-Quality Water-Soluble Near-Infrared-Emitting CdTe/CdS Quantum Dots Capped by N -Acetyl- l -cysteine Via Hydrothermal Method

Research paper thumbnail of Capillary electrophoretic study of thiolated α-cyclodextrin-capped gold nanoparticles with tetraalkylammonium ions

Journal of Chromatography a, Nov 27, 2009

Research paper thumbnail of High-performance liquid chromatographic analysis of as-synthesised N,N′-dimethylformamide-stabilised gold nanoclusters product

Research paper thumbnail of Symmetrical electrochemical cell for determination of coextraction constants of metal salts for ion-selective polymeric membranes

Analytica Chimica Acta, Jun 6, 2003

Research paper thumbnail of Near-infrared luminescence quenching method for the detection of phenolic compounds using N-acetyl- l-cysteine-protected gold nanoparticles–tyrosinase hybrid material

Biosensors and Bioelectronics, Jan 15, 2010

Research paper thumbnail of Assemblies of brilliant cresyl violet to DNA in the presence of ?-cyclodextrin

Talanta, 2010

The interactions of brilliant cresyl violet (BCV) with herring sperm DNA in γ-cyclodextrin (γ-CD)... more The interactions of brilliant cresyl violet (BCV) with herring sperm DNA in γ-cyclodextrin (γ-CD) supramolecular system were studied by UV-vis absorption spectroscopy and cyclic voltammetry (CV). Both UV-vis absorption and CV data show that the interaction of BCV with DNA depends on the concentration ratio of BCV to DNA (R), the initial concentration of BCV and γ-CD. The binding constants of BCV monomer, (BCV)2 dimer and (BCV)2-γ-CD inclusion complex with DNA are 1.64 × 105, 2.56 × 104 and 2.32 × 103 M−1, respectively. It was observed that γ-CD can affect the interactive mode of BCV with DNA. If R is larger than 0.5, the (BCV)2-γ-CD inclusion complex will retain intact and bind to DNA via the electrostatic attraction forces. By contrast, when R is smaller than 0.5, the inclusion complex will be partially dissociated and the free BCV monomer is intercalated into the double-helix structure of DNA attributing to the more favorable microenvironment of DNA for the BCV monomer. Our work postulates the importance of the initial concentration of dye and host molecule on the interaction of dye with DNA in living bodies.

Research paper thumbnail of Detection of ethanol in food: A new biosensor based on bacteria

Journal of Food Engineering, Sep 1, 2013

A microbial biosensor for determination of ethanol has been developed. The microbial ethanol bios... more A microbial biosensor for determination of ethanol has been developed. The microbial ethanol biosensor comprises a Methylobacterium organophilium-immobilized eggshell membrane and an oxygen (O2) electrode. The microbial biosensor responds linearly to ethanol in the range 0.050–7.5 mM with a detection limit of 0.025 mM (S/N = 3) and the response time is 100 s. The optimal loading of bacterial cells on the biosensor membrane is 40 mg (wet weight). The optimal working conditions for the microbial biosensor are pH 7.0 phosphate buffer (50 mM) at 20–25 °C. The interference test, operational and storage stability of the biosensor are studied in detail. Finally, the biosensor is applied to determine the ethanol contents in various alcohol samples and the results are comparable to that obtained by a gas chromatographic method. Our work demonstrates that the proposed microbial biosensor is a reliable method to determine the ethanol content in wine samples.► A microbial biosensor for determination of ethanol has been developed. ► The sensor comprises bacterial-immobilized eggshell membrane and an O2 electrode. ► The biosensor responds linearly to ethanol in the range 0.050–7.5 mM. ► The detection limit of 0.025 mM (S/N = 3) and the response time is 100 s.

[Research paper thumbnail of Facile Fabrication of Porous CuS Nanotubes Using Well-Aligned [Cu(tu))Cl · 1/2H2O Nanowire Precursors as Self-Sacrificial Templates](https://a.academia-assets.com/images/blank-paper.jpg)

Crystal Growth Design, 2009

... b) Anuar, K. ; Zainal, Z. ; Hussein, MZ ; Saravanan, N. ; Haslina, I. Sol. Energy Mat. Sol. C... more ... b) Anuar, K. ; Zainal, Z. ; Hussein, MZ ; Saravanan, N. ; Haslina, I. Sol. Energy Mat. Sol. C. 2002, 73, 351– 365 ...