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Su-Moon Park

Publications and source records attributed to Su-Moon Park.

At least 19 recordsLinked to original sources
PubMed2007

Polypyrrole-based optical probe for a hydrogen peroxide assay.

An optical sensing probe has been developed by taking advantage of the polypyrrole (PPy) chromophore. The absorbance of the oxidation product of pyrrole, i.e., solubilized PPy colloids, is shown to be directly proportional to the concentration of hydrogen peroxide, when H2O2 is used as an oxidant for pyrrole in the presence of a surfactant, sodium dodecyl sulfate, and Fe(II) in a slightly acidic aqueous solution. Based on this result, a new optical sensing method has been developed for the determination of H2O2. The probe has also been applied to optical sensing of ethanol by biocatalyzed generation of H2O2 in the presence of O2, ethanol, and alcohol oxidase. The novel methodology is expected to provide a general protocol for the determination of H2O2 as well as for numerous other oxidase-based reactions producing H2O2 as a product.

Alcohol Oxidoreductases↗
PubMed2006

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy.

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.

Journal Article↗
PubMed2006

Determination of electron transfer kinetic parameters by fourier transform electrochemical impedance spectroscopic analysis.

A new attempt to obtain electron transfer kinetic parameters at an electrified electrode/electrolyte interface using Fourier transform electrochemical impedance spectroscopic (FTEIS) analyses of small potential step chronoamperometric currents is presented. The kinetic parameters thus obtained allowed mass transport free voltammograms to be constructed in an overpotential region, where the diffusion limits the electron transfer reaction, using the Butler-Volmer (B-V) relation. The B-V voltammograms clearly distinguish electrode reactions that are not much different in their electron transfer kinetic parameters, thus showing very similar normal linear sweep voltammetric (SCV) behaviors. Electrochemical reduction of p-benzoquinone, which displays nearly the same SCV responses at a gold electrode regardless whether the electrode is covered by a thiolated beta-cyclodextrin self-assembled monolayer, was taken as an example for the demonstration. The results show that the two voltametrically similar systems display very different electron transfer characteristics.

Journal Article↗
PubMed2006

Electrochemistry of conductive polymers 38. Electrodeposited poly(3,4-ethylenedioxy-thiophene) studied by current sensing atomic force microscopy.

Electrical and morphological properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films electrodeposited on gold-on-silicon electrodes by galvanostatic, potentiostatic, and potentiodynamic methods have been determined using current sensing atomic force microscopic experiments. Surface morphologies and vertical conductivities of PEDOT films were affected by the experimental parameters including the preparation method, the current density, the potential, and the potentiodynamic cyclic number. Band gaps obtained from current-voltage curves of dedoped PEDOT were in excellent agreement with those obtained from absorption spectra. When the film thickness was increased on the gold-on-silicon electrode, the topographic images were not very well defined due to the high roughness but conductivities increased significantly in all the galvanostatically, potetiostatically, and potentiodynamically grown PEDOT films.

Journal Article↗
PubMed2006

Integrated description of electrode/electrolyte interfaces based on equivalent circuits and its verification using impedance measurements.

An integrated theory describing both faradaic and nonfaradaic currents obtained upon potential step at an electrified electrode/electrolyte interface has been developed based on equivalent circuits that had been used to explain electrochemical reactions and experimentally verified. The faradaic current is shown to consist of the mass transport-dependent and -independent parts, which is in general agreement with the expression previously derived from the diffusion equations. The decay of the capacitive current is determined by the time constant represented by the product of the resistance obtained from the parallel connection of the solution and polarization resistances and the double layer capacitance; this is not consistent with the current understanding of the capacitive current decay, which takes into account the double layer capacitance and the solution resistance only. Many insights into the electron-transfer reactions are discussed based on the interpretation of impedance representation of the system, which would not have been possible without the present theory.

Journal Article↗
PubMed2005

Electrochemistry of conductive polymers 37. Nanoscale monitoring of electrical properties during electrochemical growth of polypyrrole and its aging.

Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities. The degree of doping, as well as time evolution of the film structure and its conductivity, of the PPy films was investigated during their growth in water and ACN with 1.0% water by obtaining the current images at a few designated growing stages, and the results were compared. Well-doped, conductive films were obtained from the very early stage during the electrodeposition of PPy in the ACN solution, while the films were poorly doped in water. As the film deposition progressed further in both aqueous and nonaqueous media, the doped areas spread over the whole surface leading to a more homogeneously conducting film. The current-voltage traces were obtained at each growing stage, which showed that the conductivity increases in both media as the PPy grows; the conductivity of the film grown in ACN is much higher than that of the film grown in water at all growing stages. The electrical properties of the PPy film deteriorated gradually upon exposure to air.

Journal Article↗
PubMed2005

Programmed potential sweep voltammetry for lower detection limits.

We report a novel programmed potential sweep voltammetry for a much lower detection limit than those achieved by any other known electroanalyitcal techniques. In this technique, an input waveform is programmed such that the background current would become flat or any other predefined form in the potential region of interest where the peak current arising from the analyte is observed, followed by the amplification of the background subtracted peak current. The current thus obtained showed a much better signal integrity at very low analyte concentrations than those obtained by the traditional linear sweep voltammetric and other related voltammetric techniques. The technique was applied to the analysis of dopamine at a carbon ultramicroelectrode (10-microm diameter). The background-compensated currents showed excellent dynamic linearity for dopamine concentrations of more than 3 orders of magnitudes between 500 pM and 100 nM with an estimated detection limit of 127 pM. This method can provide a convenient way for determining biogenic amines in real time with a much higher sensitivity.

Journal Article↗
PubMed2005

Electrochemistry of conductive polymers 36. pH dependence of polyaniline conductivities studied by current-sensing atomic force microscopy.

We demonstrate from our current-sensing atomic force microscopic studies that both electrical and topographical properties of electrochemically prepared polyaniline (PAn) films are affected by their preparation conditions. The electrical properties of the fully doped PAn films prepared in 0.30 M nitric acid with its pH and ionic strength adjusted to 0.50 can be described as a conductor with an average conductivity of 49 (+/-13) S/cm with primarily a compact structure resulting from a relatively small growth rate. The doped PAn films prepared at pH 5.0, for example, have compact structures with large grains and lightly doped semiconducting properties with an average conductivity of about 1.54 (+/-0.09) x 10(-4) S/cm. From these data, we conclude that the degree of protonation of the monomers and the main reactions taking place during an early stage of the polymerization reaction are important factors determining the chemical structures as well as their conductivities and morphologies of the PAn films.

Journal Article↗
PubMed2005

Electrochemistry of conductive polymers. 34. Two-dimensional correlation analysis of real-time spectroelectrochemical data for aniline polymerization.

Electrochemical polymerization of aniline has been studied using real-time spectroelectrochemical experiments conducted concurrently with potentiodynamic scans in a nitric acid electrolyte with its pH adjusted to 0.50. Two-dimensional correlation spectral analysis and subsequent extraction of pure component spectra as well as their relative concentration profiles from complex spectroelectrochemical data employing the alternating least-squares regression iteration-based self-modeling curve resolution method led to positive identification of intermediate species. A conclusion was reached on the polymerization reaction mechanism based on these intermediate species and how their concentrations increased or decreased during the potential scans. The mechanism thus concluded represents a summary of a current understanding of the aniline polymerization reaction.

Journal Article↗
PubMed2004

Modification of indium-tin oxide (ITO) glass with aziridine provides a surface of high amine density.

The surface of indium-tin oxide (ITO) substrates was successfully modified with aziridine. Modification of the surface was achieved through facile ring-opening, and hyperbranching polymerization of the ring-strained heterocycle initiated from the reactive group on the surface. Amine density of the aziridine-modified ITO measured with UV-vis spectrophotometry is 10 amines/nm2. Cyclic voltammetric analysis showed that the aziridine-modified electrode was less active for Ru(NH3)6(3+) in comparison with the pristine electrode, while no difference was observed for Fe(CN)6(4-). Electrochemical impedance spectroscopic experiments unveiled that the modified electrode was more efficient for electron transfer to the latter species than to the former.

Amines↗
PubMed2004

Two-dimensional correlation analysis of spectroelectrochemical data for p-benzoquinone reduction in acetonitrile.

Two-dimensional (2D) spectral correlation analysis has been employed to interpret the complex spectroelectrochemical data obtained from an electrochemical system undergoing following reactions after electron transfer. The system used was electrochemical reduction of p-benzoquinone (p-BQ) in acetonitrile, which produces anion radicals and dianions at its first and second reduction potentials. The dianions undergo a fast comproporationation reaction with neutral p-BQ molecules to produce anion radicals back, complicating the spectral analysis. Upon application of 2D correlation analysis in conjunction with the self-modeling curve resolution technique, we were able not only to resolve the spectra and determine the sequence of spectral emergence but also to extract the individual spectra. The techniques offer a very powerful tool for interpreting highly convoluted spectra obtained from a system where a series of chemical reactions occur following the electron transfer at the electrode/electrolyte interface.

Journal Article↗
PubMed2004

Effects of organic additives on zinc electrodeposition at iron electrodes studied by EQCM and in situ STM.

Effects of organic additives, such as benzoic acid (BA) and poly(ethylene glycol)s (PEGs), on the initial stage of the zinc electrodeposition have been investigated at iron electrodes using cyclic voltammetry, electrochemical quartz crystal microbalance measurements and in situ electrochemical scanning tunneling microscopy in an acidic zinc chloride solution in efforts to gain a molecular-level understanding of their roles. BA is adsorbed strongly at the sites of more negative potentials on the electrode, although it is randomly adsorbed on the iron surface at around an open circuit potential. Its role seems to control the deposition rate at the dendritic sites by blocking the active surface via adsorption. On the contrary, PEGs are adsorbed more or less evenly with a well-ordered structure on the iron surface and appear to desorb in the underpotential deposition region of zinc ions, which helps inhibit proton reduction by effectively blocking the electrode surface.

Journal Article↗
PubMed2003

Fabrication of nanoscale gold disk electrodes using ultrashort pulse etching.

A novel method for preparing a nanometer-sized gold disk electrode is described. The electrode was fabricated by electrochemical etching of a gold wire, insulating the etched wire with a varnish with the exception of the apex, and cutting down the apex by applying ultrashort (40 ns) etching pulses in an HCl solution. Cyclic voltammograms of a 0.10 M ferrocyanide solution recorded at the electrode showed that a series of etching pulses gradually reduced the diffusion-limited current at the electrode by etching its apex. Characterization by cyclic voltammetry and scanning electron microscopy revealed the transformation of a cone-shaped apex into a disk-shaped electrode with a radius of typically between 50 and 250 nm.

Journal Article↗
PubMed2003

Real-time impedance measurements during electrochemical experiments and their application to aniline oxidation.

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.

Journal Article↗
PubMed2003

Rational design of biologically important chemosensors: a novel receptor for selective recognition of acetylcholine over ammonium cations.

[structure: see text] In consideration of competition between cation-pi and hydrogen bond interaction forces, we designed a novel receptor, 1,3,5-tris(pyrrolyl)benzene, which shows high selectivity for acetylcholine (ACh). The selectivity of the receptor for ACh over other ammonium cations is demonstrated by the ion-selective electrode (ISE) method in buffer solution. The binding free energy of the receptor with ACh in chloroform solution is measured to be 3.65 kcal/mol in the presence of chloride anion by nuclear magnetic resonance spectroscopy, and that in water is estimated to be much greater ( approximately 6 kcal/mol).

Acetylcholine↗
PubMed2002

An electrochemically controllable nanomechanical molecular system utilizing edge-to-face and face-to-face aromatic interactions.

[formula: see text] A new molecular system, 2,11-dithio[4,4]metametaquinocyclophane containing a quinone moiety, was designed and synthesized. As the quinone moiety can readily be converted into an aromatic pi-system (hydroquinone) upon reduction, the nanomechanical molecular cyclophane system exhibits a large flapping motion like a molecular flipper from the electrochemical redox process. The conformational changes upon reduction and oxidation are caused by changes of nonbonding interaction forces (devoid of bond formation/breaking) from the edge-to-face to face-to-face aromatic interactions and vice versa, respectively.

Journal Article↗