Electrogravimetric and Electrochemical Ac Response of Polypyrrole Films

Haesik Yang,Hochun Lee,Juhyoun Kwak 한국분석과학회 1995 분석과학 Vol.8 No.4

Electrochemical Biosensors Using Redox Cycling

Haesik YANG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.4

Electrogravimetric and Electrochemical Ac Response of Polypyrrole Films

Yang, Haesik,Lee, Hochun,Kwak, Juhyoun 한국분석과학회 1995 분석과학 Vol.8 No.4

Ion transport of a polypyrrole/chloride (PPy/Cl) film and a polypyrrole/poly(styenesulfonate) (PPy/PSS) film as a function of applied dc potential was investigated by employing electrogravimetric impedance technique and electrochemical impedance technique. The cation and anion contribution to the whole charge capacitance and the diffusion coefficients of cation and anion in a PPy/PSS film were calculated by fitting the electrogravimetric impedance data with proposed model circuit. The diffusion coefficients of $Na^+$ in a 1 M $NaClO_4$ solution are over 1 order of magnitude larger than those of $ClO{_4}^-$, and $ClO{_4}^-$ contribution to charge compensation decreases as dc potential lowers. The charge compensation of a PPy/Cl film ir a 1 M CsCl solution is carried out largely by $Cl^-$ at 0.2 V vs. Ag/AgCl and by $Cs^+$ as well as $Cl^-$ at -0.4 V.

Enzyme-based ultrasensitive electrochemical biosensors

Elsevier 2012 Current opinion in chemical biology Vol.16 No.3

Sensitive Phenol Detection Using Tyrosinase‐Based Phenol Oxidation Combined with Redox Cycling of Catechol

Noh, Soodong,Yang, Haesik WILEY‐VCH Verlag 2014 Electroanalysis Vol.26 No.12

<P><B>Abstract</B></P><P>This paper reports sensitive phenol detection using (i) tyrosinase (Tyr)‐based oxidation of phenol to catechol, combined with (ii) electrochemical‐chemical‐chemical (ECC) redox cycling involving Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP>, catechol, and tris(2‐carboxyethyl)phosphine (TCEP). Phenol is converted into catechol by Tyr in the presence of dissolved O<SUB>2</SUB>. Catechol then reacts with Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP>, generating <I>o</I>‐benzoquinone and Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>2+</SUP>. <I>o</I>‐Benzoquinone is reduced back to catechol by TCEP, and Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>2+</SUP> is accumulated over the course of the incubation. When Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>2+</SUP> is electrochemically oxidized to Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP>, ECC redox cycling occurs. For simple phenol detection, bare ITO electrodes are used without modifying the electrodes with Tyr. The detection limit for phenol in tap water using Tyr‐based oxidation combined with ECC redox cycling is ca. 10<SUP>−9</SUP> M, while that using only Tyr‐based oxidation is ca. 10<SUP>−7</SUP> M.</P>

Effects of Aging on Electrocatalytic Activities of Pt and Pd Nanoparticles

Dutta, Gorachand,Yang, Haesik The Korean Electrochemical Society 2016 Journal of electrochemical science and technology Vol.7 No.1

Although the time dependences of the electrocatalytic activities of Pt and Pd nanoparticles during electrochemical operations have been widely studied, the time dependences under nonpolarized conditions have never been investigated in depth. This study reports the changes in the electrocatalytic activities of Pt and Pd nanoparticles with aging in air and in solution. Pt (or Pd) nanoparticle-modified electrodes are obtained by adsorbing citrate-stabilized Pt (or Pd) nanoparticles on amine-modified indium-tin oxide (ITO) electrodes, or by electrodeposition of Pt (or Pd) nanoparticles on ITO electrodes. The electrocatalytic activities of freshly prepared Pt and Pd nanoparticles in the oxygen reduction reaction slowly decrease with aging. The electrocatalytic activities decrease more slowly in solution than in air. An increase in surface contamination may cause electrocatalytic deactivation during aging. The electrocatalytic activities of long-aged Pt (or Pd) nanoparticles are significantly enhanced and recovered by NaBH₄ treatment.

Effect of Different Pretreatments on Indium-Tin Oxide Electrodes

Choi, Moonjeong,Jo, Kyungmin,Yang, Haesik Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.2

The effect of pretreatment on indium-tin oxide (ITO) electrodes has been rarely studied, although that on metal and carbon electrodes has been enormously done. The electrochemical and surface properties of ITO electrodes are investigated after 6 different pretreatments. The electrochemical behaviors for oxygen reduction, $Ru(NH_3){_6}^{3+}$ reduction, $Fe(CN){_6}^{3-}$ reduction, and p-hydroquinone oxidation are compared, and the surface roughness, hydrophilicity, and surface chemical composition are also compared. Oxygen reduction, $Fe(CN){_6}^{3-}$ reduction, and p-hydroquinone oxidation are highly affected by the type of the pretreatment, whereas $Ru(NH_3){_6}^{3+}$ reduction is almost independent of it. Interestingly, oxygen reduction is significantly suppressed by the treatment in an HCl solution. The changes in surface roughness and composition are not high after each pretreatment, but the change in contact angle is substantial in some pretreatments.

Glucose-Oxidase Label-Based Redox Cycling for an Incubation Period-Free Electrochemical Immunosensor

Singh, Amardeep,Park, Seonhwa,Yang, Haesik American Chemical Society 2013 ANALYTICAL CHEMISTRY - Vol.85 No.10

<P>Catalytic reactions of enzyme labels in enzyme-linked immunosorbent assays require a long incubation period to obtain high signal amplification. We present herein a simple immunosensing scheme in which the incubation period is minimized without a large increase in the detection limit. This scheme is based on electrochemical-enzymatic (EN) redox cycling using glucose oxidase (GOx) as an enzyme label, Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP> as a redox mediator, and glucose as an enzyme substrate. Fast electron mediation of Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP> between the electrode and the GOx label attached to the electrode allows high signal amplification. The acquisition of chronocoulometric charges at a potential in the mass transfer-controlled region excludes the influence of the kinetics of Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>2+</SUP> electrooxidation and also facilitates high signal-to-background ratios. The reaction between reduced GOx and Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP> is rapid even in air-saturated Tris buffer, where the faster competitive reaction between reduced GOx and dissolved oxygen also occurs. The direct electrooxidation of glucose at the electrode and the direct electron transfer between glucose and Ru(NH<SUB>3</SUB>)<SUB>6</SUB><SUP>3+</SUP> that undesirably increase background levels occur relatively slowly. The detection limit for the EN redox cycling-based detection of cancer antigen 125 (CA-125) in human serum is slightly higher than 0.1 U/mL for the incubation period of 0 min, and the detection limits for the incubation periods of 5 and 10 min are slightly lower than 0.1 U/mL, indicating that the detection limits are almost similar irrespective of the incubation period and that the immunosensor is highly sensitive.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2013/ancham.2013.85.issue-10/ac400573j/production/images/medium/ac-2013-00573j_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac400573j'>ACS Electronic Supporting Info</A></P>

Study of SU-8 to make a Ni master-mold: Adhesion, sidewall profile, and removal

Kim, Sung-Jin,Yang, Haesik,Kim, Kyuwon,Lim, Yong Taik,Pyo, Hyeon-Bong WILEY-VCH Verlag 2006 Electrophoresis Vol.27 No.16

<P>For disposable microfluidic devices, easy and inexpensive fabrication is essential. Consequently, replication of microfluidic devices, using injection molding or hot embossing, from a master-mold is widely used. However, the conventional master-mold fabrication technique is unsatisfactory in terms of time and costs. In this regard, direct Ni growth (electroplating) from a back plate is promising when the photoresist is well-defined. Here, we demonstrate the use of SU-8 as a photoresist to define the Ni-growth region. We accomplish this application by focusing on the adhesion, the sidewall profile, and the removal of SU-8: the adhesion is enhanced by controlling the exposure dose, the soft-baking time, and by choosing the adhesion-promoting layer; the sidewall profile is regulated by selecting the intensity of each exposed wavelength, showing an aspect ratio of up to 20.9; and, easy removal is achieved by choosing a proper photoresist-stripper. Using the master-mold fabricated by this method, we test the mechanical stability of the features according to the aspect ratio and length; in the hot embossing process, the features are stable in the aspect ratio of up to 5.8 at a length of 200 µm. In addition, the plastic devices fabricated from this method are applied to the passive stop valves, showing a capillary pressure (−0.2 to −7.2 kPa).</P>

Electrochemical Immunosensing Chip Using Selective Surface Modification, Capillary-Driven Microfluidic Control, and Signal Amplification by Redox Cycling

Kim, Byung-Kwon,Yang, Sang-Youn,Aziz, Md. Abdul,Jo, Kyungmin,Sung, Daekyung,Jon, Sangyong,Woo, Han Young,Yang, Haesik Wiley (John WileySons) 2010 Electroanalysis Vol.22 No.19