Yoon-Bo Shim

Electrochemistry of Conductive Polymers VIII In Situ Spectroelectrochemical Studies of Polyaniline Growth Mechanisms

The earlier stage of the polymerization reaction of polyaniline has been studied. The results indicate that the nitrene cation appears to be a key intermediate species, which leads to all three possible dimers including a head-to-tail dimer (N-phenyl-p-phenylenediamine), a tail-to-tail dimer (benzidine), and a head-to-head dimer (hydrazobenzene). The oxidized forms of these dimers were all shown to be capable of growing polyaniline in the presence of aniline, even though aniline was not oxidized

Ultrasensitive and selective electrochemical diagnosis of breast cancer based on a hydrazine-Au nanoparticle-aptamer bioconjugate.

Human epidermal growth factor receptor 2 (HER2) and HER2-overexpressing breast cancer cells were detected using an electrochemical immunosensor combined with hydrazine and aptamer-conjugated gold nanoparticles (AuNPs). The sensor probe was fabricated by covalently immobilizing anti-HER2 onto a nanocomposite layer that was composed of self-assembled 2,5-bis(2-thienyl)-1H-pyrrole-1-(p-benzoic acid) (DPB) on AuNPs. The hydrazine-AuNP-aptamer bioconjugate, where the hydrazine reductant was directly attached onto AuNPs to avoid the nonspecific deposition of silver on the sensor surface, was designed and used to reduce silver ion for signal amplification selectively. The silver-stained target cells were visualized easily by the bare eye and an optical microscope, and the cells were quantitatively analyzed using stripping voltammetry. The parameters affecting the analytical response were optimized. The proposed sensor was capable of differentiating between HER2-positive breast cancer cells and HER2-negative cells. This method exhibited an excellent diagnosis method for the ultrasensitive detection of SK-BR-3 breast cancer cells in human serum samples with a detection limit of 26 cells/mL.

Gold Nanoparticles Doped Conducting Polymer Nanorod Electrodes: Ferrocene Catalyzed Aptamer-Based Thrombin Immunosensor

Au nanoparticles-doped conducting polymer nanorods electrodes (AuNPs/CPNEs) were prepared by coating Au nanorods (AuNRs) with a conducting polymer layer. The AuNRs were prepared through an electroless deposition method using the polycarbonate membrane (pore diameter, 50 nm, pore density, 6 x 10(8) pores/cm(2)) as a template. The AuNPs/CPNEs combining catalytic activity of ferrocene to ascorbic acid were used for the fabrication of an ultrasensitive aptamer sensor for thrombin detection. The AuNPs/3D-CPNEs were characterized employing cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Sandwiched immunoassay for alpha-human thrombin with NH(2)-functionalized-thrombin binding aptamer (Apt) immobilized on AuNPs/3D-CPNEs was studied through the electrocatalytic oxidation of ascorbic acid by the ferrocene moiety that was bound with an antithrombin antibody and attached with the Apt/3D-CPNEs probe through target binding. Various experimental parameters affecting thrombin detection were optimized, and the performance of the thrombin aptamer sensor was examined. The Apt/AuNPs/3D-CPNEs based thrombin sensor exhibited a wide dynamic range of 5-2000 ng L(-1) and a low detection limit of 5 ng L(-1) (0.14 pM). The selectivity and the stability of the proposed thrombin aptamer sensor were excellent, and it was tested in a real human serum sample for the detection of spiked concentrations of thrombin.

Label-free detection of kanamycin based on the aptamer-functionalized conducting polymer/gold nanocomposite.

Highly sensitive label-free detection of kanamycin is achieved with an aptamer sensor based on a conducting polymer/gold self-assembled nanocomposite. The sensor probe is fabricated by covalently immobilizing an in vitro selected DNA aptamer for kanamycin onto gold nanoparticle (AuNP)-comprised conducting polymer, poly-[2, 5-di-(2-thienyl)-1H-pyrrole-1-(p-benzoic acid)] (poly-DPB). The self-assembling of DPB on AuNP is investigated by TEM and UV-vis spectroscopy and the modification of the aptamer sensor is characterized using XPS and electrochemical impedance spectroscopy. The probe is applied to detect kanamycin by using voltammetric techniques. The sensor shows a pair of redox peaks around 0.26/ 0.08 V (vs. Ag/AgCl) for kanamycin captured by the aptamer-immobilized probe. The parameters that can affect the response, such as aptamer concentration, incubation time, temperature, and pH are optimized. The calibration plot shows a linear range from 0.05 μM to 9.0 μM kanamycin with a detection limit of 9.4±0.4 nM. The proposed aptamer sensor is examined with a real sample.

Direct Electrochemistry of Laccase Immobilized on Au Nanoparticles Encapsulated-Dendrimer Bonded Conducting Polymer: Application for a Catechin Sensor

The direct electrochemistry of laccase was promoted by Au nanoparticle (AuNP)-encapsulated dendrimers (Den), which was applied for the detection of catechin. To increase the electrical properties, AuNPs were captured in the interiors of the dendrimer (Den-AuNPs) as opposed to attachment at the periphery of dendrimer. To prepare Den-AuNPs, the Au(III) ions were first coordinated in the interior of dendrimer with nitrogen ligands and then reduced to form AuNPs. The size of AuNPs encapsulated within the interior of the dendrimer was determined to be 1.7 +/- 0.4 nm. AuNPs-encapsulated dendrimers were then used to covalently immobilize laccase (PDATT/ Den(AuNPs)/laccase) through the formation of amide bonds between carboxylic acid groups of the dendrimer and the amine groups of laccase. Each layer of the PDATT/Den(AuNPs)/laccase probe was characterized using CV, EIS, QCM, XPS, SEM, and TEM. The PDATT/Den(AuNPs)/laccase probe displayed a well-defined direct electron-transfer (DET) process of laccase. The quasi-reversible redox peak of the Cu redox center of the laccase molecule was observed at -0.03/+0.13 V vs Ag/AgCl, and the electron-transfer rate constant was determined to be 1.28 s (-1). A catechin biosensor based on the electrocatalytic process by direct electrochemistry of laccase was developed. The linear range and the detection limit in the catechin analysis were determined to be 0.1-10 and 0.05 +/- 0.003 microM, respectively. Interference effects from various phenolic and polyphenolic compounds were also studied, and the general applicability of the biosensor was evaluated by selective analysis of real samples of catechin.

Electrochemistry of Conductive Polymers XXII. Electrochemical and Spectroelectrochemical Studies of Polyazulene Growth and Its Characterization

Electrochemical growth of the polyazulene film and its electrochemical and spectroscopic properties were studied at platinum electrodes in acetonitrile by ac impedance and in situ spectroelectrochemical techniques. During polymer growth from the acetonitrile solution containing a millimolar concentration of azulene with 0.1 M tetra-n-butylammonium perchlorate as a supporting electrolyte, absorption bands were observed at 380, 480, and 680 nm. These bands were assigned to arise from neutral oligomers, their first oxidation products, and their second oxidation products, respectively. When the polymer film was oxidized in acetonitrile after the polymer is fully grown, absorption bands were red shifted significantly to 580 and around 800 nm, respectively, suggesting that the absorption bands are dependent on the chain lengths.

Degradation of Electrochemically Prepared Polypyrrole in Aqueous Sulfuric Acid

Detailed studies on the degradation reaction of electrochemically prepared polypyrrole have been conducted in an aqueous 1.0M H 2 SO 4 solution by anodic oxidation of the polymer film at platinum electrodes, and the results are reported. The degree of degradation was followed by recording cyclic voltammograms of polypyrrole films on the electrode as well as the absorbance of the resulting products in solutions. From ultraviolet, infrared, nuclear magnetic resonance, and mass spectra of the degradation product, we conclude that the major degradation product is a mixture of maleimide and succinimide with their respective ratio of about 1:1

Amplification strategy based on gold nanoparticle-decorated carbon nanotubes for neomycin immunosensors.

A novel amperometric immunosensor with an enhanced sensitivity for the detection of neomycin (Neo) was prepared by covalently immobilizing a monoclonal Neo antibody onto a new conducting polymer, poly-[2,5-di-(2-thienyl)-1H-pyrrole-1-(p-benzoic acid)] (pDPB), as a sensor probe. The probe was used to detect Neo in a sandwich-type approach, where the secondary antibody was attached to gold nanoparticle-decorated multi-wall carbon nanotubes labeled with hydrazine (Hyd-MWCNT(AuNP)-Ab(2)). Hydrazine on the conjugate served as a catalyst for the reduction of hydrogen peroxide, and the catalytic current was monitored at -0.45 V vs. Ag/AgCl. The performance of the immunosensor with and without AuNPs on the probe and the conjugate was compared. The parameters affecting the immunosensor response in terms of antibody dilution ratio, incubation time, pH, applied potential, and temperature were optimized. A linear dynamic range for Neo analysis was obtained between 10 ng/mL and 250 ng/mL with a detection limit of 6.76 ± 0.17 ng/mL. The proposed immunosensor was successfully applied to detect Neo content in real meat samples.

Immunosensors for detection of Annexin II and MUC5AC for early diagnosis of lung cancer.

Amperometric immunosensors were developed to diagnose lung cancer through the detection of Annexin II and MUC5AC. To fabricate the sensor probe, a conducting polymer (poly-terthiophene carboxylic acid; poly-TTCA) was electropolymerized onto a gold nanoparticle/glassy carbon electrode (AuNP/GCE) and a dendrimer (Den) was covalently bonded to the poly-TTCA through amide bond formation, where AuNPs were doped onto the dendrimer. To obtain the final sensor probe, an antibody (anti-Annexin II) and hydrazine (Hyd), which is a catalyst for the reduction of H(2)O(2) generated by glucose oxidase (GOx), were covalently attached onto the Den/AuNP-modified surface. Each surface was then characterized by SEM, impedance spectroscopy and XPS. The final sensor probe was examined before and after interaction with Annexin II and MUC5AC using impedance-spectroscopic, quartz crystal microbalance and amperometric methods. The performance of the immunosensor for the Annexin II was evaluated for the apical surface fluid labeled with GOx by the standard addition method. In this case, the detection limit of the proposed method was 0.051 ng/mL (k=3, n=5). The Annexin II concentration in the secretions collected from squamous metaplastic cells was determined to be 280+/-8.0 pg/mL (n=5).

A cytochrome c modified-conducting polymer microelectrode for monitoring in vivo changes in nitric oxide.

A nitric oxide (NO) microbiosensor based on cytochrome c (cyt c), a heme protein, immobilized onto a functionalized-conducting polymer (poly-TTCA) layer has been fabricated for the in vivo measurement of NO release stimulated by an abuse drug cocaine. Based on the direct electron transfer of cyt c, determination of NO with the cyt c-bonded poly-TTCA electrode was studied using cyclic voltammetry and chronoamperometry. Interferences for the sensory of NO by foreign species such as oxygen and hydrogen peroxide were minimized by covering a Nafion film on the modified electrode surface. Cyclic voltammograms taken using the cyt c/poly-TTCA electrode with NO solutions show a reduction peak at -0.7 V. The calibration plot showed the hydrodynamic range of 2.4-55.0 microM. The detection limit was determined to be 13+/-3 nM based on S/N=3. The microbiosensor was applied into the rat brain to test fluctuation of NO evoked by the abuse drug cocaine. The concentrations of NO levels by acute and repeated injections of cocaine were determined to be 1.13+/-0.03 and 2.13+/-0.05 microM, respectively, showing high sensitivity of the microbiosensor in monitoring NO concentrations in the in vivo intact brain.