Hui-Bog Noh

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.

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).

Investigation on the downregulation of dopamine by acetaminophen administration based on their simultaneous determination in urine

A highly sensitive and selective method is developed for the simultaneous detection of dopamine (DA) and acetaminophen (AP) by reactive blue-4 (RB4) dye entrapped poly1,5-diaminonaphthalne (polyDAN) composite film layer. The polyDAN-RB4 composite is electrochemically developed at glassy carbon electrode. The polymeric film, characterized by XPS and SEM is able to catalyze the oxidation of DA and AP. Two well-defined oxidation peaks are observed in the differential pulse voltammogram (DPV). The experimental parameters affecting the analytical performance are optimized in terms of RB4 concentration, temperature, and pH. The dynamic range for DA and AP analysis is between 0.1-150 and 0.2-164μM with a detection limit of 0.061±0.002 and 0.083±0.003μM, respectively. The anionic form of the polyDAN-RB4 composite repels common metabolites present in serum and urine, and hence no interference is observed. The effect of AP on the DA concentrations in urine is also studied after the oral administration of a single as well as multiple doses. The DA concentrations have been found to decrease nearly 50±3% after prolonged AP administration.

Separation and simultaneous detection of anticancer drugs in a microfluidic device with an amperometric biosensor

A simple and highly sensitive method for simultaneous detection of anticancer drugs is developed by integrating the preconcentration and separation steps in a microfluidic device with an amperometric biosensor. An amperometric detection with dsDNA and cardiolipin modified screen printed electrodes are used for the detection of anticancer drugs at the end of separation channel. The preconcentration capacity is enhanced thoroughly using field amplified sample stacking and field amplified sample injection techniques. The experimental parameters affecting the analytical performances, such as pH, temperature, buffer concentration, water plug length, and detection potential are optimized. A reproducible response is observed during multiple injections of samples with a RSD <5%. The calibration plots are linear with the correlation coefficient between 0.9913 and 0.9982 over the range of 2-60 pM. The detection limits of four drugs are determined to be between 1.2 (± 0.05) and 5.5 (± 0.3) fM. The applicability of the device to the direct analysis of anticancer drugs is successfully demonstrated in a real spiked urine sample. Device was also examined for interference effect of common chemicals present in real samples.

An amperometric nanobiosensor using a biocompatible conjugate for early detection of metastatic cancer cells in biological fluid

Metastasis is the major cause of cancer-associated death in humans, and its early diagnosis will help clinicians to develop suitable therapeutic strategies which may save life of cancer patients. In this direction, we designed an amperometric biosensor using a biocompatible conjugate to diagnose cancer metastasis by detecting epithelial cell adhesion molecule expressing metastatic cancer cells (Ep-MCCs). The sensor probe is fabricated by immobilizing monoclonal capture antibody (CapAnti) on the gold nanoparticles (AuNPs)/conducting polymer composite layer. The detection relies on a sandwich-type approach using a bioconjugate composed of reporter antibody (RepAnti), nanostructured collagen (nCOL), AuNPs, and hydrazine (Hyd) which served as a nonenzymatic electrocatalyst for the reduction of H2O2. The binding of Ep-MCCs with the sensor probe was confirmed using electrochemical impedance spectroscopy, cyclic voltammetry, and chronoamperometry. A dynamic range for the Ep-MCCs detection is determined between 45 and 100,000 Ep-MCCs/mL with the detection limit of 28±3 Ep-MCCs/mL. The proposed immunosensor is successfully applied to detect Ep-MCCs in serum and mixed cell samples and interferences due to nontarget cells and molecules present in the real sample matrix are also examined. The early stage of Ep-MCCs was examined by fluorescence-activated cell sorting assay, which confirms that the developed biosensor has detected Ep-MCCs in its early stage.

Total analysis of endocrine disruptors in a microchip with gold nanoparticles.

The development of a simple, sensitive, and direct method for the total analysis of certain endocrine disruptors was performed by integrating preconcentration steps to a separation step on a microchip through the modification of the field‐amplified sample stacking and field‐amplified sample injection steps. To improve the preconcentration and separation performances, the preconcentration and separation buffers were modified with citrate‐stabilized gold nanoparticles (AuNPs). For the detection of the separated samples, cellulose‐dsDNA/AuNPs‐modified carbon paste electrodes were used at the channel end. The experimental parameters affecting the analytical performances, such as the buffer concentration, water plug length, SDS concentration in the separation buffer, AuNPs concentration, preconcentration time, detection potential and electrode to channel distance, were examined. The detection limits of the test compounds were between 7.1 and 11.1 fM and that for 4‐pentylphenol was 7.1 (±1.1) fM. Dynamic ranges were in the range from 0.15 to 600.0 pM. The experiments with real samples were performed to evaluate the reliability of the proposed method.

Facile potentiostatic preparation of functionalized polyterthiophene-anchored graphene oxide as a metal-free electrocatalyst for the oxygen reduction reaction

The development of new catalysts for high-performance, cost-effective oxygen reduction is crucial in the commercialization of fuel cells. We demonstrate here the use of functionalized polyterthiophene-anchored graphene oxide (GO) composites as new non-metal catalysts for the oxygen reduction reaction. Different functional groups containing the monomers 3′-(2-aminopyrimidyl)-2,2′:5′,2′′-terthiophene (APT), 3′-(p-benzoic acid)-2,2′:5′,2′′-terthiophene (TBA) and 3′-(carboxylic acid)-2,2′:5′,2′′-terthiophene (TCA) were synthesized and polymerized with as-prepared GO to form complexes by a potential cycling method. The aminopyrimidyl groups on the poly(APT) backbone served as effective functional groups in the oxygen reduction reaction. The APT–GO complex was formed through hydrogen bonding and a ring-opening reaction of the epoxide group with the amine to form a new C–N bond. It was observed that the C–N bond in the polymer matrix was involved in the direct electrocatalytic reduction of O2 to H2O. The poly(APT–GO) composite showed much better tolerance to fuel cross-over and long-term electrode stability than commercially available Pt/C electrodes.

Selective nonenzymatic bilirubin detection in blood samples using a Nafion/Mn–Cu sensor

The specific detection of biological organics without the use of an enzyme is challenging, and it is crucial for analytical and clinical chemistry. We report specific nonenzymatic bilirubin detection through the catalytic oxidation of bilirubin molecule on the Nafion/Mn-Cu surface. The catalytic ability, true surface area, morphology, crystallinity, composition, and oxidation state of the sensor surface were assessed using voltammetry, coulometry, XPS, XRD, Brunauer-Emmett-Teller (BET), SEM, EDXS, and TOF-SIMS experiments. The results showed that the surface was composed of microporous Mn-Cu bimetallic crystal in flake shape with a large BET surface area (3.635 m(2)g(-1)), where the surface area and crystallinity mainly affected the sensor performance. Product analysis of the catalytic reaction on the sensor probe revealed a specific two-electron oxidation of dipyrromethane moiety to dipyrromethene in the bilirubin molecule. Experimental variables affecting the analysis of bilirubin were optimized in terms of probe composition, temperature, pH, and potential. At the optimized condition, the dynamic range was between 1.2 μM and 0.42 mM, which yielded the equation of ΔI (μA)=(1.03 ± 0.72)+(457.0 ± 4.03) [C] (mM) with 0.999 of correlation coefficient, and the detection limit was 25.0 ± 1.8 nM (n=5, k=3). The stability test, interference effects, and analysis of real clinical samples, human whole blood and certified serum samples were demonstrated to confirm the reliability of the proposed bilirubin sensor.

In vitro monitoring of i-NOS concentrations with an immunosensor: the inhibitory effect of endocrine disruptors on i-NOS release.

The amperometric immunosensor has demonstrated the toxicity of endocrine disrupters (EDs) through monitoring the in vitro i-NOS concentration change, where the antibody of inducible nitric oxide synthase (i-NOS) was immobilized on the conducting polymer-gold nanoparticles composite. The performance of the sensor and the experimental parameters affecting the immunoreaction were optimized. Neuronal cells treated by EDs decreased in the in vitro i-NOS concentration. The effect of bisphenol A (BPA) on the i-NOS concentration released in the cells was investigated with different incubation times, and the interfering by nonspecific binding species present in a neuronal cell lysate was also examined. Of all the tested EDs, BPA showed the inhibitoriest effect and the minimum inhibitory concentration of BPA affecting the i-NOS concentration was 0.09 ± 0.005 μM. The result shows that monitoring of i-NOS in the neuronal cells treated by EDs will be a useful method to evaluate the toxic behavior of EDs.

Catalytic activity of polymerized self-assembled artificial enzyme nanoparticles: applications to microfluidic channel-glucose biofuel cells and sensors

Synthesized catalysts composed of hydrazine-bearing conducting polymer nanoparticles (poly[2,2′:5′,2′′-terthiophene-3′-yl hydrazine] (polyTHyd) and (poly[4-([2,2′:5′,2′′-terthiophen]-3′-yl) phenyl) hydrazine] (polyTPHyd)) were prepared through self-assembling monomers on gold nanoparticles (monomers–AuNPs: dia. 7.5 ± 2.0 nm). The monomers self-assembled on AuNPs were electrochemically polymerized to form conducting polymer nanoparticles, which possessed an enzyme-like catalytic activity for the reduction of H2O2. The polymer-assembled nanoparticles immobilized on microfluidic channel electrodes revealed well defined direct electron transfer (DET) processes, which were observed at +54.5/−20.9 and +64.8/+3.6 mV for polyTHyd and polyTPHyd. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were immobilized on the carboxylated polyterthiophene (poly[2,2′:5′,2′′-terthiophene-3′-(p-benzoic acid)])-assembled nanoparticle layer to use as counter electrodes in the cells. The performances of microfluidic biofuel cells composed of a GOx-modified anode and cathodes of HRP and hydrazine-bearing polymer-assembled nanoparticles were compared using standard glucose, urine, and whole blood samples as fuels. The cell operated with a 10.0 mM glucose solution generated a maximum electrical power density of 0.78 ± 0.034 mW cm−2 and an open-circuit voltage of 0.48 ± 0.035 V. The cell was also examined as a glucose-sensing device, which had a dynamic range of 10.0 μM to 5.0 mM with a detection limit of 2.5 ± 0.2 μM under alternating current potential modulation.