Electrodeposition of paracetamol oxide for intelligent portable ratiometric detection of nicotine and ethyl vanillin ß-D-glucoside.

Herein, the electrodeposition of paracetamol oxide (PA ox) for the intelligent portable ratiometric detection of nicotine (NIC) and ethyl vanillin ß-D-glucoside (EVG) is reported. PA ox electrodeposited on a screen-printed carbon electrode (SPCE) was used as a new fixed state ratiometric reference probe. A portable electrochemical workstation combined with a smart phone was applied as an intelligent portable electrochemical sensing platform. The sensor was studied by scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR), ultraviolet-visible spectrophotometry (UV-vis), theoretical calculation, chronoamperometry, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV). Under optimized conditions, the detection range of NIC is 10-200 µmol L-1, and the detection limit is 0.256 µmol L-1. The detection range of EVG was 10-180 µmol L-1, and the detection limit was 0.058 µmol L-1. The sensor can realize the real-time detection of NIC and EVG concentration in cigarette samples quickly and accurately, and has good anti-interference, repeatability and stability.

A colorimetric sensor with dual-ratio and dual-mode for detection of nicotine in tobacco samples.

Nicotine (NIC) is a harmful substance, drug, pesticide and chemical that is widely found in tobacco. It has carcinogenic, teratogenic and neurotoxic effects that have raised serious concerns. Herein, a colorimetric sensor with dual-ratio and dual-mode for the detection of NIC in tobacco samples was reported. The localized surface plasmon resonance signals of gold nanoparticles (AuNPs) and AuNPs-NIC are used as dual-ratio signals. The absorbance ratio of NIC to AuNPs or the absorbance ratio of NIC to AuNPs-NIC and the wavelength shift value of AuNPs-NIC are applied as dual-mode. Transmission electron microscopy, energy dispersive spectroscopy, dynamic light scattering spectroscopy, ultraviolet-visible spectrophotometry, cyclic voltammetry, and potentiostatic methods were used to characterize the sensor. Further analysis of NIC was conducted through morphological fitting and theoretical calculations. Under optimal conditions, the sensor shows a wide linear range of 5-500 µM. The detection limits for NIC are 2.48 µM, 1.63 µM and 1.34 µM, respectively. The experimental result shows that the dual-ratio signal of AuNPs and AuNPs-NIC has good selectivity and sensitivity, and can effectively reduce the interference of impurities on NIC detection. And the dual-mode of detection for NIC improves the accuracy and comparability of the result significantly. In addition, the proposed sensor was also applied to test NIC in tobacco samples with satisfactory recovery.

One-step synthesis of triethanolamine-capped Pt nanoparticle for colorimetric and electrochemiluminescent immunoassay of SARS-CoV spike proteins.

Platinum nanoparticles (PtNPs) have been attracted worldwide attention due to their versatile application potentials, especially in the catalyst and sensing fields. Herein, a facile synthetic method of triethanolamine (TEOA)-capped PtNPs (TEOA@PtNP) for electrochemiluminescent (ECL) and colorimetric immunoassay of SARS-CoV spike proteins (SARS-CoV S-protein, a target detection model) is developed. Monodisperse PtNPs with an average diameter of 2.2 nm are prepared by a one-step hydrothermal synthesis method using TEOA as a green reductant and stabilizer. TEOA@PtNPs can be used as a nanocarrier to combine with antigen by the high-affinity antibody, which leads to a remarkable inhibition of electron transfer efficiency and mass transfer processes. On the basis of its peroxidase-like activity and easy-biolabeling property, the TEOA@PtNP can be used to establish a colorimetric immunosensor of SARS-CoV S-protein thought catalyzing the reaction of H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Especially, the Ru(bpy)3 2+ ECL reaction is well-achieved with the TEOA@PtNPs due to their great conductivity and loading abundant TEOA co-reactants, resulting in an enhancing ECL signal in immunoassay of SARS-CoV S-protein. As a consequence, two proposed methods could achieve sensitive detection of SARS-CoV S-protein in wide ranges, the colorimetric and ECL detection limits were as low as 8.9 fg /mL and 4.2 fg /mL (S/N = 3), respectively. We believe that the proposed colorimetric and ECL immunosesors with high sensitivity, good reproducibility, and good stability will be a promising candidate for a broad spectrum of applications.

One-Step Co-Electrodeposition of Copper Nanoparticles-Chitosan Film-Carbon Nanoparticles-Multiwalled Carbon Nanotubes Composite for Electroanalysis of Indole-3-Acetic Acid and Salicylic Acid.

A sensitive simultaneous electroanalysis of phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA) based on a novel copper nanoparticles-chitosan film-carbon nanoparticles-multiwalled carbon nanotubes (CuNPs-CSF-CNPs-MWCNTs) composite was reported. CNPs were prepared by hydrothermal reaction of chitosan. Then the CuNPs-CSF-CNPs-MWCNTs composite was facilely prepared by one-step co-electrodeposition of CuNPs and CNPs fixed chitosan residues on modified electrode. Scanning electron microscope (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) were used to characterize the properties of the composite. Under optimal conditions, the composite modified electrode had a good linear relationship with IAA in the range of 0.01-50 µM, and a good linear relationship with SA in the range of 4-30 µM. The detection limits were 0.0086 µM and 0.7 µM (S/N = 3), respectively. In addition, the sensor could also be used for the simultaneous detection of IAA and SA in real leaf samples with satisfactory recovery.

Simultaneous Electrochemical Sensing of Indole-3-Acetic Acid and Salicylic Acid on Poly(L-Proline) Nanoparticles-Carbon Dots-Multiwalled Carbon Nanotubes Composite-Modified Electrode.

Sensitive simultaneous electrochemical sensing of phytohormones indole-3-acetic acid and salicylic acid based on a novel poly(L-Proline) nanoparticles-carbon dots composite consisting of multiwalled carbon nanotubes was reported in this study. The poly(L-Proline) nanoparticles-carbon dots composite was facilely prepared by the hydrothermal method, and L-Proline was used as a monomer and carbon source for the preparation of poly(L-Proline) nanoparticles and carbon dots, respectively. Then, the poly(L-Proline) nanoparticles-carbon dots-multiwalled carbon nanotubes composite was prepared by ultrasonic mixing of poly(L-Proline) nanoparticles-carbon dots composite dispersion and multiwalled carbon nanotubes. Scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy, energy dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry were used to characterize the properties of the composite. poly(L-Proline) nanoparticles were found to significantly enhance the conductivity and sensing performance of the composite. Under optimal conditions, the composite-modified electrode exhibited a wide linear range from 0.05 to 25 µM for indole-3-acetic acid and from 0.2 to 60 µM for salicylic acid with detection limits of 0.007 µM and 0.1 µM (S/N = 3), respectively. In addition, the proposed sensor was also applied to simultaneously test indole-3-acetic acid and salicylic acid in real leaf samples with satisfactory recovery.

One-Step Electrochemical Growth of 2D/3D Zn(II)-MOF Hybrid Nanocomposites on an Electrode and Utilization of a PtNPs@2D MOF Nanocatalyst for Electrochemical Immunoassay.

To date, two-dimensional (2D) and three-dimensional (3D) metal organic frameworks (MOFs) have been promising materials for applications in electrocatalysis, separation, and sensing. However, the exploration of a simple method for simultaneous fabrication of 2D/3D MOFs on a surface remains challenging. Herein, a one-step and in situ electrosynthesis strategy for fabrication of 2D Hemin-bridged MOF sheets (Hemin-MOFs) or 2D/3D Zn(II)-MOF hybrid nanocomposites on an electrode is reported. It exhibits varied morphologies at different electrodeposition times and attains a 2D/3D complex morphology by adding 1,3,5-benzenetricarboxylic acid (H3BTC) as an organic ligand. The morphology and size of 2D Hemin-MOFs are important factors that influence their performance. Since Pt nanoparticles (PtNPs) are grown on 2D Hemin-MOF sheets, this composite can serve as the peroxidase mimics and PtNPs can act as an anchor to capture the antibody. Therefore, this hybrid nanosheet-modified electrode is used as an electrochemical sensing platform for ultrasensitive pig immunoglobulin G (IgG) and the surface-protective antigen (Spa) protein of Erysipelothrix rhusiopathiae immunodetection. Moreover, this work provides a new avenue for the electrochemical synthesis of 2D/3D MOF hybrid nanocomposites with a high surface area and biomimetic catalysts.

An antifouling polymer for dynamic anti-protein adhesion analysis by a quartz crystal microbalance.

Nowadays, the non-specific adsorption of biomolecules is a key issue in numerous fields. Herein, an improved antifouling molecule was synthesized by grafting phenol with oligopoly (ethylene glycol), named (4-(2-(2-ethoxyethoxy) ethoxy) phenol (EEP). An ideal antifouling polymer coating (PEEP) was synthesized by the mechanism of electropolymerization of phenol. Quartz crystal microbalance (QCM), a sensitive mass sensor, was used to dynamically monitor both the modification and anti-protein adhesion (with bovine serum albumin as the model) process. Quantitatively, less proteins were observed to adhere to the modified electrode (277.8 ng for bare GCE and 8.88 ng for the modified GCE). Fourier transform infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), and electrochemical methods were used to study the coatings in detail. In this study, EEP was synthesized for the electrochemical preparation of an antifouling coating and characterized by QCM and electrochemical methods. The mild preparation environment (lower potential window and in phosphate buffered saline) and one-step method enable potential applications of PEEP in the field of biomaterials and biosensors.

Dispersing gold nanoparticles on thiolated polyaniline-multiwalled carbon nanotubes for development of an indole-3-acetic acid amperometric immunosensor.

An amperometric immunosensor based on new thiolated bionanocomposite with a high dispersion of gold nanoparticles (AuNPs) for the sensitive detection of indole-3-acetic acid (IAA) is being reported herein. Briefly, a thiolated nanocomposite was prepared via the microwave-assisted thiol-ene reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) with oxidized polyaniline (PANI), which was synthesized in the presence of multiwalled carbon nanotubes (MWCNTs), yielding thiolated polyaniline (TPANI)-MWCNTs. Further, AuNPs were deposited on the TPANI-MWCNTs by microwave-assisted method to obtain a AuNPs/TPANI-MWCNTs nanocomposite. Finally, the thiolated bionanocomposite film was constructed via the specific chemical reaction between boronic acid functionalized AuNPs and the vicinal diol functionalized AuNP labeled immunoglobulin G (IgG-AuNPs). The change in the reduction peak current of Fe(CN)6 3- was used to monitor the immunoreaction between IAA and antibody. The TPANI-MWCNT nanocomposites uniformly disperse AuNPs, IgG-AuNPs and anti-IAA-AuNPs, leading to the amplification of the signal of the immunosensor. Fourier transform infrared spectra (FTIR), cyclic voltammetry (CV), transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and differential pulse voltammetry (DPV) were used to characterize the nanocomposite film and the stepwise modification of the immunosensor. The prepared thiolated bionanocomposite material has good biocompatibility, a highly uniform dispersion of the AuNPs with a narrow size distribution as verified by TEM, and high load/activity of the immobilized antibody proved via DPV. The fabricated IAA amperometric immunosensor not only exhibits a good linear arrange from 1.0 pg mL-1 to 10 ng mL-1 with the limit of detection of 0.97 pg mL-1 (S/N = 3), but also possesses good selectivity, reproducibility and stability for the detection of IAA.

Chemical pre-reduction and electro-reduction guided preparation of a porous graphene bionanocomposite for indole-3-acetic acid detection.

A porous graphene (PG) bionanocomposite of PG, gold nanoparticles (AuNPs) and anti-indole-3-acetic acid (anti-IAA) antibody for sensitive and label-free amperometric immunoassay of IAA was reported. A PG film was produced by a pre-reduction/electrochemical reduction process on a glassy carbon electrode (GCE) and then a homogeneous AuNPs layer electrodeposition on the PG film. The anti-IAA antibody was immobilized onto the AuNPs through electrostatic adsorption and covalent conjugation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), elecro-chemical impedance spectroscopy (EIS), ultraviolet visible spectroscopy (UV-vis) and differential pulse voltammetry (DPV) were used to characterize the PG film and the stepwise modification of the immunosensor. The electrochemical immunosensor exhibited a wide linear range from 2 × 10-11 to 2 × 10-8 g mL-1 with a detection limit of 0.016 ng mL-1 (S/N = 3) and showed significant linearity R2 = 0.9970. In addition, the proposed immunosensor showed acceptable selectivity and has been applied to the determination of IAA in the extract samples of several plant seeds with acceptable relative derivation (%) ranging from -5.25% to 4.24% between the immunosensor and high performance liquid chromatography. The proposed chemical pre-reduction and electro-reduction guided protocol can be extended to the preparation of many other functionalized PG nanocomposite films for wide applications.

E-Selective synthesis of vinyl sulfones via silver-catalyzed sulfonylation of styrenes.

An efficient and highly E-selective protocol for the synthesis of vinyl sulfones is described. This simple protocol demonstrates the first synthesis of vinyl sulfones via a silver-catalyzed C-S bond coupling reaction. In addition, the success of the reaction was found to be critically dependent on the use of TEMPO as the additive.

Enhanced electrocatalytic performance of platinum nanoparticles on thiolated polyaniline-multiwalled carbon nanotubes for methanol oxidation.

Pt nanoparticles (PtNPs) well-dispersed on thiolated polyaniline (TPANI)-multiwalled carbon nanotubes (MWCNTs) were prepared for enhanced electrocatalytic oxidation of methanol in acidic media. Briefly, the preparation of nanocomposites was carried out via microwave-assisted thiol-ene reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) with oxidized PANI, which was synthesized in the presence of MWCNTs, yielding TPANI-MWCNTs; then, PtNPs were deposited on TPANI-MWCNTs by a microwave-assisted method to obtain PtNPs/TPANI-MWCNT nanohybrids. Fourier transform infrared spectroscopy, cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and inductively coupled plasma-atom emission spectroscopy were used to study relevant nanohybrid properties. TEM showed that PtNPs were well dispersed on TPANI-MWCNTs. TGA showed that PtNPs/TPANI-MWCNTs exhibited better thermal stability than PtNPs/TPANI-MWCNTs and PtNPs/MWCNTs. CV studies showed that PtNPs/TPANI-MWCNT-modified glassy carbon electrode (GCE) exhibited a larger electrochemically active surface area and higher electrocatalytic performance toward methanol electro-oxidation compared with those of PtNPs/PANI-MWCNTs/GCE and PtNPs/MWCNTs/GCE. Also, the PtNPs/TPANI-MWCNTs/GCE electrode possessed high stability and maintained 86% of its initial catalytic activity after 1000-cycle CV in 1.0 M CH3OH + 0.5 M H2SO4.

Effect of wetland plants and bacterial inoculation on dissipation of phenanthrene.

This study attempts to evaluate the capacity of wetland plants' ability to dissipate phenanthrene (PHE) under waterlogged conditions. The results indicate that Typha latifolia and Vetiveria zizanioides may efficiently degrade PHE, and were much more effective when under combined plant cultivation with the inoculation of Pseudomonas frederiksbergensis (ATCC BAA-257) . Concentrations of PHE declined from 200 to less than 52 mg kg-1 in all treatments with plant cultivation. At the end of the experimental period, PHE was undetectable in combined plant cultivation in the presence of bacteria inoculation. Microbial biomass C(carbon), N(nitrogen), and P(phosphate) were significantly different (p < 0.05) in the presence and absence of bacteria inoculation with bacteria inoculation significantly (p < 0.05) increased microbial biomass P. The presence of bacteria inoculation and different plant species significantly (p < 0.05) decreased the PHE concentrations in the microcosms. The inoculation of bacteria and release of exudates from plant roots further enhanced the dissipation of PHE in sand. Concentrations of citric and malic acids were decreased up to 69% in bacteria-inoculated treatments, showing large citric and malic acids serving as a food source and growth substrate for bacteria.

Effective covalent immobilization of quinone and aptamer onto a gold electrode via thiol addition for sensitive and selective protein biosensing.

Effective covalent immobilization of quinone and aptamer onto a gold electrode via thiol addition (a Michael addition) for sensitive and selective protein (with thrombin as the model) biosensing is reported, with a detection limit down to 20 fM for thrombin. Briefly, the thiol addition reaction of a gold electrode-supported 1,6-hexanedithiol (HDT) with p-benzoquinone (BQ) yielded BQ-HDT/Au, and the similar reaction of thiolated thrombin aptamer (TTA) with activated BQ-HDT/Au under 0.3V led to formation of a gold electrode-supported novel electrochemical probe TTA-BQ-HDT/Au. The thus-prepared TTA-BQ-HDT/Au exhibits a pair of well-defined redox peaks of quinone moiety, and the TTA-thrombin interaction can sensitively decrease the electrochemical signal. Herein the thiol addition acts as an effective and convenient binding protocols for aptasensing, and a new method (electrochemical conversion of Michael addition complex for signal generation) for the fabrication of biosensor is presented. The cyclic voltammetry (CV) was used to characterize the film properties. In addition, the proposed amperometric aptasensor exhibits good sensitivity, selectivity, and reproducibility. The aptasensor also has acceptable recovery for detection in complex protein sample.

Thiol-ene chemistry guided preparation of thiolated polymeric nanocomposite for anodic stripping voltammetric analysis of Cd2+ and Pb2+.

We report on the thiol-ene chemistry guided preparation of a novel thiolated polymeric nanocomposite involving polyaniline (PANI), a functionalized thiol, e.g., sulfur-rich 2,5-dimercapto-1,3,4-thiadiazole (DMcT), and multiwalled carbon nanotubes (MWCNTs) for the sensitive differential pulse anodic stripping voltammetric determination of Cd(2+) and Pb(2+) on a glassy carbon electrode (GCE). Briefly, the thiol-ene reaction of a thiol with oxidized PANI that was chemically synthesized in the presence of solution-dispersed acidified MWCNTs yielded a thiolated polymeric nanocomposite of thiol-PANI/MWCNTs. The thiols examined include DMcT, 1,6-hexanedithiol and ß-mercaptoethanol. Quartz crystal microbalance, cyclic voltammetry, scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were used for film characterization and process monitoring. Under the optimized conditions, the obtained Bi/Nafion/DMcT-PANI/MWCNTs/GCE can sensitively sense Cd(2+) and Pb(2+) with limits of detection of 0.01 and 0.04 µg L(-1), respectively.

Preparation of thiolated polymeric nanocomposite for sensitive electroanalysis of dopamine.

We report on the thiol-ene chemistry guided preparation of novel thiolated polymeric nanocomposite films of abundant anionic carboxylic groups for electrostatic enrichment and sensitive electroanalysis of cationic dopamine (DA) in neutral solution. Briefly, the thiol-ene nucleophilic reaction of a carboxylated thiol with oxidized polypyrrole (PPy), which was electrosynthesized on an Au electrode in the presence of solution-dispersed acidified multiwalled carbon nanotubes (MWCNTs), produced an a PPy-thiol-MWCNTs/Au electrode, and the PPy can be electrochemically overoxidized (OPPy) to form an OPPy-thiol-MWCNTs/Au electrode. The carboxylic groups of the polymeric nanocomposite film originate from the acidified MWCNTs, PPy-tethered carboxylated thiol, and OPPy. The carboxylated thiols examined are mercaptosuccinic acid (MSA) and thioglycolic acid, with ß-mercaptoethanol as a control. Electrochemical quartz crystal microbalance, scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were used for film characterization and process monitoring. Under the optimized condition, the differential pulse voltammetry peak current of DA oxidation at OPPy-MSA-MWCNTs/Au electrode is linear with DA concentration from 1.00×10(-9) to 2.87×10(-6) mol L(-1), with a limit of detection of 0.4 nmol L(-1), good anti-interferent ability and stability.

Fabrication of a chitosan/glucose oxidase-poly(anilineboronic acid)-Au(nano)/Au-plated Au electrode for biosensor and biofuel cell.

Enzyme immobilization is one of the key factors in constructing high-performance enzyme biosensors and biofuel cells (BFCs). Herein, we propose a new protocol for efficient immobilization of a glycoprotein enzyme based on the interaction of the 1, 2- or 1, 3-diols in the glycoprotein with a boronic acid functionalized monomer. Briefly, casting a mixture of glucose oxidase (GOx) and anilineboronic acid (ABA) followed by a NaAuCl(4) solution to an Au-plated Au electrode surface yielded a GOx-poly(ABA) (PABA)-gold nanoparticle (Au(nano)) bionanocomposite, and chitosan (CS) was then cast and air-dried. In the present protocol, the small-sized Au(nano) or Au subnanostructures can form near/on the enzyme molecule, which greatly promotes the electron transfer of enzymatic reaction and enhances the amperometric responses. The thus-prepared CS/GOx-PABA-Au(nano)/Au-plated Au electrode worked well in the first-/second generation biosensing modes and as a bioanode in a monopolar biofuel cell, with analytical or cell-power performance superior to those of most analogues hitherto reported.

35 MHz quartz crystal microbalance and surface plasmon resonance studies on the binding of angiotensin converting enzyme with lisinopril.

Angiotensin converting enzyme (ACE) plays a pivotal role in blood pressure regulation, and its interaction with an ACE inhibitor (ACEI) is an important research topic for treatment of hypertension. Herein, a low reagent consumption, multiparameter and highly sensitive quartz crystal microbalance (QCM) at 35-MHz fundamental frequency was utilized to monitor in situ the binding process of solution lisinopril (LIS, a carboxylic third-generation ACEI) to ACE adsorbed at a 1-dodecanethiol (C12SH)-modified Au electrode. From the QCM data, the binding molar ratio (r) of LIS to adsorbed ACE was estimated to be 2.3:1, and the binding and dissociation rate constants (k(1) and k(-1)) and the binding equilibrium constant (K(a)) were estimated to be k(1)=4.1×10(6) L mol(-1) s(-1), k(-1)=7.3×10(-3) s(-1) and K(a)=5.62×10(8) L mol(-1), respectively. Comparable qualitative and quantitative results were also obtained from separate experiments of cyclic voltammetry, electrochemical impedance spectroscopy and surface plasmon resonance measurements.

Electrochemical quartz crystal microbalance study of covalent tethering of carboxylated thiol to polyaniline for electrocatalyzed oxidation of ascorbic acid in neutral aqueous solution.

The electrochemical quartz crystal microbalance (EQCM) was used to study the electrosyntheses and electrochemical properties of two kinds of polyaniline (PANI)-thiol composite films in aqueous solutions, which were prepared by covalent binding of a thiol to the oxidized forms of PANI (PANI(post)-thiol, protocol A), and electropolymerization of aniline in the presence of a thiol (PANI(poly)-thiol, protocol B), respectively. The thiols involved were mercaptosuccinic acid (MSA), thioglycolic acid (TGA) and beta-mercaptoethanol (ME). The PANI(post)-thiol binding processes were monitored in situ with the EQCM, giving molar binding ratios (r, thiol vs. aniline unit of the polymer) of ca. 0.50 at saturation for these thiols. Both PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols showed a controllable electroactivity of the PANI moiety in neutral even weakly alkaline phosphate buffer solutions (PBS), with maximum electroactivity roughly at r = 0.11 for PANI(post)-MSA or at r = 0.21 for PANI(post)-TGA. The PANI-thiol interaction was also supported by experiments of scanning electron microscopy, electrochemical surface plasmon resonance, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the interaction mechanism is briefly discussed. The PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols effectively electrocatalyzed the oxidation of ascorbic acid in pH = 7.3 PBS, and the PANI(post)-thiol exhibited electrocatalytic activity higher than the relevant PANI(poly)-thiol under our experimental conditions. The covalent anchoring of anionic thiol groups on the PANI backbone to prepare electroactive PANI in neutral solutions is conceptually new and may be extended to the development of new functional materials from many other conducting polymers and thiols for wide applications in catalysis, biosensing, molecular electronics, and so on.

Electrodeposition of carbon nanotubes-chitosan-glucose oxidase biosensing composite films triggered by reduction of p-benzoquinone or H2O2.

We report here on the electroreduction of p-benzoquinone (BQ) or H2O2 as a new trigger for simple, fast, uniform, and controllable electrodeposition of chitosan (CS) hydrogels and biosensing nanocomposite films of CS, multiwalled carbon nanotubes (MWCNTs), and glucose oxidase (GOD). The multiparameter electrochemical quartz crystal microbalance (EQCM) based on crystal electroacoustic impedance analysis was used to dynamically monitor the deposition processes. When the EQCM Au electrode was immersed in a weakly acidic solution (here pH 5.1 acetic buffer) containing BQ (or H2O2) and CS, the proton consumption during BQ (or H2O2) electroreduction increased the local solution pH near the electrode surface and led to the deposition of CS hydrogel on the electrode surface at local pH near and above the pKa value of CS. The concentration of BQ (or H2O2) required for CS electrodeposition was theoretically evaluated based on an electrogenerated base-to-acid titration model and supported by experiments. Co-deposition of GOD and MWCNTs with the CS hydrogel was achieved, and the resulting MWCNTs-CS-GOD nanocomposite films were demonstrated for glucose biosensing. The MWCNTs-CS-GOD enzyme electrode prepared by BQ reduction exhibited a current sensitivity of 6.7 microA mM-1 cm-2 to glucose, and the linear range for glucose detection at 0.7 V vs SCE was from 5 microM to 8 mM, with a detection limit of 2 microM and a Michaelis-Menten constant of 6.8 mM. The BQ-electroreduction protocol exhibited the best sensor performance, as compared with H2O2-reduction and previously reported water-reduction values. The present protocol via electroreduction of a deliberately added oxidant that is accompanied by a local pH change is highly recommended for wider applications in pH-dependent deposition of other films.

Electrochemical quartz crystal impedance and fluorescence quenching studies on the binding of carbon nanotubes (CNTs)-adsorbed and solution rutin with hemoglobin.

Electrochemical quartz crystal impedance (QCI) technique was utilized to monitor in situ the adsorption of rutin (RT) onto a carbon nanotubes (CNTs)-modified gold electrode and to study the binding process of solution hemoglobin (Hb) to RT immobilized on the electrode. Time courses of the QCI parameters including crystal resonant frequency were simultaneously obtained during the RT adsorption and Hb-RT binding. In contrast to the negligible RT adsorption at a bare gold electrode, the modification by CNTs notably enhanced the amount of adsorption, and almost all of the adsorbed RT molecules were found to be electroactive. On the basis of the frequency response from the binding of adsorbed RT to solution Hb and the diminished electroactivity of adsorbed RT after the formation of the electrochemically inactive RT-Hb adduct, the average binding molar ratio of adsorbed RT to Hb was estimated to be 23.9:1, and the association constant (Ka) for the binding was estimated to be 2.87 x 106 (frequency) and 3.92 x 106 (charge) L mol-1, respectively. Comparable results were obtained from fluorescence quenching measurements in mixed solutions containing RT of fixed concentration and Hb of varying concentrations, demonstrating that the interfacial RT here behaved equivalently in the RT-Hb binding activity compared to that in solution. This work may have presented a new and general protocol involving CNTs to study many other electroactive natural antioxidants or drugs that are at the interface or in solution, their binding with proteins or other biomolecules, and changes of their antioxidant activity after the binding.