Shuyao Wu

Fabrication of polymeric ionic liquid/graphene nanocomposite for glucose oxidase immobilization and direct electrochemistry.

A novel polymeric ionic liquid functionalized graphene, poly(1-vinyl-3-butylimidazolium bromide)-graphene (denoted as poly(ViBuIm(+)Br(-))-G), was synthesized. FTIR, UV-vis spectra and TEM were used to characterize the formation of as synthesized nanocomposites. Due to the modification of the polymeric ionic liquid, poly(ViBuIm(+)Br(-))-G can not only be dispersed well in aqueous solutions to form a homogeneous colloidal suspension of individual nanosheets, but also exhibit a strong positive charge. Based on self-assembly, the negatively charged glucose oxidase (GOD) was immobilized onto the poly(ViBuIm(+)Br(-))-G to form a GOD/poly(ViBuIm(+)Br(-))-G/glassy carbon (GC) electrode under mild conditions. With the advantage of both poly(ViBuIm(+)Br(-)) and graphene, poly(ViBuIm(+)Br(-))-G can provide a favorable and conductive microenvironment for the immobilized GOD and thus promote their direct electron transfer at the GC electrode. Furthermore, the GOD/poly(ViBuIm(+)Br(-))-G/GC electrode displayed an excellent sensitivity, together with a wide linear range and excellent stability for the detection of glucose. Accordingly, these unique properties of such novel nanocomposite generate a promising platform for the construction of mediator-free enzymatic biosensors.

Fabrication of a Biocompatible and Conductive Platform Based on a Single‐Stranded DNA/Graphene Nanocomposite for Direct Electrochemistry and Electrocatalysis

A novel electrochemical platform was designed by combining the biocompatibility of single-stranded DNA (ss-DNA) and the excellent conductivity of graphene (GP). This nanocomposite (denoted as ss-DNA/GP) was first used as an electrode material for the immobilization and biosensing of redox enzymes. On the basis of electrostatic interactions, horseradish peroxidase (HRP) self-assembled with ss-DNA/GP on the surface of a glassy carbon (GC) electrode to form an HRP/ss-DNA/GP/GC electrode. UV/Vis and FTIR spectra were used to monitor the assembly process and indicated that the immobilized HRP on the ss-DNA/GP matrix retained its native structure well. A pair of stable and well-defined redox peaks of HRP with a formal potential of about -0.26 V (vs. Ag/AgCl) in a pH 7.0 phosphate buffer solution were obtained at the HRP/ss-DNA/GP/GC electrode; this demonstrates direct electron transfer between the immobilized HRP and the electrode. In addition, the modified electrode showed good electrocatalytic performance towards H(2)O(2) with high sensitivity, wide linear range, and good stability. Accordingly, the ss-DNA/GP nanocomposite provides a novel and efficient platform for the immobilized redox enzyme to realize direct electrochemistry and has a promising application in the fabrication of third-generation electrochemical biosensors.

Poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets for electrochemical sensor to detect dopamine in the presence of ascorbic acid.

Novel poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets (PILs/PPy/GO) were prepared by the polymerization of 1-vinyl-3-ethylimidazole bromide (VEIB) on the surface of N-vinyl imidazolium modified PPy/GO nanosheets. Due to the synergistic effects of GO with well-defined lamellar structures, conductive PPy and biocompatible PILs, PILs/PPy/GO modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activity towards dopamine (DA) with good stability, high sensitivity and wide linear range in the present of ascorbic acid (AA) with high concentration. PILs played an essential role for the simultaneous determination of DA and AA in a mixture, whose existence effectively improved the transmission mode of electrons and resulted in the different electrocatalytic performance towards the oxidation of DA and AA. It is indicated that PILs/PPy/GO nanosheets can act as a good steady and sensitive electrode material for the development of improved DA sensors.

Preparation of poly(ionic liquids)-functionalized polypyrrole nanotubes and their electrocatalytic application to simultaneously determine dopamine and ascorbic acid

Novel poly(ionic liquids) functionalized polypyrrole nanotubes (PILs/PPyNTs) were successfully synthesized. 1-Vinyl-3-ethylimidazole bromide (VEIB) was polymerized on the surface of novel polymerizable vinyl imidazolium-type IL modified PPyNTs prepared by a covalent method. Due to the modification of PILs, the dispersibility of PILs/PPyNTs in aqueous solution was significantly improved and their surface charge properties were obviously changed to electropositivity. Because of the synergetic effects of conductive PPyNTs and biocompatible PILs, excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA) were achieved using a PILs/PPyNTs modified glassy carbon electrode (GCE), which gave a large potential difference enough to well distinguish DA from AA, with excellent sensitivity and good stability, for the simultaneous detection of DA and AA. The existence of PILs effectively improved the transmission mode of electrons of DA and AA oxidation on the electrode and resulted in their different electrocatalytic performance.

Influence of Surface States on the Evaluation of the Flat Band Potential of TiO2

Flat band potential (Vfb) is one of the most important physical parameters to study and understand semiconductor materials. However, the influence of surface states on the evaluating Vfb of titanium oxide (TiO2) and other semiconductor materials through a Mott-Schottky plot is ignored. Our study indicated that the influence of surface states should be introduced into the corresponding equivalent circuit even when the kinetic process did not occur. Ignoring the influence of surface states would lead to an underestimation of the space charge capacitance. Our paper would be beneficial for accurate determination of Vfb of semiconductor materials. We anticipate that this preliminary study will open new perspectives in understanding the semiconductor-electrolyte interface.

Direct electrochemistry of cholesterol oxidase and biosensing of cholesterol based on PSS/polymeric ionic liquid–graphene nanocomposite

A novel graphene nanocomposite, functionalized by polymeric ionic liquids (PILs) and poly(sodium-p-styrenesulfonate) (PSS), was successfully prepared and exhibited excellent conductivity, favourable biocompatibility and good film-forming properties as an electrode material. TEM showed that the nanocomposite possessed an individual nanosheet-like structure. Owing to the surface modification of graphene, PSS/PILs–GP can not only be well dispersed in aqueous solution, but also possesses a strong negative charge. Due to electrostatic interactions, positively charged cholesterol oxidase (ChOx) can be immobilized onto the surface of PSS/PILs–GP to form the ChOx/PSS/PILs–GP/GC electrode material. UV-vis and FT-IR spectroscopy were used to monitor the assembly process of the nanocomposite. Due to the conductivity and biocompatibility of PSS/PILs–GP, the immobilized ChOx exhibited enhanced direct electron transfer (DET) at a glassy carbon (GC) electrode. Furthermore, the ChOx/PSS/PILs–GP/GC electrode displayed excellent catalytic performance with a wide linear range of 10.5 × 10−6 to 10.4 × 10−3 mol L−1, and a low detection limit of 3.5 μmol L−1 for the detection of cholesterol.

Significant enhancement of visible light photocatalytic activity of the hybrid B12-PIL/rGO in the presence of Ru(bpy)32+ for DDT dehalogenation

A new B12-PIL/rGO hybrid was prepared successfully through immobilizing a B12 derivative on the surface of poly(ionic liquid) (PIL)-modified reduced graphene oxide (rGO) by electrostatic attraction and π–π stacking attraction among the different components. The hybrid catalyst showed an enhanced photocatalytic activity in the presence of Ru(bpy)32+ for 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) dechlorination with ∼100% conversion. Especially, the yield of didechlorinated products could reach 78% after 1 h of visible light irradiation, which should be attributed to a synergistic effect of B12, rGO and PIL in B12-PIL/rGO, including their respective catalytic performance, the excellent electron transport of rGO and the concentration of DDT and 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (DDD) on the surface of B12-PIL/rGO. Furthermore, the hybrid catalyst was easily recycled for use without obvious loss of catalytic activity.

Hydrophilic polymer/polypyrrole/graphene oxide nanosheets with different performances in electrocatalytic applications to simultaneously determine dopamine and ascorbic acid

Hydrophilic polymers (HP) functionalized polypyrrole/graphene oxide nanosheets (HP/PPy/GO) were successfully prepared by covalently modifying polyacrylamide (PAM), polyacrylic acid (PAA) and polyvinylpyrrolidone (PVP) on the surface of PPy/GO nanosheets containing vinyl groups. Besides significantly improving the dispersivity of PPy/GO in water, the different chemical properties among the three HP with different hydrophilic groups further resulted in the different performances of the obtained electrochemical biosensors (PAM/PPy/GO, PAA/PPy/GO and PVP/PPy/GO modified glassy carbon electrodes (GCEs)) in electrocatalytic applications to simultaneously determine dopamine (DA) and ascorbic acid (AA). PAM/PPy/GO and PAA/PPy/GO modified GCEs exhibited good electrochemical responses to distinguish DA from AA in their mixture at certain concentrations, which cannot be achieved by the PVP/PPy/GO modified GCE, due to their different chemical properties among the three HP with different hydrophilic groups. Particularly, compared to PAA/PPy/GO, PAM/PPy/GO can act as a good steady electrode material with good selectivity and sensitivity that can simultaneously determine the two substrates in their mixture at lower concentrations, which may be due to the different chemical properties between the electron-donating amide groups and electron-withdrawing carboxyl groups. The different electronic effects of the amide group and carboxyl group resulted in the difference in the transmission capability of electrons released from the oxidation reaction of DA and AA. Therefore, PAM/PPy/GO modified GCE can act as a good electrochemical sensor with high sensitivity and selectivity for DA and AA.

One-step preparation of flower-like poly(styrene-co-zwitterionic ionic liquid) microspheres with hierarchical structures for supported acidic heterogeneous catalysts

By using a one-step copolymerization of styrene (St) and 3-(1-vinyllimidazolium-3-yl)propane-1-sulfonate (VIPS), a kind of poly(St-co-VIPS) microsphere, with a hierarchical structure composed of nanospheres or nanoparticles with diameters in the range of 70–90 nm arranged on its surface and that look like a flower, has been simply prepared in the presence of polyvinyl pyrrolidone (PVP) in an aqueous alcohol system. A formation mechanism of the flower-like poly(St-co-VIPS) microspheres is proposed by investigating the influence of reaction conditions on its morphologies and observing its growth process with time. Because of the existence of zwitterionic liquid functional groups, flower-like poly(St-co-VIPS)-acid microspheres, a novel kind of heterogeneous catalyst, were successfully prepared by immobilizing heteropoly acids and H2SO4 on the flower-like poly(St-co-VIPS) microspheres, and the heterogeneous catalysts showed better catalytic activities for esterifications, acetalizations and transesterifications than with H2SO4 as the catalyst. Especially, the heterogeneous catalysts presented excellent catalytic efficiency for the acetalization of benzaldehyde and 1,2-propanediol, which could successfully reach 96.2%. Furthermore, the crosslinked flower-like poly(DVB-co-VIPS)–H2SO4 microspheres prepared under the same conditions where only St was replaced by divinyl benzene (DVB) have better reusability than that of the flower-like poly(St-co-VIPS)–H2SO4 with poor solvent resistance, and could be reused four times without significant loss of the catalytic activity, indicating that they could act as excellent recyclable heterogeneous catalysts for the synthesis of acetals and have potential application in industry.

Self-assembly of novel fluorescent quantum dot-cerasome hybrid for bioelectrochemistry.

A novel fluorescent nanohybrid was fabricated via the self-assembly of semiconductive quantum dots (QDs) on biocompatible cerasomes. The nanohybrid (denoted as QDs-cerasome) was used as an electrode material for visible protein immobilization and bioelectrochemistry. The morphology and surface properties of the QDs-cerasome hybrid were characterized by transmission electron microscopies, atomic force microscopies and zeta potential measurements. Because the QDs-cerasome hybrid possessed a positive charge in aqueous solution, it could be used as a matrix to immobilize negatively charged hemoglobin (Hb) via electrostatic interaction. Ultraviolet-visible spectroscopy demonstrated that Hb was immobilized on the hybrid matrix without denaturation. The fluorescence of the QDs-cerasome was quenched as Hb was immobilized, indicating that the protein immobilization process could be visibly detected. Compared with protein electrodes constructed using a single-component material, including Hb-QDs/GC and Hb-cerasome/GC electrodes, the Hb-QDs-cerasome/GC electrode not only realized enhanced direct electrochemistry, but also displayed higher sensitivity and a wider linear range toward the detection of hydrogen peroxide because of the synergistic effect of the QDs and cerasomes. The experimental results demonstrate that this fluorescent multicomponent hybrid material provides a novel and effective platform to immobilize a redox protein to realize direct electrochemistry. As such, this hybrid shows promise for application in third-generation electrochemical biosensors.