Yue Xia

Nonenzymatic amperometric response of glucose on a nanoporous gold film electrode fabricated by a rapid and simple electrochemical method

An enzyme-free amperometric method was established for glucose detection using a nanoporous gold film (NPGF) electrode prepared by a rapid one-step anodic potential step method within 5 min. The prepared NPGF had an extremely high roughness and was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. Electrochemical responses of the as-prepared NPGF to glucose in 0.1M phosphate buffer solution (PBS, pH 7.4) with or without Cl(-) were discussed. In amperometric studies carried out at -0.15 V in the absence of Cl(-), the NPGF electrode exhibited a high sensitivity of 232 μA mM(-1)cm(-2) and gave a linear range from 1mM up to 14 mM with a detection limit of 53.2 μM (with a signal-to-noise ratio of 3). In addition, the oxidation of ascorbic acid (AA) and uric acid (UA) can be completely eliminated at such a low applied potential. On the other hand, the quantification of glucose in 0.1M PBS (pH 7.4) containing 0.1M NaCl offered an extended linear range from 10 μM to 11 mM with a sensitivity of 66.0 μA mM(-1)cm(-2) and a low detection limit of 8.7 μM (signal-to-noise ratio of 3) at a detection potential of 0.2V.

A novel strategy to assemble colloidal gold nanoparticles at the water-air interface by the vapor of formic acid.

We report a novel strategy on the controlled assembly of gold nanoparticles (NPs) at the air-water interface by designing a concentration gradient of electrolytes utilizing volatile weak acidic electrolytes. Films of close-packed Au NPs can be facilely obtained by exposing citrate-protected gold colloids to the vapor of formic acid for several hours in an airtight desiccator at room temperature. Both the higher interfacial concentration of formic acid and the buffer effect of citrate solution play the key roles in the assembly. They engender a gradient distribution of hydrogen ions such that to trigger the interfacial assembly of gold NPs while preventing the bulk colloid from aggregation and coagulation. Comparative investigations have also been performed either using other volatile electrolytes like weaker acetic acid and stronger hydrochloric acid or adding an electrolyte directly into the colloids. The as-prepared films of gold NPs can serve as good substrates for surface-enhanced Raman scattering (SERS). This strategy has also been applied to the assembly of some other NPs like colloidal Pt at the air-water interface.

Fabrication of nano-network gold films via anodization of gold electrode and their application in SERS

We report here a green and facile one-step method to fabricate nano-network gold films of low roughness via anodization of gold electrodes in an aqueous solution of l-ascorbic acid (AA) or hydroquinone (H2Q) at the oxidation peak potential. The preparation involves the formation of thin gold oxide layer by anodization of gold and its simultaneous and/or subsequent reduction by AA or H2Q. The as-fabricated nano-network gold films show very strong SERS activity in comparison with the substrates prepared by some other electrochemical roughening methods.

Nanoassemblies of colloidal gold nanoparticles by oxygen-induced inorganic ligand replacement.

This article reports a novel method of the fabrication of floating ultrathin nanoporous films and superlattice-like bottom sediment flakes of colloidal gold nanoparticles (Au NPs) by the oxygen-induced ligand replacement of inorganic species. The two nanoassemblies were realized in a weighing bottle simply by aging the Au colloid, which was synthesized and stabilized using more divalent tin Sn(II) than required for the reduction of HAuCl(4). In situ Raman spectroscopy was employed to trace the assembly process, and we found that the protective Sn(II) species (mostly SnCl(3)(-)) of the gold colloid could be gradually replaced by Cl(-) ions in the solution, while the strongly chemically adsorbed Sn(II) species on the Au NPs was oxidized by O(2) from the air contact. The destabilized colloidal Au NPs by the ligand replacement of SnCl(3)(-) with Cl(-) first assembled into an ultrathin nanoporous film at the air-water interface and then sedimentated to the bottom. Superlattice-like sediment flakes of Au NPs can be obtained at lower temperature (approximately 5 degrees C). Particularly, this method does not involve any organic substances, providing clean ultrathin nanoporous films and superlattice-like flakes of Au NPs. The ultrathin nanoporous films and superlattice-like flakes of Au NPs can serve as SERS substrates with strong and long activity.

Rapid and high-capacity adsorption of sulfonated anionic dyes onto basic bismuth(III) nitrate via bidentate bridging and electrostatic attracting interactions

A new adsorbent of octahedron-structured basic bismuth(III) nitrate (OBBN), [Bi6O5(OH)3](NO3)5·3H2O, was synthesized by a mild hydrolysis route and used for the adsorption removal of sulfonated anionic dyes (SADs) from aqueous solutions. A typical SAD, methyl orange (MO), was taken to investigate the adsorption processes at different pH, adsorbent dosage, contact time, temperature and initial MO concentration. The equilibrium adsorption data were well fitted by the Langmuir isotherm model and showed high adsorption capacity (qmax = 1298 mg g−1). The adsorption kinetics was well described by the pseudo-second-order model and exhibited a short adsorption equilibrium time (<14 min for 20 mg L−1 MO). Adsorption thermodynamic parameters revealed that the adsorption is endothermic, random and spontaneous. The adsorption behavior was closely related to the combined interactions of bidentate bridging and electrostatic attraction between [Bi6O5(OH)3]5+ polycations on the OBBN surface and –SO3− groups of the SAD. The adsorbent was successfully applied to remove MO from model wastewater with a satisfactory result.

Facile preparation of ordered arrays of polystyrene spheres dissymmetrically decorated with gold nanoparticles at air/liquid interface and their SERS properties

Ordered arrays of polystyrene (PS) spheres dissymmetrically decorated with gold nanoparticles (NPs) were facilely assembled at air/liquid interface by the combination of colloidal crystal templating and modified conventional electroless plating. Distinguishingly, Sn2+ ions served as the reductant and stabilizer in the preparation of Au colloid, and the immersed part of a floating monolayer of pristine PS spheres was also sensitized by the excessive amounts of Sn2+ ions in the Au colloid. Colloidal Au NPs spontaneously aggregated onto the sensitized portion of PS spheres due to oxygen-induced ligand replacement of SnCl3− with Cl−, forming asymmetric PS/Au composite sphere arrays. Moderate heating (60 °C) accelerated the assembly process. The method presented here is convenient, cost-effective and can be extended to prepare asymmetric composite sphere arrays of PS/Pd and PS/Au–Pd. Furthermore, the surface enhanced Raman scattering (SERS) performance of the ordered arrays of asymmetric PS/Au composite spheres was examined.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au80Sn20 (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn2+ and AuCl4－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm-2 mM-1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.