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ACS Applied Materials & Interfaces 05/2012; · 4.53 Impact Factor
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ABSTRACT: Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200 °C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO(3) solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H(2)O(2) reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by immobilization of glucose oxidase on the bimodal np-Au.
Nanoscale 04/2012; 4(15):4492-7. · 5.91 Impact Factor
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ABSTRACT: Nanoporous PdCu alloys (np-PdCu) with different Pd/Cu ratios were prepared by the selective dealloying of Al from PdCuAl ternary alloys with predetermined metallic ratios in 1.0 M NaOH solution. The Cu content had a significant effect on the coarsening rate of the PdCu ligaments. A larger Cu content induced faster coarsening of the alloy ligaments. Pristine np-PdCu was facilely converted into a np-PdCu near-surface alloy with a nearly pure Pd surface and a PdCu alloy core by mild electrochemical treatment. The nanoporous near-surface alloys were more resistant to coarsening than pristine np-PdCu. Electrochemical measurements showed that the np-PdCu near-surface alloys exhibited greatly enhanced electrocatalytic activity and durability towards glucose oxidation compared with nanoporous Pd (np-Pd). The surface-specific activities of the nanoporous metals followed the order of np-Pd(1) Cu(1) >np-Pd(3) Cu(7) >np-Pd(3) Cu(1) >np-Pd. The peak-current density on np-Pd(1) Cu(1) near-surface alloy showed the highest value, which was about four times that on np-Pd. The np-PdCu near-surface alloy was also highly resistant towards poisoning by chloride ions and was capable of sensing glucose over a wide concentration range (0-36 mM) without interference from ascorbic acid, acetamidophenol, and uric acid.
Chemistry - An Asian Journal 04/2012; · 4.50 Impact Factor
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ABSTRACT: We describe a general strategy to fabricate a new type of nanoporous core/shell structured bimetallic nanocomposites with controllable metal components. Nanoporous copper (NPC) obtained by dealloying Cu/Al alloy is used as both reducing agent and three-dimensional substrate. Electron microscope and X-ray diffraction characterizations demonstrated that a simply galvanic-replacement reaction with H(2)PtCl(6) aqueous solution can easily generate nanoporous core/shell structure with a thin Pt/Cu alloy shell and Cu (or Pt/Cu alloy) core. The morphology and crystal structure evolution of the nanocomposites are studied and discussed in detail. The as-prepared bimetallic PtCu nanocomposites show greatly enhanced catalytic activity and stability toward methanol electro-oxidation as compared with commercial Pt/C catalyst. This facile in situ preparation strategy is also suitable for large-scale production of this novel and inexpensive catalyst.
ACS Applied Materials & Interfaces 12/2011; 3(12):4626-32. · 4.53 Impact Factor
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ABSTRACT: Nanoporous copper (NPC) obtained by dealloying CuAl alloy is used as both three-dimensional template and reducing agent for the fabrication of nanoporous PdCu alloy with hollow ligaments by a simple galvanic replacement reaction with H(2)PdCl(4) aqueous solution. Electron microscopy and X-ray diffraction characterizations demonstrate that after the replacement reaction, the ligaments become hollow tubular structure and the ligament shell is also comprised of small pores and nanoparticles with a typical size of ~4 nm (third order porosity). The as-prepared nanotubular mesoporous PdCu alloy (NM-PdCu) structure exhibits remarkably improved electrocatalytic activity towards the oxidation of formic acid and H(2)O(2) compared with nanoporous Pd (NP-Pd), and can be used for sensitive electrochemical sensing applications. After coupled with glucose oxidase (GOx), the enzyme modified NM-PdCu electrode can sensitively detect glucose over a wide linear range (0.5-20 mM).
Analytica chimica acta 10/2011; 703(2):172-8. · 4.31 Impact Factor
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ABSTRACT: Nanoporous silver (NPS) and copper (NPC) obtained by dealloying AgAl and CuAl alloys, respectively, were used as both three-dimensional templates and reducing agents for the fabrication of nanoporous PtAg (NPS-Pt) and PtCu (NPC-Pt) alloys with hollow ligaments by a simple galvanic replacement reaction with H(2)PtCl(6). Electron microscopy and X-ray diffraction characterizations demonstrate that NPS and NPC with similar ligament sizes (30-50 nm) have different effects on the formed hollow nanostructures. For NPS-Pt, the shell of the hollow ligament is seamless. However, the shell of NPC-Pt is comprised of small pores and alloy nanoparticles with a size of ∼3 nm. The as-prepared NPS-Pt and NPC-Pt exhibit remarkably improved electrocatalytic activities towards the oxidation of ethanol and H(2)O(2) compared with state-of-the-art Pt/C catalyst, and can be used for sensitive electrochemical sensing applications. The hierarchical nanoporous structure also provides a good microenvironment for enzymes. After immobilization of glucose oxidase (GOx), the enzyme modified nanoporous electrode can sensitively detect glucose in a wide linear range (0.6-20 mM).
Biosensors & bioelectronics 09/2011; 27(1):160-6. · 5.43 Impact Factor
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ABSTRACT: Sensitive detection of molecules by using the surface-enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag-Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5×10(5) was observed on bare NPS obtained by dealloying Ag(30) Al(70) in 2.5 wt % HCl at room temperature followed by 15 min aging at around 85 °C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6×10(8) owing to strong near-field coupling between the ligaments and nanoparticles.
ChemPhysChem 05/2011; 12(11):2118-23. · 3.41 Impact Factor
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ABSTRACT: Nanoporous copper (NPC) with a pore size of 100-200 nm was prepared by simply dealloying Al(60)Cu(40) alloy in a 5 wt.% HCl solution. The NPC was characterized by scanning electron microscopy and nitrogen adsorption techniques. Horseradish peroxidase (HRP) was immobilized on NPC by adsorption. Compared with free enzyme, the thermal stability of the immobilized enzyme was greatly improved due to the multiple attachments between the enzyme molecule and the NPC surface. After 2h incubation at 50 degrees C, the immobilized HRP retained ca. 90% of the initial activity while only ca. 10% initial activity remained for the free enzyme. The interaction between HRP and the porous surface also made the K(m) and K(cat) values of the immobilized enzyme increase (from 0.43 to 0.80 mM) and decrease (from 8.1 x 10(3) to 2.2 x 10(3)min(-1)), respectively. Based on the good electric conductivity and electrocatalytic activity of the NPC electrode, an electrochemical biosensor for O-phenylenediamine (OPD) was made. The calibration curve of the biosensor was linear from 0.5 microM to 14.5 microM OPD with a sensitivity of 0.37 microA microM(-1). The stability and reproducibility of the biosensor were also demonstrated to be good. When positioned at -0.45 V for 200 s, its current response toward 10 microM OPD remained ca. 80% of its initial value. For five HRP-loaded NPC electrodes, the relative standard deviation (RSD) of the current response toward 10 microM OPD was ca. 4.5%. All these results indicated that NPC was a good support for the HRP immobilization and its low price would facilitate its large-scale application.
Bioresource technology 12/2010; 101(24):9415-20. · 4.25 Impact Factor
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ABSTRACT: It is of great significance to develop an appropriate water-in-ionic liquid (W/IL) microemulsion suitable for the expression of the catalytic activity of a given enzyme. In this paper, the phase diagram of a new AOT/Triton X-100/H(2)O/[Bmim][PF(6)] pseudo ternary system is presented. With the aid of nonionic surfactant Triton X-100, AOT could be dissolved in hydrophobic ionic liquid [Bmim][PF(6)], forming a large single phase microemulsion region. The water-in-[Bmim][PF(6)] (W/IL) microemulsion domain was identified electrochemically by using K(3)Fe(CN)(6) as a probe. The existence of W/IL microemulsions was demonstrated spectrophotometrically by using CoCl(2) as a probe. New evidences from the FTIR spectroscopic study, which was first introduced to the W/IL microemulsion by substituting D(2)O for H(2)O to eliminate the spectral interference, demonstrated that there existed bulk water at larger ω(0) values (ω(0) was defined as the molar ratio of water to the total surfactant) in the W/IL microemulsion, which had remained unclear before. In addition to the inorganic salts, biomacromolecule laccase could be solubilized in the W/IL microemulsion. The laccase hosted in the microemulsion exhibited a catalytic activity and the activity could be regulated by the composition of the interfacial membrane.
Colloids and surfaces. B, Biointerfaces 09/2010; 82(2):432-7. · 2.60 Impact Factor
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ABSTRACT: An attempt was made in the present paper to develop a nanoporous gold (NPG)-based electrochemical aptasensor for thrombin detection. The substrate electrode NPG was in situ fabricated by a facile one-step square wave potential pulse (SWPP) treatment. The treatment involved repeated gold oxidation-reduction and intensive H(2) bubbles evolution. After 100min treatment, the active surface area of Au increased greatly (34 times). The electrochemical aptasensor was fabricated using a layer-by-layer assembling strategy. A "sandwich" structure was formed via thrombin connecting the aptamer-modified NPG and the aptamer-modified Au nanoparticles (AuNPs). The AuNPs was modified with two kinds of single strand DNA (ssDNA). One was aptamer of thrombin, but the other was not, reducing the cross-reaction between thrombin and its aptamer on the same AuNP. The electrochemical signal produced by the [Ru(NH(3))(6)](3+) bound to ssDNA via electrostatic interaction was measured by chronocoulometry. Due to the amplification effects of both NPG and AuNPs, this novel NPG-based aptasensor could detect thrombin quantitatively in the range of 0.01-22nM with a detection limit as low as 30fM. The present aptasensor also exhibited excellent selectivity, stability and reusability.
Colloids and surfaces. B, Biointerfaces 08/2010; 79(1):304-8. · 2.60 Impact Factor
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ABSTRACT: Immobilization of enzymes on porous inorganic materials is very important for biocatalysis and biotransformation. In this paper, nanoporous gold (NPG) was used as a support for lignin peroxidase (LiP) immobilization. NPG with a pore size of 40-50 nm was prepared by dealloying Au/Ag alloy (50:50 wt%) for 17 h. By incubation with LiP aqueous solution, LiP was successfully immobilized on NPG. The optimal temperature of the immobilized LiP was ca. 40, 10 degrees C higher than that of free LiP. After 2h incubation at 45 degrees C, 55% of the initial activity of the immobilized LiP was still retained while the free LiP was completely deactivated. In addition, a high and sustainable LiP activity was achieved via in situ release of H(2)O(2) by a co-immobilized glucose oxidase. The present co-immobilization system was demonstrated to be very effective for LiP-mediated dye decolourization.
Bioresource technology 05/2009; 100(17):3837-42. · 4.25 Impact Factor
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ABSTRACT: On the basis of the unique physical and chemical properties of nanoporous gold (NPG), which was obtained simply by dealloying Ag from Au/Ag alloy, an attempt was made in the present study to develop NPG-based electrochemical biosensors. The NPG-modified glassy carbon electrode (NPG/GCE) exhibited high-electrocatalytic activity toward the oxidation of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H(2)O(2)), which resulted in a remarkable decrease in the overpotential of NADH and H(2)O(2) electro-oxidation when compared with the gold sheet electrode. The high density of edge-plane-like defective sites and large specific surface area of NPG should be responsible for the electrocatalytic behavior. Such electrocatalytic behavior of the NPG/GCE permitted effective low-potential amperometric biosensing of ethanol or glucose via the incorporation of alcohol dehydrogenase (ADH) or glucose oxidase (GOD) within the three-dimensional matrix of NPG. The ADH- and GOD-modified NPG-based biosensors showed good analytical performance for biosensing ethanol and glucose due to the clean, reproducible and uniformly distributed microstructure of NPG. The stabilization effect of NPG on the incorporated enzymes also made the constructed biosensors very stable. After 1 month storage at 4 degrees C, the ADH- and GOD-based biosensors lost only 5.0% and 4.2% of the original current response. All these indicated that NPG was a promising electrode material for biosensors construction.
Biosensors & bioelectronics 04/2009; 24(10):3014-8. · 5.43 Impact Factor
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ABSTRACT: Nanoporous gold (NPG), prepared simply by dealloying Ag from Au/Ag alloy, was used in the present study as a carrier for laccase immobilization. Three immobilization strategies, i.e., physical adsorption, electrostatic attraction, and covalent coupling, were used to immobilize laccase on NPG. A detailed comparison among the three strategies was made in light of the loading, the specific activity, and the leakage of laccase. The present results indicated that the physical adsorption strategy was the best one for laccase immobilization on NPG. This was because of the potential covalent linkage between the nanoscale gold surface and the amino groups of the residue amino acids of laccase. The effects of the particle size of NPG on laccase loading and enzyme kinetics were also investigated. When the particle size of NPG got smaller, more laccase could access the inner pore and be immobilized. The kinetic study showed that the crushed NPG not only enhanced mass transfer of the substrate and its oxidation product but also favored the exposure of the active sites of the immobilized laccase to the substrate, i.e., the crushing facilitated the enhancement of the catalytic efficiency of laccase.
01/2009;
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ABSTRACT: Nanoporous gold (NPG) with different pore sizes was obtained by simple dealloying and thermal annealing methods. The morphology of the NPG was characterized by scanning electron microscopy and nitrogen adsorption technique. Laccase was immobilized on the surface of the NPG by physical adsorption. Detailed studies were made on the effect of the pore size on laccase immobilization. NPG with pore size of 40−50 nm was demonstrated to be a suitable support for laccase immobilization. Compared with free enzyme, the optimum pH of immobilized laccase did not change; the optimum temperature, however, rose from 40 to 60 °C. Both thermal and storage stabilities of laccase improved markedly via the immobilization. Laccase immobilized on NPG (100 nm in thickness) was used for enzyme electrode construction. Direct electrochemistry of laccase on NPG supported by glassy carbon electrode (NPG/GC) was achieved with high efficiency due to the outstanding physicochemical characteristics of the NPG. The laccase-loaded NPG/GC electrode also exhibited a strong electrocatalytic activity toward O2 reduction. When stored at 4 °C for 1 month, the electrode showed no obvious changes in its response. All results presented in the paper indicated that NPG was an excellent carrier for laccase immobilization and would have potential applications in biofuel cell and/or biosensor areas.
08/2008;
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ABSTRACT: A nonenzymatic amperometric glucose sensor was fabricated based on the electrocatalytic oxidation of nanoporous gold (NPG) toward glucose. The NPG electrode was in situ prepared by a facile one-step square wave potential pulse (SWPP) treatment. The surface morphology of the NPG-based electrode was characterized by scan electron microscopy. Voltammetry and amperometric methods were used to evaluate the electrocatalytic activities of the NPG-based electrodes toward the glucose oxidation in both neutral and alkaline media. The NPG electrode showed a quick and sensitive response to glucose. The electrocatalytic activity of NPG in neutral condition was further improved when a small amount of Pt was decorated on NPG (NPG–Pt). When applied for glucose sensing, the NPG–Pt electrode showed a linear range of 0.5–10 mM with a sensitivity of 145.7 μA cm−2 mM−1 and a detection limit of 0.6 μM (S/N = 3). The physiological levels of ascorbic acid (0.1 mM) and uric acid (0.02 mM) only had negligible interferences to the glucose detection. The high sensitivity and selectivity of the present sensor was due to the high roughness factor of the electrode surface and unique electrooxidation mechanism of glucose. In addition, the present nonenzymatic glucose sensor was easy in preparation and very stable.
Journal of Electroanalytical Chemistry. 643:39-45.
