Nanoporous Gold Leaf Research Articles

Nanoporous gold nanoleaf as tunable metamaterial

We have studied optical properties of single-layer and multi-fold nanoporous gold leaf (NPGL) metamaterials and observed highly unusual transmission spectra composed of two well-resolved peaks. We explain this phenomenon in terms of a surface plasmon absorption band positioned on the top of a broader transmission band, the latter being characteristic of both homogeneous “solid” and inhomogeneous “diluted” Au films. The transmission spectra of NPGL metamaterials were shown to be controlled by external dielectric environments, e.g. water and applied voltage in an electrochemical cell. This paves the road to numerous functionalities of the studied tunable and active metamaterials, including control of spontaneous emission, energy transfer and many others.

Potentiometric Biosensing of Ascorbic Acid, Uric Acid, and Cysteine in Microliter Volumes Using Miniaturized Nanoporous Gold Electrodes.

Potentiometric redox sensing is a relatively inexpensive and passive approach to evaluate the overall redox state of complex biological and environmental solutions. The ability to make such measurements in ultra-small volumes using high surface area, nanoporous electrodes is of particular importance as such electrodes can improve the rates of electron transfer and reduce the effects of biofouling on the electrochemical signal. This work focuses on the fabrication of miniaturized nanoporous gold (NPG) electrodes with a high surface area and a small footprint for the potentiometric redox sensing of three biologically relevant redox molecules (ascorbic acid, uric acid, and cysteine) in microliter volumes. The NPG electrodes were inexpensively made by attaching a nanoporous gold leaf prepared by dealloying 12K gold in nitric acid to a modified glass capillary (1.5 mm id) and establishing an electrode connection with copper tape. The surface area of the electrodes was ~1.5 cm2, providing a roughness factor of ~16 relative to the geometric area of 0.09 cm2. Scanning electron microscopy confirmed the nanoporous framework. A linear dependence between the open-circuit potential (OCP) and the logarithm of concentration (e.g., Nernstian-like behavior) was obtained for all three redox molecules in 100 μL buffered solutions. As a first step towards understanding a real system, the response associated with changing the concentration of one redox species in the presence of the other two was examined. These results show that at NPG, the redox potential of a solution containing biologically relevant concentrations of ascorbic acid, uric acid, and cysteine is strongly influenced by ascorbic acid. Such information is important for the measurement of redox potentials in complex biological solutions.

Electrochemical sensor based on dual-template molecularly imprinted polymer and nanoporous gold leaf modified electrode for simultaneous determination of dopamine and uric acid.

A novel electrochemical sensor based on dual-template molecularly imprinted polymer (MIP) with nanoporous gold leaf (NPGL) was established for the simultaneous determination of dopamine (DA) and uric acid (UA). NPGL acts as an enlarged loading platform to enhance sensing capacity, and the MIP layer was synthesized in situ in the presence of monomer and dual templates (DA and UA) to provide specific recognition. Under the optimal conditions, the sensor shows a good linear range of 2.0~180μM for DA at a working potential of 0.15V (vs. Ag/AgCl) and 5.0~160μM for UA at 0.35V (vs. Ag/AgCl), with the respective detection limit of 0.3μM and 0.4μM (S/N = 3). Good selectivity of the sensor to its dual templates was confirmed as the sensing signals are significantly different between templates and interfering species. The responses maintained higher than 96% of the initial values after 30-day storage, and the day-to-day relative standard deviation is less than 3.0%. Real sample simultaneous determination of DA and UA was conducted with bovine serum, and the results were in good agreement with those from high-performance liquid chromatography. It can be concluded that this work offers a reliable, facile, fast, and cost-effective method of simultaneous quantification of two or more chem-/bio-molecules. Graphical abstract.

Nanoporous gold peel-and-stick biosensors created with etching inkjet maskless lithography for electrochemical pesticide monitoring with microfluidics

Flexible nanoporous gold and silver leaf are patterned without photolithography and adhered to microfluidics to create disposable multiplexed electrochemical biosensors.

A novel dual-signal electrochemical sensor for bisphenol A determination by coupling nanoporous gold leaf and self-assembled cyclodextrin

Bisphenol A (BPA) is an endocrine disrupting chemical, which can mimic estrogen and bring about a series of negative impact on human health. Herein, we developed a novel dual-signal sensor by coupling nanoporous gold leaf (NPGL) with thiolated beta-cyclodextrin (SH-β-CD) to realize sensitive and selective determination of BPA. Modification with NPGL and self-assembling of SH-β-CD on gold electrode were tracked by scanning electron microscopy, energy-dispersive spectroscopy and electrochemical measurements. The dual signaling method is based on the competitive host–guest interaction by recording the signals from both target molecule BPA and probe molecule methylene blue (MB). Due to the different binding ability of host molecule (β-CD) towards BPA and MB, BPA is able to enter β-CD cavities and replace the pre-existing MB, resulting in the decreased oxidation peak current of MB and the increased oxidation peak current of BPA. The summation of both current changes (|ΔIMB| + ΔIBPA) is linearly dependent on Napierian logarithm of BPA concentration from 3 × 10−7 M to 1 × 10−4 M with a detection limit of 6 × 10−8 M (S/N = 3). It is noted that the detection limit obtained by dual-signaling is much lower than that using single ΔIBPA as the response signal. This newly developed sensor was further adopted to measure BPA in milk and tap water. The proposed dual-signal strategy and the established hybrid electrochemical sensor have great potential applications in biomarker detection, food safety testing and environmental monitoring.

A reassembled nanoporous gold leaf electrocatalyst for efficient CO2reduction towards CO

The free-standing nanoporous gold leaf has an excellent FE of 90% towards CO and a high mass activity of 20.51 A/g.

Nanoporous gold leaf as a signal amplification agent for the detection of VOCs with a quartz crystal microbalance.

In this work, a novel sensing framework coupling nanoporous gold leaf (NPGL) and sensitive materials on a quartz crystal microbalance (QCM) sensor was developed for the detection of volatile organic compounds (VOCs). A bi-layer structure was established through a two-step modification process, where NPGL served as a loading platform to anchor more sensitive materials and provide a larger surface area. Sensitive materials for different target analytes (ethanol, benzene and n-heptane) were optimized, as well as the selection of the most suitable NPGL. The morphology of the bi-layer was characterized and the sensing performance, including the detection range, response time, reversibility, stability, etc., was investigated. The thermodynamics and kinetics of the gas adsorption process were studied by employing several classical models. It was found that the adsorption of the tested VOCs was more accurately represented using the Freundlich isotherm and the adsorption kinetics of these VOCs fitted well with pseudo second-order kinetics. The results of on-line monitoring demonstrated admirable sensing properties, fully indicating that the QCM sensor modified with a composite layer of sensitive material/NPGL has promising application prospects for real-time detection.

A novel sensitive and selective electrochemical sensor based on molecularly imprinted polymer on a nanoporous gold leaf modified electrode for warfarin sodium determination

A novel electrochemical sensor was facilely fabricated by coupling nanoporous gold leaf (NPGL) with molecularly imprinted polymer (MIP), and afforded ultrasensitive and selective determination of warfarin sodium (WFS).

Electrochemical determination of trace lead(II) with enhanced sensitivity and selectivity by three-dimensional nanoporous gold leaf and self-assembled homocysteine monolayer

Abstract In this work, a novel electrochemical sensor was prepared based on self-assembled homocysteine molecular layer on the surface of a three-dimensional (3D) nanoporous gold leaf (NPGL) modified gold electrode (HCys/NPGL/GE) and applied for trace measurement of Pb(II) by differential pulse anodic stripping voltammetry (DPASV). NPGL is introduced in order to enhance electron transport efficiency and surface area of sensor, while homocysteine as an adapter on NPGL surface can capture Pb(II) and further elevate sensitivity and selectivity in detecting Pb(II). The DPASV response of Pb(II) at the HCys/NPGL/GE was about four and three times larger than that at HCys/GE and NPGL/GE, respectively. Factors influencing determination of Pb(II) including pH value, deposition potential and deposition time were investigated. Under optimal conditions, the electrochemical sensor exhibited a wide linearity range from 1 μg/L to 200 μg/L Pb(II) with a detection limit of 0.1 μg/L (S/N = 3). The detection limit is much lower than 10 μg/L, which is the guideline value in drinking water given by the World Health Organization. Application of the established sensor in detecting Pb(II) in routine samples, including Chinese herb ( Radix Scutellariae ), blood and waste water, has been realized, and the results agreed well with those obtained by hydride generation atomic fluorescence spectrometry.

Molecularly imprinted polymer decorated nanoporous gold for highly selective and sensitive electrochemical sensors.

Electrochemical nanosensors based on nanoporous gold leaf (NPGL) and molecularly imprinted polymer (MIP) are developed for pharmaceutical analysis by using metronidazole (MNZ) as a model analyte. NPGL, serving as the loading platform for MIP immobilization, possesses large accessible surface area with superb electric conductivity, while electrochemically synthesized MIP thin layer affords selectivity for specific recognition of MNZ molecules. For MNZ determination, the hybrid electrode shows two dynamic linear range of 5 × 10−11 to 1 × 10−9 mol L−1 and 1 × 10−9 to 1.4 × 10−6 mol L−1 with a remarkably low detection limit of 1.8 × 10−11 mol L−1 (S/N = 3). In addition, the sensor exhibits high binding affinity and selectivity towards MNZ with excellent reproducibility and stability. Finally, the reliability of MIP-NPGL for MNZ detection is proved in real fish tissue samples, demonstrating the potential for the proposed electrochemical sensors in monitoring drug and biological samples.

Ultra-thin layer structured anodes for highly durable low-Pt direct formic acid fuel cells

Direct formic acid fuel cells (DFAFCs) allow highly efficient low temperature conversion of chemical energy into electricity and are expected to play a vital role in our future sustainable society. However, the massive precious metal usage in current membrane electrode assembly (MEA) technology greatly inhibits their actual applications. Here we demonstrate a new type of anode constructed by confining highly active nanoengineered catalysts into an ultra-thin catalyst layer with thickness around 100 nm. Specifically, an atomic layer of platinum is first deposited onto nanoporous gold (NPG) leaf to achieve high utilization of Pt and easy accessibility of both reactants and electrons to active sites. These NPG-Pt core/shell nanostructures are further decorated by a sub-monolayer of Bi to create highly active reaction sites for formic acid electro-oxidation. Thus obtained layer-structured NPG-Pt-Bi thin films allow a dramatic decrease in Pt usage down to 3 μg·cm−2, while maintaining very high electrode activity and power performance at sufficiently low overall precious metal loading. Moreover, these electrode materials show superior durability during half-year test in actual DFAFCs, with remarkable resistance to common impurities in formic acid, which together imply their great potential in applications in actual devices.

Metal enhanced fluorescence on nanoporous gold leaf-based assay platform for virus detection

In the present study, a rapid, sensitive and quantitative detection of influenza A virus targeting hemagglutinin (HA) was developed using hybrid structure of quantum dots (QDs) and nanoporous gold leaf (NPGL). NPGL film was prepared by dealloying bimetallic film where its surface morphology and roughness were fairly controlled. Anti-influenza A virus HA antibody (ab66189) was bound with NPGL and amine (–NH2) terminated QDs. These biofunctionalized NPGL and QDs formed a complex with the influenza virus A/Beijing/262/95 (H1N1) and the photoluminescence (PL) intensities of QDs were linearly correlated with the concentrations of the virus up to 1ng/mL while no PL was observed in the absence of the virus, or in bovine serum albumin (BSA, 1µg/mL) alone. In addition, it was demonstrated that this assay detected successfully influenza virus A/Yokohama/110/2009 (H3N2) that is isolated from a clinical sample, at a concentration of ca. 50 plaque forming units (PFU)/mL. This detection limit is 2-order more sensitive than a commercially available rapid influenza diagnostic test. From these results, the proposed assay may offer a new strategy to monitor influenza virus for public health.

Nanoporous Gold Leaf for Amperometric Determination of Nitrite

AbstractUltra‐thin free‐standing nanoporous gold leaf made by dealloying exhibits excellent electrocatalytic activities toward nitrite oxidation. The electrochemical responses of nitrite ions on this novel nano‐electrode is found not dependent on pH over a wide range from 4.5 to 8.0, which is markedly different from that of gold oxidation, a process known to be highly pH‐sensitive. Amperometric study shows a linear relationship for nitrite determination in a concentration range from 1 µM to 1 mM. This nanostructured gold electrode displays good stability, repeatability and selectivity which suggests its potential for the development of new electrochemical sensors.

Electrochemiluminescence immunoassay at a nanoporous gold leaf electrode and using CdTe quantun dots as labels

An electrochemiluminescence-based immunoassay using quantum dots (QDs) as labels for the carcinoembryonic antigen (CEA) was developed using an electrode modified with leafs of nanoporous gold. CEA was initially immobilized on the electrode via a sandwich immunoreaction, and then CdTe quantum dots capped with thioglycolic acid were used to label the second antibody. The intensity of the ECL of the QDs reflects the quantity of CEA immobilized on the electrode. Thus, in the presence of dithiopersulfate as the coreactant, the ECL serves as the signal for the determination of CEA. The intensity of the electroluminescence (ECL) of the electrode was about 5.5-fold higher than that obtained with a bare gold electrode. The relation between ECL intensity and CEA concentration is linear in the range from 0.05 to 200 ng.mL-1, and the detection limit is 0.01 ng.mL-1. The method has the advantages of high sensitivity, good reproducibility and long-term stability, and paves a new avenue for applying quantum dots in ECL-based bioassays.

Electrochemiluminescence of CdTe quantum dots as labels at nanoporous gold leaf electrodes for ultrasensitive DNA analysis

A new electrochemiluminescence (ECL) DNA assay is developed using quantum dots (QDs) as DNA labels. When nanoporous gold leaf (NPGL) electrodes are used, sensitivity of the ECL assay is remarkably increased due to ultra-thin nanopores. In this assay, target DNA (t-DNA) is hybridized with capture DNA (c-DNA) bound on the NPGL electrode, which is fabricated by conjugating amino-modified c-DNA to thioglycolic acid (TGA) modified at the activated NPGL electrode. Following that, amino-modified probe DNA is hybridized with the t-DNA, yielding sandwich hybrids on the NPGL electrode. Then, mercaptopropionic acid-capped CdTe QDs are labeled to the amino group end of the sandwich hybrids. Finally, in the presence of S(2)O(8)(2-) as coreactant, ECL emission of the QD-labeled DNA hybrids on the NPGL electrode is measured by scanning the potential from 0 to -2V to record the curve of ECL intensity versus potential. The maximum ECL intensity (I(m,ECL)) on the curve is proportional to t-DNA concentration with a linear range of 5 x 10(-15) to 1 x 10(-11)mol/L. The ECL DNA assay can be used to determine DNA corresponding to mRNA in cell extracts in this study.

Functionalized Nanoporous Gold Leaf Electrode Films for the Immobilization of Photosystem I

Plants and some types of bacteria demonstrate an elegant means to capitalize on the superabundance of solar energy that reaches our planet with their energy conversion process called photosynthesis. Seeking to harness Nature's optimization of this process, we have devised a biomimetic photonic energy conversion system that makes use of the photoactive protein complex Photosystem I, immobilized on the surface of nanoporous gold leaf (NPGL) electrodes, to drive a photoinduced electric current through an electrochemical cell. The intent of this study is to further the understanding of how the useful functionality of these naturally mass-produced, biological light-harvesting complexes can be integrated with nonbiological materials. Here, we show that the protein complexes retain their photonic energy conversion functionality after attachment to the nanoporous electrode surface and, further, that the additional PSI/electrode interfacial area provided by the NPGL allows for an increase in PSI-mediated electron transfer with respect to an analogous 2D system if the pores are sufficiently enlarged by dealloying. This increase of interfacial area is pertinent for other applications involving electron transfer between phases; thus, we also report on the widely accessible and scalable method by which the NPGL electrode films used in this study are fabricated and attached to glass and Au/Si supports and demonstrate their adaptability by modification with various self-assembled monolayers. Finally, we demonstrate that the magnitude of the PSI-catalyzed photocurrents provided by the NPGL electrode films is dependent upon the intensity of the light used to irradiate the electrodes.

Platinum-Decorated Nanoporous Gold Leaf for Methanol Electrooxidation

Pt-decorated nanoporous gold (Pt-NPG) leaf was prepared by depositing an atomically thin layer of Pt over NPG substrate where Pt overlayers grow epitaxially on NPG surfaces. Their catalytic properties toward methanol and CO electrooxidation were studied, and they show structure-sensitive activities and a greatly enhanced antipoisoning effect.

Platinum-plated nanoporous gold: An efficient, low Pt loading electrocatalyst for PEM fuel cells

Platinum-plated nanoporous gold leaf (Pt-NPGL) is made by coating a conformal, atomically thin skin of platinum over the high surface area pores of a thin membrane of nanoporous gold. Because Pt loading in Pt-NPGL can be controlled down to 0.01 mg cm −2 using only simple benchtop chemistry, the material holds promise as a low Pt loading, carbon-free electrocatalyst. Here, we report successful use of Pt-NPGL as a catalyst in proton exchange membrane (PEM) fuel cells. Stable and high performance Pt-NPGL/Nafion membrane electrode assemblies (MEAs) were made using a stamping technique. The performance of Pt-NPGL MEAs is comparable to conventional carbon-supported nanoparticles-based MEAs with much higher loading, generating an output power density of up to 4.5 kW g −1 Pt in our non-optimized test configuration. Correlations between the performance of Pt-NPGL MEAs, the electrochemically accessible surface area, and material microstructure are discussed. Our success in using Pt-NPGL as a fuel cell catalyst suggests that creating precious metals skins over nanoporous metal supports is a viable strategy for designing new catalysts for PEM fuel cells. This promising approach allows tailoring catalytic activity by engineering precious metal/substrate interactions, employs materials with dual functionality acting both as current collector and catalyst, and may avoid the sintering problems plaguing conventional nanoparticle-based catalysts.

Metallic Mesoporous Nanocomposites for Electrocatalysis

We describe the fabrication, characterization, and applications of ultrathin, free-standing mesoporous metal membranes uniformly decorated with catalytically active nanoparticles. Platinum-plated nanoporous gold leaf (Pt-NPG) made by confining a plating reaction to occur within the pores of dealloyed silver/gold leaf is 100 nm thick and contains an extremely high, uniform dispersion of 3 nm diameter catalytic particles. This nanostructured composite holds promise as a prototypical member of a new class of fuel cell electrodes, showing good electrocatalytic performance at low platinum loading (less than 0.05 mg cm-2), while also maintaining long-term stability against coarsening and aggregation of catalytic nanoparticles.