Au Nanoparticle Films Research Articles

Salt-Assisted, In Situ Current Nanowelding of an Interfacial Au Nanoparticle Film for a High-Performance Electrocatalyst.

Interfacial self-assembly is a well-established method for the preparation of a two-dimensional (2D) metal nanofilm from nanoscale building blocks. However, the as-prepared nanofilm exhibits limited conductivity because of the large contact resistance at the junctions among its building blocks. Here, we report a salt-assisted, in situ current nanowelding strategy to weld an interfacial Au nanoparticle (NP) film for downstream applications, such as high-performance electrocatalysts. Particularly, we found that salt-assisted interfacial assembly can reduce the size of the nanogaps among neighboring Au NPs and, in turn, greatly improve the conductivity of the resultant Au NP film. Consequently, the Au NP film can be readily welded using current, and the welding extent can be monitored in real-time by looking at the passing current. The welding finally produces a nanoporous Au film (NPGF) with a network nanostructure, high conductivity, and abundant active sites so that it delivers a large current density of 86.96 μA·cm-2 (1.81 times higher than that from the pristine Au NP film) and shows improved cycling stability for methanol electrooxidation. Thus, these results offer a low-cost, solution-processable approach for the fabrication of a large-area, interconnected nanofilm from nanoscale building blocks beyond Au NPs, which may find diverse downstream applications.

Investigation of biosensing properties in magnetron sputtered metallized UV-curable polymer microneedle electrodes

Direct management and assessment of metal film properties applied to polymer microneedle (MN) biosensors remains difficult due to constraints inherent to their morphology. By simplifying the three-dimensional structure of MNs and adjusting the deposition time, different thicknesses of Au films were deposited on the UV-cured polymer planar and MN substrates. Several properties relevant to the biosensing of the Au films grown on the polymer surfaces were investigated. The results demonstrate the successful deposition of pure and stable Au nanoparticles onto the surface of UV-curable polymer materials. Initially, Au islands formed within the first minute of deposition; however, as the sputtering time extended, these islands transformed into Au nanoparticle films and disappeared. The hydrophilicity of the surface remains unchanged, while the surface resistance of the thin film decreases with increasing thickness, and the adhesion to the substrate decreases as the thickness increases. In short, a sputtering time of 5–6 min results in Au films with a thickness of 100–200 nm, which exhibit exceptional comprehensive biosensing performance. Additionally, MNs made of Au/UV-curable polymers and produced using magnetron sputtering maintain their original shape, enhance their mechanical characteristics, and gain new functionalities. The Au/UV-curable polymer MNs exhibited remarkable electrode performance despite being soaked in a 37 °C PBS solution for 14 days. These discoveries have important implications in terms of decreasing the dependence on valuable metals in MN biosensors, lowering production expenses, and providing guidance for the choice and design of materials for UV-curable polymer MN metallization films.

3D hotspot engineering and analytes strategy enabled ultrasensitive SERS platform for biosensing of depression biomarker

Nowadays, the diagnose of depression mainly relies on clinical examination while impossible to accurately evaluate the occurrence of depression. Chemical approaches are captivating to analyze stress biomarkers for feedbacking body's endocrine response to stress stimuli. However, it remains challenging in exploring accurate, reliable and sensitive approaches. Herein, we rationally design a newly SERS platform with integrated hotspots engineering and analyte strategy to achieve highly sensitive analysis for estrogen, a typical depression biomarker in adolescent female. On the one hand, the 3D micro/nano plasmonic substrate containing Au–Ag Alloy Nanourchins (AAA-NUs) and arrays-based monolayer films of Au nanoparticles (Au NSs) was constructed to achieve high density and availability of hotspots. On the other hand, the analyte strategy was designed via rapid azotizing reaction to further enhance the scattering cross-section of estrogen in the form of azido compounds. With the synergism of them, the proposed SERS platform displayed high sensitivity for estrogen with a limit of detection down to 10−11 mg/mL. More importantly, the blood estrogen levels of depressed patients were evaluated via the proposed SERS platform and presented high consistence with clinical diagnostic results. This integrated SERS platform paves the way for universal and ultrasensitive biosensing and possess great potential for applying in multi-target detection and disease prediction.

Plasmon resonance-enhanced superior 2D MoS2 photodetector via single-layer gold nanoparticle film with ultra-high area density

Molybdenum disulfide (MoS2) has been considered as a promising candidate material for photodetectors due to its unrivaled transistor behavior and strong light absorption. However, due to the ultra-thin nature of monolayer or few-layer MoS2, it exhibits a low optical cross-section, resulting in a very weak light–matter interaction and accordingly limiting the photoelectric conversion efficiency. In this work, we report a facile method to prepare single-layer gold (Au) nanoparticles with ultra-high area density according to the annealing of thin Au films. By transferring the single-layer Au nanoparticle film onto a prefabricated MoS2 photodetector, we demonstrate a photodetector with a responsivity as high as 1120 A W−1. Moreover, it is found that the response time is not affected by the Au nanoparticle decoration. This method provides an easy but effective way to fabricate high-performance two-dimensional material-based photodetectors.

Electrophoretic Deposition of Hybrid Calcium Alginate-Gold Nanoparticle Hydrogel Films via Catalyzed Electrooxidation of Hydroquinone

The electrophoretic deposition (EPD) of hybrid alginate (Alg)-Au nanoparticle (NP) films results from the localized pH drop at the electrode surface due to oxidation of hydroquinone (HQ) catalyzed by 4 and 15 nm diameter citrate-coated gold NPs (cit-Au NPs). The localized pH drop at the electrode leads to neutralization of both Alg and cit, leading to EPD of both Alg and cit-Au NPs simultaneously. Post-treatment of the film with Ca2+ solution leads to hybrid Ca-Alg-Au NP hydrogel films. The EPD of Alg in the presence of 4 nm cit-Au NPs occurs at ∼0.8 V (vs Ag/AgCl) as compared to ∼1.0 V in the presence of 15 nm cit-Au NPs and ∼1.4 V in the absence of cit-Au NPs. This is due to the higher catalytic activity of 4 nm cit-Au NPs compared to 15 nm cit-Au NPs for the oxidation of HQ. UV-vis spectra of Ca-Alg-Au NP hydrogel films show absorbance features for both Ca-Alg and Au NPs entrapped within the hydrogel. As the concentration of Au NPs in the EPD solution increases, the Ca-Alg absorbance and localized surface plasmon resonance (LSPR) peak of the Au NPs increases, confirming the role of the Au NPs as a catalyst for EPD of Alg. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of the Ca-Alg-Au NP hydrogel films show characteristic peaks for Ca-Alg and protonated alginic acid groups. The hydrogel thickness is greater with cit-Au NPs compared to without cit-Au NPs at constant EPD potential and time. Forming Ca-Alg and hybrid Ca-Alg-Au NP hydrogel films at low potentials has potential applications in electrochemical and optical sensor development, catalysis, and biological studies.

Surface plasmon mediated harmonically resonant effects on third harmonic generation from Au and CuS nanoparticle films

Abstract A growing class of nonlinear materials employ the localized surface plasmonic resonance (LSPR) of nanoparticles to enhance harmonic generation. Material systems containing harmonically coupled metallic and semiconductor plasmonic nanoparticles have been shown to further increase performance. Here, we explore the effect of dual plasmonic interactions in bilayer CuS and Au nanoparticle films on third harmonic generation (THG). Detuning the CuS LSPR away from the excitation frequency changes the dominant upconversion pathway from THG to multiple photon photoluminescence (MPPL). Changing the size of the Au nanoparticle red shifts the LSPR from the second harmonic of the pump frequency and also eliminates the enhancement effect. When both LSPRs satisfy the harmonic condition, simultaneous excitation of CuS-Au nanoparticle films at the resonant frequency of each nanoparticle species enhances the generation of third harmonic light by sum-frequency generation, suggesting that the enhancement of THG in dually plasmonic nanoparticle films is the result of a cascaded nonlinear mechanism. An analytic model of the interaction between the plasmonic nanoparticles due to incoherent dipolar interactions is also presented. Understanding these processes opens a pathway for developing ultrafast, high-efficiency upconversion thin-film devices by clarifying the conditions that efficiently produce third harmonic generation without background MPPL or additional harmonics.

Transfer and inkjet printing of gold thin film and graphene oxide nanoparticles for micro-oscillators

This study presents the results of micro-oscillator fabrication using the transfer printing (TP) of gold (Au) thin films and inkjet printing of graphene oxide (GO) nanoparticles. The Au thin films are formed into a double-supported microbeam to function as a micro-oscillator on a polymer substrate. The Au microbeams have a thickness of 300 nm and a length of 250 or 300 μm. To improve adhesion strength between the substrate and the Au thin film, the Au thin film is transferred and printed onto a substrate pre-coated with a 30-nm-thick Au surface via atomic diffusion bonding. Furthermore, GO nanoparticles are deposited on the transfer-printed Au thin film and the convex part of the stamp using inkjet printing to enhance the mechanical properties of the micro-oscillator. The former deposition forms a double-layered beam of Au and GO. The Au/GO/Au-layered microbeam is fabricated on a pre-structured substrate by TP after another Au thin film is then deposited on this GO/Au surface. These micro-oscillators can be driven by electrostatic force at less than 10 kHz with 90–210 V of applied voltage, while the deflection of the micro-oscillator is measured by a laser displacement meter. The Au micro-oscillators have a damping ratio of 0.166, and a resonance frequency of 0.28 kHz. This resonance frequency is smaller than that estimated by finite element method analysis. This difference in resonance frequency is attributed to the Young's modulus of the Au thin film and structural defects due to van der Waal bonding. The modulus of the laminated thin film of Au and GO nanoparticles is higher than that of the Au thin film.

Effect of gold on photo luminescence properties of Cadmium Sulphide thin films deposited by pulsed laser deposition

Cadmium Sulphide (CdS) on gold (Au) nanoparticle thin films were deposited by pulsed laser deposition (PLD) on sapphire and Silicon (Si) substrates. The films were analyzed by X-ray photo electron spectroscopy (XPS) to determine the binding energy of the constituent elements, atomic force microscopy (AFM) for surface morphology, X-ray diffraction (XRD) for crystal structure, photo luminescence (PL) and UV–VIS measurements for optical properties. The results of XPS analysis and spectroscopic ellipsometric characterization revealed the formation of CdS films. The films surface shows uniform smooth topography and having Hexagongal phase crystalline structure. The optical absorption spectra of CdS films deposited at room temperature (RT) showed absorption edge at around 580 nm which blue-shifted at high deposition temperature of 300 °C. The band edge photoluminescence of CdS films observed at 590 nm was enhanced with Au nanoparticle films present as the bottom of the layer attributed to the plasmonic related optical coupling between two materials. However, when the nanoparticles were deposited on top layer the luminescence was found to be quenched due to the internal absorption of the Au films due to plasmon resonance. The results of the study reveal that the optimum controlled deposition of Au nanoparticles with CdS thin films will be useful for fabrication of efficient opto-electronic devices.

Mass and density determination of porous nanoparticle films using a quartz crystal microbalance

A method is presented to directly measure the mass output of an impaction printer coupled with a spark ablation generator. It is based on a quartz crystal microbalance and shown to be reliable in quantifying mass deposition rate. Here, the method is demonstrated with an Au nanoparticle aerosol synthesized under several spark ablation and deposition settings. Changes in the deposition rate in response to changed synthesis conditions follow the spark ablation models on generation rate made in previous studies, validating this novel measurement method. In combination with the volume of a deposit, a good estimate of the film porosity can be made. The Au nanoparticle films synthesized here have a low porosity of 0.18 due to extensive restructuring and compaction on impact with the substrate. The porosity is found to be insensitive to deposition settings and is constant throughout the film. The simplicity and low cost of a quartz crystal microbalance setup make this an accessible method to determine porosity in porous thin films.

Low threshold and wavelength tunable SPASER based on plasmonic coupled nanostructure

We propose a low threshold and wavelength tunable plasmonic coupled nanolaser based on a plasmonic coupling between Au nanosphere and Au film. By the finite-element method, we investigate the optical properties of the plasmonic coupled nanolaser with different nanosphere diameters and gap distances between Au nanosphere and Au film. The optical cross section of the plasmonic nanolaser based on the coupled nanostructure can be 60 times larger than that based on an independent Au nanosphere. And the corresponding gain threshold of the plasmonic coupled nanolaser is only 35% of that of the nanolaser with the independent Au nanosphere. This is attributed to that the coupled nanostructure exhibits a stronger electric field and optical intensity than the independent Au nanosphere, it can more effectively improve gain to compensate for metal loss. In addition, the plasmonic coupled nanolaser also exhibits a wavelength tunability in a wide spectral range by controlling the Au nanosphere diameter and gap distance between Au nanoparticle and Au film. This work can provide us an effective way to develop the on-chip application of nanolaser.

Detection of 3,4-Methylene Dioxy Amphetamine in Urine by Magnetically Improved Surface-Enhanced Raman Scattering Sensing Strategy.

Abuse of illicit drugs has become a major issue of global concern. As a synthetic amphetamine analog, 3,4-Methylene Dioxy Amphetamine (MDA) causes serotonergic neurotoxicity, posing a serious risk to human health. In this work, a two-dimensional substrate of ITO/Au is fabricated by transferring Au nanoparticle film onto indium–tin oxide glass (ITO). By magnetic inducing assembly of Fe3O4@Au onto ITO/Au, a sandwich-based, surface-enhanced Raman scattering (SERS) detection strategy is designed. Through the use of an external magnet, the MDA is retained in the region of hot spots formed between Fe3O4@Au and ITO/Au; as a result, the SERS sensitivity for MDA is superior compared to other methods, lowering the limit of detection (LOD) to 0.0685 ng/mL and attaining a corresponding linear dynamic detection range of 5–105 ng/mL. As an actual application, this magnetically improved SERS sensing strategy is successfully applied to distinguish MDA in urine at trace level, which is beneficial to clinical and forensic monitors.

Self-Assembled Ligand-Capped Plasmonic Au Nanoparticle Films in the Kretschmann Configuration for Sensing of Volatile Organic Compounds

Films of close-packed Au nanoparticles are coupled electrodynamically through their collective plasmon resonances. This collective optical response results in enhanced light-matter interactions, which can be exploited in various applications. Here, we demonstrate their application in sensing volatile organic compounds, using methanol as a test-case. Ordered films over several cm2 were obtained by interfacial self-assembly of colloidal Au nanoparticles (~10 nm diameter) through controlled evaporation of the solvent. Even though isolated nanoparticles of this size are inherently non-scattering, when arranged in a close-packed film the plasmonic coupling results in a strong reflectance and absorbance. The in-situ tracking of vapor phase methanol concentration through UV-Vis transmission measurements of the nanoparticle film is first demonstrated. Next, in-situ ellipsometry of the self-assembled films in the Kretschmann (also known as ATR) configuration is shown to yield enhanced sensitivity, especially with phase difference measurements. Our study shows the excellent agreement between theoretical models of the spectral response of self-assembled films with experimental in-situ sensing experiments. At the same time, the theoretical framework provides the basis for the interpretation of the various observed experimental trends. Combining periodic nanoparticle films with ellipsometry in the Kretschmann configuration is a promising strategy towards highly sensitive and selective plasmonic thin-film devices based on colloidal fabrication methods for volatile organic compound (VOC) sensing applications.

Electrochemiluminescence aptasensor for vascular endothelial growth factor 165 detection based on Ru(bpy)32+/Au nanoparticles film modified electrode and double signal amplification

Vascular endothelial growth factor (VEGF165) is a signal protein that plays a central role in the regulation of angiogenesis and can stimulate angiogenesis. The development of highly sensitive and selective detection method for VEGF165 is very important for disease diagnosis and follow-up treatment monitoring. In this study, an electrochemiluminescence (ECL) aptasensor for VEGF165 has been developed based on quench of H2O2 toward Ru(bpy)32+/TPrA ECL system and RecJf exonuclease induced target recovery and hybridization chain reaction (HCR) as amplification strategy. The presence of VEGF165 makes a large number of glucose oxidase (GOD) fixed on the electrode surface through the double signal amplification strategies. The present of GOD cause the production of a large amount of H2O2 near the electrode surface under excess amount of glucose, resulting in the inhibition of the ECL signal of Ru(bpy)32+/Au nanoparticles (Ru(bpy)32+/AuNPs) film fixed on the electrode surface. The ECL response of the designed biosensor has a good linear relationship with the logarithm of the concentration of VEGF165 in the range of 0.5 pg/mL to 500 ng/mL with a detection limit of 0.2 fg/mL. The VEGF165 in serum samples has been detected by the proposed aptasensor with satisfactory results.

Bottom-up fabrication of three-dimensional nanoporous gold from Au nanoparticles using nanowelding

Three-dimensional (3D) nanoporous gold (NPG) shows promising applications in various fields. However, its most common fabrication strategy (i.e., dealloying) faces the problems of high energy consumption, resource waste, the use of corrosive solvent, and residue of the sacrificial component. Here, we report a general bottom-up nanowelding strategy to fabricate high-purity NPG from Au nanoparticles (NPs), accomplished via interfacial self-assembly of the Au NPs into monolayer Au NP film, its subsequent layer-by-layer transfer onto a solid substrate, and direct current (DC) nanowelding. We show that the DC nanowelding process can gradually evolve the layered Au NP film into NPG at low temperatures within 10 s, while not damaging their spherical structure. This is because during the nanowelding, electrons are preferred to be localized at the high-resistance NP/NP junctions, whose electrostatic repulsion in turn strengthens their surface atom diffusion to initiate a mild solid-state diffusion nanowelding. Furthermore, when using differently sized Au NPs as the starting building blocks, this strategy allows readily tuning the thickness, ligament size, and pore size, thereby offering great flexibility to create functional porous nanomaterials, e.g., electrocatalyst for methanol electrooxidation. Surely, low-temperature nanowelding can play a role for the production of diverse nanoporous materials from other NPs beyond Au NPs.

A sandwich-type electrochemical immunosensor based on Au-rGO composite for CA15-3 tumor marker detection.

A sensitive detection of carbohydrate antigen 15-3 (CA15-3) levels may allow for early diagnosis and monitoring the treatment of breast cancer, but this can only be made in routine clinical practice if low-cost immunosensors are available. In this work, we developed a sandwich-type electrochemical immunosensor capable of rapid detection of CA15-3 with an ultra-low limit of detection (LOD) of 0.08fgmL-1 within a wide linear concentration range from 0.1fgmL-1 to 1µgmL-1. The immunosensor had a matrix of a layer-by-layer film of Au nanoparticles and reduced graphene oxide (Au-rGO) co-electrodeposited on screen-printed carbon electrodes (SPCE). The high sensitivity was achieved by using secondary antibodies (Ab2) labeled with horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H2O2) as signal amplifiers, and hydroquinone (HQ) was used as an electron mediator. The immunosensor was selective for CA15-3 in human serum and artificial saliva samples, robust, and stable to permit storage at 4°C for more than 30days. With its high performance, the immunosensor may be incorporated into future point-of-care (POC) devices to determine CA15-3 in distinct biological fluids, including in blood and saliva samples.

Hydrogel Film@Au Nanoparticle Arrays Based on Self‐Assembly Co‐Assisted by Electrostatic Attraction and Hydrogel‐Shrinkage for SERS Detection with Active Gaps

AbstractA facile route to fabricate the hydrogel film@Au nanoparticle array composite for a surface‐enhanced Raman scattering (SERS) substrate with high signal sensitivity and signal uniformity based on self‐assembly co‐assisted by electrostatic reaction and hydrogel‐shrinkage is developed. First, the positive‐charged Au nanoparticles (NPs) are self‐assembled on the hydrogel film with opposite charges due to electrostatic attraction to obtain non‐close‐packed Au NP films on both surface sides of the hydrogel film. Then, the non‐close‐packed Au NP films are densified to further form hexagonal close‐packed Au NP arrays on both surfaces due to the principle of minimum free energy during the hydrogel‐shrinkage process. The shrinkage of hydrogel film is proved to be a key process to form hexagonal close‐packed Au NP arrays by densifying the non‐closely packed Au NPs achieved by electrostatically self‐assembled on the hydrogel film. Constructed SERS substrate exhibits high signal sensitivity, colorant molecule amaranth with a concentration as low as 10−8 m can be detected. This is caused by the uniform array structure with active gaps between neighboring NPs on a large area. Overall, this work paves a way to fabricate functional NP arrays on soft hydrogel, which will be highly helpful to prepare the micro/nano‐structured devices.

Refractive Index versus Coupling Effects for Naked and Surfactant-Coated Au Nanoparticle Films: Implications for Selective Detection of Vapor–Liquid Analytes

From a single dispersion of surfactant-coated Au nanoparticles (NPs), we can assemble colorimetric films of different thickness, organic content, and structure. In this work, we demonstrate how these variables play a fundamental role in determining what sensing mechanism predominates when these films are subjected to liquid-phase ethanol (EtOH), acetone (Ace), and toluene (Tol) analytes. Theoretical calculations, performed with the Korringa–Kohn–Rostoker (KKR) model, agree very well with the experiments if we consider that thinner films with lesser organic/inorganic content (or no organic at all) offer more vacancies for the solvents to partition, leading to effective changes in the permittivity. Instead, thicker films with a more compacted structure suffer minimal changes in the effective permittivity (lesser vacancies), causing color changes dominated by changes in the distance between the Au NPs. These films may be incorporated into a sensor array for improving selectivity toward the detection of vapor/liquid-phase analytes.

Metal-Organic Framework and Silver Nanowire Composites As Chemiresistive Gas Sensors Operating at the Percolation Threshold

The high internal service areas and consequent high numbers of sites for analyte adsorption of Metal-Organic Frameworks, MOFs, make them attractive candidates for gas sensing applications. Through synthesis of conductive MOFs we present a novel way of fabricating chemiresistive sensors able to detect NO2 gas in the low ppm range. A suspension of MOF and Ag nanowires in solution is prepared and drop cast onto paper to form the sensing medium. Sufficient conductive MOF is added to an insulating concentration of nanowires to give a conductive sample operating in the percolation region. The percolation region refers to the point before a thin film has formed where a small change in the number of conductive pathways leads to the largest change in material conductivity, as depicted in figure 1.1 By fabricating sensors operating in this region, a small interruption in the conductive network due to analyte interaction leads to a large change in measurable conductivity, allowing higher sensor sensitivities to be accessed.2 , 3 Moreover, the use of MOFs lends itself to the systematic synthesis of sensing media tailored to respond to desired gaseous analytes. Through selection of organic linkers with particular functional groups and/or particular metal nodes, the functionality and pore sizes of the resulting MOFs can be manipulated. We have synthesised MOFs with Cu, Ni and Fe metal centres linked by hexahydroxytriphenylene ligands4 and fabricated chemiresistive sensors through combination with Ag nanowires. Their different sensing responses to NO2 and NH3 gases with concentrations below 5 ppm have been recorded, and the simultaneous exposure of all three MOF sensors in an array to gaseous analytes is anticipated to further increase sensor selectivity. Figure 1: Schematic of a percolation curve, demonstrating how the conductivity between two electrodes changes as the concentration of conductive material, such as conductive polymer, between the electrodes is increased. The optimum region for sensing experiments is where the gradient is steepest; the percolation region. Image reproduced from reference 1. References Murugappan K, Castell MR. Bridging electrode gaps with conducting polymers around the electrical percolation threshold. Electrochem commun. 2018;87:40-43. doi:10.1016/j.elecom.2017.12.019Lefferts MJ, Murugappan K, Wu C, Castell MR. Electrical percolation through a discontinuous Au nanoparticle film. Appl Phys Lett. 2018;112(25):251602. doi:10.1063/1.5023163Armitage BI, Murugappan K, Lefferts MJ, Cowsik A, Castell MR. Conducting polymer percolation gas sensor on a flexible substrate. J Mater Chem C. 2020;8:12669. doi:10.1039/d0tc02856hCampbell MG, Liu SF, Swager TM, Dincə M. Chemiresistive Sensor Arrays from Conductive 2D Metal-Organic Frameworks. J Am Chem Soc. 2015;137(43):13780-13783. doi:10.1021/jacs.5b09600 Figure 1

H2S sensing for breath analysis with Au functionalized ZnO nanowires

This work presents a H2S selective resistive gas sensor design based on a chemical field effect transistor (ChemFET) with open gate formed by hundreds of high temperature chemical vapour deposition (CVD) grown zinc oxide nanowires (ZnO NW). The sensing ability of pristine ZnO NWs and surface functionalized ZnO NWs for H2S is analysed systematically. ZnO NWs are functionalized by deposition of discontinuous gold (Au) nanoparticle films of different thicknesses of catalyst layer ranging from 1 to 10 nm and are compared in their gas sensing properties. All experiments were performed in a temperature stabilized small volume compartment with adjustable gas mixture at room temperature. The results allow for a well-founded understanding of signal-to-noise ratio, enhanced response, and improved limit of detection due to the Au functionalisation. Comprehension and controlled application of the beneficial effects of Au catalyst on ZnO NWs allow for the detection of very low H2S concentrations down to 10 ppb, and a theoretically estimated 500 ppt in synthetic air at room temperature.

Nanoscale flexible Ag grating/AuNPs self-assembly hybrid for ultra-sensitive sensors

In this paper, Au nanoparticles (AuNPs) are prepared using wet chemical reduction transfer of dense AuNPs film by self-assembly to the surface of Ag grating, which is inverted from the inner DVD after evaporation. The Ag grating/AuNPs self-assembly hybrid substrate commonly used in surface-enhanced Raman scattering (SERS) research is produced. The coupling effect between AuNP-AuNP and AuNPs-Ag slugs can evidently enhance the local electric field. Experimental results show that the hybrid SERS substrate can detect 10−9 M Rh6G, and the enhancement factor reaches 4.4 × 105. This small, cheap hybrid substrate has enormous potential in the field of SERS sensing.