Gold Nanoparticle Thin Films Research Articles

Motion Sensing by a Highly Sensitive Nanogold Strain Sensor in a Biomimetic 3D Environment.

Recent advancements in flexible electronics have highlighted their potential in biomedical applications, primarily due to their human-friendly nature. This study introduces a new flexible electronic system designed for motion sensing in a biomimetic three-dimensional (3D) environment. The system features a self-healing gel matrix (chitosan-based hydrogel) that effectively mimics the dynamics of the extracellular matrix (ECM), and is integrated with a highly sensitive thin-film resistive strain sensor, which is fabricated by incorporating a cross-linked gold nanoparticle (GNP) thin film as the active conductive layer onto a biocompatible microphase-separated polyurethane (PU) substrate through a clean, rapid, and high-precision contact printing method. The GNP-PU strain sensor demonstrates high sensitivity (a gauge factor of ∼50), good stability, and waterproofing properties. The feasibility of detecting small motion was evaluated by sensing the beating of human induced pluripotent stem cell (hiPSC)-derived cardiomyocyte spheroids embedded in the gel matrix. The integration of these components exemplifies a proof-of-concept for using flexible electronics comprising self-healing hydrogel and thin-film nanogold in cardiac sensing and offers promising insights into the development of next-generation biomimetic flexible electronic devices.

Electrically conductive gold films formed by sintering of gold nanoparticles at room temperature initiated by ozone

Understanding and controlling the sintering behaviour of gold nanoparticles is important in the field of ligand-protected nanoparticles for their use as precursors for thin film fabrication. Lowering the temperature of the sintering event of gold nanoparticles by facilitating desorption of the ligand through oxidation can provide compatibility of sintered gold nanoparticle thin films onto heat-sensitive substrates. Here we examine the processes by which 1-butanethiol-protected gold nanoparticles sinter under an ozone-rich environment. Upon heating, an ozone-rich environment significantly reduces the temperature of the sintering event when compared to sintering under ambient conditions. At room temperature, exposure to an ozone-rich environment induces sintering over a period of 2.5 h. Upon exposure to ozone, the surface-bound butanethiol ligands are oxidised to 1-butanesulfonic acid which facilitates sintering.

Plasmonic Properties of Self-Assembled Gold Nanocrescents: Implications for Chemical Sensing.

A bottom-up approach, the Langmuir-Blodgett technique, is used for the preparation of composite thin films of gold nanoparticles and polymers: poly(styrene-b-2-vinylpyridine), poly-2-vinylpyridine, and polystyrene. The self-assembly of poly(styrene-b-2-vinylpyridine) at the air-water interface leads to the formation of surface micelles, which serve as a template for the organization of gold nanoparticles into ring assemblies. By using poly-2-vinylpyridine in conjunction with low surface pressure, the distance between nanostructures can be increased, allowing for optical characterization of single nanostructures. Once deposited on a solid substrate, the preorganized gold nanoparticles are subjected to further growth by the reduction of additional gold, leading to a variety of nanostructures which can be divided into two categories: nanocrescents and circular arrays of nanoparticles. The optical properties of individual structures are investigated by optical dark-field spectroscopy and numerical calculations. The plasmonic behavior of the nanostructures is elucidated through the correlation of optical properties with structural features and the identification of dominant plasmon modes. Being based on a self-assembly approach, the reported method allows for the formation of interesting plasmonic materials under ambient conditions, at a relatively large scale, and at low cost. These attributes, in addition to the resonances located in the near-infrared region of the spectrum, make nanocrescents candidates for biological and chemical sensing.

Tuning the Morphological and Optical Properties of Pulsed Laser-Deposited Gold Nanoparticle Thin Films by Varying Number of Laser Pulses

Tuning the Morphological and Optical Properties of Pulsed Laser-Deposited Gold Nanoparticle Thin Films by Varying Number of Laser Pulses

Fabrication of Eco-Friendly Wearable Strain Sensor Arrays via Facile Contact Printing for Healthcare Applications.

Wearable flexible strain sensors with spatial resolution enable the acquisition and analysis of complex actions for noninvasive personalized healthcare applications. To provide secure contact with skin and to avoid environmental pollution after usage, sensors with biocompatibility and biodegradability are highly desirable. Herein, wearable flexible strain sensors composed of crosslinked gold nanoparticle (GNP) thin films as the active conductive layer and transparent biodegradable polyurethane (PU) films as the flexible substrate are developed. The patterned GNP films (micrometer- to millimeter-scale square and rectangle geometry, alphabetic characters, and wave and array patterns) are transferred onto the biodegradable PU film via a facile, clean, rapid and high-precision contact printing method, without the need of a sacrificial polymer carrier or organic solvents. The GNP-PU strain sensor with low Young's modulus (≈17.8MPa) and high stretchability showed good stability and durability (10000 cycles) as well as degradability (42% weight loss after 17 days at 74°C in water). The GNP-PU strain sensor arrays with spatiotemporal strain resolution are applied as wearable eco-friendly electronics for monitoring subtle physiological signals (e.g., mapping of arterial lines and sensing pulse waveforms) and large-strain actions (e.g., finger bending).

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.

Electrophoretic deposited gold nanoparticle thin film on silver substrate

AbstractEffects of the deposition time and voltage on the characteristics of gold nanoparticles (NPs) thin films, prepared by the electrophoretic deposition (EPD) method on the silver substrate, were investigated experimentally. Au NPs were synthesised using the pulsed laser ablation method in distilled water. The suspended solution of the gold NPs was used as the electrolyte of EPD. An irradiation was carried out by the fundamental wavelength of a Q‐switched NdYAG laser at 1064 nm and 7 ns pulse width. The electrophoretic deposition apparatus consisted of two 2 × 2 cm pieces of silver plates as the electrodes. They were immersed in parallel with a 7 mm gap in the gold NP suspension. Five samples of gold NP thin films were prepared at different deposition times and applied voltages. Results show that the roughness, thickness and surface quality of EPD prepared thin films can be strongly controlled by the deposition time and applied voltage. The thickness of deposited films was dependent on the voltage of deposition in which their roughness was increased with increasing the deposition time. Furthermore, the reflection of deposited films was affected by the surface roughness.

Nonlinear Photoluminescence from Gold Nanoparticle Thin Films Studied by Scanning Near-Field Optical Microscopy

Nonlinear Photoluminescence from Gold Nanoparticle Thin Films Studied by Scanning Near-Field Optical Microscopy

Optimization of Piezoresistive Strain Sensors Based on Gold Nanoparticle Deposits on PDMS Substrates for Highly Sensitive Human Pulse Sensing

In this study, highly-sensitive piezoresistive strain sensors based on gold nanoparticle thin films deposited on a stretchable PDMS substrate by centrifugation were developed to measure arterial pulse waveform. By controlling carbon chain length of surfactants, pH value and particle density of the colloidal solutions, the gauge factors of nanoparticle thin film sensors can be optimized up to 677 in tensile mode and 338 in compressive mode, and the pressure sensitivity up to 350. Low pH and thin nanoparticle films produce positive influences to superior gauge factors. It has been demonstrated that nanoparticle thin film sensors on PDMS substrates were successfully applied to sense arterial pulses in different body positions, including wrist, elbow crease, neck, and chest.

Relaxation Phenomena in Chitosan-Au Nanoparticle Thin Films.

Chitosan–gold nanoparticle (CS/AuNP) thin films were synthesized through the chemical reduction of HAuCl4 in sodium citrate/chitosan solutions. The dielectric and dynamic mechanical behaviors of CS/AuNP films have been investigated as a function of moisture and HAuCl4 content. Two relaxation processes in the nanocomposites have been observed. The α-relaxation process is related to a glass transition in wet CS/AuNP films. However, in dry composites (with 0.2 wt% of moisture content), the glass transition vanished. A second relaxation process was observed from 70 °C to the onset of thermal degradation (160 °C) in wet films and from 33 °C to the onset of degradation in dry films. This relaxation is identified as the σ-relaxation and may be related to the local diffusion process of ions between high potential barriers in disordered systems. The α- and σ-relaxation processes are affected by the HAuCl4 content of the solutions from which films were obtained because of the interaction between CS, sodium succinate, and gold nanoparticles. With about 0.6 mM of HAuCl4, the conductivity of both wet and dry films sharply increased by six orders, corresponding to the percolation effect, which may be related to the appearance of a conductivity pathway between AuNPs, HAuCl4, and NaCl.

Simulation of the optical properties of gold nanoparticles on sodium alginate

In this contribution, we report on the simulation of optical reflectance and transmittance (R&T) taken on a set of gold nanoparticles thin film, deposited on sodium alginate by magnetron sputtering. The gold layer is very thin, so that the films are not continuous and the material is arranged in nanostructured layers. R&T spectra are simulated using the Generalized Transfer Matrix method applied to the film-on-substrate model. The gold NP films are simulated using the Drude-Lorentz model, by taking into account that the optical function of nanostructured gold exhibits increased collision frequency and reduced relaxation time. Moreover, the signal of localized surface plasmon, evident in the spectra, is simulated by introducing a dedicated modified Lorentz oscillator. The experimental results are well reproduced by the applied model. All trends (amplitude and energy position of the plasmon oscillator, film thickness, relaxation time) are correlated with the deposition parameters. The procedure represents a useful tool in the characterisation of such nanoparticles thin films.

Tuning optical and optoelectronic properties of gold nanoparticle and ZnO thin film hetero-structures

Thin film hetero-structures (TFHSs) involving metal oxide thin films and noble metal nanoparticles are very important for many optoelectronics based device applications. This work reports the growth, characterization, and tuning of photoluminescence and I–V properties of TFHSs involving zinc oxide (ZnO) and gold nanoparticles (GNPs). ZnO thin films and GNPs were respectively deposited by the Pulsed Laser Deposition (PLD) and DC sputtering with subsequent annealing. Three different TFHSs were prepared by varying the relative positions of ZnO and GNPs, namely Si-GNPs-ZnO, Si-ZnO-GNPs, and Si-ZnO-GNPs-ZnO. X-ray diffraction results confirmed the high crystallinity of the films, with single phase nature of the ZnO and GNPs. Scanning electron microscopy micrograph analysis confirmed that the morphology of structures containing both GNPs and ZnO is influenced by the bottom layer. Diffuse reflectance spectroscopy results also indicated that the position of GNPs relative to ZnO affects the plasmon resonance of GNPs as well as the overall optical properties of the TFHSs. Photoluminescence studies revealed that the presence of GNPs affects the defect concentration in the TFHSs. The I–V characteristics showed that the TFHSs where ZnO contains GNPs in embedded form are better suited for photodiode application. This study adds a new dimension to the research on optoelectronics devices.

Full Atomistic Simulation of Cross-Linked Gold Nanoparticle Assemblies

Nanoparticles (NPs) comprised of noble metal cores and organic ligands have been widely used in many engineering applications in the recent years due to their exceptional material properties. Numerous studies have explored the tunability of the elastic and electronic transport properties of nano-scale thin films made of gold nanoparticles. However, the nanoscale mechanisms, such as the conformation of ligands, cross-linking behavior, are still not well understood. In this study, we developed a full atomistic modeling approach to construct full atomistic cross-linked gold nanoparticle thin films to explore the nanoscale features and molecular configurations of cross-linked gold nanoparticle assemblies at the nano-scale.

Fabrication of Nanostructured Electrochemical Sensor Based on Gold Nanoparticles Thin Film Modified FTO Electrode for Detection of Arsenic in Aqueous Media

Although arsenic is naturally present in the environment, 99% of human exposure to arsenic is through ingestion. Throughout history, arsenic is known as “the king of poisons”; it is mutagenic, carcinogenic, and teratogenic. Even in smaller concentrations, it accumulates in the body and takes decades before any physical symptoms of arsenic poisoning show. According to the World Health Organization (WHO), the safe concentration of arsenic in drinking water is 10 µg/L. However, this limit is often ignored until it is decades too late, and people begin showing symptoms of having been poisoned. This is the current situation for Vietnam, whose legal arsenic concentration limit is 50 µg/L, five times higher than the WHO guidelines. Groundwater in Vietnam was already naturally high in arsenic due to arsenic‐rich soils releasing arsenic into groundwater. Then, in the past half-century, with the use of arsenic‐laden herbicides dispersed during Vietnam. This work aimed to fabricate a gold nanoparticles (AuNPs) electrochemical sensor on the surface of the conductive glass (FTO), which can detect the tiny concentration of arsenic. The AuNPs electrochemical sensors (Au thin films) are prepared on the surface of FTO following three methods: (i) electro-deposition, (ii) electrophoresis, and (iii) screen-printing. All methods allow the control of size and shape (nanorod, nano-star, branched-shape, quasi-spherical shape, spherical shape) of AuNPs that benefit the limit of detection (LOD).

Characterization of gold nanoparticle thin film prepared by electrophoretic deposition method

Gold nanoparticle thin films were deposited on copper substrate using electrophoretic deposition (EPD) method. At first, gold nanoparticles were synthesized, using pulsed laser ablation method of a high-purity gold target in distilled water. Ablation was carried out, employing the fundamental wavelength of a Q-switched Nd:YAG laser at 1064 nm and pulse width of 7 ns. Suspension of gold nanoparticle was used as the electrolyte of EPD, in which two copper electrodes with 7 mm gap were immersed. Five samples of gold nanoparticle thin films were prepared at different deposition times and applied voltages. Nanoparticles and thin films were characterized by different diagnostics such as X-ray diffraction pattern, atomic force microscopy (AFM), and scanning electron microscopy (SEM) images as well as optical spectroscopy. XRD pattern determined crystalline structure of gold thin films. SEM image showed the effect of deposition time and applied voltage on the morphology of deposited films. AFM results demonstrated the variations in roughness, thickness, and surface quality due to changes in applied voltage and deposition time. Also, the optical properties of thin films were studied by UV-vis reflection spectroscopy.

Formation of anisotropic gold nanoparticles on indium tin oxide substrates as a plasmonic sensing material

A simple technique of seed-mediated growth has been successfully performed to grow anisotropy gold nanoparticles on solid substrates. The growth of the gold nanoparticles has been carried out in the presence of a binary surfactant mixture of hexadecyltrimethylammonium bromide with two different molecular weights of a capping agent, namely polyvinylpyrrolidone: 40,000 and 55,000. In this study, the effect of process parameters, growth time and molecular weight of capping agent was investigated. The growth time shows a significant impact on the shape and size of nanoparticles. The shorter growth time produced small spherical to square-like shape particles, whereas bigger particles including nanorods, nanosquares and nanotriangles were formed with longer growth time. The shape controlling agent, polyvinylpyrrolidone, was used to synthesis gold nanoparticles. It was found that monodisperse gold nanoparticles with uniform shape and size are hardly obtained when polyvinylpyrrolidone 40,000 was used as capping agent. Polyvinylpyrrolidone 55,000 produced more uniform shape and size of gold nanoparticles. Thus, these process parameters were found affected to the size, shape, surface density and uniformity of gold nanoparticles. This sample was further applied as a sensing material in the detection of toxic fungicide, namely chlorothalonil. The sensitivity of the sensor system was determined by the changes in peak positions and intensities of the transverse and longitudinal surface plasmon resonance peaks on different medium, that is, air, deionized water and chlorothalonil solution. The sensor response of gold nanoparticles thin film in 30 mM chlorothalonil showed two resonance peaks in comparison to the control experiment without gold nanoparticle thin film. The gold nanoparticles thin film sensor was successfully synthesized and potentially useful as a sensing material for fungicide detection.

Shaping Liquid Crystals with Gold Nanoparticles: Helical Assemblies with Tunable and Hierarchical Structures Via Thin-Film Cooperative Interactions.

The availability of helical assemblies of plasmonic nanoparticles with precisely controlled and tunable structures can play a key role in the future development of chiral plasmonics and metamaterials. Here, a strategy to efficiently yield helical structures based on the cooperative interactions of liquid crystals and gold nanoparticles in thin films is developed. These nanocomposites exhibit exceptional long-range hierarchical order across length scales, which results from the growth mechanism of nanoparticle-coated twisted nanoribbons and their ability to form organized bundles. The helical assembly formation is governed by the presence of rationally functionalized nanoparticles. Importantly, the thickness of the achieved nanocomposites can be reversibly reconfigured owing to the polymorphic nature of the liquid crystal. The versatility of the proposed approach is demonstrated by preparing helices assembled from nanoparticles of different geometries and dimensions (spherical and rod-like). The described strategy may become an enabling technology for structuring nanoparticle assemblies with high precision and fabricating optically active materials.

Highly Responsive PEG/Gold Nanoparticle Thin-Film Humidity Sensor via Inkjet Printing Technology.

In this study, a highly responsive humidity sensor is developed by printing gold nanoparticles (GNPs) grafted with a hygroscopic polymer. These GNPs are inkjet-printed to form a uniform thin film over an interdigitated electrode with a controllable thickness by adjusting the printing parameters. The resistance of the printed GNP thin film decreases significantly upon exposure to water vapor and exhibits a semi-log relationship with relative humidity (RH). The sensor can detect RH variations from 1.8 to 95% with large resistance changes up to 4 orders of magnitude with no hysteresis and small temperature dependence. In addition, with a small thickness, the sensor can reach absorption equilibrium quickly with response and recovery times of ≤1.2 and ≤3 s, respectively. The fast response to humidity changes also allows the GNP thin-film sensor to distinguish signals from intermittent humidification/dehumidification cycles with a frequency up to 2.5 Hz. The printed sensors on flexible substrates show little sensitivity to bending deformation and can be embedded in a mask for human respiratory detection. In summary, this study demonstrates the feasibility of applying printing technology for the fabrication of thin-film humidity sensors, and the methodology developed can be further applied to fabricate many other types of nanoparticle-based sensor devices.

Tunable Switching Characteristics of Low Operating Voltage Organic Bistable Memory Devices Based on Gold Nanoparticles and Copper Phthalocyanine Thin Films

The influence of the top contact electrode on the switching characteristics of a low operating voltage organic bistable memory device, using copper phthalocyanine and gold nanoparticle thin films, was investigated using Au, Al, and Hg electrodes. While the ON/OFF ratio higher than 105 was achieved for all the devices, the nature of the memory behavior was found to be dependent on the top electrodes. Thermally evaporated Au and Al electrodes resulted in write-once–read-many times (WORM) behavior, whereas Hg drop soft contact led to write–read–erase–read (rewritable) characteristics, with the device retaining the ON state in the former and returning to the OFF state in the latter. The switching voltage was found to be influenced by the top electrode with the devices switching to the ON state at around 2 V for Hg and close to 1 V for Au and Al electrodes. Additionally, though the ON state conduction mechanism was dominated by Fowler–Nordheim (FN) tunneling through AuNP trap states in all the devices, the dyn...

Efficient Solar-Thermal Energy Harvest Driven by Interfacial Plasmonic Heating-Assisted Evaporation.

The plasmonic heating effect of noble nanoparticles has recently received tremendous attention for various important applications. Herein, we report the utilization of interfacial plasmonic heating-assisted evaporation for efficient and facile solar-thermal energy harvest. An airlaid paper-supported gold nanoparticle thin film was placed at the thermal energy conversion region within a sealed chamber to convert solar energy into thermal energy. The generated thermal energy instantly vaporizes the water underneath into hot vapors that quickly diffuse to the thermal energy release region of the chamber to condense into liquids and release the collected thermal energy. The condensed water automatically flows back to the thermal energy conversion region under the capillary force from the hydrophilic copper mesh. Such an approach simultaneously realizes efficient solar-to-thermal energy conversion and rapid transportation of converted thermal energy to target application terminals. Compared to conventional external photothermal conversion design, the solar-thermal harvesting device driven by the internal plasmonic heating effect has reduced the overall thermal resistance by more than 50% and has demonstrated more than 25% improvement of solar water heating efficiency.