Gold Nanoparticle Films Research Articles

Direct Writing of SERS Substrates Using Femtosecond Laser Pulses.

Achieving a high-density, repeatable, and uniform distribution of "hotspots" across the entire surface-enhanced Raman scattering (SERS) substrate is a current challenge in facilitating the efficient preparation of large-area SERS substrates. In this study, we aim to produce homogeneous surface-enhanced Raman scattering (SERS) substrates based on the strong interaction between femtosecond laser pulses and a thin film of colloidal gold nanoparticles (AuNPs). The SERS substrate we obtained consists of irregularly shaped and sharp-edged gold nanoparticle aggregates with specially extruding features; meanwhile, a large number of three-dimensional AuNP stacks are produced. The advantages of such configurations lie in the production of a high density of hotspots, which can significantly improve the SERS performance. When the laser fluence is 5.6 mJ/cm2, the substrate exhibits the best SERS enhancement effect, and a strong SERS signal can still be observed when testing the concentration of R6G at 10-8 mol/L. The enhancement factor of such SERS substrates prepared using femtosecond laser direct writing is increased by 3 orders of magnitude compared to the conventional furnace annealing process. Furthermore, the relative standard deviation for the intensities of the SERS signals was measured to be 5.1% over an area of 50 × 50 μm2, indicating a highly homogeneous SERS performance and excellent potential for practical applications.

Poly(3,4-Ethylenedioxythiophene)/Functional Gold Nanoparticle films for Improving the Electrode-Neural Interface.

Implantable neural electrodes are indispensable tools for recording neuron activity, playing a crucial role in neuroscience research. However, traditional neural electrodes suffer from limited electrochemical performance, compromised biocompatibility, and tentative stability, posing great challenges for reliable long-term studies in free-moving animals. In this study, a novel approach employing a hybrid film composed of poly(3,4-ethylenedioxythiophene)/functional gold nanoparticles (PEDOT/3-MPA-Au) to improve the electrode-neural interface is presented. The deposited PEDOT/3-MPA-Au demonstrates superior cathodal charge storage capacity, reduced electrochemical impedance, and remarkable electrochemical and mechanical stability. Upon implantation into the cortex of mice for a duration of 12weeks, the modified electrodes exhibit notably decreased levels of glial fibrillary acidic protein and increased neuronal nuclei immunostaining compared to counterparts utilizing poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate). Additionally, the PEDOT/3-MPA-Au modified electrodes consistently capture high-quality, stable long-term electrophysiological signals in vivo, enabling continuous recording of target neurons for up to 16weeks. This innovative modification strategy offers a promising solution for fabricating low-impedance, tissue-friendly, and long-term stable neural interfaces, thereby addressing the shortcomings of conventional neural electrodes. These findings mark a significant advancement toward the development of more reliable and efficacious neural interfaces, with broad implications for both research and clinical applications.

Optical Characteristics of Directly Deposited Gold Nanoparticle Films

Optical Characteristics of Directly Deposited Gold Nanoparticle Films

In-situ self-assembly growth of controllable gold nanoparticles film

Because of the strong light absorption and/or scattering, nano scaled gold has many favorable optic and electric properties. With the continuous miniaturization of nano photoelectronic devices and nano electromechanical systems, there is an urgent demand for controllable and tailored gold nanoparticles film with excellent performance. Here, a modified HAuCl4-NaOH-CTAB (cetyltrimethylammonium bromide) aqueous solution system was utilized to self-assembly synthesize gold nanofilm on glass substrates. The high concentration NaOH is not only reducing Au3+ to Au0, but facilitating interfacial assembly of gold nanostructure at liquid–solid interface via etching glass surface. Based on this growth kinetic, the gradient, well-designed and in-situ growing gold nanoparticles film can be achieved on any SiO2 contained substrates by controlling the growth time in the reaction system. Furthermore, the in-situ self-assembled gold nanoparticles film can be act as plasmon substrates for surface-enhanced Raman scattering (SERS) or plasmonic enhanced semiconductor lasing, even gold electrodes.

Quantitative analysis model based on surface‐enhanced Raman spectroscopy of malachite green adsorbed on gold nanoparticles film substrates

AbstractIn order to investigate the adsorption process of malachite green (MG) on gold nanoparticles, a simple gold nanoparticles‐assembled film was prepared as a substrate of surface‐enhanced Raman spectroscopy (SERS), and it was soaked in MG solutions of different concentrations. The kinetic adsorption process was investigated by SERS method and density functional theoretical calculations. When saturated adsorption was achieved, the relationship between the characteristic SERS band signal intensity and the logarithm of solution concentration of MG was consistent with Temkin adsorption isotherm model, where the R2 value was greater than 0.995, and the linear range was 1 × 10−3–1 × 10−7 M. Finally, a SERS quantitative analysis model of the relationship between the adsorption properties of surface species and the bulk concentration was established. According to the electrostatic interaction and co‐adsorption, we proposed the surface adsorption configurations and adsorption process of MG on the nanostructured gold films.

Highly stable and efficient gold nanoparticles films facilitated by thiourea for catalytic reduction of nitrophenol in water

Water pollution from nitrophenol, a common nitrogen-containing aromatic pollutant, is becoming increasingly significant. Making the conversion of nitrophenol to the less toxic and more easily biodegradable aminophenol is a promising strategy to treat industrial wastewater. A simple and efficient method for treating nitrophenol was investigated using gold nanoparticles (AuNPs) with thiourea and fabricating AuNPs films via filtration for the first time. The prepared AuNPs film with nanoporous structure exhibits good structural stability and excellent catalytic activity. The results show that the optimal concentration of adding thiourea is 20 μg/mL, and the optimal concentration of adding NaBH4 is 1000 mM. After treatment with 20.0 μg/mL thiourea, the prepared AuNPs film catalyzes the degradation of 1.0 mM 2-nitrophenol to 2-aminophenol in just 150 sec. The AuNPs film provides a high density of active sites at the interface, and its stable nanoporous structure brings the substrate nitrophenol closer to the active center, thus enhancing the efficiency of catalytic reduction. Besides, the AuNPs films treated with thiourea still maintained good catalytic performance after seven cycles of catalysis and the catalytic efficiency is still as high as 90%. The thiourea-treated AuNPs film sets a precedent for the innovation of novel catalysts that is a very promising industrial strategy for reducing nitrophenol to aminophenol, offering significant economic advantages.

Tuning the Interfacial Chemistry of Nanoparticle Assemblies via Spin‐Coating: From Single Sensors to Monolithic Sensor Arrays

AbstractSensor arrays based on gold nanoparticle (GNP) films are promising candidates for numerous applications, including medical diagnosis and health monitoring. Their economic fabrication, however, remains challenging. This study presents a facile route to GNP chemiresistors with tunable properties via layer‐by‐layer spin‐coating (LbL‐SC). Key steps involve the alternating deposition of dodecylamine‐stabilized GNPs and mixtures of monothiols (MTs) with 1,9‐nonanedithiol (9DT). The 9DT molecules serve to reinforce the growing film via GNP cross‐linking while the MT ligands are used to tune the interfacial chemistry of the GNP assembly. Hence, by employing differently functionalized MTs the sensors' chemical selectivity can easily be adjusted. Further, by varying the MT‐9DT ratio and adjusting the size of the MT ligands the sensitivity can be tuned along with the conductivity and optical properties of the films. In general, decreasing the 9DT fraction significantly enhances the sensitivity while the response isotherms change from Langmuir‐Henry to Henry type. Finally, the cross‐linked GNP films are robust enough to be patterned via photolithography. Hence, this study demonstrates the fabrication and application of monolithic sensor arrays. Different features of the responses to numerous analytes are used as input data for linear discriminant analyses (LDA), revealing that very similar analytes can be distinguished.

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.

Sol-gel immobilization of lipase enzyme on FTO modified with silica-zirconia and gold nanoparticles films for design of triglyceride impedimetric biosensor

A novel electrochemical sensing platform was created using the formation of a sequence of films, over a conductive fluorine-doped tin oxide glass (FTO), obtained using the sol-gel method and the dip coating technique. Firstly, thin films of silica-zirconia mixed oxides were deposited, in sequence an ionic silsesquioxane film stabilizing and controlling the size of gold nanoparticles (6.5 ± 2.4 nm) was settled, and after the lipase enzyme, obtained from Candida rugosa, was entrapped into a silica film maintaining its operational stability. The films were characterized by scanning electron microscopy (SEM) with EDX, UV–Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The thickness of each film on the FTO glass was evaluated by optical profilometry. The presence of the enzyme on the platform was confirmed by cyclic voltammetry with the ρ-nitrophenyl palmitate method. This platform was applied successfully as a biosensor for tributyrin (TB) determination by electrochemical impedance spectroscopy EIS, showing low limit of detection (LD) of 1.86 μmol L−1 and high sensitivity of 5.37 μΩ μmol−1 L. The biosensor presented a low KMapp value of 22.69 μmol L− 1 and the Vmaxapp value of 85.57 μmol L−1 min−1 suggesting that the enzyme, immobilized with this method retained activity promoting a fast enzymatic reaction with the TB.

In Situ ATR Spectroscopy Study of the Interaction of Acacia senegal Gum with Gold Nanoparticles Films at the Solid-Liquid Interface.

The adsorption process of Acacia gum (A. senegal), a complex heteropolysaccharide, was followed by using a spectroscopic method to unravel the relative contribution of the protein moieties and the carbohydrate blocks on the adsorption process. In situ ATR-FTIR was used to investigate the kinetics and conformational changes associated with the adsorption of A. senegal gum on gold nanoparticle films (Au-NPs) at different pHs. The results of this thorough study highlighted the adsorption of A. senegal gum through its protein moieties, in particular, AGPs of low molecular weight and high protein content, close to the Au-NPs surface. Isotherm experiments, by gradually increasing the concentration, showed that the gum adsorption was heterogeneous and followed the Freundlich model for the amide part, while the polysaccharide part followed the Langmuir model. In addition, the hydration and structural organization of the gum layer depended on the gum concentration. A. senegal gum adsorbed irreversibly on Au-NPs whatever the pHs, but the adsorbed layer presented a different behavior depending on pH. A more aggregated and less hydrated structure was observed at acidic pH, while a very hydrated and continuous layer was detected at higher pH. The secondary structure analysis through amide III band revealed a change in the gum secondary structure at high pH with the increase in β-turn while random coil decreased.

The quality factor enhancement on gold nanoparticles film for localized surface plasmonic resonance chip sensor

Gold nanoparticles film as a part of an optical sensor is considered as active support in the development of specific chemical or biological biosensors optically. Well-organized gold nanoparticles can be prepared through inexpensive approaches where gold nanoparticles are easily obtained on a glass substrate. Herein, the authors propose a low-cost thermal synthesis of active plasmonic nanostructures on thin gold layers modified by a short annealing time (1 min and 15 min) at 550 °C and quickly followed by simple quenching. The results proved a good reproducibility of localized surface plasmon resonance (LSPR) optical responses with investigate the effects of modified thermal treatment on the morphology of gold thin films, the extinction LSPR spectra characteristics in the range between 350−1000 nm, and the quality factor (Q-factor) of the plasmonic resonance. The present findings that the proposed method gives evidence enhancement with the enrichment factor (EF-factor) values by about 310 %–460 %. We believe our study may have provided a strategy to enhance the fabrication of gold nanoparticles film based on plasmonic nanostructures for LSPR chip sensor applications.

The Label-Free Detection and Identification of SARS-CoV-2 Using Surface-Enhanced Raman Spectroscopy and Principal Component Analysis.

The World Health Organization (WHO) declared in a May 2023 announcement that the COVID-19 illness is no longer categorized as a Public Health Emergency of International Concern (PHEIC); nevertheless, it is still considered an actual threat to world health, social welfare and economic stability. Consequently, the development of a convenient, reliable and affordable approach for detecting and identifying SARS-CoV-2 and its emerging new variants is crucial. The fingerprint and signal amplification characteristics of surface-enhanced Raman spectroscopy (SERS) could serve as an assay scheme for SARS-CoV-2. Here, we report a machine learning-based label-free SERS technique for the rapid and accurate detection and identification of SARS-CoV-2. The SERS spectra collected from samples of four types of coronaviruses on gold nanoparticles film, fabricated using a Langmuir-Blodgett self-assembly, can provide more spectroscopic signatures of the viruses and exhibit low limits of detection (<100 TCID50/mL or even <10 TCID50/mL). Furthermore, the key Raman bands of the SERS spectra were systematically captured by principal component analysis (PCA), which effectively distinguished SARS-CoV-2 and its variant from other coronaviruses. These results demonstrate that the combined use of SERS technology and PCA analysis has great potential for the rapid analysis and discrimination of multiple viruses and even newly emerging viruses without the need for a virus-specific probe.

Nanostructure Tuning of Gold Nanoparticles Films via Click Sintering.

Colloidal metal nanoparticles dispersions are commonly used to create functional printed electronic devices and they typically require time-, energy- and equipment-consuming post-treatments to improve their electrical and mechanical properties. Traditional methods, e.g. thermal, UV/IR, and microwave treatments, limit the substrate options and may require expensive equipment, not available in all the laboratories. Moreover, these processes also cause the collapse of the film (nano)pores and interstices, limiting or impeding its nanostructuration. Finding a simple approach to obtain complex nanostructured materials with minimal post-treatments remains a challenge. In this study, a new sintering method for gold nanoparticle inks that called as "click sintering" has been reported. The method uses a catalytic reaction to enhance and tune the nanostructuration of the film while sintering the metallic nanoparticles, without requiring any cumbersome post-treatment. This results in a conductive and electroactive nanoporous thin film, whose properties can be tuned by the conditions of the reaction, i.e., concentration of the reagent and time. Therefore, this study presents a novel and innovative one-step approach to simultaneously sinter gold nanoparticles films and create functional nanostructures, directly and easily, introducing a new concept of real-time treatment with possible applications in the fields of flexible electronics, biosensing, energy, and catalysis.

Two-dimensional superlattice films of gold nanoparticle-polystyrene composites: a bioactive platform for bone homeostasis maintenance

Osseo-integration between the implant and bone is a crucial factor to create a strong, durable bond that allows the implant to function effectively. However, regular implant surface with poor osseo-integration ability may cause aseptic loosening, resulting in the failure of implants. Herein, a serial of macroscopic one-particle thick superlattice films generated by self-assembly of diverse size of gold nanoparticles (GNPs) were termed as SFGs and were considered as bioactive implant coatings for enhancing osseo-integration. A hydroquinone-assisted seed method is established to fabricate homogenous GNPs with controllable sizes (20, 60, and 90 nm), which were further employed as building blocks to generate macroscopic one-particle thick superlattice films of GNPs (SFGs-20, SFGs-60, and SFGs-90) with the assistance of ploystryrene. The SFGs present a size-dependent performance on bone homeostasis, where SFGs-90 demonstrated the most pronounced facilitation of osteogenic differentiation of osteoblasts as well as deactivation of osteoclasts compared with SFGs-20 and SFGs-60. Considering the universal applicability of SFGs for depositing on various substrates, these SFGs with enhanced osseo-integration capabilities could serve as a bioactive platform for surface modification of orthopedic implants, effectively addressing the issue of aseptic loosening.Graphical abstractTwo-dimensional superlattice films of gold nanoparticle-polystyrene composites exhibit enhanced osteogenic-stimulation and osteoclastic-inhibition effects for regulating bone homeostasis maintenance.

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.

Gold vs. Silver Colloidal Nanoparticle Films for Optimized SERS Detection of Propranolol and Electrochemical-SERS Analyses.

The increasing pollution of surface and groundwater bodies by pharmaceuticals is a general environmental problem requiring routine monitoring. Conventional analytical techniques used to quantify traces of pharmaceuticals are relatively expensive and generally demand long analysis times, associated with difficulties in performing field analyses. Propranolol, a widely used β-blocker, is representative of an emerging class of pharmaceutical pollutants with a noticeable presence in the aquatic environment. In this context, we focused on developing an innovative, highly accessible analytical platform based on self-assembled metal colloidal nanoparticle films for the fast and sensitive detection of propranolol based on Surface Enhanced Raman Spectroscopy (SERS). The ideal nature of the metal used as the active SERS substrate was investigated by comparing silver and gold self-assembled colloidal nanoparticle films, and the improved enhancement observed on the gold substrate was discussed and supported by Density Functional Theory calculations, optical spectra analyses, and Finite-Difference Time-Domain simulations. Next, direct detection of propranolol at low concentrations was demonstrated, reaching the ppb regime. Finally, we showed that the self-assembled gold nanoparticle films could be successfully used as working electrodes in electrochemical-SERS analyses, opening the possibility of implementing them in a wide array of analytical applications and fundamental studies. This study reports for the first time a direct comparison between gold and silver nanoparticle films and, thus, contributes to a more rational design of nanoparticle-based SERS substrates for sensing applications.

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).

Performance improvement of macroscopical film of gold nanoparticles as temperature sensor derived from its mono-crystallinity

Macroscopically monocrystalline, self-assembled monolayers (M2-SAM) of gold nanoparticles coated with oleylamine (Au@OLA NPs) are achieved by optimizing their surface charges, which can create proper long-rang order electrostatic repulsive interactions to help balance the strong van der Waals attractive force and the hydrophobic repulsion force between neighboring Au NPs. The mono-crystallinity of the resulting M2-SAM of Au@OLA NPs is embodied in unconventional Moiré patterns beyond the low magnification imaging limit of scanning electron microscopy. The mono-crystallinity not only makes the M2-SAM of Au@OLA NPs be SERS substrates for quantitative analysis, but also enables them to fabricate temperature sensors with high precision and broad measurement span. Both the electrical resistivity-based temperature sensor with a precision of 0.001 °C in the range of −243 to 77 °C and the SERS-based temperature sensor with a precision of 0.5 °C in a range of 33 to 130 °C are implemented.

Langmuir and Langmuir-Blodgett Films of Gold and Silver Nanoparticles.

Recently the focus of the Langmuir-Blodgett technique as a method of choice to transfer monolayers from the air/water interface onto solid substrates in a controllable fashion has been shifting toward purely hydrophobic gold and silver nanoparticles. The fundamental interactions between particles that become relevant in the absence of polar groups range from dispersive attractions from the metal cores and repulsions between ligand shells to weaker entropic factors. The layer evolution is explored, starting with interfacial self-assembly upon solution spreading and domain and circular island formation, which subsequently merge into a complete monolayer and finally form multilayers or macroscopic wrinkles. Moreover, structural properties such as the core:ligand size ratio are investigated in the context of dispersive forces, whereby the nanoparticles with small cores and long ligands tend not to aggregate sufficiently to produce continuous films, those with large cores and short ligands were found to aggregate irreversibly, and those in between the two extremes were concluded to be able to form highly organized crystalline films. Similarly, the characteristics of the spreading solution such as the concentration and the solvent type crucially influence the film crystallinity, with the deciding factor being the degree of affinity between the capping ligand and the solvent used for spreading. Finally, the most common strategies employed to enhance the mechanical stability of the metal nanoparticle films along with the recent attempts to functionalize the particles in attempts to improve their applicability in the industry are summarized and evaluated in relation to their future prospects. One of the objectives of this feature article is to elucidate the differences between hydrophobic metal nanoparticles and typical amphiphilic molecules that the majority of the literature in the field describes and to familiarize the reader with the knowledge required to design Langmuir-Blodgett nanoparticle systems as well as the strategies to improve existing ones.

Layer-by-Layer Assembly of Two-Dimensional Monolayer Films of Gold Nanoparticles for Electrochemical Determination of Melamine

L-Cysteine (L-Cys) and two-dimensional monolayer films of gold nanoparticles (2D MFGS) were employed to modify gold electrodes to build uniform and stable multilayer films by layer-by-layer (LbL) self-assembly, denoted by Au/(L-Cys/2D MFGS)n (n = number of layers). Electrochemical measurements showed that the specific surface area and current amplification capacity of the modified electrode increased with the value of n. In addition, considering the orderliness inside the multilayer 2D MFGS assembly and experimental accessibility, Au/(L-Cys/2D MFGS)n=4 was selected to be the working electrode and dopamine (DA) as the signal quantification molecule for the indirect detection of melamine (MA). The results showed that the oxidation current of DA was inhibited due to the competitive adsorption of melamine upon the working electrode. Under the optimal conditions, the decrease of the dopamine peak anode current is proportional to the melamine concentration from 10−12 to 10−3 M with a detection limit of 0.13 pM. The results demonstrate the potential of 2D MFGS for applications in food and biological analysis. The scheme for fabricating the multilayer electrodes is convenient and environment-friendly, without expensive instrumentation or complex modifications.