Search Results (25)

In this work, atmospheric pulsed laser deposition was used to prepare photosensitive elements. This technology is a practical and relatively inexpensive way of obtaining highly porous nanostructures composed of nanoparticles or nanoaggregates characterized by a large surface-to-volume ratio. Samples were produced via laser nanosecond or picosecond laser ablation of pure ZnO or mixed ZnO-TiO₂ targets on quartz substrates with pre-deposited gold electrodes. The structure, morphology, optical, and electrical properties of the nanostructures obtained were studied regarding the sample composition and laser ablation regime applied. The ablation of a mixed ZnO-TiO₂ target led to the fabrication of composite samples consisting of ZnO and Zn₂TiO₄ nanoparticles. The electrical properties of pure and composite samples were studied under exposure to UV light irradiation. It was found that the photosensitive properties of the samples depended on the ablation regime applied. The dark current measured for the nanosecond-deposited samples was a few nA, which was an order of magnitude larger compared to the picosecond-deposited samples. The value of the photogenerated current of the nanosecond-deposited samples was 10³-times higher than that of the picosecond-deposited samples. This is due to the lower absorption of the picosecond-deposited samples, as well as to the presence of defect-related radiative recombination in the picosecond-deposited samples, which limits the photocurrent rise. The estimated rise and decay times were longer for the composite samples independently of the deposition regime applied. Full article

Pyocyanin is considered a maker of Pseudomonas aeruginosa (P. aeruginosa) infection. Pyocyanin is among the toxins released by the P. aeruginosa bacteria. Therefore, the development of a direct detection of PYO is crucial due to its importance. Among the different optical techniques, the Raman technique showed unique advantages because of its fingerprint data, no sample preparation, and high sensitivity besides its ease of use. Noble metal nanostructures were used to improve the Raman response based on the surface-enhanced Raman scattering (SERS) technique. Anodic metal oxide attracts much interest due to its unique morphology and applications. The porous metal structure provides a large surface area that could be used as a hard template for periodic nanostructure array fabrication. Porous shapes and sizes could be controlled by controlling the anodization parameters, including the anodization voltage, current, temperature, and time, besides the metal purity and the electrolyte type/concentration. The anodization of aluminum foil results in anodic aluminum oxide (AAO) formation with different roughness. Here, we will use the roughness as hotspot centers to enhance the Raman signals. Firstly, a thin film of gold was deposited to develop gold/alumina (Au/AAO) platforms and then applied as SERS-active surfaces. The morphology and roughness of the developed substrates were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The Au/AAO substrates were used for monitoring pyocyanin secreted from Pseudomonas aeruginosa microorganisms based on the SERS technique. The results showed that the roughness degree affects the enhancement efficiency of this sensor. The high enhancement was obtained in the case of depositing a 30 nm layer of gold onto the second anodized substrates. The developed sensor showed high sensitivity toward pyocyanin with a limit of detection of 96 nM with a linear response over a dynamic range from 1 µM to 9 µM. Full article

We present a two-step physical method for the fabrication of composite nanoparticle-based nanostructures. The proposed method is based on the pulsed laser deposition (PLD) technique performed sequentially in vacuum and in air. As a first step, thin-alloyed films of iron with noble metal were deposited by PLD in vacuum. The films were prepared by ablation of a mosaic target formed by equal iron and gold sectors. As a second step, the as-prepared alloyed films were ablated in air at atmospheric pressure as the laser beam scanned their surface. Two sets of experiments were performed in the second step, namely, by applying nanosecond (ns) and picosecond (ps) laser pulses for ablation. The structure, microstructure, morphology, and optical properties of the samples obtained were studied with respect to the laser ablation regime applied. The implementation of the ablation process in open air resulted in the formation of nanoparticle and/or nanoparticle aggregates in the plasma plume regardless of the ablation regime applied. These nanoparticles and/or nanoaggregates deposited on the substrate formed a complex porous structure. It was found that ablating FeAu films in air by ns pulses resulted in the fabrication of alloyed nanoparticles, while ablation by ps laser pulses results in separation of the metals in the alloy and further oxidation of Fe. In the latter case, the as-deposited structures also contain core–shell type nanoparticles, with the shell consisting of Fe-oxide phase. The obtained structures, regardless of the ablation regime applied, demonstrate a red-shifted plasmon resonance with respect to the plasmon resonance of pure Au nanoparticles. Full article

Glutamate, a non-essential amino acid produced by fermentation, plays a significant role in disease diagnosis and food safety. It is important to enable the real-time monitoring of glutamate concentration for human health and nutrition. Due to the challenges in directly performing electrochemical oxidation–reduction reactions of glutamate, this study leverages the synergistic effect of glutamate dehydrogenase (GLDH) and nanoporous gold (NPG) to achieve the indirect and accurate detection of glutamate within the range of 50 to 700 μM by measuring the generated quantity of NADH during the enzymatic reaction. The proposed biosensor demonstrates remarkable performance characteristics, including a detection sensitivity of 1.95 μA mM⁻¹ and a limit of detection (LOD) of 6.82 μM. The anti-interference tests indicate an average recognition error ranging from −3.85% to +2.60%, spiked sample recovery rates between 95% and 105%, and a relative standard deviation (RSD) of less than 4.97% for three replicate experiments. Therefore, the GLDH-NPG/GCE biosensor presented in this work exhibits excellent accuracy and repeatability, providing a novel alternative for rapid glutamate detection. This research contributes significantly to enhancing the precise monitoring of glutamate concentration, thereby offering more effective guidance and control for human health and nutrition. Full article

Pure Ce_0.5Zr_0.5O₂ and Au (0.1–1.0 wt.%)-deposited Ce_0.5Zr_0.5O₂ nanomaterials were synthesized via hydrothermal and non-aqueous precipitation methods using gold acetate as a chloride-free Au precursor. The synthesized nanostructures exhibited enhanced photocatalytic activity for hydrogen production via aqueous bioethanol photoreforming under visible light. Different characterization tools such as powder XRD, HRTEM, FT-IR, DR UV-vis, XPS and N₂ gas adsorption were used to analyze the physicochemical properties of the synthesized photocatalysts. The band gap value was lowered from 3.25 eV to 2.86 eV after Au nanoparticles were deposited on the surface of Ce_0.5Zr_0.5O₂. The 1.0 wt.% Au-deposited Ce_0.5Zr_0.5O₂ sample exhibited the highest photocatalytic activity for H₂ production (3210 μmol g⁻¹) due to its low band gap, the presence of more oxygen vacancies and its porous character. The EIS results reveal that the deposition of 1.0 wt.% Au nanoparticles is responsible for the highest charge separation efficiency with an increased lifetime of photogenerated e⁻/h⁺ species compared to the other samples. In addition, the presence of plasmonic Au is responsible for the effectiveness of the electron trap in improving the rate of H₂ formation. Full article

Plasmonic nanostructures with a high density of confined areas with high local electromagnetic fields (hot spots) are sine qua nonto increase the efficiency of surface-enhanced Raman spectroscopy (SERS). These nanostructures can be used both to identify biological molecules and to monitor photochemical reactions occurring on the metal surface. In this work, using the method of pulsed laser deposition, three-dimensional (3D) porous wedge-shaped arrays of gold nanoparticles (Au NPs) were obtained with structural parameters varying along the substrate, such as film thickness, porosity, nanoparticles size, and the distance between them. The resulting arrays were structures with a regularly changing density of hot spots along the substrate, in which the enhancement of the electromagnetic field strength is due to the geometric parameters of the nanostructure.By analyzing the evolution of fluorescence and Raman scattering of fluorescein molecules adsorbed on the surface of porous gold under illumination at 532 nm, the processes in the region of extreme values of the electromagnetic field of surface nanostructures was studied. A correlation has been established between the amplification of optical signals and the structural features of the surface. A correlation between SERS and fluorescence signals indicates the predominant contribution of hot spots to the electromagnetic amplification of optical signals. The observed time evolution of the fluorescence and SERS intensity of fluorescein can be explained by the combination of molecular photodegradation, the reconstruction of the hot spot architecture due to local heating, and potent relocation of analyte molecules outside the area of measurement owing to the effects of thermal gradients. Full article

Detection of greenhouse gases is essential because harmful gases in the air diffuse rapidly over large areas in a short period of time, causing air pollution that will induce climate change with catastrophic consequences over time. Among the materials with favorable morphologies for gas detection (nanofibers, nanorods, nanosheets), large specific surfaces, high sensitivity and low production costs, we chose nanostructured porous films of In₂O₃ obtained by the sol-gel method, deposited on alumina transducers, with gold (Au) interdigitated electrodes (IDE) and platinum (Pt) heating circuits. Sensitive films contained 10 deposited layers, involving intermediate and final thermal treatments to stabilize the sensitive film. The fabricated sensor was characterized using AFM, SEM, EDX and XRD. The film morphology is complex, containing fibrillar formations and some quasi-spherical conglomerates. The deposited sensitive films are rough, thus favoring gas adsorption. Ozone sensing tests were performed at different temperatures. The highest response of the ozone sensor was recorded at room temperature, considered to be the working temperature for this specific sensor. Full article

Biofuel cells (BFCs) with enzymatic electrocatalysts have attracted significant attention, especially as power sources for wearable and implantable devices; however, the applications of BFCs are limited owing to the limited O₂ supply. This can be addressed by using air-diffusion-type bilirubin oxidase (BOD) cathodes, and thus the further development of the hierarchical structure of porous electrodes with highly effective specific surface areas is critical. In this study, a porous layer of gold is deposited over magnesium-oxide-templated carbon (MgOC) to form BOD-based biocathodes for the oxygen reduction reaction (ORR). Porous gold structures are constructed via electrochemical deposition of gold via dynamic hydrogen bubble templating (DHBT). Hydrogen bubbles used as a template and controlled by the Coulomb number yield a porous gold structure during the electrochemical deposition process. The current density of the ORR catalyzed by BOD without a redox mediator on the gold-modified MgOC electrode was 1.3 times higher than that of the ORR on the MgOC electrode. Furthermore, the gold-deposited electrodes were modified with aromatic thiols containing negatively charged functional groups to improve the orientation of BOD on the electrode surface to facilitate efficient electron transfer at the heterogeneous surface, thereby achieving an ORR current of 12 mA cm⁻² at pH 5 and 25 °C. These results suggest that DHBT is an efficient method for the fabrication of nanostructured electrodes that promote direct electron transfer with oxidoreductase enzymes. Full article

New methods for the preparation of metal–organic frameworks UiO-66 and NH₂-UiO-66 with a hierarchical porous structure were developed using the MW-assisted technique under atmospheric pressure. The synthesized nanostructured meso-UiO-66 and meso-NH₂-UiO-66 matrices were utilized as Au nanoparticle carriers. The resulting Au@meso-UiO-66 and Au@NH₂-UiO-66 nanohybrids were studied in the reaction of phenylacetylene hydroamination with aniline into imine ([phenyl-(1-phenylethylydene)amine]) for the first time. Their catalytic behavior is significantly determined by a combination of factors, such as a small crystal size, micro–mesoporous structure, and functionality of the UiO-66 and NH₂-UiO-66 carriers, as well as a high dispersion of embedded gold nanoparticles. The Au@meso-UiO-66 and Au@NH₂-UiO-66 nanocatalysts demonstrate high activities (TOF), with conversion and selectivity values over 90. This excellent catalytic performance is comparable or even better than that demonstrated by heterogeneous systems based on conventional inorganic and inorganic supports known from the literature. Full article

Porous silicon (PS) is a promising material for nanostructure fabrication providing a precise control over its size, shape, and spatial distribution. This makes it an excellent candidate for constructing highly sensitive, reproducible, and low-cost platforms for surface enhanced Raman scattering (SERS) spectroscopy. In this work, we connect the PS structural parameters with the morphology of the gold nanostructures fabricated on its surface, placing the emphasis on the SERS response. Two different types of PS are considered here, namely meso- and macro-PS. The former is prepared by Si electrochemical etching, applying three different current densities: 100 mA cm⁻², 60 mA cm⁻², and 30 mA cm⁻², while the technological parameters for the latter are selected to mimic metal nanovoids’ (Me NVs) configuration. The gold-coated PS surfaces are produced via an electroless chemical deposition method for different time periods. By performing comprehensive structural, morphological, and optical characterization, we show the importance of the size and density of the PS pore openings, which govern the Au growth kinetics. The results presented in this work assure a simple yet flexible approach for the fabrication of large-area plasmonic gold nanostructures, which are not only suitable for advanced SERS spectroscopy studies but can also serve for a wider range of plasmonic applications. Full article

Bio- and chemical SERS-sensing using plasmonic nanostructures can be dramatically improved by creating hot spots—i.e., sub-10 nm gaps between nanoparticles—which confine large electromagnetic fields on nanometric volume. Here we report a 3D porous wedge-shaped gold nanostructure that contains high-density Raman-active nanogaps produced by pulsed laser deposition. The resulting structures consist of arrays of densely packed gold nanoparticles and nanopores that exhibit a number of functionalities, including size selectivity, spectral tunability and strong electromagnetic field amplification. The possibility of effective enhancement of the Raman intensity of Rhodamine 6G molecules upon resonant excitation that is outside the region of surface plasmon resonance excitation in 3D Au nanostructures is demonstrated. Full article

Novel concepts for developing a surface-enhanced Raman scattering (SERS) sensor based on biocompatible materials offer great potential in versatile applications, including wearable and in vivo monitoring of target analytes. Here, we report a highly sensitive SERS sensor consisting of a biocompatible silk fibroin substrate with a high porosity and gold nanocracks. Our silk-based SERS detection takes advantage of strong local field enhancement in the nanoscale crack regions induced by gold nanostructures evaporated on a porous silk substrate. The SERS performance of the proposed sensor is evaluated in terms of detection limit, sensitivity, and linearity. Compared to the performance of a counterpart SERS sensor with a thin gold film, SERS results using 4-ABT analytes present that a significant improvement in the detection limit and sensitivity by more than 4 times, and a good linearity and a wide dynamic range is achieved. More interestingly, overlap is integral, and a quantitative measure of the local field enhancement is highly consistent with the experimental SERS enhancement. Full article

The method of realizing nanostructures using porous alumina templates has attracted interest due to the precise geometry and cheap cost of nanofabrication. In this work, nanoporous alumina membranes were utilized to realize a forest of nanowires, providing a bottom-up nanofabrication method suitable for surface-enhanced Raman spectroscopy (SERS). Gold and iron were electroplated through the straight channels of the membrane. The resulting nanowires are, indeed, made of an active element for plasmonic resonance and SERS as the hexagonal distribution of the nanowires and the extreme high density of the nanowires allows to excite the plasmon and detect the Raman signal. The method to reduce the distance between pores and, consequently, the distance of the nanowires after electrodeposition is optimized here. Indeed, it has been predicted that the light intensity enhancement factor is up to 10¹² when the gap is small than 10 nm. Measurements of Raman signal of thiol groups drying on the gold nanowires show that the performance of the device is improved. As the thiol group can be linked to proteins, the device has the potential of a biosensor for the detection of a few biomolecules. To assess the performance of the device and demonstrate its ability to analyze biological solutions, we used it as SERS substrates to examine solutions of IgG in low abundance ranges. The results of the test indicate that the sensor can convincingly detect biomolecules in physiologically relevant ranges. Full article

The modern development of nanotechnology requires the discovery of simple approaches that ensure the controlled formation of functional nanostructures with a predetermined morphology. One of the simplest approaches is the self-assembly of nanostructures. The widespread implementation of self-assembly is limited by the complexity of controlled processes in a large volume where, due to the temperature, ion concentration, and other thermodynamics factors, local changes in diffusion-limited processes may occur, leading to unexpected nanostructure growth. The easiest ways to control the diffusion-limited processes are spatial limitation and localized growth of nanostructures in a porous matrix. In this paper, we propose to apply the method of controlled self-assembly of gold nanostructures in a limited pore volume of a silicon oxide matrix with submicron pore sizes. A detailed study of achieved gold nanostructures’ morphology, microstructure, and surface composition at different formation stages is carried out to understand the peculiarities of realized nanostructures. Based on the obtained results, a mechanism for the growth of gold nanostructures in a limited volume, which can be used for the controlled formation of nanostructures with a predetermined geometry and composition, has been proposed. The results observed in the present study can be useful for the design of plasmonic-active surfaces for surface-enhanced Raman spectroscopy-based detection of ultra-low concentration of different chemical or biological analytes, where the size of the localized gold nanostructures is comparable with the spot area of the focused laser beam. Full article

Nanocomposite membranes have been actively developed in the last decade. The involvement of nanostructures can improve the permeability, selectivity, and anti-fouling properties of a membrane for improved filtration processes. In this work, we propose a novel type of ion-selective Glass/Au composite membrane based on porous glass (PG), which combines the advantages of porous media and promising selective properties. The latter are achieved by depositing gold nanoparticles into the membrane pores by the laser-induced liquid phase chemical deposition technique. Inside the pores, gold nanoparticles with an average diameter 25 nm were formed, which was confirmed by optical and microscopic studies. To study the transport and selective properties of the PG/Au composite membrane, the potentiometric method was applied. The uniform potential model was used to determine the surface charge from the experimental data. It was found that the formation of gold nanoparticles inside membrane pores leads to an increase in the surface charge from −2.75 mC/m² to −5.42 mC/m². The methods proposed in this work allow the creation of a whole family of composite materials based on porous glasses. In this case, conceptually, the synthesis of these materials will differ only in the selection of initial precursors. Full article