Search Results (8)

Femtosecond lasers have garnered widespread attention owing to their subdiffraction processing capabilities. However, their intricate natures, involving intrapulse feedbacks between transient material excitation and laser propagation, often present significant challenges for near-field ablation predictions and simulations. To address these challenges, the current study introduces an improved finite-difference time-domain method (FDTD)–plasma model (plasma)–two-temperature model (TTM) framework for simulating the ablation processes of various nanospheres on diverse substrates, particularly in scenarios wherein dynamic and heterogeneous excitations significantly influence optical-field distributions. Initially, FDTD simulations of a single Au nanosphere on a Si substrate reveal that, with transitions in the excitation states of the substrate, the field-intensity distribution transforms from a profile with a single central peak to a bimodal structure, consistent with experimental reports. Subsequently, simulations of a polystyrene nanosphere array on a SiO₂ substrate reveal that different excitation states of the nanospheres yield two distinct modes, namely near-field enhancement and masking. These modes cannot be adequately modeled in the FDTD simulations. Our combined model also considers the intrapulse feedback between the electromagnetic-field distribution resulting from near-field effects and material excitations. Furthermore, the model can quantitatively analyze subsequent electron–phonon coupling and material removal processes resulting from thermal-phase transitions. Consequently, our model facilitates predictions of the femtosecond-laser ablation of single nanospheres or nanosphere arrays with varying sizes and materials placed on substrates subjected to near-field effects. Full article

In this paper, three different structures of surface plasmon resonance (SPR) sensors based on the Kretschmann configuration: Au/SiO₂ thin film structure, Au/SiO₂ nanospheres and Au/SiO₂ nanorods are designed by adding three different forms of SiO₂ materials behind the gold film of conventional Au-based SPR sensors. The effects of SiO₂ shapes on the SPR sensor are investigated through modeling and simulation with the refractive index of the media to be measured ranging from 1.330 to 1.365. The results show that the sensitivity of Au/SiO₂ nanospheres could be as high as 2875.4 nm/RIU, which is 25.96% higher than that of the sensor with a gold array. More interestingly, the increase in sensor sensitivity is attributed to the change in SiO₂ material morphology. Therefore, this paper mainly explores the influence of the shape of the sensor-sensitizing material on the performance of the sensor. Full article

Due to the abuse of antibiotics, the sensitivity of patients to antibiotics is gradually reduced. This work develops a Fe₃O₄@SiO₂@Au/PDA nanochain which shows an interesting magnetic-field-induced improvement of its photothermal antibacterial property. First, SiO₂ was wrapped on Fe₃O₄ nanospheres assembled in a chain to form a Fe₃O₄@SiO₂ nanocomposite with a chain-like nanostructure. Then, the magnetic Fe₃O₄@SiO₂@Au/PDA nanochains were prepared using in situ redox-oxidization polymerization. Under the irradiation of an 808 nm NIR laser, the temperature rise of the Fe₃O₄@SiO₂@Au/PDA nanochain dispersion was obvious, indicating that they possessed a good photothermal effect. Originating from the Fe₃O₄, the Fe₃O₄@SiO₂@Au/PDA nanochain showed a typical soft magnetic behavior. Both the NIR and magnetic field affected the antimicrobial performance of the Fe₃O₄@SiO₂@Au/PDA nanochains. Escherichia coli and Staphylococcus aureus were used as models to verify the antibacterial properties. The experimental results showed that the Fe₃O₄@SiO₂@Au/PDA nanochains exhibited good antibacterial properties under photothermal conditions. After applying a magnetic field, the bactericidal effect was further significantly enhanced. The above results show that the material has a broad application prospect in inhibiting the growth of bacteria. Full article

Surface-enhanced Raman spectroscopy (SERS) has long been an ultrasensitive technique for trace molecule detection. However, the development of a sensitive, stable, and reproducible SERS substrate is still a challenge for practical applications. Here, we demonstrate a cost-effective, centimeter-sized, and highly reproducible SERS substrate using the nanosphere lithography technique. It consists of a hexagonally packed Ag metasurface on a SiO₂/Au/Si substrate. A seconds-lasting etching process of a self-assembled nanosphere mask manipulates the geometry of the deposited Ag metasurface on the SiO₂/Au/Si substrate, which attains the wavelength matching between the optical absorbance of the Ag/SiO₂/Au/Si substrate and the excitation laser wavelength as well as the enhancement of Raman signals. By spin-coating a thin layer of graphene oxide on the substrate, a SERS performance with 1.1 × 10⁵ analytical enhancement factor and a limit of detection of 10⁻⁹ M for melamine is achieved. Experimental results reveal that our proposed strategy could provide a promising platform for SERS-based rapid trace detection in food safety control and environmental monitoring. Full article

In this work, we developed a new type of SERS probe, which was composed of glass-SiO₂-Au@MBN@Ag nanoparticles (NPs) three-dimensional Surface-enhanced Raman spectroscopy (SERS) substrate. When the laser passed through the quartz glass sheet, on the one hand, the SiO₂ NPs supporting the Au@MBN@Ag NPs increase the roughness of the substrate surface, resulting in a large number of hot spots among nanoparticles. On the other hand, based on the focusing effect of silicon dioxide nanospheres, the laser can better focus on the surface of nanoparticles in the inverted SERS probe, thus showing better SERS enhancement. Furthermore, the Au@MBN@Ag NPs core-shell structure was used with 4-mercaptobenzoonitrile (MBN) as an internal standard molecule, and the quantitative determination of tyrosine and urea was realized by internal standard correction method. The standard working curves of the two had good linear correlation with R² above 0.9555. The detection limits of tyrosine and urea were in the range of 2.85 × 10⁻¹⁰ M~7.54 × 10⁻⁶ M, which confirms that this design can be used for quantitative and specific detection of biological molecules, demonstrating great practical significance for the research of diseases such as skin lesions and endocrine disorders. Full article

The precise synthesis of fine-sized nanoparticles is critical for realizing the advantages of nanoparticles for various applications. We developed a technique for preparing finely controllable sizes of gold nanoparticles (Au NPs) on a silica template, using the seed-mediated growth and interval dropping methods. These Au NPs, embedded on silica nanospheres (SiO₂@Au NPs), possess peroxidase-like activity as nanozymes and have several advantages over other nanoparticle-based nanozymes. We confirmed their peroxidase activity; in addition, factors affecting the activity were investigated by varying the reaction conditions, such as concentrations of tetramethyl benzidine and H₂O₂, pH, particle amount, reaction time, and termination time. We found that SiO₂@Au NPs are highly stable under long-term storage and reusable for five cycles. Our study, therefore, provides a novel method for controlling the properties of nanoparticles and for developing nanoparticle-based nanozymes. Full article

Surface-enhanced Raman scattering (SERS) sensors are constructed from metallic plasmonic nanostructures providing high sensitivity and spectral reproducibility. In many cases, irradiation of the SERS substrate by the laser beam leads to an increase of the local temperature and consequently to thermal degradation of metallic nanostructure itself and/or adsorbed analyte. We report here a “bottom-up” technique to fabricate new thermally resistant gold “film over nanosphere” (FON) substrates for SERS. We elaborated the simple and straightforward method of preparation of homogeneously and closely packed monolayer of SiO₂ nanoparticles (50 nm in diameter) and covered it by a thin (20 nm) layer of magnetron-sputtered gold. The spectral testing using biologically important molecules (methylene blue, cationic porphyrin, and fungicide 1-methyl-1H-benzimidazole-2-thiol) proved a sensitivity and reproducibility of our AuSiO₂ substrates. The main advantage of such SERS-active substrates is high thermal stability and low intensity of background and signal of graphitic carbon. Full article

Hybrid materials prepared by encapsulation of plasmonic nanoparticles in porous silica systems are of increasing interest due to their high chemical stability and applications in optics, catalysis and biological sensing. Particularly promising is the possibility of obtaining gold@silica nanoparticles (Au@SiO₂ NPs) with Janus morphology, as the induced anisotropy can be further exploited to achieve selectivity and directionality in physical interactions and chemical reactivity. However, current methods to realise such systems rely on the use of complex procedures based on binary solvent mixtures and varying concentrations of precursors and reaction conditions, with reproducibility limited to specific Au@SiO₂ NP types. Here, we report a simple one-pot protocol leading to controlled crystallinity, pore order, monodispersity, and position of gold nanoparticles (AuNPs) within mesoporous silica by the simple addition of a small amount of sodium silicate. Using a fully water-based strategy and constant content of synthetic precursors, cetyl trimethylammonium bromide (CTAB) and tetraethyl orthosilicate (TEOS), we prepared a series of four silica systems: (A) without added silicate, (B) with added silicate, (C) with AuNPs and without added silicate, and (D) with AuNPs and with added silicate. The obtained samples were characterised by transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and UV-visible spectroscopy, and kinetic studies were carried out by monitoring the growth of the silica samples at different stages of the reaction: 1, 10, 15, 30 and 120 min. The analysis shows that the addition of sodium silicate in system B induces slower MCM-41 nanoparticle (MCM-41 NP) growth, with consequent higher crystallinity and better-defined hexagonal columnar porosity than those in system A. When the synthesis was carried out in the presence of CTAB-capped AuNPs, two different outcomes were obtained: without added silicate, isotropic mesoporous silica with AuNPs located at the centre and radial pore order (C), whereas the addition of silicate produced Janus-type Au@SiO₂ NPs (D) in the form of MCM-41 and AuNPs positioned at the silica–water interface. Our method was nicely reproducible with gold nanospheres of different sizes (10, 30, and 68 nm diameter) and gold nanorods (55 × 19 nm), proving to be the simplest and most versatile method to date for the realisation of Janus-type systems based on MCM-41-coated plasmonic nanoparticles. Full article