Surface-enhanced Raman scattering-active Au/SiO2 nanocomposites prepared using sonoelectrochemical pulse deposition methods

Non-covalent interaction, adsorption characteristics and solvent effect of procainamide anti-arrhythmias drug on silver and gold loaded silica surfaces: SERS spectroscopy, density functional theory and molecular docking investigations†

First-principle calculations were systematically carried out to explore the structural and electronic properties of the non-covalent interaction of procainamide (PA) anti-arrhythmias drug molecules on silver-loaded and gold-loaded silica nanostructures. Computed adsorption energies presented a higher affinity of PA towards the Ag–SiO₂ as compared with Au–SiO₂ surfaces. The non-covalent interaction analysis revealed a weak van der Waals type of forces and hydrogen bonding, associated with a noticeable repulsive steric interaction. It was conceived that silver and gold decorated silica can be used for drug administration in biological systems due to the fact that their frontier molecular orbital energy levels were considerably altered upon absorption, decreasing the pertinent energy gaps. Moreover, the electronic spectra of PA⋯Ag–SiO₂ and PA⋯Au–SiO₂ structures investigated in different solvents display a notable blue shift, suggesting that noble metal-loaded silica can be effective in the context of drug delivery systems. Therefore, silver- and gold-decorated silica of three possible drug adsorption scenarios was fully analyzed to realize the associated bioactivity and drug likeness. Theoretical findings suggest that Ag- and Au–SiO₂ nanocomposites can be considered potential drug delivery platforms for procainamide in medication protocols.

The structural and electronic properties of the non-covalent interaction of procainamide (PA) anti-arrhythmias drug molecules on silver-loaded and gold-loaded silica nanostructures were explored using first-principle calculations.

Stable SERS substrate based on highly reflective metal liquid-like films wrapped hydrogels for direct determination of small molecules in a high protein matrix

The study of the interaction between small molecules and proteins is important. Surface-enhanced Raman spectroscopy (SERS) is suitable for such applications since it has the power of detecting a molecule based on its intrinsic nature and without labeling. Herein, the MeLLFs@PAAG SERS substrate supporting highly reflective metal liquid-like films (MeLLFs) with polyacrylamide hydrogels (PAAG) has high-density "hot spots" to provide excellent SERS activity. The MeLLFs@PAAG formed by AgNPs only has less than 15% SERS activity loss when stored in the air for more than three weeks. By using rhodamine 6G (R6G) as a model analyte, the AgNPs based MeLLFs@PAAG SERS substrate exhibits an enhancement factor (EF) as high as 8.0 × 10⁶, a limit of detection (LOD) of 76.8 pM (S/N = 3). Also, the formed PAAG provided a 3D molecular network to orderly secure the assembled nanoparticles (NPs), which not only improves the stability of NPs but also shields the Raman signal of proteins as high as 45 g/L allowing the direct determination of the binding rate of human serum albumin (HSA) and doxorubicin (DOX). A binding rate of about 70% was detected, which is consistent with previous reports. Thus, proposed the MeLLFs@PAAG SERS substrate can be used as a promising candidate for SERS measurement in complex biological samples.

Direct comparison with terahertz metamaterials and surface-enhanced Raman scattering in a molecular-specific sensing performance

Signal enhancement of spectroscopies including terahertz time-domain spectroscopy (THz-TDS) and surface-enhanced Raman scattering (SERS) is a critical issue for effective molecular detection and identification. In this study, the sensing performance between THz-TDS and SERS individually accompanied by the proper plasmonic subwavelength structures was compared. For the precisely quantitative study on the optical properties of rhodamine 6G (R6G) dyes, SERS incorporates with the non-linearly enhanced Raman emissions at the molecular characteristic peaks while THz-TDS refers to the transmittance change and the shift of the spectral resonance. The local molecular density-dependent trade-off relationship between limit-of-detection and quenching was observed from both measurements. The specificity for two samples, R6G and methylene blue, is determined by the discriminations in spectral features such as the intensity ratio of assigned peaks in SERS and transmittance difference in THz-TDS. The comprehension of field enhancement by the specific nanostructures was supported by the finite-element method-based numerical computations. As a result, both spectroscopic techniques with the well-tailored nanostructures show great potential for highly sensitive, reproducible, label-free, and cost-effective diagnosis tools in the biomedical fields.

Influence of Silica Particle Size on the Corrosion Behavior of Electroplated Silica-Ni Hybrid Layer

Silica-Ni hybrid layers were electroplated on a Q235 steel plate in a Watt nickel plating solution with varying sizes of silica, and a pure nickel layer was prepared as a blank sample. The surface morphology, composition, and crystal structure of the electroplated layers were examined using a field emission scanning electron microscope (FESEM), an energy-dispersive spectrometer (EDS), and a X-ray diffractor (XRD). The corrosion resistance of the samples was evaluated by the experiments of potentiodynamic polarization, electrochemical impedance spectroscopy, and salt spray test in NaCl solutions. The results showed that the smaller the particle size of silicon, the higher the content of silicon in the layer was, and the better the corrosion resistance of the layer was. However, when the particle size is 10 nm, agglomeration would happen, which leads to a decrease in the corrosion resistance performance, 50 nm silica-Ni hybrid layer showed the optimal corrosion resistance with the highest silica content.

Interfacial effect of dual ultra-thin SiO2 core-triple shell Au@SiO2@Ag@SiO2 for ultra-sensitive trinitrotoluene (TNT) detection

Nanostructured hybrid Au@SiO₂@Ag@SiO₂ was developed, which greatly enhanced the surface plasmon resonance effect due to the interfacial effect of dual ultra-thin SiO₂ in which the double-superimposed long-range plasmon transfer between Au and Ag and determinand molecules. In addition, the interfacial effect between the inner and outermost silica layer can contribute to the presence of an amplified electric field between Au core and Ag shell, which prevents aggregation and oxidation of nanoparticles. At the same time, the influence of the amount of silica in SiO₂ shells on the Surface Enhanced Raman Scattering (SERS) was explored by controlling the experimental conditions. In our experiments, the ultrathin silica coating Au@SiO₂@Ag@SiO₂ showed the best SERS performance, generating an analytical enhancement factor (AEF) of 5 × 10⁶. At the same time, nanoparticles modified by 4-aminothiophenol (4-ATP) can detect 2,4,6-TNT as low as 2.27 × 10⁻⁶ ppb (10⁻¹⁴ M) and exhibit excellent versatility in the detection of nitroaromatics. The results demonstrated that the interfacial effect of double-layer dielectric silica achieved the localized surface plasmon resonance enhancement effect in Au@SiO₂@Ag@SiO₂.

The ultra-sensitive detection of trinitrotoluene (TNT) demonstrates that interfacial effect of double-layer dielectric silica achieves the LSPR enhancement effect in Au@SiO₂@Ag@SiO₂.

Enhanced Charge Transfer by Passivation Layer in 3DOM Ferroelectric Heterojunction for Water Oxidation in HCO3 - /CO2 System

Photoelectrochemical carbon dioxide conversion to fuels such as carbon monoxide, methanol, and ethylene exhibits great potential to solve energy issues. Unfortunately, CO₂ conversion efficiency is still low due to violent charge recombination at the photoanode. Herein, a novel 3D macroporous ferroelectric heterojunction composed of BiFeO₃ and LiNbO₃ is developed by a template-assisted sol-gel method, aiming at facilitating charge transfer kinetics. As expected, a tremendous enhancement of photocurrent density (300 times vs bare planar BiFeO₃ film) and charge transfer efficiency (up to 76%) is obtained in the HCO₃ ^- /CO₂ system without any cocatalyst. The photoelectrochemical performance is switchable by poling to form a depolarization electric field. Photoelectrochemical impedance spectroscopy reveals that the charge transfer resistance decreases due to the synergistic effect of BiFeO₃ 3D macroporous skeleton and LiNbO₃ passivation layer by tuning surface states. These results suggest a novel strategy for enhancing photoelectrochemical water oxidation as the anodic reaction of CO₂ reduction.

Direct electron-beam patterning of transferrable plasmonic gold nanoparticles using a HAuCl4/PVP composite resist

Reliable fabrication of gold nanoparticles with desirable size, geometry and spatial arrangement is essential for plasmonic applications. A common fabrication flow usually involves electron-beam lithography and a vacuum-evaporation-based lift-off process or etching. In this work, we evaluate an alternative approach to directly fabricate a plasmonic gold nanoparticle array without involving the vacuum evaporation process by using a chloroauric acid/poly(vinyl pyrrolidone) (HAuCl4/PVP) hybrid as a functional electron-beam resist. Systematic experiments were conducted to investigate the patterning behaviors in the fabrication process. With the optimized fabrication parameters, we show that the HAuCl4/PVP composite resist has a high patterning resolution and pure gold nanoparticles with tens of nanometers can be obtained after an annealing-based pyrolysis process. More particularly, compared to the patterned plasmonic gold nanoparticles obtained by conventional methods, the gold nanoparticles fabricated by our method can be transferred to soft substrates due to the absence of an adhesion layer, enabling various potential applications in flexible and stretchable optics. As an example, we demonstrated that the transferred gold nanoparticle array can be conformably assembled onto a flat gold surface to form a particle-on-film structure for surface-enhanced Raman scattering (SERS) applications.

Surface-enhanced Raman scattering-active desert-rose-like Ag mesoparticles prepared using cyclic voltammetric methods

Desert-rose-like Ag mesoparticles prepared by cyclic voltammetric method possess excellence SERS-activity, reproducibility, thermal stability and aging behavior.

Aqueous route to facile, efficient and functional silica coating of metal nanoparticles at room temperature

Various metal (Ag, Au, and Pt)@thiol-functionalized silica (SiO2-SH) nanoparticles (NPs) are successfully prepared at room temperature by a facile, efficient, functional, universal and scalable coating process in alcohol-free aqueous solution using pre-hydrolyzed 3-(mercaptopropyl)trimethoxysilane (MPTMS). The controlled pre-hydrolysis of the silane precursor in water and the consecutive condensation processes are the key to achieve the effective and uniform silica coating on metal NPs in aqueous solution. The thickness of the silica shell is tuned by simply varying the coating time. The silica shell can act as an effective protecting layer for Ag NPs in Ag@SiO2-SH NPs under conditions for silica coating in aqueous solution; however, it leads to a directional dissolution of Ag NPs in a more strongly basic ammonia solution. The environmentally friendly silica coating process in water is also applied to prepare highly surface-enhanced Raman scattering (SERS)-active Ag@SiO2-SH NPs with different types of Raman molecules for highly sensitive SERS-based applications in various fields.

Electrospun TiO₂ nanofelt surface-decorated with Ag nanoparticles as sensitive and UV-cleanable substrate for surface enhanced Raman scattering

In this study, the free-standing electrospun nanofibrous mat (i.e., nanofelt) consisting of anatase-phase TiO2 nanofibers with diameters of ∼200 nm was prepared, and the nanofelt was subsequently surface-decorated with Ag nanoparticles via an electroless plating method. The sensitivity toward surface enhanced Raman scattering (SERS) and UV-cleanable property of electrospun TiO2/Ag nanofelt were then investigated. In the SERS tests, the target analyte (i.e., 4-mercaptobenzoic acid, Rhodamine 6G, and 4-aminothiophenol) was first adsorbed onto the TiO2/Ag nanofelt as the probe analyte; this was followed by the measurements of Raman intensity and SERS maps. Thereafter, the nanofelt adsorbed with target analyte was cleaned and regenerated/recovered upon UV irradiation in O2-saturated water, and the removal of target analyte was attributed to photodegradation property of anatase-phase TiO2. This study suggested that the electrospun TiO2/Ag nanofelt would be promising as SERS-active substrate with UV-cleanable property for cost-effective and reproducible SERS applications.

Controllable preparation of graphene oxide/metal nanoparticle hybrids as surface-enhanced Raman scattering substrates for 6-mercaptopurine detection

In this contribution, a new simple and cost-effective strategy for the preparation of hybrids of graphene oxide (GO) and metal nanoparticles (MNPs) through the mediation of polyethyleneimine (PEI) molecules was reported.

Creating SERS hot spots on MoS(2) nanosheets with in situ grown gold nanoparticles

Herein, a reliable surface-enhanced Raman scattering (SERS)-active substrate has been prepared by synthesizing gold nanoparticles (AuNPs)-decorated MoS2 nanocomposite. The AuNPs grew in situ on the surface of MoS2 nanosheet to form efficient SERS hot spots by a spontaneous redox reaction with tetrachloroauric acid (HAuCl4) without any reducing agent. The morphologies of MoS2 and AuNPs-decorated MoS2 nanosheet were characterized by TEM, HRTEM, and AFM. The formation of hot spots greatly depended on the ratio of MoS2 and HAuCl4. When the concentration of HAuCl4 was 2.4 mM, the as-prepared AuNPs@MoS2-3 nanocomposite exhibited a high-quality SERS activity toward probe molecule due to the generated hot spots. The spot-to-spot SERS signals showed that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1362, 1511, and 1652 cm(-1)) of Rhodamine 6G were about 20%, which displayed good uniformity and reproducibility. The AuNPs@MoS2-based substrate was reliable, sensitive, and reproducible, which showed great potential to be an excellent SERS substrate for biological and chemical detection.

Nanostructured materials for applications in surface-enhanced Raman scattering

This highlight summarizes current advances in the design and the employment of nanostructured materials in SERS substrates especially from the dimensional point of view. We then talk about synthesis methods and the novel properties of these nanostructured materials with their potential applications in SERS.