Bilayer composites consisting of gold nanorods and titanium dioxide as highly sensitive and self-cleaning SERS substrates

Cationic starch styrene acrylic antibacterial emulsion based on subject object recognition of β-cyclodextrin for paper surface modification

There are some drawbacks such as the propagation and spread of bacteria and viruses during the use of normal paper. Therefore, this work designed a starch styrene-acrylic antibacterial emulsion for improving the paper properties. The modified antimicrobial monomer was prepared by the subject-object recognition of β-cyclodextrin with hydrophobic modified titanium dioxide. The antibacterial performance of prepared emulsion was tested by Escherichia coli, Staphylococcus aureus. And the mechanical properties of the modified paper were measured according to the national standards. The results showed that the antibacterial emulsion has excellent comprehensive performance with the viscosity of 1750 mPa·s, the inhibition ring diameter of 11.82 mm, the good chemical stability and storage stability. Therefore, the proposed cationic starch styrene-acrylic antibacterial emulsion has promising applications in paper surface modification.

TiO2 nanofilms for surface-enhanced Raman scattering analysis of urea

In this study, titanium dioxide (TiO2) nanofilms with nanoparticle structure were grown in situ on metallic aluminum (Al) sheets using a simple sol-hydrothermal method. Al sheets were chosen because they can form Schottky junctions with TiO2 during the calcination process, thus achieving a tight bonding between the nanoparticles and the solid substrate, which cannot be achieved with conventional glass substrates. The substrates synthesized with different contents of titanium butoxide [Ti(OBu)4] were investigated using 4-mercaptobenzoic acid as a probe molecule, and the results showed that the substrate with 9 % of the total volume of Ti(OBu)4 had the highest surface-enhanced Raman scattering (SERS) performance. As a low-cost SERS substrate that is simple to synthesize, it has excellent signal reproducibility, with a relative standard deviation of 4.51 % for the same substrate and 6.43 % for different batches of synthesized substrates. Meanwhile, the same batch of substrate can be stored at room temperature for at least 20 weeks and still maintain stable SERS signals. In addition, the synthetic substrate was used to quantitatively detect urea with a detection limit of 4.23 × 10-3 mol/L, which is comparable to the application of noble metal substrates. The feasibility of this method was verified in human urine, and the results were consistent with the clinical results, indicating that this method has great potential for clinical application.

In situ assembly of silver nanoparticles throughout electrospun oriented alginate nanofibers for hazardous rust trace detection on bronze

A convenient and reliable surface-enhanced Raman scattering (SERS) substrate has been developed for the surface corrosion analysis of bronze artifacts. The substrate consists of oriented alginate nanofiber membranes containing silver nanoparticles (Ag NPs), which were obtained through electrostatic spinning, ion exchange, and in-situ reduction. By controlling the reduction time, Ag/alginate nanofiber membranes with different contents, sizes, and distributions were obtained. The Ag/alginate nanofiber#20 membranes, obtained with a reduction time of 20 min, reached a detection limit of 10-12 M for R6G with an enhancement factor of 6.64 × 107. In the trace detection of bronze patina, the intensity of the characteristic peaks of harmful patina located at 513, 846, 911, and 974 cm-1 were increased by more than 500 %. This was due to the uniform loading of a large number of Ag NPs on the surface of the nanofiber membrane obtained by reduction for 20 min, and the formation of a large number of hot spots between the oriented nanofibers. This significantly improved the SERS performance of the flexible substrate layer under the joint action with the Ag NPs. These results indicate that the flexible substrate layer can greatly enhance the Raman characteristic peaks of alkali copper chloride and be effectively used for trace analysis of the surface composition of bronze artifacts.

Modulation of photo-induced Raman enhancement in Ag nanoparticles deposited on nanometer-thick TiO2 films. An interplay between plasmonic properties and irradiation energy

Photo-induced enhanced Raman spectroscopy (PIERS) is an innovative technology that offers additional enhancement in Raman signal compared to surface-enhanced Raman spectroscopy (SERS). In this study, we fabricated nanohybrids consisting of silver nanoparticles on an ultra-thin anatase film using a photoreduction method. This approach allowed for the controllable synthesis of SERS and PIERS nanoplatforms, characterized by oval-shaped nanoparticles, yet varying in size and surface coverage, leading to distinct plasmonic properties. A mere 15-minute UV pre-treatment with low photon density already initiated significant charge-transfer processes followed by Raman spectra under non-resonant conditions of the molecule and estimated by enhancement factor in the range of 12---17. This phenomenon was observed for a molecular monolayer of a thiol derivative. Not only boosting electron migration appeared. This unique interface of the Ag-anatase composite undoubtedly contributed to extended relaxation times of photo-induced enhancement. Furthermore, we investigated how plasmonic and morphological features of the nanoplatforms, in conjunction with UV and Vis illumination, modulated the migration of photoinduced electrons from the semiconductor to the metal. These findings highlighted the variety of processes contributing to the creation of efficient PIERS materials.

Plasmonic Paper based Flexible SERS Biosensor for Highly Sensitive Detection of Lactic and Uric Acid

Selective detection and quantification of biomarkers related to human diseases are essential for preventive healthcare. Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical tool offering high sensitivity. However, the success of this promising analytical tool relies on the ability to effectively fabricate SERS substrate. Herein we have demonstrated a plasmonic paper-based flexible substrate (PPFS) for SERS sensing. In situ growth of silver nanostructures (AgNS) on the paper-based substrate was achieved by using a simple one-step silver mirror reaction (SMR). FESEM and TEM results depicts that the increasing silver ion content influences the morphology (growth of multifacets), as well as size of AgNS. Further, the PPFS substrate was tested with Rhodamine-6G (Rh-6G) dye and an attomole sensitivity with a LOD of 4.54 x 10-18 M was achieved. Further, two biomarkers, lactic acid (LA) and uric acid (UA) were detected on the PPFS substrate, with μM and pM sensitivity, having LOD values of 0.6 x 10-6 and 0.3 x 10-12 M respectively. Above detection levels for UA on PPFS is two orders better than reported values, whereas for LA it is comparable with reported substrates. Finally, UA, LA and their mixtures were tested on PPFS and results compared with commercial substrate. The performance of PPFS were found better in all cases, thus, multifaceted AgNS paper based PPFS offers the potential to be used as a biosensor for detection of various biomarkers from body fluids, responsible for the detection of the critical disease for preventive health care.

Fabrication of Highly Ordered Ag/TiO2 Nanopore Array as a Self-Cleaning and Recycling SERS Substrate

Silver nanoparticles deposited on a titania nanopore array (Ag/TiO2 NPA) has been designed as a surface-enhanced Raman scattering (SERS) substrate for sensitive and recycling application of organic molecule detection. A TiO2 NPA was fabricated by a surface oxidization reaction of a titanium sheet by a double anodization process. A Ag/TiO2 NPA was then formed by depositing silver nanoparticles onto the TiO2 NPA by a cycling chemical reduction deposition process. The Ag/TiO2 NPA has a uniform mono-layer dispersion of Ag nanoparticles with a size of 30–50 nm on TiO2 nanopores with a diameter of 100–110 nm. The Ag/TiO2 NPA SERS substrate could facilitate interfacial adsorption of Rhodamine 6G (R6G), which achieves a sensitive detection limit of 10−8 M R6G through SERS spectrum measurement. The Ag/TiO2 NPA SERS substrate achieves an analytical enhancement factor value of 2.6 × 105. The Ag/TiO2 NRA could promote the UV light-excited photocatalytic degradation reaction of R6G adsorbed on its surface which gives rise to a refreshed Ag/TiO2 NRA under UV irradiation for 60 min and accordingly behave as a self-cleaning and recycling SERS substrate. The Ag/TiO2 NPA exhibits a much higher R6G degradation reaction rate constant (0.05764 min−1) than the TiO2 NPA (0.02600 min−1), indicating its superior photocatalytic activity and self-cleaning activity. The refreshed Ag/TiO2 NPA was able to be recycled for the Raman detection of R6G, maintaining a high stability, reproducibility, and cyclability. The highly ordered Ag/TiO2 NPA with well controlled Ag nanoparticle dispersion and TiO2 nanopore shape could act as a suitable SERS substrate for recycling and self-cleaning application for stable and sensitive molecule detection.

Controlling Gold Electrodeposition on Porous Polymeric Templates Produced by the Breath-Figure Method: Fabrication of SERS-Active Surfaces

Porous structured surfaces decorated with gold nanoparticles can be fabricated in an economical two-step process. Sub-micrometric porous polymethyl methacrylate (PMMA) templates are formed by using the breath-figure method (BFM) with a single-step spin-coating onto a conducting substrate to result in a set of delimited microdomains for gold electrodeposition. By controlling electrochemical parameters, distinct morphologies are engendered, among them, nanoparticles that present useful local Raman enhancement in the order of up to 10⁶ with stability of a solid-phase platform and characteristic chemical resistance of gold. The spatial confinement of metallic structures resulted in electromagnetic field enhancement, here compared to flat metallic surfaces where contributions of area effect and fluorescence quenching are responsible for a significant apparent enhancement to Raman spectra that has not been frequently reported to date.

A 3D spongy flexible nanosheet array for on-site recyclable swabbing extraction and subsequent SERS analysis of thiram

A sponge inspired three dimensional flexible aluminum foil based ZnO nanosheet array substrate is described for use in real-world surface enhanced Raman spectroscopic detection. Gold and silver nanoparticles were employed to form numerous hot spots on uniformly grown ZnO nanosheets on the substrate. This flexible spongy substrate can extract analytes (such as the fungicide thiram) from various complex sample surfaces by physical swabbing. Specifically, this substrate was applied to detect thiram on the surface of fruits and vegetables. Non-destructive recycling detection with a relative standard deviation of 6.1% was accomplished by monitoring the characteristic Raman peak at 1382 cm^-1. This modified substrate has a low detection limit (0.2 ng cm^-2 of thiram for apple and tomato), outstanding uniformity (relative standard deviation = 8.9%) and thermal stability (relative standard deviation = 0.9%). Graphical abstract Schematic representation of using a aluminum foil modified with ZnO nanosheets as a flexible and recyclable substrate for SERS analysis of pollutants. The substrate can be cleaned after use by UV irradiation.

Galvanic displacement-induced codeposition of reduced-graphene-oxide/silver on alloy fibers for non-destructive SPME@SERS analysis of antibiotics

This work describes the integration of solid-phase microextraction (SPME) and surface-enhanced Raman spectroscopy (SERS) by codeposition of a hybrid consisting of reduced graphene oxide and silver on silver-copper alloy fibers. The morphology and structure of the coating were characterized by a variety of microscopic and spectroscopic techniques that confirmed the hybrid structure of the material. A galvanic-displacement-induced process is assumed to be involved during the codeposition of the hybrid coating on the alloy. In this process, Ag(I) is reduced to Ag(0) by Cu(0), and the presence of conjugated domains in GO facilitates the long-range transfer of electrons from Cu to Ag+. Simultaneously, GO accepts electrons and is converted into RGO. The hybrid coating exhibits a high SERS enhancement factor and good spatial uniformity. The needle-like coated alloy fibers are shown to be a viable tool for non-destructive sampling and SERS-based determination of trace levels of the antibiotics sulfadiazine and sulfamethoxazole in a spiked tissue mimic. The SERS peaks at 1149 cm^-1 for sulfadiazine and 1144 cm^-1 for sulfamethoxazole are selected as the reference peaks in the quantitative analysis. The linear range is from 0.01 to 100 μg·cm^-3. The detection limits are 1.9 ng·cm^-3 for sulfadiazine and 4.4 ng·cm^-3 for sulfamethoxazole. Graphical abstract Schematic presentation of I: Galvanic-displacement-induced reduction of graphene oxide (brown films) and Ag⁺ (purple dots) on silver-copper alloy; II: Codeposition of reduced-graphene-oxide (grey films)/Ag (blue stars) on alloy fiber; III: Non-destructive SPME of antibiotics from spiked tissue mimic; IV: SERS detection using Raman spectroscope.