New branched flower-like Ag nanostructures for SERS analysis

Preparation of Flower-like Nanosilver Based on Bioderived Caffeic Acid for Raman Enhancement and Dye Degradation

In this study, a simple, green, and low-cost room temperature synthesis of broccoli-like silver nanoflowers (AgNF) with a particle size of about 300-500 nm was developed using plant-derived caffeic acid as a reducing agent and polyvinylpyrrolidone as a dispersant under ultrasound assistance. The flower clusters covered by small nanocrystals of 20-50 nm significantly enhance the electromagnetic field signals. AgNF was deposited on the surface of silicon wafers as a surface-enhanced Raman spectroscopy sensor for the detection of probe molecules such as rhodamine 6G (R6G) and malachite green with high sensitivity, homogeneity, and reproducibility. AgNF was deposited on cotton fabrics in the form of composites to catalyze the degradation of dye pollutants such as R6G, MG, and methyl orange in the presence of sodium borohydride. 0.1 g of AgNF/cotton fabric could assist 15 mmol/L NaBH4 to achieve over 90% degradation of various dyes as well as a high concentration of dyes in 12 min with good reusability and recyclability. The AgNF synthesized in this work can not only monitor the type and amounts of pollutants (dyes) in wastewater but also catalyze the rapid degradation of dyes, which is expected to be valuable for industrial applications.

Cotton swabs wrapped with three-dimensional silver nanoflowers as SERS substrates for the determination of food colorant carmine on irregular surfaces

A lightweight, portable, low-cost, and accessible cotton swab was employed as surface enhanced Raman spectroscopy (SERS) matrix template. The silver nanoflowers were in situ grown on the surface of cotton swabs to form three-dimensional Ag nanoflower@cotton swabs (AgNF@CS) SERS substrate with high-density and multi-level hot spots. The SERS performance of AgNFs@CS substrates with various reaction time was systematically studied. The optimal AgNF-120@CS SERS substrate exhibits superior detection sensitivity of 10-10 M for methylene blue, good signal reproducibility, high enhancement factor of 1.4 × 107, and excellent storage stability (over 30 days). Moreover, the AgNF-120@CS SERS substrate also exhibits prominent detection sensitivity of 10-8 M for food colorant of carmine. Besides, the portable AgNF-120@CS SERS substrate is also capable of detecting food colorant residues on irregular food surfaces.

AgTNP@TiO2@Ag core-satellite composites for sensitive sensing and in situ monitoring photodegradation of organic dyes by portable Raman spectrometer

The development of sensitive, reliable, and robust substrates for surface-enhanced Raman spectroscopy (SERS) heavily relies on the creation of numerous hot spots. In this study, we propose a simple approach to fabricate core-satellite composites composed of AgTNP@TiO2@Ag, where Ag triangular nanoplates (AgTNPs) act as the cores, TiO2 serves as the interlayer, and Ag nanoparticles are deposited around them to form Ag satellites. By adjusting the amount of AgNO3, we precisely control the coverage of Ag nanoparticles on AgTNP@TiO2@Ag, thus fine-tuning their SERS sensitivity. Various characterization techniques were employed to examine their composition, morphology, and crystal structure. Thanks to the abundant hot spots created by the Ag satellites, these composites exhibit significantly enhanced SERS sensitivity and they demonstrate the capability to detect methylene blue (MB) at a concentration of 10-10 M by portable Raman spectrometer. Moreover, the AgTNP@TiO2@Ag composites effectively enable in situ SERS monitoring of the photodegradation reaction of MB. Overall, the novel AgTNP@TiO2@Ag composites prepared in this study exhibit high SERS sensitivity and excellent photocatalytic performance, making them highly valuable for environmental detection and ecological restoration purposes.

Fabrication of silver nanostructure array patterns (SNAPs) on silicon wafer for highly sensitive and reliable SERS substrates

Metal nanostructure arrays with large amounts of nano-gaps are important for surface enhanced Raman scattering applications, though the fabrications of such nanostructures are difficult due to the complex and multiple synthetic steps. In this research, we report silver nanostructure array patterns (SNAPs) on silicon wafer, which is fabricated with semiconductor manufacturing technology, Cu2O electrochemistry deposition, and Ag In-situ oxidation-reduction growth. Benefiting from the dense and uniform distribution of Ag nanowires, the fabricated SNAPs demonstrate a very strong and uniform surface-enhanced Raman scattering (SERS) effect. The efficiency of SNAPs was investigated by using rhodamine 6G (R6G) dye as an analyte molecule. The results show that the minimum detectable concentration of R6G can reach as low as 10-11 M, and the Raman signals in the random region show good signal homogeneity with a low relative standard deviation (RSD) of 4.77 %. These results indicate that the SNAPs perform a great sensitivity and uniformity as a SERS substrate. Furthermore, we used the SNAPs substrate to detect antibiotic sulfadiazine. The main peaks in sulfadiazine Raman and vibration modes assignments were obtained and the quantitative analysis model was established by principal component analysis (PCA). The detection and application results of sulfadiazine indicate that the SNAPs substrate can be applied for trace detection of antibiotics. In addition, we have cited the application of the SNAPs substrate in anti-counterfeiting labels. These practical applications demonstrate that the fabricated SNAPs can potentially provide a way to develop low-cost SERS platforms for environmental detections, biomedicine analysis, and commodities anti-counterfeiting.

Biological Response Evaluation of Human Fetal Osteoblast Cells and Bacterial Cells on Fractal Silver Dendrites for Bone Tissue Engineering

Prosthetic joint replacement is the most widely used surgical approach to repair large bone defects, although it is often associated with prosthetic joint infection (PJI), caused by biofilm formation. To solve the PJI problem, various approaches have been proposed, including the coating of implantable devices with nanomaterials that exhibit antibacterial activity. Among these, silver nanoparticles (AgNPs) are the most used for biomedical applications, even though their use has been limited by their cytotoxicity. Therefore, several studies have been performed to evaluate the most appropriate AgNPs concentration, size, and shape to avoid cytotoxic effects. Great attention has been focused on Ag nanodendrites, due to their interesting chemical, optical, and biological properties. In this study, we evaluated the biological response of human fetal osteoblastic cells (hFOB) and P. aeruginosa and S. aureus bacteria on fractal silver dendrite substrates produced by silicon-based technology (Si_Ag). In vitro results indicated that hFOB cells cultured for 72 h on the Si_Ag surface display a good cytocompatibility. Investigations using both Gram-positive (S. aureus) and Gram-negative (P. aeruginosa) bacterial strains incubated on Si_Ag for 24 h show a significant decrease in pathogen viability, more evident for P. aeruginosa than for S. aureus. These findings taken together suggest that fractal silver dendrite could represent an eligible nanomaterial for the coating of implantable medical devices.

The Role of Inorganic Fillers in Electrostatic Discharge Composites

The occurrence of uncontrolled electrostatic discharge (ESD) is among the major causes of damage in unprotected electronic components during industrial processes. To counteract this undesired phenomenon, ESD composites showing static-dissipative and antistatic responses are developed. In particular, static-dissipative materials are able to slow down the flow of electric charges, whereas antistatic materials directly suppress the initial charges induced by undesired charging by properly dispersing conductive fillers within an insulant matrix and thus forming a conductive filler network. In this context, the purpose of this review is to provide a useful resume of the main fundamentals of the technology necessary for facing electrostatic charging. The formation mechanisms of electrostatic charges at the material surface were described, providing a classification of ESD composites and useful characterization methods. Furthermore, we reported a deep analysis of the role of conductive fillers in the formation of filler networks to allow electric charge movements, along with an overview of the different classes of inorganic conductive fillers exploitable in ESD composites, evidencing pros/cons and criticalities of each category of inorganic fillers.

Current methods and emerging approaches for detection of programmed death ligand 1

Various tumor cells overexpress programmed death ligand 1 (PD-L1), a main immune checkpoint protein (ICP) embedded in the tumor cells membrane, to evade immune recognition through the interaction between PD-L1 and its receptor programmed death 1 (PD-1) which is from T-cells for maintaining immune tolerance. So inhibitors targeting the PD-1 or PD-L1 can block the PD-1/PD-L1 signaling pathway to restore the recognition activity of the immune system to tumor cells, which also have been utilized as a novel approach to improve the clinical therapeutic effect for cancer patients. Since not all cancer patients can respond to these inhibitors effectively, previous diagnosis of PD-L1 is significant to target the right treatments for cancer patients. This review pays attention to the PD-L1 detection and recent progress in the measurement of PD-L1 concentration, including various detection methods based on optical sensors as well as electrochemical assays. Apart from above those, we also focus on the prospects of PD-L1 detection in precision medicine.

Silver Nanoparticle-Decorated Silica Nanospheres and Arrays as Potential Substrates for Surface-Enhanced Raman Scattering

Poly(vinylpyrrolidone) (PVP) was used as both a modifier and reductant to in situ deposit silver nanoparticles (denoted Ag NPs) on the surface of silica nanospheres (nanosilica or nano-SiO₂), affording Ag-decorated nanosilica (denoted SiO₂@Ag). The as-obtained SiO₂@Ag composite can form silver nanoparticle-decorated silica nanosphere arrays (denoted SiO₂@Ag arrays) via evaporation-induced self-assembly. The as-prepared SiO₂@Ag composite and SiO₂@Ag array were used as the SERS substrates to measure the Raman signals of the dilute solutions of rhodamine 6G (denoted R6G), an organic dye that is a potential pollutant to the environment. The findings indicate that the as-prepared SiO₂@Ag composite and SiO₂@Ag array as potential SERS substrates simultaneously exhibit a high degree of metal coverage and small size of Ag NPs as well as good stability and abundant "hot spots", which contributes to their desired Raman enhancement capacities. For the detection of trace R6G, they provide a limit of detection of as low as 10^-9-10^-11 M as well as good reproducibility, showing promising potential for monitoring chemical and biological molecules.

Construction of flexible, transparent and mechanically robust SERS-active substrate with an efficient spin coating method for rapidin-situtarget molecules detection

Flexible, transparent and mechanically robust surface enhanced Raman scattering (SERS)-active substrates is currently the most attractive research focus in the field of Raman detection, and also a powerful analysis and identification technique in the biological research. Herein, we introduced a low-cost and large-scale method to fabricate flexible and transparent AgNPs/WPU plasmonic metafilm with monolayer-island phase nanostructures based on silver nanoparticles (AgNPs) and waterborne polyurethane emulsion (WPU) film. The obtained AgNPs/WPU plasmonic metafilm demonstrated excellent SERS sensitivity, signal uniformity and reproducibility, and the SERS substrates could still maintain excellent stability even after being bent or stretched over 100 cycles. The detection concentration was as low as 10^-9M with 4-Mercaptobenzoic acid (4-MBA) as probe molecule, and the enhancement factor was high to 2.2 × 10⁷. More importantly, the flexibility and adhesivity of AgNPs/WPU plasmonic metafilm could be directly conformal coverage on the apple surface forin situdetection of thiram residue, and the detection limit was as low as 9.0165 ng cm^-2. This versatile AgNPs/WPU plasmonic metalfilm would be a promising SERS substrate for the detection of pesticide residue in chemical and biological applications.

Optimization of High-Density Fe-Au Nano-Arrays for Surface-Enhanced Raman Spectroscopy of Biological Samples

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.

Dendritic Forest-Like Ag Nanostructures Prepared Using Fluoride-Assisted Galvanic Replacement Reaction for SERS Applications

Dendritic forest-like Ag nanostructures were deposited on a silicon wafer through fluoride-assisted galvanic replacement reaction (FAGRR) in aqueous AgNO₃ and buffered oxide etchant. The prepared nanostructures were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma–optical emission spectroscopy, a surface profiler (alpha step), and X-ray diffraction. Additionally, the dendritic forest-like Ag nanostructures were characterized using surface-enhanced Raman scattering (SERS) when a 4-mercaptobenzoic acid (4-MBA) monolayer was adsorbed on the Ag surface. The Ag nanostructures exhibited intense SERS signal from 4-MBA because of their rough surface, and this intense signal led to an intense local electromagnetic field upon electromagnetic excitation. The enhancement factor for 4-MBA molecules adsorbed on the Ag nanostructures was calculated to be 9.18 × 10⁸. Furthermore, common Raman reporters such as rhodamine 6G, 4-aminothiolphenol, 5,5′-dithiobis-2-nitrobenzoic acid, and carboxyfluorescein (FAM) were characterized on these dendritic forest-like Ag nanostructures, leading to the development of an ultrasensitive SERS-based DNA sensor with a limit of detection of 33.5 nM of 15-mer oligonucleotide.

Growth of Nanostructured Silver Flowers by Metal-Mediated Catalysis for Surface-Enhanced Raman Spectroscopy Application

Metallic flowers with nanoscale surface roughness can provide a platform for highly sensitive and reproductive surface-enhanced Raman spectroscopy (SERS). Here, we present a method to grow a nanostructured silver flower (NSF) at the apex of a plasmonic tip based on metal-mediated catalysis, where the NSF was rapidly generated in no more than 1 min. The NSF was used as the SERS substrate under linear polarization beam (LPB) excitation to achieve a 10^-9 M detection sensitivity for the malachite green analyte. The reproducibility for SERS is examined to have been guaranteed by comparing Raman intensity enhanced by different NSFs. Compared with the LPB, the azimuthal vector beam (AVB) excitation can further improve the SERS activity of the NSF, which is consistent with the simulation result that the gap mode can be effectively generated between two adjacent Ag nanoparticles (NPs) and between the NPs and the Ag pyramids on the surface of the NSF under AVB illumination. This work makes it promising for plasmonic tip-mediated catalysis to be applied in nanofabrication, the products of which can be further exploited in nanostructure-based ultrasensitive detection.