Spectroscopy Active Substrates Research Articles

Ag nanoflowers as single-particle, multi-wavelength SERS active platforms

Surface-enhanced Raman spectroscopy (SERS) has been successfully employed in several fields of interest such as biosensing, in-situ catalysis studies, and archeology, in this regard, the production of nanostructures for the SERS effect is the core of scientific research. Up to now a lot of different types of metallic nanoparticles and nanosurfaces were produced in trying to match the theoretical enhancement of 1014. This work presents a novel SERS active substrate with a high enhancement and a wide range of exciting wavelengths. Specifically, we synthesize Ag Nanoflowers (AgNFs), spherical silver micro-particles with a diameter of 1.7 μm and a nano-rough surface. When AgNFs are deposited onto a substrate thanks to their dimension is possible, to find a single isolated micro-particle and study the signal enhancement of an analyte adsorbed onto its surface. The SERS properties at a single-particle level were studied using a standard molecule 4-mercaptobenzoic acid (4-MBA). Thanks to their extinction spectrum, expanding throughout the visible range, we were able to systematically study the enhancement for several single Ag NFs with 532, 633, and 785 nm laser wavelengths, finding a maximum enhancement factor in the order of 108- 109. This result is of great interest because demonstrates that such nanomaterial can be easily used to study every kind of analyte at low concentrations with any exciting wavelength thus avoiding other undesired optical phenomena, such as luminescence or degradation of the analyte.

Green fabrication of Au nanoparticles as SERS-active substrate for enhancement hydroquinone detection in cosmetics

The detection of hydroquinone (HQ) compounds in cosmetics is a recent challenge due to the limitations of analytical methods and instrumentation. In this research, Au nanoparticles with various concentrations were successfully fabricated, characterized, and used as active substrates at the surface-enhanced Raman spectroscopy (SERS) for HQ detection in cosmetics. The morphological images show the spherical-like structure of Au nanoparticles with an average size diameter of 16.06 nm. The crystalline plane of Au nanoparticles has a diffraction peak at the 2θ: 38.12°, 44.44°, 64.79°, and 77.79° related to miller indices of (111), (200), (220), and (311). The particle size distribution of Au colloid was 32 nm with a potential zeta charge value of − 28.5 mV. The HQ molecules are adsorbed on SERS active substrates with various concentrations of Au nanoparticles. Raman spectroscopy spectrum showed a significant increase in HQ molecules intensity peaks at 441, 797, 898, 1054, and 1162 cm−1, respectively. Colloids of Au nanoparticles implied potential as an active substrate in SERS-based detection and application.

Sensitive and handy detection of pesticide residue on fruit surface based on single microsphere surface-enhanced Raman spectroscopy technique

Hypothesis: Surface-enhanced Raman spectroscopy (SERS) has become an emerging and reliable tool for detecting pesticide residues due to its high sensitivity, fast testing speed and easy sample handling. SERS active substrates are the key to achieve efficient and sensitive detection. However, for the most widely used noble metal nanoparticles, there are problems of high noble metal nanoparticle usage and random aggregation. The micron-scale Raman spot is focused on multiple randomly aggregated nanoparticles during the test, resulting in poor reproducibility. Therefore, the development of micron-scale cost-effective SERS substrates with good reproducibility and simple detecting method is of great significance in practical detection.Experiments: Through deposition of silver nanoparticles (Ag-NPs) by chemical reduction on the surface of monodisperse sulfonated polystyrene (SPS) microspheres, micron-sized PS@Ag-NPs core–shell microspheres were prepared with excellent SERS activity. After that, two simple protocols (Method I and Method II) were explored for the determination of thiram on apple epidermis.Findings: Based on our developed strategy of the single microsphere SERS technique, we successfully fabricated uniform PS@Ag-NPs substrate with high SERS activity and excellent detection sensitivity. The single microsphere SERS technique possesses the capability of anti-dilutability and the utilization of ultra-low PS@Ag-NPs microsphere dosage, realizing qualitative and quantitative detection of thiram on apple with detection limits far below the standard stipulated by China and the European Union.

Preparation of Fe3O4@PDA@Au@GO Composite as SERS Substrate and Its Application in the Enrichment and Detection for Phenanthrene.

In this study, highly active Fe3O4@PDA@Au@GO surface-enhanced Raman spectroscopy (SERS) active substrate was synthesized for application in the enrichment and detection of trace polycyclic aromatic hydrocarbons (PAHs) in the environment. The morphology and structure were characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and UV–visible absorption spectrum (UV–vis spectra). The effect of each component of Fe3O4@PDA@Au@GO nanocomposites on SERS was explored, and it was found that gold nanoparticles (Au NPs) are crucial to enhance the Raman signal based on the electromagnetic enhancement mechanism, and apart from enriching the PAHs through π–π interaction, graphene oxide (GO) also generates strong chemical enhancement of Raman signals, and polydopamine (PDA) can prevent Au from shedding and agglomeration. The existence of Fe3O4 aided the quick separation of substrate from the solutions, which greatly simplified the detection procedure and facilitated the reuse of the substrate. The SERS active substrate was used to detect phenanthrene in aqueous solution with a detection limit of 10−7 g/L (5.6 × 10−10 mol/L), which is much lower than that of ordinary Raman, it is promising for application in the enrichment and detection of trace PAHs.

Highly efficient sers performance from the silver nanoparticles/graphene nanoribbons/ cellulose paper

Introduction: Metal/graphene heterojunction structure has been one of the most crucial tools in the growth of high-performance Surface-enhanced Raman spectroscopy (SERS) platform, which is appropriate for sensing applications. In this research, we developed a SERS platform, graphene nanoribbons (GNRs) decorated silver nanoparticles (AgNPs) on cellulose paper substrate, in which GNRs was synthesized by wet chemical based on unzipping process of Multi-walled carbon nanotubes (MWCNTs), then GNRs hybridized with AgNPs through magnetron sputtering method.
 Methods: The morphology of graphene nanoribbons coated-Ag (AgNPs@GNRs) was analyzed by field emission scanning electronic microscopy (FESEM) and transmission electron microscopy (TEM). The quality and thermal stability of GNRs were characterized using thermogravimetric analysis. Besides, its structure and quality were also characterized by Raman spectroscope.
 Results: The results show that the unzipping process of MWCNTs to form GNRs was strongly affected by dispersing time and stirring temperature. The suitable condition creating the Graphene Nanoribbons using MWCNTs was the dispersing time of 10 mins in an acid environment, stirring in 30 mins at room temperature and in 45 min at 100°C. Moreover, SERS platform of AgNPs@GNRs exhibit the outstanding SERS signal enhancement with rhodamine 6G (R6G) low concentration of 10-5 M compared with pristine graphene and silver thin film. This could be attributed to the synergistic effect between AgNPs, GNRs and analyze molecules based on the enhancement of electromagnetic mechanism (EM) and chemical mechanism (CM), which plays a vital role in promoting the improvement SERS behavior.
 Conclusion: Ag NPs assembled onto graphene nanoribbons/ cellulose paper substrate could also serve as SERS active substrates for practical applications in various fields at trace levels.

Ag/ZnO heterostructure fabricated on AZO platform for SERS based sensitive detection of biomimetic hydroxyapatite

Versatile surface-enhanced Raman spectroscopy (SERS) active Ag/ZnO heterostructures grown on glass and conducting Al-doped ZnO (AZO) have been developed to enable detection of analytes having very low molar concentration. The SERS substrate is composed of Ag nanoparticles decorated on ZnO microrods arranged mostly in flower-like patterns. ZnO microrods are synthesized by a hydrothermal method followed by the photo-deposition of Ag nanoparticles to fabricate Ag/ZnO heterostructure. The demonstration of the SERS activity is first accomplished by probing methyl orange and rhodamine 6G with a band specific SERS substrate enhancement factor (SSEF) as high as 5.4 × 107 and analytical enhancement factor (AEF) of 1.3 × 1010, exceptionally high enhancement achieved through use of the metal-semiconductor heterostructure where charge transfer at the interface plays an important role during SERS. The nanocrystalline hydroxyapatite prepared by a biomimetic process is detectable using the SERS active substrate with considerable enhancement of the characteristic Raman signals. This work is a novel attempt to probe biomimetic hydroxyapatite using SERS which would pave the way to understand early stages of bone mineralization. The use of AZO, an indium free transparent conductor is crucial to facilitate enhanced charge transfer at the interface which accentuates Raman active modes at low concentration of biomimetic apatite.

Synthesized Au NPs@silica composite as surface-enhanced Raman spectroscopy (SERS) substrate for fast sensing trace contaminant in milk.

With increased concerns on milk safety issues, the development of a simple and sensitive method to detect 2,4-dichlorophenoxyacetic acid (2,4-D), a common contaminant in milk, becomes relevant in safeguarding human health threats that results from its consumption. Surface-enhanced Raman spectroscopy (SERS) shows excellent ability for various targets analysis but its usage for rapid and accurate determination of analyte via SERS presents challenges. This study attempted the quantification of 2,4-dichlorophenoxyacetic acid (2,4-D) residue in milk using a novel SERS active substrate- decorated silica films with Au nanoparticles (Au NPs@ silica) coupled to chemometric algorithms. Au NPs@ silica composite was synthesized as a SERS sensor through self-assembly. Thereafter, the SERS spectrum of 2,4-D extract from milk with different concentrations based on the developed SERS sensor was collected and the spectra were analyzed by partial least squares (PLS), and variable selection algorithms - genetic algorithm-PLS (GA-PLS), competitive-adaptive reweighted sampling-PLS (CARS-PLS) and ant colony optimization-PLS (ACO-PLS), to develop quantitative models for 2,4-D prediction. The results obtained showed that the CARS-PLS model gave the optimum result with LOD of 0.01 ng/mL realized and a determination coefficient in the prediction set of (RP) = 0.9836 within a linear range of 10-2 to 106 ng/mL was achieved. Au NPs@ silica SERS sensor combined with CARS-PLS may be employed for rapid quantification of 2,4-D extract from milk towards its quality and safety monitoring.

Detection and Quantification of Bucinnazine Hydrochloride Injection Based on SERS Technology.

In this investigation, surface-enhanced Raman spectroscopy (SERS) technology was performed to detect bucinnazine hydrochloride (BH) injection in water and urine. The theoretical Raman spectrum of BH with characteristic peaks was calculated and identified by density functional theory (DFT). Employing an improved silver sol as a SERS active substrate, the SERS spectra of a BH solution with different concentrations were acquired with a 0.5 mol/L KI solution as an aggregation agent. It was determined that the limit of detection (LOD) was low, to 0.01 μg/mL. A good linear relationship of BH between the Raman intensity and the concentrations was obtained in water at a concentration range from 0.5 to 6 μg/mL (R2 = 0.9914), which laid a favorable foundation for quantitative analysis. In addition, the recovery rate of spiked samples from 95.13 to 120.54% were calculated. Finally, the detection of BH injection in artificial urine was completed and the detection limit could reach 0.5 μg/mL, which met the requirements of a rapid on-site detection of drugs in urine. As a result, it indicates that the inspection of BH by the SERS method is with simplicity and high sensitivity, having a great potential for real-time detection.

Facile fabrication of silver nanoparticle decorated α-Fe2O3 nanoflakes as ultrasensitive surface-enhanced Raman spectroscopy substrates

Although great progress has been made on designing noble metal nanoparticle aggregates/assemblies as surface-enhanced Raman spectroscopy (SERS) substrates, an ever increasing research interest has focused on fabrication of hierarchical nanostructures for superior SERS performance. Here, we report effective decoration of silver nanoparticles (AgNPs) onto vertically and densely grown α-Fe2O3 nanoflakes (NFs) as SERS active substrates. The SERS substrate was prepared by thermally annealing Fe foil at 450 °C to grow α-Fe2O3 NFs and electroless deposition of AgNPs onto α-Fe2O3 NFs, with excellent ability to control the particle size and density. The AgNP-decorated α-Fe2O3 NFs offer high density hot spots and exhibited high SERS performance with enhancement factor of 8.1 × 106. Integration of α-Fe2O3 nanostructure functions as intrinsic internal standard and selective binder for specific analytes like the toxic arsenic. The substrate was successfully used for quantitative detection of arsenic with spatial uniformity (relative standard deviation, RSD, 8.8%) and good reproducibility (RSD, 9.7%). The Raman signal of α-Fe2O3 integrated to the SERS substrate was utilized as internal standard which significantly improves reproducibility. The substrate exhibited a high sensitivity for arsenic detection with a limit of detection down to 1.5 μg L−1, which is much lower than permissible limit (10 μg L−1) set by the WHO. Moreover, the SERS substrates showed excellent practicability and selectivity for determination of arsenic in environmental waters which is valuable for environmental and human health protection.