Enhancing SERS Intensity by Coupling PSPR and LSPR in a Crater Structure with Ag Nanowires

The sensitive characteristics of surface-enhanced Raman scattering (SERS) can be applied to various fields, and this has been of interest to many researchers. Propagating surface plasmon resonance (PSPR) was initially utilized but, recently, it has been studied coupled with localized surface plasmon resonance that occurs in metal nanostructures. In this study, a new type of metal microstructure, named crater, was used for generating PSPR and Ag nanowires (AgNWs) for the generation of LSPR. A crater structure was fabricated on a GaAs (100) wafer using the wet chemical etching method. Then, a metal film was deposited inside the crater, and AgNWs were uniformly coated inside using the spray coating method. Metal films were used to enhance the electromagnetic field when coupled with AgNWs to obtain a high SERS intensity. The SERS intensity measured inside the crater structure with deposited AgNWs was up to 17.4 times higher than that of the flat structure with a deposited Ag film. These results suggest a new method for enhancing the SERS phenomenon, and it is expected that a larger SERS intensity can be obtained by fine-tuning the crater size and diameter and the length of the AgNWs.

Highly Sensitive and Stable Copper-Based SERS Chips Prepared by a Chemical Reduction Method

Cu chips are cheaper than Ag and Au chips for practical SERS applications. However, copper substrates generally have weak SERS enhancement effects and poor stability. In the present work, Cu-based SERS chips with high sensitivity and stability were developed by a chemical reduction method. In the preparation process, Cu NPs were densely deposited onto fabric supports. The as-prepared Cu-coated fabric was hydrophobic with fairly good SERS performance. The Cu-coated fabric was able to be used as a SERS chip to detect crystal violet, and it exhibited an enhancement factor of 2.0 × 106 and gave a limit of detection (LOD) as low as 10–8 M. The hydrophobicity of the Cu membrane on the fabric is favorable to cleaning background interference signals and promoting the stability of Cu NPs to environment oxidation. However, this Cu SERS chip was still poor in its long-term stability. The SERS intensity on the chip was decreased to 18% of the original one after it was stored in air for 60 days. A simple introduction of Ag onto the clean Cu surface was achieved by a replacement reaction to further enhance the SERS performances of the Cu chips. The Ag-modified Cu chips showed an increase of the enhancement factor to 7.6 × 106 due to the plasmonic coupling between Cu and Ag in nanoscale, and decreased the LOD of CV to 10–11 M by three orders of magnitude. Owing to the additional protection of Ag shell, the SERS intensity of the Cu-Ag chip after a two-month storing maintained 80% of the original intensity. The Cu-Ag SERS chips were also applied to detect other organics, and showing wide linearity range and low LOD values for the quantitative detection.

How gap distance between gold nanoparticles in dimers and trimers on metallic and non-metallic SERS substrates can impact signal enhancement

.The impact of variation in the interparticle gaps in dimers and trimers of gold nanoparticles (AuNPs), modified with Raman reporter (2-MOTP), on Surface-Enhanced Raman Scattering (SERS) intensity, relative to the...

High-Speed Fluctuations in Surface-Enhanced Raman Scattering Intensities from Various Nanostructures

The observation of single molecule events using surface-enhanced Raman scattering (SERS) is a well-established phenomenon. These events are characterized by strong fluctuations in SERS intensities. High-speed SERS intensity fluctuations (in the microsecond time scale) have been reported for experiments involving single metallic particles. In this work, the high-speed SERS behavior of six different types of nanostructured metal systems (Ag nanoshells, Ag nanostars, Ag aggregated spheres, Au aggregated spheres, particle-on-mirror, and Ag deposited on microspheres) was investigated. All systems demonstrated high-speed SERS intensity fluctuations. Statistical analysis of the duration of the SERS fluctuations yielded tailed distributions with average event durations around 100 μs. Although the characteristics of the fluctuations seem to be random, the results suggest interesting differences between the system that might be associated with the strength distribution and density of the localized SERS hotspots. For instance, systems with more localized fields, such as nanostars, present faster fluctuation bursts compared to metallic aggregates that support spread-out fields. The results presented here appear to confirm that high-speed SERS intensity fluctuations are a fundamental characteristic of the SERS effect.

Synthesis of Monolayer Gold Nanorings Sandwich Film and Its Higher Surface-Enhanced Raman Scattering Intensity

Most previous studies relating to surface-enhanced Raman spectroscopy (SERS) signal enhancement were focused on the interaction between the light and the substrate in the x-y axis. 3D SERS substrates reported in the most of previous papers could contribute partial SERS enhancement via z axis, but the increases of the surface area were the main target for those reports. However, the z axis is also useful in achieving improved SERS intensity. In this work, hot spots along the z axis were specifically created in a sandwich nanofilm. Sandwich nanofilms were prepared with self-assembly and Langmuir-Blodgett techniques, and comprised of monolayer Au nanorings sandwiched between bottom Ag mirror and top Ag cover films. Monolayer Au nanorings were formed by self-assembly at the interface of water and hexane, followed by Langmuir-Blodgett transfer to a substrate with sputtered Ag mirror film. Their hollow property allows the light transmitted through a cover film. The use of a Ag cover layer of tens nanometers in thickness was critical, which allowed light access to the middle Au nanorings and the bottom Ag mirror, resulting in more plasmonic resonance and coupling along perpendicular interfaces (z-axis). The as-designed sandwich nanofilms could achieve an overall ~8 times SERS signals amplification compared to only the Au nanorings layer, which was principally attributed to enhanced electromagnetic fields along the created z-axis. Theoretical simulations based on finite-difference time-domain (FDTD) method showed consistent results with the experimental ones. This study points out a new direction to enhance the SERS intensity by involving more hot spots in z-axis in a designer nanostructure for high-performance molecular recognition and detection.

4-Mercaptobenzoic Acid Labeled Gold-Silver-Alloy-Embedded Silica Nanoparticles as an Internal Standard Containing Nanostructures for Sensitive Quantitative Thiram Detection

In this study, SiO2@Au@4-MBA@Ag (4-mercaptobenzoic acid labeled gold-silver-alloy-embedded silica nanoparticles) nanomaterials were investigated for the detection of thiram, a pesticide. First, the presence of Au@4-MBA@Ag alloys on the surface of SiO2 was confirmed by the broad bands of ultraviolet-visible spectra in the range of 320–800 nm. The effect of the 4-MBA (4-mercaptobenzoic acid) concentration on the Ag shell deposition and its intrinsic SERS (surface-enhanced Raman scattering) signal was also studied. Ag shells were well coated on SiO2@Au@4-MBA in the range of 1–1000 µM. The SERS intensity of thiram-incubated SiO2@Au@4-MBA@Ag achieved the highest value by incubation with 500 µL thiram for 30 min, and SERS was measured at 200 µg/mL SiO2@Au@4-MBA@Ag. Finally, the SERS intensity of thiram at 560 cm−1 increased proportionally with the increase in thiram concentration in the range of 240–2400 ppb, with a limit of detection (LOD) of 72 ppb.

Application of Fe-graphene oxide nanocomposite to improve SERS intensity of polyaromatic hydrocarbons-=SUP=-*-=/SUP=-

Raman spectroscopy is used to provide a structural finger-print by which molecules can be identified. SERS technique offers many orders of magnitude enhancement in initial weak Raman signal of some molecules. To detect Raman signal of pyrene, magnetic properties of iron nanoparticles (Fe NPs) was employed along with graphene oxide (GO). Significant differences were discovered in performance of five different SERS substrates which were prepared using magnetized and non-magnetized Fe NPs-GO nanocomposites (FNRC) and Ag nanoparticles. UV-Vis, Raman and FE-SEM analysis presented complete formation of Ag-NPs, GO and FNRCs. The quantity of enhancement measured showed different enhancements from 1.09 up to 3.54 times for pyrene solution on magnetized Fe NP-GO nanocomposite. SERS enhancement showed a reverse relation with GO/Fe precursor rate. Raman shift suggested formation of new bonds. 2.017 RSD factor presented very fast performance only 10 seconds after irradiation of magnetized FNRCs.

P-Glycoprotein Detection for Multidrug Resistance of Leukemia Using SERS Immunoassay

Corresponding author: Baoan Chen, MD, PhD; E-mail: [email protected] Zhuyuan Wang, PhD; E-mail: [email protected] Yiping Cui, PhD; E-mail: [email protected] Keywords: leukemia; multi-drug resistance; P-glycoprotein; surface-enhanced Raman scattering; SERS intensity. Background Acquisition of multidrug resistance (MDR) in the chemotherapy of leukemia could decrease the survival rate of refractory/relapsing patients. One of the best characterized mechanisms of MDR in leukemia is mediated by multidrug resistance protein-1 and its product, P-glycoprotein (P-gp). Thus, accurate detection of P-gp is necessary for MDR diagnosis. In the recent years, surface-enhanced Raman scattering (SERS) has emerged as a new detection technology of biological label for immunoassay with the advantages of ultrasensitive screening ability and extensive adaptability. However, few researches have focused on the application of SERS immunoassay in the diagnostics of leukemia MDR. The aim of our study is to investigate the expressions of P-gp on the cell surface of K562/ADM cells, and in the whole-blood samples of leukemia using a SERS-based immunoassay technique. Methods To simulate the MDR occurrence, we mixed the K562 and K562/ADM cells at different ratios. Besides, we built up the concentration gradient of K562/ADM cells for the quantitative analysis. We also divided 30 blood samples (AML n=14, ALL n=16; female n=12, male n=18; age<60 n=17, age≥60 n=13) into two groups (primary patients in Group A; relapsing patients with over-expressed P-gp in Group B) and compared their SERS-based results with those measured by FCM assay. After preparation of our targeted samples, we synthesized a sandwich immunocomplex, which comprised of magnetic nanobeads (MBs) decorated with anti-CD45, SERS nanoprobes (NPs) decorated with P-gp antibodies, and our targeted samples. Then, SERS measurements were performed on the sandwich immunocomplex. Briefly, the immunocomplex can be precipitated by magnet and the SERS signals could be detected in the precipitates due to the specific binding. Without target samples, only negligible SERS signals could be detected. In this way, the SERS immunoassay can be used to evaluate the presence or expression level of P-gp. Results There were positive and stable SERS signals of peak intensity at 1078 cm-1 after suspended with target samples. First, the SERS intensity of K562/ADM was significantly higher than that of K562 (P <0.01). Second, the SERS intensities of different K562/ADM fractions showed a good linear response to the fractions of K562/ADM cells. Furthermore, the SERS intensities decreased with the decliningK562/ADM concentrations (from 5×106 to 50 cells/mL) and the limit of detection (LOD) could reach 50 cells/ml, which was significantly lower than FCM. Furthermore, the SERS intensity of whole blood samples in Group B were about five folds more than those in Group A (P <0.01). It indicated great application potential and reliability of SERS for MDR assessment in clinic. Conclusion We have proposed a SERS-based immunoassay to evaluate the expression of P-gp, a product of MDR protein of leukemia. Qualitative and quantitative analysis of K562/ADM indicated excellent specificity, high sensitivity and detection limit, as well as great reproducibility of this immunoassay. It was also demonstrated that this immunoassay was with acceptable accuracy and detection reproducibility for clinical whole blood samples, which was of great importance and convenience for practical clinical application. These features have made SERS-based immunoassay a selective and convenient technique for the identification of leukemia MDR diagnosis. Disclosures No relevant conflicts of interest to declare.