Rhodamine 6G Molecules Research Articles

Flexible bipyramid-AuNPs based SERS tape sensing strategy for detecting methyl parathion on vegetable and fruit surface

In present study, a simple and effective surface enhanced Raman scattering (SERS) tape sensing strategy based on bipyramid gold nanoparticles (BP-AuNPs) was developed for sensitive and selective monitoring of methyl parathion residues on vegetable and fruit surface through a simple sampling-and-detection procedure. BP-AuNPs were synthesized by a seed meditated method and systematically characterized using transmission electron microscope (TEM), UV–vis spectrometer, selected area electron diffraction (SAED) and X-Ray diffraction (XRD). The as-synthesized BP-AuNPs showed excellent Raman enhancement effect because their sharp ends provide high electric field enhancement, as revealed by electrodynamic simulations. Also the localized plasmon resonance of the BP-AuNPs matches well with the NIR (785 nm) laser of portable Raman spectrometer, thus maximizing the Raman signal. Two standard SERS probe molecules Rhodamine 6G (R6G) and crystal violet (CV) were first used to prove the effective SERS detection on the model solid (silicon) surface using the BP-AuNPs based tape sensing strategy. The SERS sensor was then applied to detect methyl parathion on surface of cucumbers, tomatoes and apples. A detection limit of ng/cm2 level was easily achieved. The studies have demonstrated that the BP-AuNPs based SERS tape sensing platform can be potentially used to monitor the trace amount of chemical hazards for food and agricultural safety.

Effect of Precursor Structure on Unibody Core-Shell Properties and the in-vitro Study of a Dual Anti-drug/ Drug System

Abstract This work was concerned with the modification of a new type of functional innovative platform termed unibody core-shell (UCS). UCS is comprised of two covalent-bonded polymers differing only in the functional groups present in the core and the shell. This work used two approaches, first, the precursor that is polymerized to produce the shell was altered and compared in terms of particle morphology and size as well as pH-selective release of active agents, measure via Transmission electron microscopy (TEM) and fluorescence assay respectively. Three precursors were investigated (1,3-phenylenediamine, 3-aminophenol alcohol or 3-aminobenzyl alcohol) with different structure and pendant group arrangement for particle fabrication and pH-selectivity. These particles were investigated for pH response to achieve selective drug release between pH 3 and 11 first using rhodamine 6G (R6G). The amount of R6G molecules released were found under acidic conditions with a pH of 3.0 giving the most. Of the three precursors, 1,3-phenylenediamine gave the best pH-selectivity and particle morphology. Therefore, was taken forward to the second approach, which was the inclusion of the drug / anti-drug (Doxorubicin / Crocin) combination. The fabricated drug / anti-drug particles possessed spherical shape and were pH-selective release in acidic conditions of both Doxorubicin and Crocin. Thus, this system will be able to protect against the cardiotoxicity effects of Doxorubicin.

A facile method to directly deposit the large-scale Ag nanoparticles on a silicon substrate for sensitive, uniform, reproducible and stable SERS substrate

In this study, we report a facile replacement reduction method to directly deposit the large-scale Ag nanoparticles on a silicon substrate at the room temperature and short reaction time (3 min). The reaction process is a straightforward wet chemistry approach using silver nitrate and hydrogen fluoride as a silver source and reducing reagent, respectively. The Ag nanoparticles as a surface-enhanced Raman scattering (SERS) substrate present high sensitivity, excellent uniformity, and high stability for rhodamine 6G molecules. Also, Ag nanoparticles are also shown to provide a unique platform for the SERS detection of melamine, 5-fluorouracil, amoxicillin in different aqueous media. The fabrication of Ag nanoparticles is facile, low cost, strong enhancement, low detection limit, high reproducibility, and stability, which is advantageous for the applications of other SERS-based sensors.

Exfoliation of graphite as flexible SERS substrate with high dye adsorption capacity for Rhodamine 6G

Adsorption is one of the most important processes in wastewater treatment, especially for dye removal. In addition to adsorption, there must be a vigilant technique, such as Surface Enhanced Raman spectroscopy (SERS), for detection of low concentration of dye molecules to detect water foiling. Herein, we report a simple, low cost, rapid and efficient technique for the production of exfoliated graphite (EG) under microwave irradiation at 800 W in 1 min, as excellent adsorption material for Rhodamine 6G (R6G) dye. The effect of adsorption process parameters such as pH, contact time, isotherm models (Langmuir and Freundlich) and kinetic models (pseudo-first and pseudo-second-order) on dye removal under aqueous solutions, were investigated. The maximum adsorption capacity for R6G dye is 212.72 (±5.3) mg/g. Meanwhile compressing of EG, into a flexible graphite sheet (FGS) demonstrates responsive SERS for R6G molecules up to detection limit of 10−7 mol/L. However, with silver nanoparticle incorporation, the detection limit increases up to 10−12 mol/L. Performance of flexible sheet checked over a month by rubbing sheet through paper and cloth doesn’t have any impact on the synthesis of exfoliated graphite. Aging factor of the sheet also shows reproducible SERS spectra after a month. These are the highest reported values till today, for adsorption of R6G dye on Exfoliated graphite, with reasonable SERS detection.

Surface‐Enhanced Raman Scattering Enabled by Metal‐Coated Dielectric Microspheres

Dielectric microspheres have been demonstrated as an efficient tool for non‐plasmonic surface‐enhanced Raman scattering (SERS) due to the curvature‐induced local electromagnetic enhancement. By combining a metal layer onto the microsphere surface, one can study SERS which is activated by both surface plasmons and microsphere‐induced modulation of Raman emission. In this work, a new strategy of enhanced Raman scattering using silver‐coated polystyrene microspheres is reported. The Raman signal up to 10−6 M Rhodamine 6G molecules measured on the microsphere top surface is up to seven times larger than that measured from a flat silver film. An enhancement factor of ≈108 is estimated compared with the case of a non‐plasmonic microsphere surface. The enhancement is attributed to localized surface plasmon resonances and also the modification of emission directionality which increases both Raman scattering and the collection efficiency of the detecting system. Besides, whispering gallery mode resonance potentially leads to additional cavity‐field enhancement effect of Raman signals. Both experimental statistics and numerical calculations reveal that efficient enhancement occurs without purposely spectral matching optical resonance with Raman emission wavelengths.

Reduced graphene oxide supporting Ag meso-flowers and phenyl-modified graphitic carbon nitride as self-cleaning flexible SERS membrane for molecular trace-detection

There is an imperious demand on developing of self-cleaning surface enhanced Raman scattering (SERS) substrates, for eliminating traditional single-use substrates. Herein, ternary flexible membranes of reduced graphene oxide (r-GO) supporting Ag meso-flowers (Ag-MFs) and phenyl-modified graphitic carbon nitride nanosheets (PCNs) were fabricated for photocatalysis-driven self-cleaning SERS detection. In-situ growth of Ag-MFs with tunable morphology (such as coral-like, urchin-like, highly-branched, etc.) on r-GO surfaces provide abundant options for optimizing SERS detection limit, and thus, these PCNs/Ag-MFs@r-GO membranes exhibited strong SERS activity attributed to high density of intraparticle “hotspot” in Ag-MFs and preconcentration ability to probe molecules via π-π stacking. Among these membranes, the optimum PCNs/Ag-MFs@r-GO membrane shown a detection limit of 10−15 M for rhodamine 6G (R6G) molecules, and this membrane could effectively remove probe molecules due to the excellent photocatalytic activity. We used R6G or methylene blue (MB) molecules for investigating the self-cleaning repeatability and stability of this PCNs/Ag-MFs@r-GO membrane, and the signal intensity for SERS detection maintained a high degree of 95% after five cycle-runs. Besides, this PCNs/Ag-MFs@r-GO membrane can be used as a high-efficiency filter membrane for simultaneous detection and purification in wastewater treatment (10 mg/mL imidacloprid solution as the example).

Ag/ZnO/Au 3D hybrid structured reusable SERS substrate as highly sensitive platform for DNA detection

Ultra-sensitive hybrid Silver/Zinc oxide/Gold (Ag/ZnO/Au) structure based three dimensional (3D) surface enhanced Raman scattering (SERS) substrates have been prepared by three step fabrication process using thermal evaporation, hydrothermal growth, and sputtering techniques. The size and inter-particle (IP) gap of decorated Au nanoparticles (NPs) on ZnO nanorods (NRs) in the sub-nanometer range have been achieved through varying the sputtering time of Au. The superhydrophobic nature, the formation of the Schottky barrier at ZnO/Au interface and the broad optical absorption spectrum facilitated towards higher SERS activity of Ag/ZnO/Au hybrid structures. The higher SERS activity of 3D SERS substrate as compared with two dimensional (2D) SERS substrate has been studied. The good SERS signal reproducibility of 3D hybrid structures have been explored through Raman mapping. Higher SERS enhancement factor (EF) of 1 × 1010 has been achieved with a limit of detection (LOD) up to 10−16 M and 10 ng/μL for Rhodamine-6 G (Rh6G) and lambda DNA (λ-DNA), respectively. The degradation of Rh6G and λ-DNA molecules have been studied through photocatalytic degradation process to explore the reusability of the SERS substrates up to 10 and 4 times, respectively, with maintaining good SERS signal reproducibility. This metal/semiconductor/metal hybrid structure based SERS substrate with reusable capability indicates potential application towards biosensor for the detection of biologically important molecules at very low concentration level.

Plasmonic quenching of rhodamine 6G molecules fluorescence in the polyvinyl alcohol films on rough silver surfaces

The optical processes of plasmonic quenching of rhodamine 6G (R6G) molecules fluorescence in polyvinyl alcohol dielectric films formed on rough silver (Ag) surfaces were researched. The depth of penetration of the surface plasmon field into the dielectric film with R6G molecules is calculated. The angular and spectral-kinetic characteristics of dye molecules fluorescence decay on rough Ag surfaces are determined.

The grating of micro-holes as a chemosensor with rhodamine 6G molecules

Chemo-sensing of the produced 4×4 mm2 gratings of micro-holes (approx. half-million of micro-holes) on the 30-nm thick silver film on the IR-transparent CaF2 substrate was investigated in terms of their resonant EOT-enhanced IR-transmission as surface-enhanced IR-absorption (SEIRA). Selective IR absorption at 1261 cm−1 enhanced by 455 times, was demonstrated for rhodamine 6G molecules. The reference absorption lines were taken near 2900 cm−1, where the IR radiation is freely channeling through the microholes, indicating the reference substrate coverage by the dye molecules for its relative internal calibration.

High Contrast Detection of Water‐Filled Terahertz Nanotrenches

AbstractThe convergence of nano‐optics with an aqueous environment is promising for future chemical or biological applications. While the rapid development in nanofabrication has led to the realization of sub‐10 nm nanogaps of various structures, coupling water into high aspect ratio metallic nanogaps with a well‐defined area is not yet demonstrated. Here, arrays of 10 nm wide metallic trenches are reported filled with dielectric, air, liquid water, and various molecules in optical hotspots. Due to the high height‐to‐width aspect ratio of 20:1 and strong gap plasmon coupling in the 10 nm width, the trenches show distinct spectral changes at terahertz frequencies under changing gap materials, from which the full etching and water filling of the 10 nm gap can be unambiguously confirmed. A 75% transmitted amplitude decrease is observed through 200 nm deep trenches upon water filling, which converts to an effective 1100‐fold increase in the water absorption coefficient. The gap‐filling scheme can be applied to distinguish different liquids with 400 attoliters of volume or to detect rhodamine 6G molecules inside the gap with surface‐enhanced Raman scattering. Accordingly, the scheme can also be applied to a general class of polar organic molecules suitable for various biological or chemical applications.

Quantitative SERS by electromagnetic enhancement normalization with carbon nanotube as an internal standard.

Quantitative surface-enhanced Raman scattering (SERS) in practical applications still remain unresolved, mainly due to low reproducibility relying on the quality of the SERS substrates. In this paper, a carbon nanotube and Ag nanoparticles composite (CNT/AgNPs) is reported, and the carbon nanotube is as an internal standard for the calibration of SERS intensity of analyte molecules. The quantification of analyte molecules rhodamine 6G (R6G) is demonstrated in an aqueous solution with the concentration of 10-9 to 10-7 M. Raman mapping is used to investigate the stability of SERS spectra in a large scanning area, and the corresponding relative standard deviation (RSD) is calculated. SERS mapping reveals that the uniformity of Raman enhancement is improved through the build-in calibration with 2D Raman peak of CNT. Meanwhile, CNT/AgNPs samples are used to detect N2 in natural air, indicating that such self-calibration method can improve the reliability of the SERS analysis.

Surface-Enhanced Raman Spectroscopy of Two-Dimensional Tin Diselenide Nanoplates.

Surface-enhanced Raman spectroscopy (SERS) is a powerful spectroscopy technique to detect and characterize molecules at a very low concentration level. The two-dimensional (2D) semi-conductor layered material, tin diselenide (SnSe2), is used as a new substrate for enhancing the Raman signals of adsorbed molecules. Three kinds of molecules-Rhodamine 6G (R6G), crystal violet (CV), and methylene blue (MB)-are used as probe molecules to evaluate the SERS performance of SnSe2. The Raman signals of different molecules can be enhanced by SnSe2 nanoplates (NPs). The distinguishable Raman signal of R6G molecules can be obtained for adsorbent concentrations as low as 10-17 mol/L. Based on a detailed analysis of the bandgap structure and opto-electrical properties of SnSe2 NPs, we discuss the process of charge transfer and the Raman enhancement mechanism of SnSe2 NP. The high Raman sensitivity of SnSe2 NPs is related to the charge transfer between molecules and SnSe2, 2D layered structure, and indirect bandgap of few-layered SnSe2. The research results will help to expand the application of SnSe2 in microanalysis, improve the measurement accuracy of SERS, and possibly find use in optoelectronic device integration.

Synthesis and Surface-Enhanced Raman Scattering of Ultrathin SnSe₂ Nanoflakes by Chemical Vapor Deposition.

As a new atomically layered, two-dimensional material, tin (IV) diselenide (SnSe2) has attracted extensive attention due to its compelling application in electronics and optoelectronics. However, the great challenge of impurities and the preparation of high-quality ultrathin SnSe2 nanoflakes has hindered far-reaching research and SnSe2 practical applications so far. Therefore, a facile chemical vapor deposition (CVD) method is employed to synthesize large-scale ultrathin SnSe2 flakes on mica substrates using SnSe and Se powder as precursors. The structural characteristics and crystalline quality of the product were investigated. Moreover, Raman characterizations indicate that the intensity of A1g peak and Eg peak, and the Raman shift of Eg are associated with the thickness of the SnSe2 nanoflakes. The ultrathin SnSe2 nanoflakes show a strong surface-enhanced Raman spectroscopy (SERS) activity for Rhodamine 6G (R6G) molecules. Theoretical explanations for the enhancement principle based on the chemical enhancement mechanism and charge transfer diagram between R6G and SnSe2 are provided. The results demonstrate that the ultrathin SnSe2 flakes are high-quality single crystal and can be exploited for microanalysis detection and optoelectronic application.

Self-Support Surface Enhanced Raman Scattering Substrates with the Function of Enriching Analytes

Ultrasensitive detection of surface-enhanced Raman scattering (SERS) signals is in high demand in the fields of physical, chemical, biological medicine, and environmental monitoring. Plasmonic noble metal nanocrystals localize electromagnetic field on their surfaces, which can lead to a great increase of Raman intensity of the adsorbed molecules. Herein, self-supporting Ag nanowire networks with abundance of multiscale gaps as well as with function of enriching analytes are proposed to be simply synthesized to act as an excellent substrate for surface-enhanced Raman spectroscopy ultrasensitive detection. By effectively combining the hotspots effect of nanogaps and the enriching effect of gaps, the Raman signal is significantly enhanced by a factor of 6 x 10(5) and the detection limit of Rhodamine 6G (R6G) can reach 1 x 10(-7)m. Moreover, The R6G molecules can be adsorbed to these hot spots, leading to greatly enhanced Raman signals. This study introduces an effective SERS substrate to achieve ultrasensitive Raman detection in the fields of physical, chemical, biological medicine, and environmental monitoring.

Silicon Nanowires as Sensory Material for Surface-Enhanced Raman Spectroscopy

This paper shows steps for silicon nanowires substrates synthesis in detail. The research is focused on experimental techniques optimization while the targeted application was a fabrication of highly sensitive substrates for surface-enhanced Raman spectroscopy (SERS). Horizontal silicon nanowires on top of two-inch wafers were obtained by vapour-liquid-solid growth inside the low-pressure chemical vapour deposition reaction tube. The silicon nanowires morphology was monitored by scanning electron microscope after a short and long growth period which defined an adequate deposition time for SERS applications. Surface-enhanced Raman spectroscopy features were tested on silver nanoparticles decorated substrates and the detection concentration limit of 10− 9 M of rhodamine 6G molecules was reached. Raman spectroscopy showed that the 532 nm laser excitation powers of less than 4 mW (∼0.57 kW/cm2) do not widen the phonon peak or shift its frequency and the nanostructure distribution parameter of 3.7 nm was calculated. The horizontally placed Ag decorated nanowires are proved to be sensitive substrates for surface-enhanced Raman spectroscopy only if the silicon nanowires thickness, length, volume density as well as metal nanoparticle size and distribution are carefully designed.

Achieving High-Performance Surface-Enhanced Raman Scattering through One-Step Thermal Treatment of Bulk MoS2

We present a strong Raman enhancement substrate through one-step thermal treatment of bulk MoS2. The substrate provides very efficient hot spots by using the rhodamine 6G (R6G) molecule as a probe. Raman and photoluminescence spectra of modified MoS2 reveal the detailed mechanism for enhancing Raman signal of R6G. It is found that both the substrate roughness and the slight chemical bond broken on the surface are the main driven forces to induce the surface enhanced Raman scattering (SERS) effects. The minimum detectable concentration of R6G on the most optimized thermally treated MoS2 can be as low as 10–8 M. This synthetic approach is facile, sensitive, and reliable, which shows great potential to be an excellent SERS substrate for biological and chemical detection.

Rationally Designed Graphene/Bilayer Silver/Cu Hybrid Structure with Improved Sensitivity and Stability for Highly Efficient SERS Sensing.

A simple and cost-effective strategy was rationally designed to fabricate a special sandwich structure consisting of graphene, bilayer silver, and a copper plate, which was used as a surface-enhanced Raman scattering (SERS) substrate for highly efficient SERS sensing and detection of trace molecules. Silver dendrite (AgD) nanostructures were subsequently grown on a silver nanosphere (AgNS)/Cu surface to form a bilayer silver/Cu structure, which showed a 1.5-fold Raman enhancement compared to that of the AgNS/Cu substrate. After depositing graphene on the bilayer silver/Cu substrate to obtain a sandwich structure, a higher SERS enhancement and better durability were enabled. The SERS performances, measured by a portable Raman instrument, showed that the optimized sandwich structure substrate exhibited high SERS sensitivity to crystal violet (CV) and rhodamine 6G (R6G) with low limit of detection of 10–9 and 10–8 M, respectively. Such a sandwich-structured substrate exhibited good reproducibility across the entire detection areas with an average relative standard deviation less than 5.9%, which permits its reliable quantitative detection of CV and R6G molecules. In addition, graphene both effectively improved the SERS performances and protected Ag nanocrystals from oxidation, which endowed the sandwich structure a long-term stability with deviation of characteristic peaks’ intensity lower than 3.6% after 25 days. This study indicates that the graphene/bilayer silver/Cu sandwich structure as a SERS substrate has a great potential in detecting environmental pollutants.

A Simplified Hollow-Core Photonic Crystal Fiber SERS Probe with a Fully Filled Photoreduction Silver Nanoprism.

In this paper, a simplified hollow-core photonic crystal fiber surface-enhanced Raman scattering (SERS) probe is presented. Silver nanoprisms are grown with a photoreduction method and account for the SERS, which have better electromagnetic enhancement than spherical silver nanoparticles at 785 nm. Due to the antiresonant reflecting guidance mechanism, the excited laser and SERS signal are effectively guided in such a fully filled hollow-core photonic crystal fiber SERS probe and complicated selective filling with target sample is avoided. Rhodamine 6G molecules are used as probe molecules and the simplified hollow-core photonic crystal fiber SERS probe is test. Detection of low concentration Rhodamine 6G down to 10−8 M is achieved with a short integration time of 300 ms.

Surface-enhanced Raman spectroscopy using 2D plasmons of InN nanostructures

We explored the surface enhanced Raman scattering (SERS) activity of the InN nanostructures, possessing surface electron accumulation (SEA), using the Rhodamine 6G (R6G) molecules. SERS enhancement is observed for the InN nanostructures which possess surface electron accumulation (SEA). In case of high temperature grown InN samples, a peak is observed in the low wave number (THz region) of Raman spectra of InN nanostructures originating from excitation of the two dimensional (2D) plasmons of the SEA. The enhancement factor of four orders was calculated with the assumption of monolayer coverage of analyte molecule. SERS enhancement of InN nanostructures is attributed to the 2D plasmonic nature of InN nanostructures invoking SEA, rather than the contributions from 3D surface plasmon resonance (SPR) and chemical interaction. The role of 2D plasmon excitation in SERS enhancement is corroborated by the near-field light-matter interaction studies using near-field scanning optical microscopy.

Visible light-induced charge transfer to improve sensitive surface-enhanced Raman scattering of ZnO/Ag nanorod arrays

Noble-metal/semiconductor heterostructures that show extended multiple functionalities have attracted ever-increasing attention for using as sensitive surface-enhanced Raman scattering (SERS) substrates. Thus the studies of enhanced mechanism for SERS activity are favorable to fabricate other noble-metal/semiconductor heterostructure substrates and exploit their applications. In this study, we take an insight into the enhanced mechanism for SERS activity of Ag nanoparticle-decorated ZnO nanorod arrays (ZnO/Ag NAs) through studying the Raman vibrational signals of rhodamine 6G (R6G) molecules and photoresponse performance under visible light irradiation. Visible light photoresponse performance shows that the “hot electrons” of plasmonic Ag nanoparticles (NPs) are excited to the conduction band (CB) of ZnO nanorod arrays (ZnO NAs) due to the surface plasmon resonance (SPR). Used as a surface-enhanced Raman scattering (SERS) substrate to test Raman signals of rhodamine 6G (R6G) molecules, the prepared ZnO/Ag NAs show superior SERS performance compared to pure Ag NPs substrate. The visible light photoresponse activities and Raman performances experimentally show that the superior SERS performance of ZnO/Ag NAs is attributed to an effective charge transport within the plasmonic Ag, semiconductor ZnO and R6G molecule. In the charge transport process, the “hot electrons” of Ag NPs are first excited by visible light to the CB of semiconductor ZnO, and then to the lowest unoccupied molecular orbital (LUMO) level of R6G molecule. This work demonstrates that the SERS activity of semiconductor-based hybrid Raman substrate can be significantly improved by effectively turning the charge transport within the hybrid substrate.