Raman Signal Of Rhodamine 6G Research Articles

Graphene–silver nanohybrids for ultrasensitive surface enhanced Raman spectroscopy: size dependence of silver nanoparticles

The surface-enhanced Raman scattering (SERS) mechanism of graphene–silver (GE–Ag) nanohybrids was investigated by studying the Raman signals of rhodamine 6G (R6G) adsorbed onto nanohybrids with different sizes of Ag nanoparticles (NPs). The results showed that the SERS intensity ratios between GE–Ag NPs with Ag NPs with sizes of 9, 25 and 35 nm and pure Ag substrate were estimated to be 2.7, 5.0 and 8.9 respectively. GE sheets did improve the SERS activity due to their high adsorption ability, strong fluorescence quenching and additional chemical enhancement mechanism (CM)-based SERS effect. However, Ag NPs with relatively larger size (∼nm) play a major role in SERS activity of molecules adsorbed on the nanohybrids. Furthermore, the free-standing GE–Ag NP nanohybrid film was fabricated through the vacuum filtration of the optimized GE–Ag NP composite suspension followed by thermal annealing. The as-prepared film has the larger size of Ag NPs and narrower interparticle distance, which provides more “hot spots” for sensitive detection of R6G molecules, with a detection limit at 1 × 10−12 M. Additionally, the relative standard deviation (RSD) values are measured to be below 0.13, revealing a good consistency and reproducibility across the entire area of the film, suggesting this substrate holds a promise for routine SERS detection.

Morphology and composition controlled synthesis of flower-like silver nanostructures

Flower-like silver nanostructures with controlled morphology and composition were prepared through wet-chemical synthesis. The reaction rate is simply manipulated by the amount of catalyzing agent ammonia added which is the key point to determine the ratio of hexagonal close-packed (HCP) to face-centered cubic (FCC) phase in silver nanostructures. The existence of formic acid that is the oxidation product of aldehyde group is demonstrated to play a crucial role in achieving the metastable HCP crystal structures by replacing ionic surfactants with polyvinylpyrrolidone (PVP). Utilizing flower-like silver nanostructures as surface-enhanced Raman scattering (SERS) substrates, Raman signal of Rhodamine 6G, or 4-aminothiophenol with concentration as low as 10−7 M was detected. Moreover, it is demonstrated that phase composition has no direct relation to the SERS enhancing factor which is mainly determined by the amount of hot spots.

The Kinetically Dominated Overgrowth of Flower-Like Silver Nanostructures and its Application for Surface-Enhanced Raman Scattering

Herein flower-like silver nanostructures with different size and ratio of hexagonal close-packed (HCP) to face-centered cubic (FCC) phase were synthetized. By comparing with the results utilizing different surfactants, the growth process of Ag nanostructures has been investigated. Flower-like Ag nanoparticles containing numerous hot spots could serve as excellent surface-enhanced Raman scattering (SERS) substrates, and the Raman signal of Rhodamine 6G with the concentration as low as 10-6 M can be recognized.

Comparison of surface-enhanced Raman scattering on graphene oxide, reduced graphene oxide and graphene surfaces

Abstracts To explore the role of the interaction between the adsorbed molecules and substrates for the charge transfer (CT) induced Raman enhancement, we systematically study the surface enhanced Raman scattering (SERS) on graphene, graphene oxide (GO) and reduced graphene oxide (r-GO) using rhodamine 6G (R6G) as the probe molecule. The Raman spectra of R6G molecules deposited on these three SERS substrates show remarkable difference in spectral features due to the different enhancement contributions from the local chemical groups and the global π-conjugation network of the substrates. What is more surprising is that for 1–4 layers graphene-based materials, the Raman signals of R6G on GO are found to increase intensity with the number of GO layers, while the Raman signals of R6G on different graphene/r-GO layers show inverse trends due to dominant π–π stacking mechanism. Our results provide a comprehensive understanding of the influence of local chemical groups and the global π-conjugation network on the SERS enhancements. In addition to high reproducibility, low cost, and good biocompatibility of GO, the rich chemical structures and the absence of electromagnetic enhancement make it an excellent choice as a tunable substrate to study the chemical enhancement resulting from the adsorbent–substrate interaction.

Biosynthesis of gold nanoparticles using chloroplasts

In this paper, a new method of one-pot biosynthesizing of gold nanoparticles (GNPs), using chloroplasts as reductants and stabilizers is reported. The as-prepared GNPs were characterized by ultraviolet visible spectroscopy, transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy (FTIR). The cytotoxicity of the GNPs was evaluated using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method against gastric mucous cell line GES-1 and gastric cancer cell line MGC-803. Rhodamine 6G as a Raman probe was used for investigating surface-enhanced Raman spectroscopy (SERS) enhancement of GNPs. The transmission electron microscopy results indicated that the GNPs were spherical in structure and almost 20 nm in diameter. Ultraviolet visible spectroscopy exhibited an absorption peak at 545 nm. The GNPs exhibited high crystallinity, with the (111) plane as the predominant orientation, clarified by X-ray powder diffraction. In addition, a potential mechanism was proposed to interpret the formation process of GNPs, mainly based on the analysis of FTIR results. The FTIR spectrum confirmed that the GNPs were carried with N–H groups. Toxicological assays of as-prepared GNPs revealed that the green GNPs were nontoxic. SERS analysis revealed that the GNPs without any treatment could substantially enhance the Raman signals of rhodamine 6G. The Raman enhancement factor was calculated to be nearly 1010 orders of magnitude. In conclusion, the GNPs with good biocompatibility and excellent SERS effect were successfully synthesized using chloroplasts. These biogenetic GNPs have great potential for ultrasensitive detection of biomarkers in vitro and in vivo based on SERS.

Randomly-grown high-dielectric-constant ZnO nanorods for near-field enhanced Raman scattering

We investigate the dependence of the size parameter in the Mie scattering theory on the near-field enhanced Raman scattering properties for high dielectric constant ZnO nanorods grown randomly by PLD (pulsed laser deposition). High Raman signals of Rhodamine 6G (R6G) at 532 nm excitation wavelength were observed with nanorods of 400 nm average diameter. This experimental result was explained theoretically by the size parameter described in the Mie scattering theory, not by surface plasmon polaritons. This was also confirmed by the near-field distribution calculated by the FDTD (Finite-Difference Time Domain) method. The ZnO nanorods with 400 nm average diameter can detect as low as 1 μM of R6G. This near-field enhancement factor is equivalent to that with 10-nm-thick gold-coated ZnO nanorods (nanoshells) with an average core diameter of 100 nm. Controlling the diameter of bare ZnO nanorods is effective for obtaining large enhancement factors without an additional process of gold thin film coating on them.