Plasmon-Sampled Surface-Enhanced Raman Excitation Spectroscopy † (original) (raw)
Related papers
The interaction between adsorbates of different nature and plasmonic nanoparticles is reviewed here on the basis of the work done in our laboratory in the past few years. The paper is structured for analyzing the interaction of adsorbates with metal nanoparticles as function of the interacting atom (O, N, or S) and the adsorbate conformation. In the study of the adsorption of molecular species on metals, it is necessary to take into account that different interaction mechanisms are possible, leading to the existence of different molecular forms (isomers or conformers). These forms can be evidenced by changing the excitation wavelength, due to a resonant selection of these wavelengths. Charge-transfer complexes and electrostatic interactions are the usual driving forces involved in the interaction of adsorbates on metal surfaces when these metallic systems are used in wet conditions. The understanding of the metal-adsorbate interaction is crucial in the surface functionalization of metal surfaces, which has a growing importance in the development of sensing systems or optoelectronic devices. In relation to this, special attention is paid in this work to the study of the adsorption of calixarene host molecules on plasmonic nanoparticles.
Physical Review B, 2015
Since the discovery of surface-enhanced Raman scattering (SERS) 40 years ago, the origin of the "background" that is systematically observed in SERS spectra has remained questionable. To deeply analyze this phenomenon, plasmon-resonant Raman scattering was recorded under specific experimental conditions on a panel of composite multilayer samples containing noble metal (Ag and Au) nanoparticles. Stokes, anti-Stokes, and wide, including very low, frequency ranges have been explored. The effects of temperature, size (in the nm range), embedding medium (SiO 2 , Si 3 N 4 , or TiO 2) or ligands have been successively analyzed. Both lattice (Lamb modes and bulk phonons) and electron (plasmon mode and electron-hole excitations) dynamics have been investigated. This work confirms that in Ag-based nanoplasmonics composite layers, only Raman scattering by single-particle electronic excitations accounts for the background. This latter appears as an intrinsic phenomenon independently of the presence of molecules on the metallic surface. Its spectral shape is well described by revisiting a model developed in the 1990s for analyzing electron scattering in dirty metals, and used later in superconductors. The g s factor, that determines the effective mean-free path of free carriers, is evaluated, g expt s = 0.33 ± 0.04, in good agreement with a recent evaluation based on time-dependent local density approximation g theor s = 0.32. Confinement and interface roughness effects at the nanometer range thus appear crucial to understand and control SERS enhancement and more generally plasmon-enhanced processes on metallic surfaces.
Understanding the SERS Effects of Single Silver Nanoparticles and Their Dimers, One at a Time
The Journal of Physical Chemistry Letters, 2010
This perspective article highlights recent developments in a class of surface-enhanced Raman scattering (SERS) experiments that aim to correlate SERS enhancement factors with the physical parameters of metal nanostructures. In a typical study, the SERS substrate is fabricated by depositing colloidal nanoparticles on a silicon wafer to obtain individual particles isolated from each other, or small aggregates such as dimeric units. With the help of registration marks, the same nanoparticle, or dimer of nanoparticles, can be quickly located under a Raman microscope (for SERS spectra) and a scanning electron microscope (for structural characterization). The nanoscale characterization achieved by these studies has resulted in unparalleled investigations into the nature of polarization dependency for SERS, the hot spot nature of single nanoparticles and dimers, and the manipulation of hot spots through shape-controlled synthesis and self-assembly. We discuss the new insights these studies have offered, and the future progress they can deliver to the advancement of SERS. Surface-enhanced Raman scattering (SERS) is a fascinating process by which normally weak Raman signals can be amplified by many orders of magnitude. 1 This impressive enhancement is mainly caused by the enhanced, light-induced electric fields (E-fields) on the surface of a metallic nanoparticle (Figure 1). When the incident light is in resonance with the oscillations of conduction electrons in a metallic nanoparticle, all the conduction electrons will be driven to oscillate collectively in an optical phenomenon known as localized surface plasmon resonance (LSPR). 2 The LSPR is responsible for the strong scattering and absorption of light typical of a metallic nanoparticle; it is also responsible for generating the enhanced local Efields on the surface of a nanoparticle at sites known as "hot spots". Molecules within hot spots experience enormous enhancement in terms of their Raman scattering cross section, and in some cases single molecule detection is possible.3 , 4 This superb sensitivity has been a catalyst for the resurgence of SERS studies in recent years. These studies have focused on understanding the mechanisms of SERS and, equally, how to implement this technique as a reliable method for trace detection.5 ,6 Both thrusts have resulted in evolution of SERS experiments to studies characterized by a high level of scrutiny and control at the nanometer level. 7-9 SERS is, after all, a nanoscale phenomenon and to fully understand it one must take into account the myriad of subtle variables that have mired SERS studies from the very beginning. It is with this goal in mind that correlated-SERS studies have been introduced and further developed into a prominent methodology. Correlated-SERS studies feature full characterization of the nanoparticle from which the SERS is supposed to originate, allowing
2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2015
In recent years, the SERS-related materials research has gradually moved to the much cheaper semiconductor materials against the barriers from noble metals. [9-21] However, compared with noble metals, their relatively weak enhancement factor (EF) is not high enough for molecule to trace detection. Therefore, how to efficiently improve the SERS performance of semiconductors is the focus of a related study. Fortunately, scientists have found that some semiconductive materials could show great Raman scattering enhancement to trace of substances, reaching an ultralow limit of detection (LOD) and an ultrahigh EF. One excellent example is an urchin-like W 18 O 49 reported by Zhao and co-workers; the EF is up to the 3.4 × 10 5 level by means of the surface plasmon resonance. [17] And the single Cu 2 O superstructure particle reported by Guo and coworkers, obtaining an LOD of 10 −9 m and an EF of 8.0 × 10 5 , may be the best enhancement effect among the non-noble metal substrates reported so far. [14] Besides, considering promoting the interfacial charge-transfer process (ICTP) is an important premise to improve the sensitivity of semiconductorbased SERS, Guo's group further developed amorphous ZnO nanocages (a-ZnO NCs). Their study indicates that the remarkable SERS sensitivity can be obtained from the high-efficiency ICTP within the amorphous ZnO NCs-molecules system. [20] Based on previous research, the optimization of the geometry morphology and promotion of the ICTP between the semiconductor and molecules are considered two determining factors for EF improvement in semiconductor SERS. If we obtain an amorphous structure and simultaneously reduce the size of nanoparticles greatly, even to quantum size, we can achieve enhanced SERS. However, achieving both of them simultaneously is challenging. In our previous work, we have prepared 2D MoO 3 nanosheets that indicated excellent LSPR performance. [22] But due to the relatively larger size in the 2D region, its SERS is not so satisfied. In this work, we designed an alternative strategy to fabricate uniform amorphous molybdenum oxide quantum dots. By carrying out a series of efficient regulation strategies on the reaction system, this as-prepared peculiar nanostructure possesses excellent quantum size in uniformity, accompanied with an intensively enhanced plasmonic resonance property. Our experimental results demonstrate the
Analytical and Bioanalytical Chemistry, 2009
Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In this report, we introduce several gold and silver nanoparticle-based SERSactive substrates developed solely by us and use these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations. With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method. Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations.
Journal of Raman Spectroscopy, 2012
Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near-dipole and near-quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used.
How relevant can the SERS effect in isolated nanoparticles be?
RSC Advances, 2013
Gold nanoparticles electrostatically stabilized with negatively charged ruthenium complexes were individually monitored based on their characteristic plasmon bands, by means of hyperspectral dark field microscopy. Very strong SERS enhancements were observed for the isolated gold nanoparticles at exciting wavelengths in resonance with the surface plasmon band, using confocal Raman microscopy, revealing a contrasting behaviour between the agglomerated and non-agglomerated systems. The results highlighted the relevant role played by the surface enhanced resonance Raman mechanisms (SERRS) in isolated nanoparticles, more than compensating for the lack of local hot spots, in relation to the agglomerated systems.
doi:10.1155/2009/475941 Research Letter Surface Plasmons and Surface Enhanced Raman Spectra of
2016
Effects of size, morphology, and composition of gold and silver nanoparticles on surface plasmon resonance (SPR) and surface enhanced Raman spectroscopy (SERS) are studied with the purpose of optimizing SERS substrates. Various gold and silver films made by evaporation and subsequent annealing give different morphologies and compositions of nanoparticles and thus different position of the SPR peak. SERS measurements of 4-mercaptobenzoic acid obtained from these films reveal that the proximity of the SPR peak to the exciting laser wavelength is not the only factor leading to the highest Raman enhancement. Silver nanoparticles evaporated on top of larger gold nanoparticles show higher SERS than gold-silver alloyed nanoparticles, in spite of the fact that the SPR peak of alloyed nanoparticles is narrower and closer to the excitation wavelength. The highest Raman enhancement was obtained for substrates with a two-peak particle size distribution for excitation wavelengths close to the SP...
Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications VI, 2014
NIR-to-visible up-conversion nanomaterials have been investigated in many promising applications including nextgeneration displays, solar cells, and biological labels. When doped with different trivalent lanthanide ions, NaYF 4 nanoparticles can produce up-converted emission from visible to infra-red wavelengths. However, the quantum yield of this class of materials is low. Noble metals in the vicinity of the phosphor can increase the phosphorescence by local field enhancement due to plasmonic resonances, and by modification of the radiative rate of the phosphor. Most previous studies have investigated the phenomenon by placing nanophosphors onto a metal substrate, or by fabrication of nano structures with spacers such as polymers, dielectric materials (silica). By contrast, we have studied the interaction between the luminescence and the surface plasmon using a core-shell type nanostructure where a uniform shell of silver is shown to grown on doped-NaYF 4 nanophosphors by Ostwald ripening. We further demonstrate the proximity effect of metal-enhanced luminescence by exciting an undoped NaYF 4 shell. The result shows a significant synergistic enhancement of up-conversion luminescence due to the active shell as spacer layer. In addition, we have shown this novel nanostructure may be useful in surface-enhanced Raman spectroscopy (SERS).