等离激元激励表面增强拉曼光谱检测技术与仪器

本文总结了近年来基于传播型表面等离激元（Propagafingsurfaceplasmons,PSPs）参与的表面增强拉曼（Surface—enhancedRamanscattering,SERS）技术和仪器方面的研究进展．内容主要包括3部分：（1）基于PSPs激励拉曼散射的装置和技术,包括在消逝场下激发PSPs共振增强拉曼的原理与装置、与表面等离子体共振（Surfaceplasmonresonance,SPR）传感技术的联用及新型结构的长程等离激元激励拉曼技术的研究进展;（2）通过引入局域型表面等离激元（Localizedsurfaceplasmons,LSPs）进一步增强SERS,进而实现PSPs-LSPs共同增强拉曼的超灵敏检测技术,包括在消逝场激发的PSPs基础上,增加纳米粒子实现的PSPs与LSPs共同增强拉曼的原理、装置,以及用该方法进行生物体系的免疫识别检测,此外,还在微纳周期结构上实现了PSPs与LSPs共同激励拉曼;（3）基于PSPs耦合的定向SERS技术,包括在消逝场结构和周期结构上实现SERS定向耦合发射以达到高激发和高收集效率的新技术．     

Surface-enhanced Raman scattering as a probe for exotic electronic excitations induced by localized surface plasmons

Exotic electronic excitations beyond normal selection rules would open novel possibilities for photoenergy conversion. The large intensity gradient of electromagnetic fields resulting from the confinement of localized surface plasmons at the molecular scale could exceed the limit of light–matter interactions via modification of electronic excitation selection rules. We discuss the possible application of surface-enhanced Raman scattering as a probe for exotic electronic excitations by reviewing studies on small numbers of molecules at the surface of plasmonic metal nanostructures. Future innovative photo-functionalization is also discussed by considering the excited states produced by the exotic electronic excitations.     

Laser-induced surface migration via surface plasmons

A classical model coupling a charged adspecies to a laser-induced surface plasmon is presented. Such coupling can enhance the rate and specify the direction of surface migration. For the particular case of an atomic oxygen ion of charge ?1 adsorbed on aluminum which is exposed to CO₂ laser radiation of intensity 1 W/cm², the velocity of migration (61.3 μm/s) is five orders of magnitude greater than the usual thermal velocities observed at room temperature.     

Regio-selective decoration of nanocavity metal arrays: contributions from localized and delocalized plasmons to surface enhanced Raman spectroscopy

Spherical cap gold nanocavity arrays with internal diameters of 240, 430, 600 and 820 nm were fabricated on smooth gold films using nanosphere lithography with electrochemical metal deposition. Each array was prepared to the same normalized film thickness to diameter ratios, t(N), of 0.8 ± 0.04. Selective modification of the top surface and interior walls of the gold nanocavity arrays with [Ru(bpy)(2)(Qbpy)](2+), where bpy is 2,2'-bipyridyl and Qbpy is 2,2':4,4':4,4'-quarterpyridyl, was accomplished using a two step adsorption process exploiting the assembled polystyrene spheres as masks. This selective modification approach permitted direct quantitative comparison, for the first time, of plasmonic enhancement of Raman signal and luminescence signal from a monolayer adsorbed at the top surface versus interior walls of all-gold nanocavity arrays. For all cavity sizes, significantly greater Raman and luminescence signal enhancement was observed from [Ru(bpy)(2)(Qbpy)](2+) monolayer adsorbed at the top surface of the array compared with the cavity walls. This disparity in Raman intensity from top versus cavity interior increased as the cavity dimensions decreased. For example, the Raman signal intensity from [Ru(bpy)(2)(Qbpy)](2+) adsorbed at the top surface of 240 nm gold arrays was 170 times greater than SERS signal for this material adsorbed at the interior walls of this array, whereas the relative Raman signal enhancement was 6 from top versus interior for the 820 nm internal radius arrays under 785 nm excitation. The origin of the relatively greater signal at the top surface is discussed in the context of plasmonic distribution at each surface.     

Practical understanding and use of surface enhanced Raman scattering/surface enhanced resonance Raman scattering in chemical and biological analysis

The unique ability to obtain molecular recognition of an analyte at very low concentrations in situ in aqueous environments using surface enhanced Raman scattering (SERS) and surface enhanced resonance Raman scattering (SERRS) detection makes these spectroscopies of considerable interest. Improved understanding of the effect coupled to improvements in practical techniques make the use of SERS/SERRS much simpler than has been the case in the past. This article is designed as a tutorial review targeted at aiding in the development of practical applications.     

Whispering-gallery mode resonators: Surface enhanced Raman scattering without plasmons

Calculations based on the Mie theory are performed to determine the locally enhanced electric fields due to whispering-gallery mode resonances for dielectric microspheres, with emphasis on electromagnetic "hot spots" that are located along the wavevector direction on the surface of the sphere. The local electric field enhancement associated with these hot spots is used to determine the surface enhanced Raman scattering enhancement factors for a molecule, here treated as a classical dipole, located near the surface of the sphere. Both incident and Raman emission enhancements are calculated accurately using an extension of the Mie theory that includes interaction of the Raman dipole field with the sphere. The enhancement factors are calculated for dielectric spheres in vacuum with a refractive index of 1.9 and radii of 5, 10, and 20 microm and for wavelengths that span the visible spectrum. Maximum Raman scattering enhancement factors on the order of 10(3)-10(4) are found at locations slightly off the propagation axis when the incident excitation but not the Stokes-shifted radiation is coincident with a whispering-gallery mode resonance. The enhancement factors are found to vary inversely with the resonance width, and this determines the influence of the mode number and order on the results. Additional calculations are performed for the case where the Stokes-shifted radiation is also on-resonance and Raman enhancement factors as large as 10(8) are found. These enhancement factors are typically a factor of 10(2) smaller than would be obtained from /E/4 enhancement estimates, as enhancement of the Raman dipole emission is significantly reduced compared to the local field enhancement for micron size particles or larger. Conditions under which single-molecule or few-molecule measurements are feasible are identified.     

Micro-chemical sensors based on fiber-optic excitation of surface plasmons

In this paper the theoretical base and experimental results of a new class of fiber optical supported surface plasmon resonance spectroscopy (SPRS) transducer is given. Surface plasmons were excited by polychromatic light, and the resonant excitation is detected as an intensity minimum in the measured spectra at certain wavelengths. The excitation takes place at the end zone of a multimode fiber coated with a thin surface plasmon resonance supporting metal layer. As examples for the large application field of this transducer a fiber optical immunosensor for the detection of antibodies against bovine serum albumin and a gas sensor for remote detection of tetrachloroethene was constructed and tested successfully. The sensors were constructed following the theoretical predictions for an optimal performance.     

Nonlinear optical detection of proteins based on localized surface plasmons in surface immobilized gold nanospheres

A new nonlinear optical method is presented to detect proteins binding to a gold surface without using fluorescent-dye labeling. After exposure of the protein-binding surface to a gold nanosphere solution, the nanospheres are immobilized above a gold surface with a nanogap supported by the protein. The gold nanospheres immobilized on the gold surface show strong localized surface plasmon (LSP) resonance, and the formation of this structure results in a marked increase in the optical second harmonic (SH) activity of the gold surface arising from a large enhancement of the electric field localized adjacent to the nanospheres on the LSP resonance. The SH image, therefore, gives a high contrast ratio, 7.0:1, of protein-binding spots to control spots. The contrast ratio is much greater than those obtained by linear reflectivity imaging.     

Enhancement of protein adsorption induced by surface roughness

Using quartz crystal microbalance with dissipation and ellipsometry, we show that during adsorption of fibrinogen on evaporated tantalum films the saturation uptake increases with increasing root-mean-square roughness (from 2.0 to 32.9 nm) beyond the accompanying increase in surface area. This increase is attributed to a change in the geometrical arrangement of the fibrinogen molecules on the surface. For comparison, the adsorption of a nearly globular protein, bovine serum albumin, was studied as well. In this case, the adsorption was less influenced by the roughness. Simple Monte Carlo simulations taking into account surface roughness and the anisotropic shape of fibrinogen reproduce the experimentally observed trend.     

Noble-metal nanostructures for controlling surface plasmons and sensing molecules

Arrays of nanoapertures in thin silver film were fabricated by deposition of metal through a self-organizing distribution of polystyrene nanospheres. We demonstrate that both the surface-enhanced Raman scattering (SERS) and fluorescence decay of probe molecules are strongly dependent on the plasmonic environment exhibited as fabricated nanostructures.     

Enhancement of ion intensity in time-of-flight secondary-ionization mass spectrometry

Enhancement of ion intensity in static secondary-ionization mass spectrometry (SIMS) has been achieved by using a matrix-assisted sample preparation technique. Previous investigations of polymers and biomolecules by SIMS indicated that secondary-ion (SI) yield is dependent on substrate coverage. Recently we discovered a sample preparation technique that enhanced the SI yield of cyclosporin A (CsA) in an allograft patient sample and neat samples of CsA (1202 u) and polystyrene (M _w=2650 u). The preparation technique involves deposition of a submonolayer of cocaine hydrochloride (5 µL of a 20-µg/mL MeOH solution) on an etched silver substrate, solvent evaporation, and subsequent deposition of the analyte. This preparation method resulted in ～300% increase in the SI yield of CsA and polystyrene when deposited from neat solutions. The original discovery was observed when a blood extract that contained CsA was deposited on an etched Ag substrate that had been soaking in a dilute cocaine solution for ～2 months. In these initial experiments, the SI yield of CsA was enhanced by over 1 order of magnitude.     

钕的电子拉曼光谱和一种新的拉曼增强机理

拉曼光谱是研究分子体系微观结构的一种有力工具 [1] ,由于拉曼信号弱 ,在一定程定上影响了拉曼光谱的应用 .为解决此问题 ,人们一方面采用各种先进的光谱测试技术 ,另一方面广泛运用各种拉曼增强机理 ,以提高拉曼光谱的灵敏度 .到目前为止 ,公认的拉曼增强机理只有共振拉曼增强和表面拉曼增强两种 .最近 ,文献报道了一种称为聚集增强的拉曼增强机理[2 ] .众所周知 ,f电子使稀土具有极丰富的电子能级结构 ,使得稀土元素在发展各种高性能的功能材料方面具有巨大的潜在价值 [3～ 5] .人们利用稀土的能级结构发展各种探针技术以表征分子体系在…     

Enhancement of low energy photon intensity caused by coherent scattering with collimator

The low energy photon counting rate normalized to the source-detector geometry showed an enhancement in intensities, when the source was placed in the vicinity of the detector. Isotopic X-ray source of known output /^93mNb,⁵⁵Fe and⁴⁹V/ was used. This enhancement is interpreted to be due, at least, to the occurrence of diffractional coherent scattering with the lead collimator.     

Tailoring surface plasmons through the morphology and assembly of metal nanoparticles

Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.     

Chemical Enhancement and Quenching in Single-Molecule Tip-Enhanced Raman Spectroscopy

Despite intensive research in surface enhanced Raman spectroscopy (SERS), the influence mechanism of chemical effects on Raman signals remains elusive. Here, we investigate such chemical effects through tip-enhanced Raman spectroscopy (TERS) of a single planar ZnPc molecule with varying but controlled contact environments. TERS signals are found dramatically enhanced upon making a tip–molecule point contact. A combined physico-chemical mechanism is proposed to explain such an enhancement via the generation of a ground-state charge-transfer induced vertical Raman polarizability that is further enhanced by the strong vertical plasmonic field in the nanocavity. In contrast, TERS signals from ZnPc chemisorbed flatly on substrates are found strongly quenched, which is rationalized by the Raman polarizability screening effect induced by interfacial dynamic charge transfer. Our results provide deep insights into the understanding of the chemical effects in TERS/SERS enhancement and quenching.     

Raman and surface Raman spectroscopy with ultraviolet excitation

We record the accurate and reliable Raman spectra of benzoic acid (BA), p-nitrobenzoic acid (PNBA) and o-nitrobenzoic (ONBA) in aqueous solution with ultraviolet excitation. And we find that the ultraviolet (UV) Raman spectrum of aqueous BA solution has one-to-one correspondence to that of BA solid whereas the others are less resemble to the solid counterparts. We also report surface Raman spectroscopy of them in silver colloid without any enhancement in UV region and call it surface-unenhanced Raman spectroscopy (SUERS) while the surface-enhanced Raman scattering (SERS) effects are perfect in near infrared or visible regions. It demonstrates the SERS effects are strongly dependent on the excitation wavelength. On the basis of the experiments, we discuss the mechanism of SERS excited in different regions.     

The use of near infrared Fourier Transform techniques in the study of surface enhanced Raman spectra

Near infrared Fourier Transform Raman spectroscopy has been used to study the SERS of a number of electrode-solution interfaces. These measurements are illustrated by the following examples: the adsorption of pyridine on Ag, Cu and An surfaces; the adsorption of ferri- and ferrocyanide ions on An electrodes in two different support electrolytes; the behaviour of the corrosion inhibitors benzotriazole and 2-aminopyrimidine at Cu surfaces. Measurements of the DSERS spectra of pyridine at Ag electrodes and of normal Raman spectra of pyridine at Pt electrodes are also reported. The results are also compared with data taken by conventional methods in the visible region and the advantages of this newly developed technique are assessed.     

Enhancement of peroxyoxalate chemiluminescence intensity by surfactants and its application to detect detergent

Enhancement of peroxyoxalate chemiluminescence (PO-CL) intensity by a surfactant in the H₂O₂/bis(2,4,6-trichlorophenyl)oxalate (TCPO)/rhodamine B system was described. The effects of 15 surfactants were evaluated by comparing the ratio of a relative CL intensity (RCI) with surfactant to that of the blank in each system. In preliminary study, H₂O₂/imidazole-HNO₃ buffer/TCPO/rhodamine B system was used to study the effects of surfactants on PO-CL intensity. Fourteen surfactants reduced the CL intensity at the 2% concentration, where their relative CL intensities ranged from 0.6 to 93.5%. Some of these phenomena may be caused by a notable change of pH that was occurred by adding the surfactant.Additionally, enhancement of PO-CL intensity was studied by using system (1) H₂O₂/TCPO/rhodamine B and (2) H₂O₂/imidazole-HNO₃ buffer/TCPO/systems. In the system 1, the favorable enhancement of CL intensity (ranged from 124 to 472%) was observed with 9 surfactants at the 0.5% concentration. This result suggested that several surfactants might play a role as a catalyst in the PO-CL reaction. There was no tendency to enhance CL intensity among the surfactant types. In the system 2, the enhancement of CL intensity was also observed by adding with 11 surfactants, which might be mainly caused by the fluorescent impurities of surfactants used.Furthermore, detection of detergent commercially available was applied by using the system 1.