Surface-enhanced Raman scattering development

A large number of possible applications of arrays of nanoparticles on solid surfaces is reviewed in Refs. [23,24]. They include, for example, development of new (elect-ro)catalytical systems for applications as chemical sensors, biosensors or (bio)fuel cells, preparation of optical biosensors exploiting localized plasmonic effect or surface enhanced Raman scattering, development of single electron devices and electroluminescent structures and many other applications. 

Ina similarmarmerto surface-enhanced Raman scattering, surface-enhancement of hyper-Raman scattering is a promising method to study adsorbed molecules on metal surfaces [24]. Based on recent developments in plasmonics, design and fabrication of metal substrates with high enhancement activities is now becoming possible [21]. Combination of the surface enhancement with the electronic resonances would also be helpful for the practical use of hyper-Raman spectroscopy. Development of enhanced hyper-Raman spectroscopy is awaited for the study of solid/liquid interfaces. 

Murphy T., Schmidt H., Kronfeldt H., Use of sol-gel techniques in the development of surface-enhanced Raman scattering (SERS) substrates suitable for in situ detection of chemicals in sea-water, Appl. Phys. B, 1999 69(2) 147-150. 

In the future, we will see developments involving surface enhanced Raman scattering technologies in combination with AuNPs and waveguides as well as combinations of immobilized and solution-bom AuNPs and functional bridges in-between them. It can also be expected that applied medical research, namely the detection of antigens, enzymes, and proteins in body fluids, will benefit fi om the sensor developments with its extreme sensitivities. 

Liu, Y.-C., Yu, C.-C. and Hsu, T.-C. (2007) Trace molecules detectable by surface-enhanced Raman scattering based on newly developed Ag and Au nanoparticles-containing substrates. Electrochem. Commun. 9 639-644. 

Yang MX, Chen T, Lau WS, Wang Y, Tang QH, Yang YH, Chen HY (2009) Development of polymer-encapsulated metal nanopartictes as surface-enhanced Raman scattering probes. Small 5 198... 

However, the low sensitivity problem of Raman spectroscopy can be overcome by the optical phenomenon called surface-enhanced Raman scattering (SERS), which originates from the conjugation of molecules with the novel metal nanomaterials such as gold or silver. After the first report of such a phenomenon in 1974 [16], several techniques were developed for a wide variety of applications. Current development in nanotechnology has accelerated the researches about SERS to realize accurate, sensitive, selective, and practical sensing platform in several areas including biomolecular detection. 

A prerequisite for the development indicated above to occur, is a parallel development in instrumentation to facilitate both physical and chemical characterization. TEM and SPM based methods will continue to play a central role in this development, since they possess the required nanometer (and subnanometer) spatial resolution. Optical spectroscopy using reflection adsorption infrared spectroscopy (RAIRS), polarization modulation infrared adsorption reflection spectroscopy (PM-IRRAS), second harmonic generation (SFIG), sum frequency generation (SFG), various in situ X-ray absorption (XAFS) and X-ray diffraction spectroscopies (XRD), and maybe also surface enhanced Raman scattering (SERS), etc., will play an important role when characterizing adsorbates on catalyst surfaces under reaction conditions. Few other methods fulfill the requirements of being able to operate over a wide pressure gap (to several atmospheres) and to be nondestructive. 

Although nothing can be done to make the Raman cross-section of vibrational bands any greater without the application of techniques such as resonance Raman spectroscopy or surface-enhanced Raman scattering, several important technological developments have led to the design of today s truly powerful Raman spectrometers. These included (in no particular historical order) the development of... 

The quantum yield of the classical (or so-called linear) Raman effect is rather poor. Only a fraction of to 10 of the exciting photons are converted into Raman photons. This excludes the detection of low concentration analytes. Moreover, due to the quantum yield of fluorescence, even traces of fluorescent impurities may mask the Raman signal by their fluorescence. Therefore, there has been much scientific effort towards the development of Raman based methods which allow one to overcome this problem. Methods to overcome these problems are Resonance Raman Scattering and Surface Enhanced Raman Scattering. 

Raman scattering gives information about molecular or sohd-state vibrations. In the presence of some electrode materials (e.g. silver or copper) a considerably enhanced sensitivity for molecules adsorbed at the electrode surface in the form of a monolayer can be achieved. This surface-enhanced Raman scattering effect can be transferred to other electrode materials coated in the form of a very thin layer onto a silver or copper substrate [32]. The recently developed TERS technique (Tip-Enhanced Raman Spectroscopy [33]) provides additional and highly resolved mapping information. 

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