Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single molecular level, comparable to single-molecule fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realise a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A number of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (molecule or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to molecules with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as 'smart dust' over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various molecules adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants.

http://www.dstuns.iitm.ac.in/grouppresentations/2010/Shell-isolated%20nanoparticle%20-%20enhanced%20Raman%20spectroscopy.pdf

Shell-isolated nanoparticle-enhanced Raman spectroscopy

When light interacts with a metal nanoparticle (NP), its conduction electrons can be driven by the incident electric field in collective oscillations known as localized surface plasmon resonances (LSPRs). These give rise to a drastic alteration of the incident radiation pattern and to striking effects such as the subwavelength localization of electromagnetic (EM) energy, the formation of high intensity hot spots at the NP surface, or the directional scattering of light out of the structure. LSPRs can also couple to the EM fields emitted by molecules, atoms, or quantum dots placed in the vicinity of the NP, leading in turn to a strong modification of the radiative and nonradiative properties of the emitter. Since LSPRs enable an efficient transfer of EM energy from the near to the far-field of metal NPs and vice versa, we can consider plasmonic nanostructures as nanoantennas, because they operate in a similar way to radio antennas but at higher frequencies. Typically, plasmonic nanoantennas at optical frequencies are made of gold and silver due to their goodmetallic properties and low absorption. Controlling and guiding light has been one of science’s most influential achievements. It affects everyday life in many ways, such as the development of telescopes, microscopes, spectrometers, and optical fibers, to name but a few. These examples exploit the wave nature of light and are based on the reflection, refraction and diffraction of light by optical elements such as mirrors, lenses or gratings. However, the wave nature of light limits the resolution to which an object can be imaged, as well as the size of the transverse cross section of efficient guiding structures to the wavelength dimension. Plasmonic resonances in nanoantennas overcome these constraints, allowing unprecedented control of light-matter interactions within subwavelength volumes (i.e., within the nanoscale at optical frequencies). Such properties have attracted much interest lately, due to the implications they have both in fundamental research and in technological applications. Metal NPs have been used since antiquity. Due to their strong scattering properties in the visible range, they show attractive colors. One of their first applications, dating back to the Roman Empire more than 2000 years ago, was as a colorant for clothing. In art, they were used to stain window glass and ceramics. Obviously, it was not known then that the colorants being used contained metal NPs or that the spectacular colors were due to the excitation of LSPRs. The first reported intentional production of metal NPs dates from 1857, when Faraday synthesized gold colloids. However, at the time there was not much interest in understanding the physics behind the optical properties of colloids due to the impossibility of synthesizing NPs with well-controlled shapes and sizes, as well as the lack of accurate detection techniques. The first theoretical work on the scattering of light by particles smaller than the incident wavelength was carried out by Lord Rayleigh at the end of the 19th century. He analyzed the diffusion of light by diluted gases, and his theory explained physical phenomena such as the blueness of the sky, the redness of the sunset, or the yellow color of the sun. Mie took the next step forward by deriving an analytical solution to Maxwell’s equations to describe the interaction of light with spheres of arbitrary radius and composition. Subsequently, based on the results of Rayleigh and Mie, Gans considered elliptical geometries. He demonstrated that the optical response of metal NPs is

Plasmonic nanoantennas: fundamentals and their use in controlling the radiative properties of nanoemitters.

Nanoparticle-based theranostic agents

Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

This critical review will present the role of nanoparticles (NPs) in the directions that are vital to the new field of nanomedicine, including imaging and drug delivery. We reflect on the physical properties that make NPs advantageous for in vivo efficacy, and review recent advances in major NP based biomedical applications. Critical questions of transport, uptake, and clearance will be discussed and illustrated through the success and opportunities of NP imaging and therapy on a photodynamic therapy (PDT) based NP system that has been developed in our lab over the past decade (540 references).

The unique role of nanoparticles in nanomedicine: imaging, drug delivery and therapy

We review the syntheses, optical properties, and biological applications of cadmium selenide (CdSe) and cadmium selenide-zinc sulfide (CdSe-ZnS) quantum dots (QDs) and gold (Au) and silver (Ag) nanoparticles (NPs). Specifically, we selected the syntheses of QDs and Au and Ag NPs in aqueous and organic phases, size- and shape-dependent photoluminescence (PL) of QDs and plasmon of metal NPs, and their bioimaging applications. The PL properties of QDs are discussed with reference to their band gap structure and various electronic transitions, relations of PL and photoactivated PL with surface defects, and blinking of single QDs. Optical properties of Ag and Au NPs are discussed with reference to their size- and shape-dependent surface plasmon bands, electron dynamics and relaxation, and surface-enhanced Raman scattering (SERS). The bioimaging applications are discussed with reference to in vitro and in vivo imaging of live cells, and in vivo imaging of cancers, tumor vasculature, and lymph nodes. Other aspects of the review are in vivo deep tissue imaging, multiphoton excitation, NIR fluorescence and SERS imaging, and toxic effects of NPs and their clearance from the body.

Semiconductor quantum dots and metal nanoparticles: syntheses, optical properties, and biological applications

In this decade, electrospun membrane based water purification system is an emerging area of research. Electrospun nanofibrous membranes offer a multitude of interesting features such as high specific surface area, high porosity, excellent functionalization ability and good mechanical behavior. This review deals with a detailed description of recent research works in non-woven electrospun water purification membranes. The roles, fabrication procedures, and purification mechanism of various hydrophobic and hydrophilic electrospun polymeric water purification membranes have been categorized and explained. Electrospun polymeric membrane employed under both adsorption and filtration principles have been classified and elucidated in detail. Enhancement of membrane properties by incorporation of inorganic nanofillers, blending with polymers, surface modification, and the use of thin film nanocomposite membranes is also discussed.

Athiyanathil Sujith

Papers

Semiconductor quantum dots and metal nanoparticles: syntheses, optical properties, and biological applications

Electrospun Nanofibrous Membranes for Water Purification

Cure characteristics and mechanical properties of styrene–butadiene rubber/acrylonitrile butadiene rubber

Low density polyethylene–chitosan composites: A study based on biodegradation

Multifunctional graphene oxide loaded nanofibrous membrane for removal of dyes and coliform from water.