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Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl(2), K(2)TeO(3) and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods.CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd(+2) and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, "greener" methods to synthesize cadmium-containing QDs.

The use of chromic materials for responsive surface-enhanced resonance Raman scattering (SERRS) based nanosensors is reported. The potential of nano-chromic SERRS is demonstrated with the use of the halochrome methyl yellow to fabricate an ultrasensitive pH optical sensor. Some of the challenges of the incorporation of chromic materials with metal nanostructures are addressed through the use of computational calculations and a comparison to measured SERRS and surface-enhanced Raman scattering (SERS) spectra is presented. A strong correlation between the measured SERRS and the medium’s proton concentration is demonstrated for the pH range 2–6. The high sensitivity achieved by the use of resonance Raman conditions is shown through responsive SERRS measurements from only femtolitres of volume and with the concentration of the reporting molecules approaching the single molecule regime. [ABSTRACT FROM AUTHOR]

The intensity of high harmonics and the background observed in the SERRS spectra of the bis(4-chlorbenzylimido)perylene (CLPTCD), spin-coated onto silver nanostructures are discussed. The SERRS spectra of an Ag island film spin coated with 50 μL of a 8.7 × 10−7 M of CLPTCD in CH2Cl2 excited at 514.5 nm show signals from the first to the third overtones and combinations of fundamental vibrational modes observed between 1200 and 1600 cm−1. SERRS spectra were obtained where 2nd overtones were seen with relative intensity equal to that of the 1st overtones and in other SERRS spectra the 3rd overtones were more intense than the 2nd overtones. These varying intensity patterns are seen at submonolayer coverage where there is a breakdown of statistical average, and the spatial distribution of enhancement factors becomes evident. The apparent correlation between the background intensity profile and the enhancement of the overtones and combinations is also discussed. [ABSTRACT FROM AUTHOR]

Our main objective in this tutorial review is to provide insight into some of the questions surrounding single molecule detection (SMD) using surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). Discovered thirty years ago, SERS is now a powerful analytical tool, strongly tied to plasmonics, a field that encompasses and profits from the optical enhancement found in nanostructures that support localized plasmon excitations. The spectrum of the single molecule carries the quantum fingerprints of the system modulated by the molecule–nanostructure interactions and the electronic resonances that may result under laser excitation. This information is embedded in vibrational band parameters. The dynamics and the molecular environment will affect the bandwidth of the observed Raman bands. In addition, the localized surface plasmon resonances (LSPR) empower the nanostructure with a number of optical properties that will also leave their mark on the observed inelastic scattering process. Therefore, controlling size, shape and the formation of the aggregation state (or fractality) of certain metallic nanostructures becomes a main task for experimental SERS/SERRS. This molecule–nanostructure coupling may, inevitably, lead to spectral fluctuations, increase photobleaching or photochemistry. An attempt is made here to guide the interpretation of this wealth of information when approaching the single molecule regime. [ABSTRACT FROM AUTHOR]

Humic acid (HA) solutions provide an unexpected medium for direct fabrication of gold nanoparticles (HA–AuNP) and a clear window for surface-enhanced Raman scattering (SERS) with many potential applications in the ultrasensitive chemical analysis of environmental pollutants. It is demonstrated that the HA–AuNP fabrication can be easily achieved in a wide range of pH (2 to 12). The background SERS spectra of HA is relatively weak in absolute intensity, allowing the detection of the enhanced Raman signal from trace amount of contaminants. An in-situ approach is illustrated where the HA–AuNP fabrication is carried out with a HA solution containing the target pollutant. The technique may allow for the direct detection of organic pollutants present in the humic fraction of soil. [ABSTRACT FROM AUTHOR]

One of the avenues for the development of the analytical applications of surface enhanced spectroscopy is the engineering of enhancing substrates that would be selective and target specific. In the present report, the proof of this concept is demonstrated using the layer-by-layer (LbL) technique to fabricate portable selective substrates containing metal nanoparticles which can provide surface enhanced fluorescence (SEF) or surface enhanced Raman scattering (SERS). The selectivity to ionic species is attained by adding metal-free top layers of polymer electrolytes to an LbL SERS enhancing substrate. In addition, it was observed that the surface charge of the top layer determines the dye aggregation, leading to the formation of adsorbed J or H aggregates. [ABSTRACT FROM AUTHOR]

The vibrational spectra and surface-enhanced Raman scattering (SERS) of 1,6-diphenyl-1,3,5-hexatriene (DPH) are discussed. The fundamental vibrational frequencies, overtones, and combinations observed in the infrared and Raman spectra of DPH are reported. The interpretation of the observed vibrational spectra was supported by a complete geometry optimization, followed by vibrational frequency and intensity computations for the cis- and trans- isomers of the DPH using density functional theory at the B3LYP/6-31G(d,p) level of theory. Because the molecule is photo-chemically active on Ag metal surfaces, the best SERS results for silver islands were obtained at low temperature and low energy density of the exciting laser line. DPH SERS on Au films was obtained at room temperature. [ABSTRACT FROM AUTHOR]