Nanostructured porous silicon as functionalized material for biosensor application.

In this work by means of PL, FTIR and XPS techniques, state-of-the-art porous silicon (PS) films with good mechanical and optical properties have been effectively utilized for the biofunctionalization purpose for its possible application in immunosensors. The functionalization of the PS surface has been achieved by silanization process using aminopropyltriethoxysilane (APTS) as a precursor. The presence of reactive amino groups on the PS surface along with glutaraldehyde as a linker aids in the covalent binding of the antibody (Human IgG) onto the PS surface. Different antigen concentrations can be detected with a good reproducibility with this technique which opens a huge possibility of using this biofunctionalized material for future biosensors.

Formation of water-soluble and biocompatible TOPO-capped CdSe quantum dots with efficient photoluminescence.

In this work, polysorbate surfactants with same functional groups but with varying molecular masses (Tween-80, Tween-40 and Tween-20) in different concentrations (0.1% to 20% w/w) were used to study the effect of the length of the surfactant chain on the luminescence of the entrapped TOPO-capped CdSe nanocrystals. Various phospholipids with different functional headgroups such as ethylene glycol (-PEG) and amine (-NH2) were used to improve biocompatibility and provide sites for bioconjugation respectively. It is understood that that the hydrophobic ends of the surfactant binds with the water repelling groups of the cap layer, thus modifying the CdSe cap layer and making it soluble in aqueous media. It was observed that the PL emission intensity of CdSe increases with increase in concentration of Tween-series surfactant unlike in the case of thiol-coated CdSe nanoparticles. However, higher PL intensity was obtained in the case of stoichiometric CdSe with Tween-40 corresponding to 20% w/w. The efficient PL sustainability of water-soluble CdSe QD's can be attributed to the simpler chain structure of Tween-40 surfactant resulting in better passivation of the micelle.

Effect of oxidation induced surface state formation on the properties of colloidal CdSe quantum dots.

This article addresses on the issue of oxidation on the organically capped CdSe nanoparticles. The surface states properties of the nanoparticles were monitored as a function of time during the natural exposure to oxygen and light, to determine the long term stability of the CdSe quantum dots. CdSe nanoparticles were chemically prepared using three different compositional regimes, viz., Cd rich, Se rich, and stoichiometric and were of different sizes in the range of 5-7 nm. The optical and the structural properties in the three cases were significantly different when the nanoparticles were subjected to natural oxidation. The CdSe nanoparticles were probed using Ar+ ion sputtering used in conjunction with X-Ray Photoelectron Spectroscopy for structural analysis, where as the optical studies were done using UV-VIS and the Photoluminescent measurements. The results showed a blue shift and a considerable decrease in the intensity associated to surface states (lambda approximately 600-700 nm) in case of Se rich case, no shift in stoichiometric CdSe suggesting that its stable against oxidation, and a red shift in PL position in Cd rich regime. The Stoke's shift observed in the nonstoichiometric cases can be associated with the quantum confinement and the stress/strain effects. The result demonstrate the role of Cd/Se stoichiometry in tuning the surface states for tailoring the desired optical properties.