Plasma-assisted nanoscale protein patterning on Si substrates via colloidal lithography.

Selective immobilization of proteins in well-defined patterns on substrates has recently attracted considerable attention as an enabling technology for applications ranging from biosensors and BioMEMS to tissue engineering. In this work, a method is reported for low-cost, large scale and high throughput, selective immobilization of proteins on nanopatterned Si, based on colloidal lithography and plasma processing to define the areas (<300 nm) where proteins are selectively immobilized. A close-packed monolayer of PS microparticles is deposited on oxidized Si and, either after microparticle size reduction or alternatively after metal deposition through the PS close-packed monolayer, is used as etching mask to define SiO2 nanoislands (on Si). C4F8 plasma was used to selectively etch and modify the SiO2 nanoislands while depositing a fluorocarbon layer on the Si surface. The plasma-treated surfaces were chemically characterized in terms of functional group identification through XPS analysis and reaction with specific molecules. Highly selective protein immobilization mainly through physical adsorption on SiO2 nanoislands and not on surrounding Si was observed after C4F8 plasma-induced chemical modification of the substrate. The thickness of the immobilized protein monolayer was estimated by means of AFM image analysis. The method reported herein constitutes a cost-efficient route toward rapid, large surface, and high-density patterning of biomolecules on solid supports that can be easily applied in BioMEMS or microanalytical systems.

Formation of core-shell and hollow nanospheres through the nanoscale melt-solidification effect in the Sm-Fe(Ta)-N system.

Sm-Fe-Ta-N-O nanospheres were synthesized by pulsed-laser deposition from a Sm(13.8)Fe(82.2)Ta(4.0) target in a nitrogen atmosphere. Three structurally and compositionally distinct types were identified: amorphous, core-shell and hollow nanospheres. Amorphous spheres were compositionally homogeneous and completely oxidized. The core-shell spheres were composed of an iron-rich crystalline core with up to 10 at.% interstitially incorporated nitrogen, surrounded by an amorphous and oxidized shell. The hollow spheres were characterized by voids filled with N(2) gas. It was found that the formation of either amorphous or complex nanospheres is defined by an initial Fe/Sm ratio within the molten droplet. The formation of hollow spheres is believed to be related to the general affinity of liquid metals for gas intake. During rapid solidification the dissolved gas in the melt is trapped within the surrounding solid rim, preventing the outwards diffusion of gas. As long as the amount of gas atoms in the melt is kept below its solubility limits it can be completely interstitially incorporated into the solid, thus forming crystalline Fe(N)-rich cores. If the melt contains more than an equilibrium amount of nitrogen it is possible that the gas recombines to form N(2) molecules, which are condensed inside the spheres.

Self-assembly in mixed aqueous solutions of amphiphilic block copolymers and vesicle-forming surfactant.

The self-assembly behavior of mixed solutions consisting of poly(isoprene-b-ethylene oxide) (IEO) copolymer micelles and vesicle-forming didodecyldimethylammonium bromide (DDAB) was investigated. Dynamic light scattering indicated the presence of two populations of nanoassemblies in the solutions. By aid of atomic force microscopy, the larger ones were identified as block copolymer modified surfactant vesicles (BCMSVs) and the smaller ones as surfactant-modified block copolymer micelles (SMBCMs). This identification is based on the amphiphilic character of the low and high molecular weight molecules and the notion that exchange of unimers of both types can take place between the initial nanoassemblies in aqueous solution. Electrophoretic light scattering experiments showed that the nanostructures carry positive charges originating from the surfactant. The sizes of the nanoassemblies depend on the relative concentrations of both components. The behavior of the mixed systems was also found to depend on block copolymer composition and temperature. Nanoassemblies of smaller sizes were formed at higher temperatures. BCMSVs and SMBCMs are thermosensitive, in contrast to the temperature stability of pure block copolymer micelles. On the other hand, BCMSVs showed lesser sensitivity to temperature increase compared to the pure DDAB vesicles. This indicates that incorporation of macromolecules into the DDAB bilayer increases the stability of the vesicles.

Photodissociation dynamics of DNA bases.

In order to access the damaging mechanismsof DNA and its bases on themolecular level by T Hz radiation, it isnecessary to create a database of assessingdamage at different spectral regions.Possible damage by T Hz radiation will beassessed by comparison. Furthermore, theexpose of the cytosine to radiation at157 nm, suggest that photochemical bondbreaking is the only damaging mechanism inthe vacuum ultraviolet region of thespectrum, (157-170) nm where one photonbreaks one chemical bond.

VUV and UV fluorescence and absorption studies of Pr(3+)-doped LiLuF(4) single crystals.

The laser-induced fluorescence spectrum of LiLuF(4):Pr(3+) single crystals, pumped by an F(2) pulsed-discharge molecular laser at 157 nm, was obtained in the VUV and UV regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time to our knowledge. They were assigned to the dipole-allowed transitions 4f5d ? 4f(2) of Pr(3+) ion. In addition, the absorption spectrum of the crystal samples was recorded. The positions of the bands with the 4f5d configuration were found to be 46 412, 53 267, and 63 397 cm(-1) from the ground state, (3)H(4), of the Pr(3+) ion. The edge (onset) of the 4f5d bands was at 45 100 cm(-1).