No abstract

Three different methods are described for uniformly anchoring metal colloids (Pt, Pd, and Au) onto the surface of polystyrene microspheres (PSMS). The first method we have employed is electrostatic deposition of preformed anionic colloidal particles onto a polycationic surface. In this method the functional groups on the surfaces of the microspheres (amine or carboxylic acid) are used to give the surface a net charge. These ionic spheres were then treated with polyelectrolytes of the opposite charge, which uniformly cover the surface. When the spheres have a net positive charge at the surface they show excellent adhesion of Au colloids. These metal-derivatized spheres can be prepared with electroactive viologen groups as well. In the second method investigated here, metal colloids are adsorbed to the surface of neutral functionalized PSMS. We report the synthesis and characterization of catalytically important noble monometallic colloids using various chemical and sonochemical methods. These metal colloids are then adsorbed onto suitably functionalized PSMS. The metal-immobilized microspheres are reacted with a linker such as 4-mercaptobutyl phosphonic acid and subsequently used for growing multilayers of ZrPV(Cl) (zirconium and N,N′-dialkyl-4,4′bipyridinium dichloride) by alternating Zr 4+ and PV(Cl). The third method described here for supporting metal particles on PSMS involves depositing a precursor metal oxide or hydroxide onto the PSMS, followed by reduction to give fine metal particles on the surface of the PSMS. Metal particle sizes formed by this method are 2-4 nm. The colloids, microspheres, and resulting catalysts prepared by all three methods have been characterized by electron microscopy (TEM and SEM) and by energy-dispersive X-ray (EDX) microanalysis, and those prepared by method 2 have been characterized by diffuse reflectance UV-vis spectroscopy as well.

Monodisperse poly(4- and poly(2-vinylpyridine) nanospheres in the 500 nm diameter range were prepared by emulsifier-free emulsion polymerization techniques under free radical initiation of the respective monomers with 4 wt % divinylbenzene as the cross-linking agent. The size, integrity, and nature of the nanospheres were investigated by Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, Auger spectroscopy, and Fourier-transform infrared spectroscopy measurements. The rigid and highly stable nanospheres with exposed pyridine nitrogen on the surface serve as an excellent support for Pd0 nanoparticles in the range of 1−4 nm. The Pd-coated nanospheres were also characterized by transmission electron microscopy and inductively coupled plasma mass spectrometry measurements. Four weight percent palladium-coated nanospheres serve as good catalysts for Suzuki-, Heck-, and Stille-type coupling reactions for carbon−carbon bond formation.

Highly functional Si and glass surfaces for protein immobilization have been prepared by a facile activation of native surface silanol groups. Poly(propyleneimine) dendrimers of generations 1-5 were immobilized onto the surface using a facile room-temperature coupling procedure that involved activation of native silanol groups of glass using 1,1'-carbonyldiimidazole under anhydrous conditions. The dendrimer-coated surfaces were used to immobilize proteins and were characterized with respect to surface loading and activity. A number of different chemical, physical, and biochemical techniques including contact angle measurement, ellipsometry, and fluorescence microscopy were used to characterize the resulting surfaces. Increasing the dendrimer generation past G-3 led to increased surface amine content, immobilized protein concentration, and the activity of immobilized alkaline phosphatase (used as a test system). Very high activity of the immobilized proteins in the case of higher generation (G-4 and G-5) dendrimers led us to conclude that such an approach has true potential for creating highly functional surfaces for protein chip applications.

A strategy for achieving geometrical patterning of DNA is described. The approach comprises patterning of oligonucleotides on a glycidyl oxypropyl trimethoxy silane modified Si wafer by spin casting a photoresist mixture consisting of a photoacid generator and a reactive blocking group and exposing through a photomask. Highly specific micrometer-sized DNA geometrical patterns were obtained, activity (multiple hybridization−dehybridization cycles with no loss of activity) and specificity of which were assessed using labeled complementary oligonucleotides. To further use such an approach toward integration, a novel two-stage strategy has been demonstrated, where the first stage lithography was employed to pattern electrodes and a second stage alignment/exposure was employed to define oligonucleotides between the electrodes.