We have designed a modular protein tagging system that allows different functionalities to be linked onto a single genetic fusion, either in solution, in living cells, or in chemically fixed cells. The protein tag (HaloTag) is a modified haloalkane dehalogenase designed to covalently bind to synthetic ligands (HaloTag ligands). The synthetic ligands comprise a chloroalkane linker attached to a variety of useful molecules, such as fluorescent dyes, affinity handles, or solid surfaces. Covalent bond formation between the protein tag and the chloroalkane linker is highly specific, occurs rapidly under physiological conditions, and is essentially irreversible. We demonstrate the utility of this system for cellular imaging and protein immobilization by analyzing multiple molecular processes associated with NF-kappaB-mediated cellular physiology, including imaging of subcellular protein translocation and capture of protein--protein and protein--DNA complexes.

Pt nanoparticle array model catalysts with 28 ( 2 nm diameters and 100 ( 2 nm interparticle spacing have been fabricated with electron beam lithography on alumina supports. A novel method for cleaning the Pt nanoparticle arrays, involving low dosages of NO 2 and CO and mild temperature flashing, was established. This cleaning procedure was crucial for measuring reaction rates over the nanoparticle arrays. The reactivity of the Pt/Al 2 O 3 arrays was compared to a Pt(111) single crystal for the ethylene hydrogenation reaction. The activation energy and the pressure dependence of the H 2 and C 2 H 4 on the nanoparticle array were in excellent agreement with the kinetic data on the Pt(111) single-crystal model catalyst. Because the ethylene hydrogenation reaction is structure insensitive, the rate equation for Pt(111) can be applied to the Pt nanoparticle arrays. The calculated turnover frequency led to a calculated active metal surface area that compared very well with an active metal surface area on the basis of geometry. This reaction can therefore be used to determine the active metal surface area of the Pt nanoparticle array model catalysts. The arrays were characterized with AFM, SEM, XPS, and AES before and after being exposed to reaction conditions.

Mesoporous silica was synthesized in the presence of metal (Au, Pt, and Ag) nanoparticles in the 2-20 nm range. Sample characterization was performed by X-ray diffraction and electron microscopy. The metal nanoparticles in the 2-10 nm range were successfully incorporated into the ordered mesoporous SBA-15 structures; 20 nm particles, whose diameter is larger than the SBA-15 pore size, could not be inserted. In the case of 5 and 10 nm diameter nanoparticles, regardless of which metal, the mesopore channels expanded in order to accommodate the metal particles. By using mixtures of metal nanoparticles of two different sizes, it was found that the inclusion and the resultant pore size were controlled by the larger size metal particles.