A novel method for the controlled embedding of multiple nanoparticles of various materials, such as gold nanoparticles, quantum dots, and magnetic nanoparticles, in silica colloids is presented. After adsorption of the amphiphilic polymer poly(vinylpyrrolidone) on hydrophobic or hydrophilic stabilized nanoparticles, these are adsorbed on silica spheres and covered by variable-thickness silica shells. This silica coating protects the embedded nanoparticles against chemical transformations, which is of crucial importance for the biocompatibility of particles containing toxic elements. Moreover, it is found that the optical properties of the nanoparticles are retained. Possible applications of multicore particles are briefly discussed.
A study of the influence of the local environment on the light-induced luminescence enhancement of CdSe/ZnS quantum dots (QD) embedded in silica colloids that are dispersed in various solvents is presented. The photoluminescence of the embedded QD is enhanced up to a factor of ten upon photoactivation by ultraviolet or visible light. This enhancement is strongly dependent on the local environment. The thickness-dependent permeability of the silica shell covering the QD controls the influence of the solvent on the QD. If foreign ions are present the activation state is stabilized after termination of the activation, whereas in their absence the process is partially reversible. A new qualitative model for the photoactivation of QD in various environments is developed. It comprises light-induced passivation and subsequent oxidation processes. The embedded QD also retain their fluorescence quantum yield inside living cells. Moreover, they can be activated for many hours in living cells by laser radiation in the visible regime.
Recombinant antibodies are promising tools for a wide range of bioanalytical and medical applications. However, the chemical modification of such molecules can be challenging, which limits their broader utilization. Here we describe a universal method for the site-specific labeling of antibody fragments and protein ligands by genetically fusing them to an engineered version of the human DNA-repair enzyme O(6)-alkyllguanine DNA alkyltransferase (AGT), known as SNAP-Tag (1-3) . Substrates containing O(6)-benzylguanine are covalently bound to the fusion proteins via a stable thioether bond in a rapid and highly specific self-labeling reaction. The coupling is site-directed, allowing the design and synthesis of antibody conjugates with predefined stoichiometry. We cloned a series of ligand SNAP-Tag fusion proteins and expressed them in HEK 293T cells. The antibody/ligand-fusions were characterized by labeling with different fluorophores, labeling with biotin, or by coupling them to fluorescent nanobeads, followed by analysis by flow cytometry and confocal microscopy. All ligands retained their original antigen-binding properties when fused to the SNAP-Tag. The combination of recombinant antibodies or protein ligands with the SNAP-Tag facilitates simple and efficient covalent modification with a broad range of substrates, thus providing a useful and advantageous alternative to existing coupling strategies.
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