MP26:Nanocrystal Clusters for Highly Efficient Bioseparation

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Zhenda Lu, Yadong Yin

Department of Chemistry, University of California, Riverside

Nanoparticles have many superior characteristics for the bioseparation compared to those of the conventional micrometer-sized resins or beads, such as good dispersability, the fast and effective binding of biomolecules due to their small size and high surface area. However, there are several intrinsic difficulties of the nanoparticles in separation. First, they can not be conveniently separated from the mixture by centrifugation because of their samll sizes. Second, these monodisperse nanoparticles are normally dispersed in nonpolar solvents, which is a great limitation for the bioapplications. Third, the surfaces of these nanoparticles are always coated with a layer protecting ligands, which prevents nanoparticles from trapping the biomolecules. To address these challenges, we have recently developed a general bottom-up assembly route to prepare nanocrystal clusters with affinity to biomolecules.

Titanium dioxide (TiO2) is used as an example here for demonstrating the advantages of the self-assembled nanoparticle clusters due to TiO2 materials can highly selectively trap phosphopeptides from biosamples. Clusters of densely packed TiO2 nanocrystals are first prepared, and then stabilized by coating with a thin layer of silica. Calcination of the materials at high temperatures connects the neighboring TiO2 nanocrystals together and enhances the mechanical stability of the clusters, and at the same time removes the organic surfactants and makes the TiO2 surface fully accessible to phosphopeptides. By coating the nanocrystal clusters with a layer of silica before calcination and removing it afterwards through chemical etching, we have been able to make the cluster surface hydrophilic and negatively charged, and eventually make the cluster easy to be dispersed in aquous solution. The high specificity and capacity of these mesoporous TiO2 clusters have been demonstrated by effectively enriching phosphopeptides from digests of phosphoprotein (alpha- or beta-casein), nonfat milk and human serum samples. We also demonstrate that the self-assembly process brings the flexibility of incorporation of multiple components, such as superparamagnetic nanocrystals to further facilitate the peptide separation. The pore sizes of the TiO2 clusters can be conveniently controlled by changing the size and shape of the building blocks during assembly. As an example, we have fabricated three samples of clusters by assembling TiO2 nanodots and nanorods: NCC1 from ~5.1-nm nanodots, NCC2 from ~6.6-nm nanodots, and NCC3 from ~3.0-nm×28.1-nm nanorods. The different pore sizes of these TiO2 clusters allow selective enrichment of posphorylated proteins with various sizes based on size exclusion mechanism.

It is expected that this self-assembly strategy opens the door to a new class of mesoporous materials that may have wide applications in isolating biomolecules by properly selecting the oxide nanocrystals and their size and shape.
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