Here we introduce a new synthetic approach to grow mesoporous silica thin films with vertical mesochannels on centimeter-sized substrates via an oil-induced co-assembly process. Adding an oil, i.e., decane, into a CTAB-EtOH-TEOS ammonia solution leads to thin-film formation of mesoporous silica of controlled thickness between 20 and 100 nm with vertical mesochannels on various surfaces. The vertical mesoporous channels were evidenced by grazing incidence small-angle X-ray scattering (GISAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) characterizations. Decane played two roles: (a) as a pore expansion agent (up to 5.7 ± 0.5 nm) and (b) inducing vertically oriented hexagonal mesophases of micelle-silica composite. The production of periodic and vertical nanochannels is very robust, over many different substrate surfaces (from silicon to polystyrene), various silica precursors (TEOS, fumed silica, or zeolite seed), and many oils (decane, petroleum ether, or ethyl acetate). This wide robustness in the formation of vertical nanophases is attributed to a unique mechanism of confined synthesis of surfactant-silicate between two identical thin layers of oils on a substrate.

It is highly desirable to study the kinetics and spectroscopy of enzymes in a crowded and controllable microenvironment. In this work, we employ mesoporous silica of matching pore sizes to confine lysozyme in order to mimic enzyme in a crowded environment. The stability and activity of lysozyme immobilized in mesoporous silica nanoparticle (MSN) of various pore sizes were studied and correlated to spectroscopic data of the immobilized enzyme. By siteselective surface functionalization, we were able to avoid protein adsorbing on the external surfaces of MSNs and study specifically the protein immobilized in the nanochannels. Solution spectroscopic methods, CD and fluorescence, were used to study the secondary and tertiary structures of the immobilized enzyme because MSNs could be suspended very well in solution. To study the catalytic activity of lysozyme, we employed 4-methylumbelliferyl β-D-N,N′,N″-triacetylchitotrioside as a substrate that was hydrolyzed and detected by fluorescence spectroscopy. 8-Anilino-1-naphthalenesulfonic acid was utilized as a fluorescence probe to characterize the protein-binding site. The conformation, thermal stability, and catalytic activity of lysozyme were sensitive to the curvature of the silica materials. The activity of the lysozyme immobilized in the 5.6 nm mesopores of MSNs was higher than those of native enzymes. The enhanced activity was attributed to subtle change in tertiary structure of lysozyme in the crowded microenvironment in the mesopores.

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We incorporated a near-infrared (NIR) fluorescent dye, indocyanine green (ICG), in amine-modified layered double hydroxide nanoparticles (LDHs) by electrostatic attractions to render LDHs-ICG as an efficient NIR contrast agent for in vivo optical imaging. The further coating of chitosan on the external surfaces of LDHs-ICG was achieved through the cross-linking of amine-modified LDHs and different amounts of chitosan by using glutaraldehyde (GA) as a cross-linked agent. The hybridization of this organic-inorganic nanocomposite produced an efficient NIR optical contrast agent because the adsorbed ICG molecules were stabilized in the layered structures of LDHs to prevent them from leaching and/or metabolizing in physiological conditions. The cell viability and hemolysis assay also showed low cytotoxicity and low release of hemoglobin from the cell lysis of red blood cells (RBCs). The in vivo biodistribution results demonstrated that the coating of LDHs with different amounts of chitosan can develop organ-specific drug delivery systems, which can efficiently regulate the nanoparticle accumulation in various organs with un-coated LDHs-ICG targeting the liver and spleen, mono-chitosan-coated LDHs-ICG targeting the lungs, double chitosan-coated LDHs-ICG targeting the lungs and liver, and trimethylammonium (TA) modified double chitosan-coated LDHs-ICG samples targeting the liver. In addition to the high potential for the employment of chitosan-coated LDHs-ICG samples for developing contrast agents for in vivo imaging, the LDH nanoparticles can deliver therapeutic drugs to desired target organs by controlling the coating amounts of chitosan. Therefore, this approach can improve efficiency for traditional cancer diagnosis and cancer chemotherapy.

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