**1. Introduction**

310 Practical Applications in Biomedical Engineering

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Functional hybrid inorganic nanomaterials have received substantial attention for their promising performance in nanotechnological applications.[1] A combination of more than one nanocomponent into a hybrid structure gives rise to new collective properties different from the constituents.[1] The hybrid nanostructures not only have multifunctional properties, but also may induce synergistic properties, arising from interfacial particleparticle interactions.[2] Coupling of two or more components produces a hybrid nanostructure that allows electronic transfer across the junction to change local electronic structure. The engineering chemical reactivity on the particle surface is thus dependent on the internal and external interfacing capacilities and the particle size distribution of the deposited particles onto the nanosupports.[1, 3] These behaviours make them to generally have potential applications in solar energy conversion, catalysis, and potential biomedical methods for drug delivery, bioimaging, and cancer theragnosis.[4-6]

The morphology of the hybrid nanostructures impacts a critical factor affecting their active performance.[7] The shape-controlled synthesis of these materials have been made in recent years. This objective could be performed by conducting heterogeneous nucleation-growth kinetics during the synthesis. Wet-chemistry methods, such as seed-mediated growth, ionexchange deposition, thermal decomposition, hydro-solvothermal process used to synthesize single nanoparticles have been extended to the hybrid nanostructures. The nanohybrids with specific shapes (e.g., dumbbell and core-shell) formed by sequential growth of second components onto the preformed seeds through directed attachment. The hybrid structures formed during heterogeneous growth are dependent on organic linkers used and lattice parameters of each components, which is relative to the electron transferred capacity at the particle-particle interfaces. A combination of synthetic control along with

© 2012 Tran and Nguyen, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Tran and Nguyen, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

understanding of the interfacial interactions is therefore a significant basis for the fabrication of the multifunctional hybrid nanomaterials.

Functional Inorganic Nanohybrids for Biomedical Diagnosis 313

**Figure 1.** A general sketch of reaction mechanisms for the formation of the hybrid nanostructures: (a-c) Heterogeneous nucleation and growth of secondary precursors on the preformed seeds; (d) Secondary precursors adsorbed on the opposite charged surfaced supports by photo-irradiation; (e) Reduced precipitation of secondary precursors on hydrophilic-surfaced supports; (f) Secondary precursor growth

been achieved in the synthesis of the core-shell and dumbbell nanoparticles combining two different components. When the individual components involved have similar crystal structures and lattice parameters, each component fuses together giving the dumbbell shape. In a dumbbell structure consisted of one particle-bounded another, charged transfer across nanoscale junction could significantly change local electronic configuration that give the remarkable properties. While large lattice space difference of the individual components

on the activated-surfaced supports; (g) One-pot self-controlled nucleation-growth.

The functional inorganic hybrid nanomaterials with combined plasmonic-magnetic, plasmonic-fluorescent, or magnetic-fluorescent structures have unique optoelectronic properties for biomedical applications.[5, 8-10] The optical, electronic, magnetic properties could be controlled by adjusting their sizes, shapes, compositions, and surface chemistry. Several types of the hybrid nanostructures are potentially useful for biomedical applications.[5, 8] For example, the plasmonic-fluorescent materials would be interesting as dual-use biological tags, giving the ability to visualize labeled cells using both magnetic resonance and fluorescence imaging techniques, while external magnetic fields could be employed for the directed assembly of such materials.[11] In order to be compatible with biomedical environment, the surface of the nanohybrids is functionalized with appropriate amphiphilic polymer, silica, targeting ligand through chemisorption, covalent linkage, and ligand exchange.[12] After surface modification, the coated hybrid nanoparticles have the possibility of highly colloidal stabilization in aqueous media compatible with bioconjugation.[13] The delivery of the hybrid nanoparticles to targeted cells is an important and challenging approach in medical diagnosis and therapy. Development of biomoleculeconjugated strategies allows the hybrid nanoparticles delivering to targeted tissues through either antibody-antigen or ligand-receptor interactions.[12] Biomolecules, such as small molecules (vitamin, peptide, lipid, sugar) and larger ones (protein, DNA, antibody, enzyme, carbohydrate), are often used to conjugate onto the hybrid particles. Biomolecule-conjugated nanohybrid colloids have the possibility of highly selective binding with alive organ made them to be "biocompatible" behaviour and superior bioactivity at the supermolecular level.[5, 14, 15] These features have potentially applied in smart drug delivery vehicles, contrast agents, and theranostic biomedical applications.

This Chapter reviews the design, fabrication, and theranostic biomedical applications of the inorganic hybrid nanomaterials with combined plasmonic-magnetic, plasmonic-fluorescent, or magnetic-fluorescent structures. New collected properties of the hybrid nanostructures arising from the particle-particle interactions and the geometries are discussed from specific results of recent publications. The functionalizations of the hybrid nanostructures with amphiphilic polymer and silica coatings yielded water-soluble nanohybrid colloids are described. The subsequent conjugation of biomolecules with the coated nanohybrids afforded cellular targeting agents and the use of them as multimodal bioprobes for multimodal imaging and therapy are highlighted.
