Surface Biofunctionalization of Inorganic Silica Nanoparticles

The optimal fusion of surface and internal biofunctionalization of silica nanoparhcles can lead to the creation of useful multifunctional nanoparticles. Although several reviews [8-10] have detailed the advances in biofunctionalization of inorganic siUca nanoparhcles, none of these has summarized recent developments in this area, such as ORMOSIL and funchonal organosilica nanoparhcles. In the following section we describe both surface and internal biofunchonalizahon strategies for various types of inorganic sihca and organosilica nanoparhcles. 

The amino group is commonly used for the immobUization of enzymes and antibodies hence, TEOS nanoparticles may be silanized with Nl-[3-(trimethoxysilyl)-propyl]diethylenetriamine, N-(2-amino-ethyl)-3-aminopropyltrimethoxysilane, N-(6-amino-hexyl)-3-aminopropyltrimethoxysilane or APS for the direct preparation of amino-modified TEOS nanoparticles [65-75]. Alternatively, an indirect preparation may be carried out through silanization with 3-glycidoxypropyltrimethoxysi-lane, followed by diamines [76]. Amino-modified TEOS nanoparticles are positively charged due to the cationic amino (—NH3 ) groups on the surface, and further biofunctionalization may be conducted using various methods. 

A peptide has also been conjugated on the surface of amino-modified TEOS nanoparticles. TAT peptide [48-56], an amino acid residue of the HIV-coded TAT regulatory protein, is a cell-penetrating peptide and was conjugated with amino- 

DNA can also be conjugated with amino-modified TEOS nanoparticles following their activation with 1,2,3-triazine and 1,2,4-triazine, and subsequent reaction with amino-labeled synthetic oligonucleotides [69]. Alternatively, the amino-modified TEOS nanoparticles can be activated with m-maleimidobenzoyl-N-hydroxysuccin-imide ester cross-hrikers and then reacted with thiol-labeled synthetic oligonucleotides [70]. 

Silanization followed by physical adsorption represents another method for the biofunctionaUzation of TEOS nanopartides. The cationic properties of the surfaces of these nanopartides can be used for biofunctionahzation with negatively charged biomolecules, and the formation of a complex consisting of amino-modified TEOS nanoparticles and plasmid DNA has been reported [73-75]. Such a complex is formed simply by mixing amino-modified TEOS nanopartides and plasmid DNA the resultant complex is stable and capable of transfecting plasmids into cells in vitro. 

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