Inorganic Silica Nanoparticles

Inorganic silica nanoparticles have been prepared using both the Stober method [44] and reverse microemulsion [45]. With the Stober method, submicron-sized TEOS nanoparticles can be obtained, and the synthetic mixtures typically contain ethanol, ammonium hydroxide and water. Although the method is simple and 

---

Traditionally, inorganic silica nanoparticles have been prepared from either TEOS (1) or tetramethoxyorthosilicate (TMOS) (2). When prepared, TEOS nanoparticles are composed internally of a simple silica network (—O—Si—O—), and have silanol groups on their surfaces. However, as they lack any exposed organic residues, both inside and on their surfaces (as shown schemahcally in Figure 4.1), they will require further modification with funchonal residues (e.g. amine or thiol) prior to their surface biofunctionalization. 

Figure 4.1 Schematic structure of inorganic silica nanoparticles.

TEM) images of inorganic silica nanoparticles prepared from TEOS as a function of time and TEOS concentration. TEOS nanoparticles prepared under condition A (a), condition B (b) and condition C (c)... 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

Traditionally, the sol-gel process has been used for the preparation of silica nanoparticles via the hydrolysis of alkoxides in organic solvents [52,53]. Similar hydrolysis and condensation carried out in w/o microemulsion offers robust control over the synthesis process. W/o emiflsion-mediated sol-gel synthesis is currently used for the fabrication of pure sihca, as well as inorganic and organic dye-doped silica nanoparticles. The synthesis of sihca and dye-doped nanoparticles is classified in the following sections on the basis of the classification of the head group fimctionahty of the major surfactant used. 

From our research group Santra et al. [11,41,42] reported the development of novel luminescent nanoparticles composed of inorganic luminescent dye RuBpy, doped inside a sihca network. These dye-doped silica nanoparticles were synthesized using a w/o microemulsion of Tx-lOO/cyclohexane/ n-hexanol/water in which controlled hydrolysis of the TEOS leads to the formation of mono dispersed nanoparticles ranging from 5-400 nm. This research illustrates the efficiency of the microemulsion technique for the synthesis of uniform nanoparticles. These nanoparticles are suitable for biomarker application since they are much smaller than the cellular dimension and they are highly photostable in comparison to most commonly used organic dyes. It was shown that maximum liuninescence intensity was achieved when the dye content was around 20%. Moreover, for demonstration... 

Shin JH, Schoenfisch MH. Inorganic/organic hybrid silica nanoparticles as a nitric oxide delivery scaffold. Chemical Materials 2008, 20, 239-249. 

Newer immunodetection applications, and particularly the so-called microarrays, employ new fluorescent probes such as europium chelates (Scorilas et al., 2000), lanthanide oxide nanoparticles (Dosev et al., 2005 Nichkova et al., 2006), fluoro-phore loaded latex beads (Orth et al., 2003), dye-doped silica nanoparticles (Zhou and Zhou, 2004 Yao et al., 2006), and inorganic nanocrystals (Gerion et al., 2003 Geho et al., 2005). 

Different inorganic materials have been used as supports in SAPC glass beads of controlled pore size [6,14—17, 24, 39—42,44,45, 53] porous [11,15,18,19, 21, 23, 28-32, 35, 36, 38, 39, 43, 48, 49] and nonporous [28, 33, 48] silica nanoparticles synthetic phosphate [27] carbon [39], and alumina [15,39]. It was shown that glass beads, siKca, and synthetic phosphate gave the best performance. All these supports have a high specific surface with an average diameter of the pores, in the case of porous supports, between 60 and 345 A. The use of chitosan as a natural polymeric support of SAP catalysts for the synthesis of fine chemicals has been reported recently [54]. 

---