Nanoparticle Surface Functionalization

PEI has also found use as a eoating for inorganic nanoparticles, either to impart eell-penetrating properties, as a platform for further modification or simply to provide cationic colloidal stabilization. Some reeent examples will be diseussed to exemplify the use of PEI as nanopartiele eoating. 

Lanthanide/CaF2 upconversion nanoparticles coated with poly(actylic acid) (PAA) and then PEI showed the ability to internalize into rat mesenehymal stem cells and were not observed to exocytose. In contrast, nanoparticles without the eovalendy linked PAA or without PEI showed veiy different behaviour, as they were found to aggregate and did not enter the eells. 

PEI-funetionalized iron oxide nanoparticles loaded with doxorubicin (DOX) have been synthesized by a complex multistep synthetic procedure. First of all, PEI was modified with Traut s reagent to introduce free thiol 

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Si02 nanoparticles (surface functionalized) Si02 nanoparticles (surface functionalized) Si02 nanoparticles (surface functionalized) Si02 nanoparticles (surface functionalized) Si02 nanoparticles... 

Gnichwitz J-F et al (2010) Efficient synthetic access to cationic dendrons and their application for ZnO nanoparticles surface functionalization new building blocks for dye-sensitized solar cells. J Am Chem Soc 132 17910-17920... 

This approach of using 2D and 3D monodisperse nanoparticles in catalytic reaction studies ushers in a new era that will permit the identification of the molecular and structural features of selectivity [4,9]. Metal particle size, nanoparticle surface-structure, oxide-metal interface sites, selective site blocking, and hydrogen pressure have been implicated as important factors influencing reaction selectivity. We believe additional molecular ingredients of selectivity will be uncovered by coupling the synthesis of monodisperse nanoparticles with simultaneous studies of catalytic reaction selectivity as a function of the structural properties of these model nanoparticle catalyst systems. 

In 1994, thiols were firstly used as stabilizers of gold nanoparticles [6a]. Thiols form monolayer on gold surface [18] and highly stable nanoparticles could be obtained. Purification of nanoparticles can be carried out, which makes chemical method of metal nanoparticles a real process for nanomaterial preparation. Various thiol derivatives have been used to functionalize metal nanoparticles [6b, 19]. Cationic and anionic thiol compounds were used to obtain hydrosols of metal nanoparticles. Quaternary ammonium-thiol compounds make the nanoparticle surface highly positively charged [20]. In such cases, cationic nanoparticles were densely adsorbed onto oppositely charged surfaces. DNA or other biomolecule-attached gold nanoparticles have been proposed for biosensors [21]. 

Keywords Biocompatible Cancer diagnostics Functionalization Imaging Nanoparticles Surface modification Targeted drug delivery... 

Nanoparticle surface modification is of tremendous importance to prevent nanoparticle aggregation prior to injection, decrease the toxicity, and increase the solubility and the biocompatibility in a living system [20]. Imaging studies in mice clearly show that QD surface coatings alter the disposition and pharmacokinetic properties of the nanoparticles. The key factors in surface modifications include the use of proper solvents and chemicals or biomolecules used for the attachment of the drug, targeting ligands, proteins, peptides, nucleic acids etc. for their site-specific biomedical applications. The functionalized or capped nanoparticles should be preferably dispersible in aqueous media. 

Shi, X., Wang, S., Sun, H., and Baker Jr., J.R. (2007) Improved biocompatibility of surface functionalized dendrimer-entrapped gold nanoparticles. Soft Matter 3, 71-74. 

It is difficult to predict the effect of surface functionalization on the optical properties of nanoparticles in general. Surface ligands have only minor influence on the spectroscopic properties of nanoparticles, the properties of which are primarily dominated by the crystal field of the host lattice (e.g., rare-earth doped nanocrystals) or by plasmon resonance (e.g., gold nanoparticles). In the case of QDs, the fluorescence quantum yield and decay behavior respond to surface functionalization and bioconjugation, whereas the spectral position and shape of the absorption and emission are barely affected. 

Based on well established silica chemistry, the surface of silica nanomaterials can be modified to introduce a variety of functionalizations [3, 11, 118]. The toxicity of surface-modified nanomaterials is largely determined by their surface functional groups. As an example, Kreuter reported that an apolipoprotein coating on silica nanoparticles aided their endocytosis in brain capillaries through the LDL-receptor [122-124]. Overall, silica nanomaterials are low-toxicity materials, although their toxicity can be altered by surface modifications. 

Zhang, H.L, et ah, Vapour sensing using surface functionalized gold nanoparticles. Nanotechnology, 2002.13(3) p. 439. 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

Figure 13. Selective Surface Functionalization and Selective deposition of Pd Nanoparticles in the micropores of SBA-15.

Figure 6.9 A schematic representation of orthogonal process for nanoparticles self-assembly (a) a patterned silicon wafer with Thy-PS and PVMP polymers fabricated through photolithography and (b) orthogonal surface functionalization through Thy-PS/DP-PS recognition and PVMP/acid-nanoparticle electrostatic interaction. Reprinted with permission from Xu et al. (2006). Copyright 2006 American Chemical Society.

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