Dye-coated silica nanoparticles

Such a covalent approach also allows one to obtain luminescent silica nanoparticles capping the surface with fluorophores. These emitting systems are usually indicated as dye coated silica nanoparticles (DCSNs) (Fig. 7). 

Fig. 7 Stober synthesis of dye coated silica nanoparticles (DCSNs)...

We will discuss hereafter many recent examples of chemosensors based only on luminescent silica nanoparticles but, even if this can appear to be a narrow field, the scenario is instead very wide. Therefore, with the aim of clarity, we have divided them in two main sections, one dealing with systems presenting the signalling units on the surface (dye coated silica nanoparticles, DCSNs) and the other with systems presenting it segregated inside the silica matrix (DDSNs). Moreover, for both... 

Fig. 28 Schematic of a poly(lipid)-coated silica nanoparticle. Fluorescent dyes are encapsulated in the sol-gel silica core the nanoparticle is then coated with cross-linked bis-SorbPC doped with...

Fig. 4 Schematic illustration of synthesis of multifunctional nanoparticles starting from a w/o microemulsion, b solubilization of fluorescent dye in the microemulsion core, c formation of silica nanoparticle and encapsulation of fluorescent dye, d condensation of silane ligand and chelation of Gd(lll), e post coating with silica, and f extraction of nanoparticles...

Figure 22 Schematic representation, (a) Preparation of eosin-doped silica-coated silver nanoparticles (b) addition of fluorescein-doped sihca shells onto eosin-doped silica-coated silver nanoparticles (c) preparation of dye-doped hollow silica nanoshells by dissolution of the silver core. (Reproduced with permission from Ref. 41. 2009, American Chemical Society.)...

Fig. 22 Ligands and fluorescent dyes used for the coating of silica nanoparticles (where X can be -Si(OEt>3 or-H)...

This last property has been often utilized recently for the design of magnetic field-responsive nanocarriers, in combination with thermosensitive polymers. As an example, Baeza et al. (2012) coated mesoporous silica nanoparticles with pNIPAAm and loaded them with a fluorescent dye and SPIONs. They observed that application of an alternating magnetic field caused release of the dye from the particles, which could be attributed to... 

Figure 14.24 Fluorescent silica nanobubbles have been created using gold nanoparticle seeds that initially are coated by adsorption with a fluorescent dye. The particles then are capped by a layer of silica by polymerizing TEOS and entrapping the dye molecules within it. Finally, the gold core is dissolved by reaction with cyanide, leaving behind hollow fluorescent silica nanobubbles.

Figure 11.9 Schematic representation of the SiC>2 nanoparticles prepared by Greenway and coworkers64 for the detection of lipid peroxidation 15 nm Si02 nanoparticles covalently coated with the coumarin dye are embedded in a 100 nm silica protecting shell.

Quenching At shorter distances, ranging from few nanometers to the physical contact with the metallic structure, a mechanism tends to increase the total decay rate. This effect, which is responsible for fluorescence quenching, is due to the absorption of fluorescence photons in the metallic structure itself (99). Another effect is based on interactions of the fluorophore with free electrons in the metal, wherein the plasmon absorption leads to lower fluorescent emission efficiency (100). Theoretical study asserts that the optimized distance between the excitation source and the fluorophore is around 2-5 nm (99, 101,102). Nanoparticles coated with a thin shell (e.g. silica, 5nm in thickness) and the dye attached to the dielectric shell could overcome quenching effects (84, 103). The quenching effect can also be found in the quantum dot / GNP system (104). It is noted that as the concentration of fluorophore is high, the self-quenching effect should also be considered. (100)... 

The system was quite efficient and was probably an inspiration for Jong Hwa Jung et al. [143] who, more recently, have proposed a similarly engineered system for the sensing and separation of toxic species like lead and mercury in different matrices. They have synthesized nickel nanoparticles coated with a silica shell (30 0 nm in diameter), then grafted with a di-silanized 4,4-difluoro-4-bora-3a,-4a-diaza-s-indacene (BODIPY) derivative (Fig. 29). This dye, buffered at pH 7, is... 

---