Silica nanoparticles luminescent

Fluorescent silica nanoparticles, called FloDots, were created by Yao et al. (2006) by two synthetic routes. Hydrophilic particles were produced using a reverse micro-emulsion process, wherein detergent micelles formed in a water-in-oil system form discrete nanodroplets in which the silica particles are formed. The addition of water-soluble fluorescent dyes resulted in the entrapment of dye molecules in the silica nanoparticle. In an alternative method, dye molecules were entrapped in silica using the Stober process, which typically results in hydrophobic particles. Either process resulted in luminescent particles that then can be surface modified with... 

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... 

Santra S, Liesenfeld B, Bertolino C, Dutta D, Cao Z, Tan WH, Moudgil BM, Mer-icle RA (2006) Fluorescence lifetime measurements to determine the core-shell nanostructure of FlTC-doped silica nanoparticles An optical approach to evaluate nanoparticle photostability. J Luminesc 117 75-82... 

A very interesting approach for specific immunoassays was recently reported by Wang, Yang, and Tan [108]. They employed silica nanoparticles of varying sizes with different mixtures of [Os(bpy)3]2+ and [Ru(bpy)3]2+ incorporated in the particles, imparting different relative emission intensities for the Ru and Os chromophores. The nanoparticles were then modified with either mouse or human IgG antibodies and exposed to microspheres modified with, for instance, anti-mouse IgG. Luminescence results revealed that the mouse IgG nanoparticles associated specifically with the anti-mouse IgG microspheres. Further, mixtures of the microspheres modified with anti-mouse and anti-human IgG could be distinguished because of selective doping ratios of the nanoparticles with the Os and Ru complexes. 

In addition. Yuan and coworkers described spherical silica-based luminescent europium nanoparticles with a uniform size of about 10 nm in diameter [87]. Interestingly, the nanoparticles can be excited over a wavelength range from the UV to visible light (200 50 nm) in aqueous solution, and could be used for time-resolved luminescence imaging of an environmental pathogen, Giardia lamblia. 

LLCs are promising candidates as probes for humidity sensors due to the distinct quenching effect of water molecules which can reversibly coordinate to lanthanide ions. The decrease in lifetime of the Dq transititMi of europiumflll) perchlorate was used for the determination of small amounts of water in DMF and DMSO [106]. Wang and Li have presented luminescent nanospheres for die determination of small amounts of water (0.05-3.0 vol%) in ethanol [107]. They coated silica nanoparticles with a thin layer of a salicylic acid-La /Tb " coordination compound. The green fluorescence peaking at 549 nm corresponds to the D4 transition of Tb and is strongly quenched by trace amounts of water. The nanoparticles can be excited at wavelengths around 350 nm. 

Silica nanoparticles (Si02NPs), differently from some other oxide nanoparticles such as Ti02 NPs, do not behave as semiconductors. This means that they are not involved in photoinduced electron-transfer processes and that differently from QDs they are not intrinsically luminescent. Si02NPs alone albeit attractive containers for fluorophores are not discussed herein. However, the Si02NPs may be successfully used as matrices, within which the ET components are surrounded by a protective matrix that prevents fluorophore degradation. Most importantly, the donor-acceptor fluorophores may be organized in a well-defined manner, a feamre of utmost importance for ET... 

Bonacchi S, Genovese D, Juris R et al (2010) Luminescent chemosensors based on silica nanoparticles. Top Curr Chem [this volume]... 

Keywords Chemical sensors. Fluorescence, Luminescence, Signal amplification. Silica nanoparticles... 

In the past few years, many reports have described the distinct advantages of luminescent silica nanoparticles over traditional dye molecules [54, 55]. These advantages allow their convenient use as fluorescent probes for applications ranging from biosensors [56, 57] to interfacial interaction studies such as immunoassays [58], multiplexed bio-analysis [59-61], nucleic acid analysis [62] and drug delivery [63] to name but a few (Fig. 6). 

Luminescent silica nanoparticles are, in our opinion, the most promising and valuable of aU the species presented till now in this brief introduction they are potentially interesting for many applications like energy production and storage, catalysis and in particular sensing. After a description of the most common preparation methods in Sect. 2, we will present the state of the art for these particles as far as their application as chemosensors is concerned. 

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). 

Inspired by the work of Liu and co-workers who have described a new kind of core-shell (sUica-PEG) nanoparticles as platform for dmg-delivery [71], we have very recently proposed [93] a synthetic strategy that affords monodispersed and ordered core-shell silica nanoparticles. Such systems allow the irreversible inclusion of dye molecules in the silica core and present a stable biocompatible and water soluble polymeric protective shell. For these reasons these materials appear particularly promising in the development of luminescent probes for in vitro and, hopefully, in vivo medical and bio-analytical applications. 

Introducing this chapter, we have demonstrated the advantages in passing from conventional luminophores to complex architectures, and in particular why in our opinion luminescent silica nanoparticles are the most interesting and promising... 

Hereafter we discuss in more detail how luminescent silica nanoparticles can potentially fulfil all of these crucial features ... 

To summarize, energy transfer processes can induce in luminescent silica nanoparticles very valuable collective properties, yielding species that can be... 

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... 

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