Fluorescent silica nanoparticles

Add 32 mg of silica nanoparticles (fluorescent or plain) to 20 ml of 1 mM acetic acid containing 1 percent trimethoxysilyl-propyldiethylenetriamine with stirring. Other concentrations of silane derivatives used for particle modification typically range from 1 to 5... 

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...

Silica particles have been exploited in virtually every assay or detection strategy that polymer particles have been used in for bioapplication purposes. Recently, fluorescent dye-doped silica nanoparticles have been developed by a number of groups that have similar fluorescence characteristics to quantum dot nanocrystals (Chapter 9, Section 10). Fluorescent silica nanoparticles can be synthesized less expensively than quantum dots due to the fact that the silica particles incorporate standard organic dyes (Ow et al., 2005 Wang et al., 2006) and are not dependent on making reproducible populations of semiconductor particles with precise diameters to tune emission wavelengths. 

These Ru(H)bpy32+ fluorescent silica nanoparticles were used to detect single bacterial cells using antibodies conjugated to the surface after functionalization with trimethoxysilyl-propyldiethylenetriamine followed by succinylation to create carboxylates. Specific antibody molecules against E. coli 0157 then were coupled to this modified fluorescent particle using the carbodiimide method with EDC and NHS (Zhao et al., 2004). 

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... 

Figure 14.23 Silica nanoparticles containing fluorescent dye molecules can be prepared using a reverse micelle suspension process (a) The water-in-oil emulsion is formed with the aqueous phase droplets containing TEOS and dye molecules in detergent, (b) The final particles contain entrapped dye within the silica particle matrix, creating highly fluorescent particles.

Figure 14.25 The preparation of highly controlled fluorescent silica nanoparticles can be done by first polymerizing APTS that has been covalently modified with an amine-reactive dye to form fluorescent core particles. The core then is capped by a shell of silica by polymerization of TEOS. The shell layer can be further derivatized with silane coupling agents to provide functional groups for conjugation.

Ow, H., Larson, D.R., Srivastava, M., Baird, B.A., Webb, W.W., and Wiesnet, U. (2005) Bright and stable core-shell fluorescent silica nanoparticles. Nano Lett. 5, 113-117. 

H. Ow, D. R. Larson, M. Srivastava, B. A. Baird, W. W. Webb and U. Wiesner, Bright and Stable Core-Shell Fluorescent Silica Nanoparticles, Nano Lett., 2005, 5, 113. 

Montalti M, Prodi L, Zaccheroni N et al (2002) Solvent-induced modulation of collective photophysical processes in fluorescent silica nanoparticles. J Am Chem Soc 124 13540-13546... 

Bonacchi S, Rampazzo E, Montalti M et al (2008) Amplified fluorescence response of chemosensors grafted onto silica nanoparticles. Langmuir 24 8387-8392... 

Kim S, Pudavar FIE, Prasad PN (2006) Dye-concentrated organically modified silica nanoparticles as a ratiometric fluorescent pH probe by one- and two-photon excitation. Chem Commun (Camb) 19 2071-2073... 

A series of silica nanoparticles doped with cyanine dye DY-635 (Dyomics) were also prepared, characterized, and investigated in flow cytometry and fluorescence imaging applications [77]. Also these dye-nanoparticles demonstrate high, stable, and tunable fluorescence intensity and are useful for multicolor detection. 

Yang W, Zhang CG, Qu HY, Yang HH, Xua JG (2004) Novel fluorescent silica nanoparticle probe for ultrasensitive immunoassays. Anal Chim Acta 503 163-169... 

Bums AA, Vider J, Ow H, Herz E, Penate-Medina O, Baumgart M, Larson SM, Wiesner U, Bradbury M (2009) Fluorescent silica nanoparticles with efficient urinary excretion for nanomedicine. Nano Lett 9 442-448... 

Keywords Fluorescence Lifetime Photostability Quantum yield Silica nanoparticle... 

In this chapter, the first section will focus on the designs of different structures of DDSNs. The basic synthesis methods of pure silica nanoparticles will be briefly summarized at the beginning. The general methods for doping dye molecules into a silica matrix will then be covered followed by the introduction of several DDSN designs. The second section will be a major focus of this chapter. Various advantageous properties of DDSNs will be discussed. These discussions will involve reaction kinetics, solubility, photostability, and fluorescence intensity including quantum yield and lifetime, as well as toxicity. With the rapid development of DDSNs, more features and functionalities of DDSNs are expected in the near future. 

The high photostability and acute fluorescence intensity are two major features of DDSNs compared to dye molecules in a bulk solution. The early DDSN studies have focused on these two properties [8, 13]. For example, Santra et al. studied the photostability of the Ru(bpy)32+ doped silica nanoparticles. In aqueous suspensions, the Ru(bpy)32+ doped silica nanoparticles exhibited a very good photostability. Irradiated by a 150 W Xenon lamp for an hour, there was no noticeable decrease in the fluorescence intensity of suspended Ru(bpy)32+ doped silica nanoparticles, while obvious photobleaching was observed for the pure Ru(bpy)32+ and R6G molecules. To eliminate the effect from Brownian motion, the authors doped both pure Ru(bpy)32+ and Ru(bpy)32+-doped silica nanoparticles into poly(methyl methacrylate). Under such conditions, both the pure Ru(bpy)32+ and Ru(bpy)32+ doped silica nanoparticles were bleached. However, the photobleaching of pure Ru(bpy)32+ was more severe than that of the Ru(bpy)32+ doped silica nanoparticles. 

Wang YS, Liu B (2007) Silica nanoparticle assisted DNA assays for optical signal amplification of conjugated polymer based fluorescent sensors. Chem Commun 34 3553-3555... 

Wang Y, Liu B (2009) Conjugated polyelectrolyte sensitized fluorescent detection of thrombin in blood serum using aptamer-immobilized silica nanoparticles as the platform. Langmuir 25 12787-12793... 

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...

Santra S, Bagwe RP, Dutta D, Stanley JT, Walter GA, Tan W, Moudgil BM, Meri-cle RA (2005) Synthesis and characterization of fluorescent, radio-opaque, and paramagnetic silica nanoparticles for multimodal hioimaging applications. Adv Mater 17 2165-2169... 

He XX, Duan JH, Wang KM, Tan WH, Lin X, He CM (2004) A novel fluorescent label based on organic dye-doped silica nanoparticles for HepG liver cancer ceU recognition. J Nanosci Nanotechnol 4 585-589... 

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... 

Ye ZQ, Tan MQ, Wang GL, Yuan JL (2004) Novel fluorescent europium chelate-doped silica nanoparticles preparation, characterization and time-resolved fluorometric application. J Mater Chem 14 851-856... 

Fig. 5 Smart UV-responsive coating on silica nanoparticles with PNIPAM brushes functionalized with FRET donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,l,3-benzoxadiazole (NBDAE), and photoswitchable acceptors, l -(2-methacryloxyethyl)-3, 3 -dimethyl-6-nitro-spiro(2//-l-benzo-pyran-2,2 -indoline) (SPMA). The UV radiation induces the change from colorless spiropyran derivatives in the outer part of the coating (7) to the fluorescent merocyanine form (2). Thus, FRET with the benzoxadiazole moieties in the inner part of the coating is enabled and the fluorescence color changes from green to red. By variation of the temperature and induction of a collapse of the PNIPAM chains (3), the FRET efficiency can be tuned (4). Reprinted, with permission, from [70], Copyright (2009) American Chemical Society...

Further progress in the development of sensing systems based on silica nanoparticles was achieved by doping with fluorescent probes. In these systems, the nanoparticles act as transporters delivering the probe across membranes into the cell, thus improving both performance and protection from matrix interferences.19-22 As we will see later, the possibility to confine several probes and dye molecules within the same particle also allows the design of more complex sensing schemes. 

The sensitivity of fluorescence-based assays can hence be greatly improved by the use of dye-doped silica nanoparticles and this approach has been pioneered and subsequently deeply investigated by Tan and coworkers.15 Their luminophore of choice was the water-soluble, positively charged tris(2,2 -bipyridyl)dichlororuthenium(II) [Ru(bpy)3]2+ hydrochloride that can be easily incorporated into silica nanoparticles prepared using the reverse microemulsion method. The charge complementarity between the dye and the silica matrix prevents leaching from the particles.15... 

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