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A fresh generation of silica encapsulated single quantum dots (QDs) was

A fresh generation of silica encapsulated single quantum dots (QDs) was synthesized based on recent breakthroughs made in coating magnetic nanoparticles and their clusters. engineers PCPTP1 over the past two decades due to their fascinating optical and electronic properties that are not available from either isolated molecules or bulk solids. Recent research has stimulated considerable interest in developing these quantum-confined nanocrystals as fluorescent probes for biomedical applications.1-3 In comparison with organic dyes and fluorescent proteins, QDs offer several unique advantages such as size- and composition-tunable emission from ultraviolet to infrared wavelengths, large absorption coefficients across a wide spectral range, and very high degrees of brightness and photostability. Because of their wide excitation profiles and narrow/symmetric emission spectra, high-quality QDs are also perfect for combinatorial optical encoding, where ARRY-438162 distributor multiple shades and intensities are mixed to encode a large number of genes, proteins, or small-molecule compounds.4-6 High-quality QDs are usually prepared at elevated temperature ranges in organic solvents, such as for example tri-n-octylphosphine oxide and ARRY-438162 distributor hexadecylamine (TOPO and HDA, both which are high boiling-stage solvents containing longer alkyl chains). These hydrophobic organic molecules not merely serve because the reaction mass media, but also coordinate with unsaturated steel atoms on the QD surface area to avoid formation of mass semiconductors. Because of this, the nanoparticles are capped with a monolayer of the organic ligands and so are soluble just in organic solvents such as for example chloroform and toluene. For biological applications, these hydrophobic dots are created water-soluble generally by three techniques, ligand exchange, silica shell capping, and the lately created amphiphilic polymer covering. The ligand exchange strategy is simple to perform, however the resulting water-soluble QDs are just steady for ARRY-438162 distributor a brief period and its own quantum yield reduces significantly,7 as the first hydrophobic surface area ligands are changed by hydrophilic ligands such as for example mercaptoacetic acid. The recently uncovered amphiphilic polymer covering strategy solved these complications by retaining the coordinating organic ligands on the QD surface area.8 Typically, amphiphilic polymers include both a hydrophobic segment or side-chain (mostly hydrocarbons) and a hydrophilic segment or group (such as for example polyethylene glycol or multiple carboxylate groupings). Several polymers have already been reported which includes octylamine-altered low molecular fat polyacrylic acid, polyethylene glycol (PEG) derivatized phospholipids, block copolymers, and polyanhydrides.9-12 The hydrophobic domains strongly connect to TOPO on the QD surface area, whereas the hydrophilic groupings encounter outward and render QDs drinking water soluble. Even though amphiphilic polymer covering represents the most recent addition to the region of QD surface area engineering and will be offering several advantages, silica shell capping continues to be as a stylish strategy for QD solublization because of its balance, biocompatibility, and flexible surface chemistry. Moreover, the top coating thickness can be precisely controlled in the range of 1-100s nm, which is hard, if not impossible, to achieve based on the ligand exchange and amphiphilic polymer coating methods. A number of papers have reported the successful encapsulation of QDs with silica, and the methods can be grouped into two general groups, St?ber sol-gel chemistry and microemulsion.13-22 For example, one of the earliest papers on the biological applications of silica capped QDs was reported by Alivisatos and co-workers.14 Although it demonstrates the potential of using QDs for multicolor cell labeling, the silica capping process itself is complicated and prone to formation of QD aggregates. Recently, a breakthrough process on coating magnetic nanoparticles (MNPs) and their clusters with mesoporous ARRY-438162 distributor silica was developed by Hyeon em et al. /em 23, 24 In comparison with the St?ber and microemulsion methods, the surfactant templated mesoporous silica coating is simple, high-yield, and capable of tuning the silica shell thickness, yielding QDs with excellent optical properties and biocompatibility. MATERIALS AND METHODS Reagents and instruments Unless specified, chemicals were purchased from Sigma-Aldrich (St. Louis, MO) and used without further purification. TOPO coated CdSe/ZnS core/shell QDs were provided by Oceannanotech LLC as a gift. Methoxy poly(ethylene glycol) succinimidyl glutarate (MW 2000) was purchased from Laysan Bio, Inc. (Arab, AL). A UV-2450 spectrophotometer (Shimadzu, Columbia, MD) and a Fluoromax4 fluorometer (Horiba Jobin Yvon, Edison, NJ) were used to characterize the absorption and emission spectra of the original and modified QDs. The dry and hydrodynamic radii of QDs were measured on a CM100 transmission electron microscope (Philips EO, Netherlands) and a Zetasizer NanoZS size analyzer (Malvern, Worcestershire, UK). True-color fluorescence images were obtained with a Nikon digital camera. Synthesis of mesoporous silica coated QDs The synthesis of mesoporous silica coated QDs was developed based on the MNP encapsulation protocols explained by Hyeon em et al /em .23, 24 Briefly, for approximately 20 nm-thick silica coating, 3.0 M CdSe/ZnS QDs (emission peak 622nm) in 0.5 ml chloroform was mixed with 5 ml cetyltrimethylammonium.