Lewis acid-base interactions enhance explosives sensing in silacycle polymers

The high sensitivity of silole- and silafluorene-containing polymers for detecting organic nitro, nitrate, and nitramine explosives cannot be solely attributed to favorable analyte-polymer hydrophobic interactions and amplified fluorescence quenching due to delocalization along the polymer chain. The Lewis acidity of silicon in conjugated poly(silafluorene-vinylene)s is shown to be important. This was established by examining the29Si NMR chemical shifts (Δ) for the model trimer fragment of the polymer CH3-silafluorene-(trans-C2H2)-silafluorene- (trans-C2H2)-silafluorene-CH3. The peripheral and central silicon resonances are up-field from a TMS reference at -9.50 and -18.9 ppm, respectively. Both resonances shift down-field in the presence of donor analytes and the observed shifts (0 to 1 ppm) correlate with the basicity of a variety of added Lewis bases, including TNT. The most basic analyte studied was acetonitrile and an association constant (Ka) of 0.12 M-1was calculated its binding to the peripheral silicon centers using the Scatchard method. Spin-lattice relaxation times (T1) of 5.86(3) and 4.83(4)s were measured for the methyl protons of acetonitrile in benzene-d6at 20°C in the absence and presence of the silafluorene trimer, respectively. The significant change in T1values further supports a binding event between acetonitrile and the silafluorene trimer. These studies as well as significant changes and shifts observed in the characteristic UV-Vis absorption of the silafluorene group support an important role for the Lewis acid character of Si in polymer sensors that incorporate strained silacycles. The nitro groups of high explosives may act as weak Lewis-base donors to silacycles. This provides a donor-acceptor interaction that may be crucial for orienting the explosive analyte in the polymer film to provide an efficient pathway for inner-sphere electron transfer during the electron-transfer quenching process

Self-assembled Targeting of Cancer Cells by Iron(III)-doped, Silica Nanoparticles.

Iron(III)-doped silica nanoshells are shown to possess an in vitro cell-receptor mediated targeting functionality for endocytosis. Compared to plain silica nanoparticles, iron enriched ones are shown to be target-specific, a property that makes them potentially better vehicles for applications, such as drug delivery and tumor imaging, by making them more selective and thereby reducing the nanoparticle dose. Iron(III) in the nanoshells can interact with endogenous transferrin, a serum protein found in mammalian cell culture media, which subsequently promotes transport of the nanoshells into cells by the transferrin receptor-mediated endocytosis pathway. The enhanced uptake of the iron(III)-doped nanoshells relative to undoped silica nanoshells by a transferrin receptor-mediated pathway was established using fluorescence and confocal microscopy in an epithelial breast cancer cell line. This process was also confirmed using fluorescence activated cell sorting (FACS) measurements that show competitive blocking of nanoparticle uptake by added holo-transferrin

Self-assembled Targeting of Cancer Cells by Iron(III)-doped, Silica Nanoparticles.

Iron(III)-doped silica nanoshells are shown to possess an in vitro cell-receptor mediated targeting functionality for endocytosis. Compared to plain silica nanoparticles, iron enriched ones are shown to be target-specific, a property that makes them potentially better vehicles for applications, such as drug delivery and tumor imaging, by making them more selective and thereby reducing the nanoparticle dose. Iron(III) in the nanoshells can interact with endogenous transferrin, a serum protein found in mammalian cell culture media, which subsequently promotes transport of the nanoshells into cells by the transferrin receptor-mediated endocytosis pathway. The enhanced uptake of the iron(III)-doped nanoshells relative to undoped silica nanoshells by a transferrin receptor-mediated pathway was established using fluorescence and confocal microscopy in an epithelial breast cancer cell line. This process was also confirmed using fluorescence activated cell sorting (FACS) measurements that show competitive blocking of nanoparticle uptake by added holo-transferrin

Mechanically Tunable Hollow Silica Ultrathin Nanoshells for Ultrasound Contrast Agents.

Perfluoropentane (PFP) gas filled biodegradable iron-doped silica nanoshells have been demonstrated as long-lived ultrasound contrast agents. Nanoshells are synthesized by a sol-gel process with tetramethyl orthosilicate (TMOS) and iron ethoxide. Substituting a fraction of the TMOS with R-substituted trialkoxysilanes produces ultrathin nanoshells with varying shell thicknesses and morphologies composed of fused nanoflakes. The ultrathin nanoshells had continuous ultrasound Doppler imaging lifetimes exceeding 3 hours, were twice as bright using contrast specific imaging, and had decreased pressure thresholds compared to control nanoshells synthesized with just TMOS. Transmission electron microscopy (TEM) showed that the R-group substituted trialkoxysilanes could reduce the mechanically critical nanoshell layer to 1.4 nm. These ultrathin nanoshells have the mechanical behavior of weakly linked nanoflakes but the chemical stability of silica. The synthesis can be adapted for general fabrication of three-dimensional nanostructures composed of nanoflakes, which have thicknesses from 1.4-3.8 nm and diameters from 2-23 nm

Mechanically Tunable Hollow Silica Ultrathin Nanoshells for Ultrasound Contrast Agents.

Perfluoropentane (PFP) gas filled biodegradable iron-doped silica nanoshells have been demonstrated as long-lived ultrasound contrast agents. Nanoshells are synthesized by a sol-gel process with tetramethyl orthosilicate (TMOS) and iron ethoxide. Substituting a fraction of the TMOS with R-substituted trialkoxysilanes produces ultrathin nanoshells with varying shell thicknesses and morphologies composed of fused nanoflakes. The ultrathin nanoshells had continuous ultrasound Doppler imaging lifetimes exceeding 3 hours, were twice as bright using contrast specific imaging, and had decreased pressure thresholds compared to control nanoshells synthesized with just TMOS. Transmission electron microscopy (TEM) showed that the R-group substituted trialkoxysilanes could reduce the mechanically critical nanoshell layer to 1.4 nm. These ultrathin nanoshells have the mechanical behavior of weakly linked nanoflakes but the chemical stability of silica. The synthesis can be adapted for general fabrication of three-dimensional nanostructures composed of nanoflakes, which have thicknesses from 1.4-3.8 nm and diameters from 2-23 nm