Molecular Self-assembly of amphiphilic phospholipid molecules (containing a hydrophobic acyl chain and a hydrophilic phosphate group attached to glycerol backbone) and other amphiphiles offers a versatile approach to form ordered structures. Stabilization of lipid microstructures by polymerization renders them useful for practical applications in the areas ranging from controlled release technology to template mediated synthesis of metals. Our efforts are focussed on the development and use of polymerizable diacetylenic phospholipids and their microstructures as template for chemical synthesis. The surface of vesicles and lipid microcylinders (0.5 µm dia.) is made reactive by chemically modifying the hydrophilic region of phospholipids. Lipids with chemically reactive sites were incorporated into lipid membranes predominantly formed from charge neutral lipids and used for binding metal ions and growing fine metal particles.

The effects of surface imprinting on the adsorption and desorption properties of benzene- and diethylbenzene-bridged periodic mesoporous organosilicas (PMOs) acting as GC stationary-phase preconcentration sorbents for benzene and xylene were examined. Surface-imprinted and nonimprinted PMOs with diethylbenzene (DEB), benzene (BENZ), and ethane (BTSE) bridges and nonimprinted mesoporous silica (MCM-41) were prepared via well-established surfactant templating synthetic methods. The imprinted materials were synthesized using a surfactant demonstrated to produce trinitrotoluene (TNT) selective sorbents with increased adsorption capacity for cresol and 4-nitrophenol as well as TNT. Powder XRD and nitrogen sorption measurements revealed that all of the materials were mesoporous with the DEB materials having a random pore structure and lower surface area than the other materials which had ordered pore structures. Results for maximum uptake of benzene and p-xylene indicate a small but consistent positive effect on the adsorption of benzene and p-xylene due to surface imprinting. Comparing the surface area normalized uptakes (mg/m(2)) for materials having the same organic bridge with and without imprinting (DEB vs TDMI-DEB and BENZ vs TDMI-BENZ) shows that in seven of eight comparisons the imprinted analogue had a higher aromatic uptake. The imprinted samples showed higher weight normalized uptakes (mg/g) in five of eight cases. When used as a GC stationary phase, the organosilica materials yield more symmetrical chromatographic peaks and better separation than MCM-41, indicating superior trapping of BTX analytes, particularly at low concentrations. Additionally, these materials rapidly desorb the preconcentrated compounds.

A displacement immunosensor for the detection of 2,4,6-trinitrotoluene (TNT) using inline integrated microfluidic mixer grooves is demonstrated. The key components of the microfluidic mixer are chevrons and stripes, layered in opposite directions on the top and bottom of the microchannel, to create a turbulent mixing of biomolecules as they migrate through the channel. This mixing phenomenon generates advection patterns that provide increased antibody-antigen interaction resulting in enhanced immunoassay sensitivity. Displacement immunoassays for TNT demonstrated femto-mole detection levels (50 nanograms/liter). Combining sol-gel based chemistry, a microchannel-based immunosensor milled in polymethyl methacrylate (PMMA) and the unique features of a grooved surface offers the potential for a field-portable, ruggedized sensor.

We describe the use of nanoporous organosilicas for rapid preconcentration and extraction of trinitrotoluene (TNT) for electrochemical analysis and demonstrate the effect of template-directed molecular imprinting on TNT adsorption. The relative effects of the benzene (BENZ)- and diethylbenzene (DEB)-bridged organic-inorganic polymers, having narrow or broad pore size distributions, respectively, on electrochemical response and desorption behavior were examined. Sample volumes of 0.5-10 mL containing 5-1000 ppb TNT in a phosphate-buffered saline buffer were preconcentrated in-line before the detector using a microcolumn containing 10 mg of imprinted BENZ or DEB. Square-wave voltammetry was used to detect the first reduction peak of TNT in an electrochemical flow cell using a carbon working electrode and a Ag/AgCl reference electrode. Imprinted BENZ released TNT faster than imprinted DEB with considerably less peak tailing and displayed enhanced sensitivity and an improvement in the limit of detection (LOD) owing to more rapid elution of TNT from that material with increasing signal amplitude. For imprinted BENZ, the slope of signal versus concentration scaled linearly with increasing preconcentration volume, and for preconcentrating 10 mL of sample, the LOD for TNT was estimated to be 5 ppb. Template-directed molecularly imprinted DEB (TDMI-DEB) was 7-fold more efficient in adsorption of TNT from aqueous contaminated soil extract than nonimprinted DEB.

Molecularly imprinted polymers and silica have been studied as receptor binding site mimics for use in a wide range of separation, catalysis, and detection applications employing transduction mechanisms including conductometric, amperometric, and capacitance. Porphyrins are also well known as sensor components due to the extreme sensitivity of their spectrophotometric characteristics to changes in their immediate environment. We have developed periodic mesoporous organosilicas (PMO) which incorporate a porphyrin into the material for use as an optical indicator of target binding. This material combines the stability, selectivity, and high density of binding sites characteristic of the molecularly imprinted PMO with the sensitivity and selectivity of the porphyrin. We demonstrate binding of p-nitrophenol, p-cresol, 2,4,6-trinitrotoluene, and RDX by the porphyrin-embedded PMOs with selective adsorption of TNT over the other analytes. In addition, the binding of each of the organics by the PMO results in unique changes in the spectrophotometric characteristics of the incorporated porphyrin. These changes can be observed by visual inspection or through the use of fluorescence spectra collected in 96-well format.

Surface interactions in molecular recognition of phosphonate imprinted organosilicates and the role of water have been studied. NMR and calorimetry studies have shown the changing nature of the surface water structure on silicate surfaces due to template directed molecular imprinting. Results indicate the interaction of an organophosphonate compound with the functionalized silica surfaces to be through surrounding water molecules. However, with nonfunctionalized surfaces, additional higher energy interactions were possible. Further, our results support the possible templating effect of water during the imprint process.

Benzene, diethylbenzene, and ethylenediamine-bridged bistrialkoxy precursors were used in the synthesis of multifunctional PMO copolymers for the adsorption of phenols and metal ions. Polyoxyethylene(10) stearyl ether (Brij 76) was used as the structure director with the surfactant template approach in the synthesis. The resulting PMO copolymers with two or more bridging groups have been characterized by nitrogen gas adsorption, powder X-ray diffraction, and 13C and 29Si solid-state NMR. These organosilicas exhibit large surface areas, narrow pore size distributions, large total pore volumes, and pore ordering consistent with well ordered, hexagonally packed p6mm structures. Minimal competitive effects were observed on the adsorption of p-chlorophenol to the copolymers in the presence of copper ions in solution. Similarly, the presence of p-chlorophenol in solution or adsorbed onto the copolymers did not interfere with copper adsorption. Replacement of a small portion of the benzene bridge in the 90:10 BENZ:EDA copolymer with diethylbenzene produced a copolymer 2.5-fold more efficient for p-chlorophenol adsorption. ICP analysis revealed that greater than 98% of adsorbed copper was removed during extraction with HCl, and this extraction process can be repeated with no difference in copper adsorption after regeneration.

A synthetic protocol for the preparation of a variety of high-quality periodic mesoporous organosilicas (PMOs) is presented. These nanostructured organosilicas have been synthesized by the acid-catalyzed hydrolysis and condensation of bis(triethoxysilyl) precursors containing different organic bridging groups. Polyoxyethylene(10) stearyl ether (Brij 76) is employed as the structure director using the surfactant template approach. Methylene, ethylene, ethenylene, and phenylene-bridged PMOs have been synthesized. Surfactant extraction is accomplished by refluxing the mesoscopic composite precipitates in acidified ethanol. The resulting PMOs have been characterized by nitrogen gas sorption, powder X-ray diffraction, 13C and 29Si solid-state NMR, and high-resolution thermogravimetric analysis. These organosilicas exhibit large surface areas, narrow pore size distributions, and large total pore volumes. This is the first report of a synthetic protocol with the versatility to make high-quality PMOs containing aliphatic, aromatic, or olefinic carbon functional groups. This versatility is discussed in terms of template and precursor structures under the acidic reaction conditions.

We have investigated the effects of using two different oils, cyclohexane and chloroform, and two different surfactants, nonylphenyl pentaethylene glycol (NP-5) and dimethyldodecylamine oxide (DDAO) in a modified Stöber process for synthesizing silica colloids. Mean particle size was affected by both the oil and the surfactant used, and a significant interaction was also observed between these two factors: DDAO produced larger particles in cyclohexane, and NP-5 produced larger particles in chloroform. Water-to-surfactant and water-to-silicate ratios, as well as volume of oil added, were also observed to affect mean particle size. Only the volume of added oil was determined to affect the size dispersity of particles, with the use of a smaller volume of oil leading to a lower dispersity in particle size.

The effect of the time of addition of organosilanes to silica particle formation reaction mixtures on the resulting surface availability of the added functional groups was investigated. Base catalyzed particle formation was initiated by the addition of tetraethyl orthosilicate (TEOS) to a water-in-oil microemulsion. Subsequently, amine, mono-carboxylate, ethylenediaminetriacetic acid, or dihydroimidazole-terminated organosilanes were added to the microemulsion. Continuous growth in size of monodispersed spherical particles over time was monitored by transmission electron microscopy and light-scattering measurements. Surface primary amine and carboxylate groups on the resulting particles were labeled with fluorescamine and 1-pyrenyldiazomethane (PDAM), respectively, and the effect of varying the time of organosilane addition to the microemulsion was determined by fluorescence spectroscopy. The effect of the time of organosilane addition on surface expression of dihydroimidazole groups was determined using a direct titration method. The results demonstrate that the degree of surface functionalization of the silica particles varied with the time of organosilane addition. For each type of amine terminated organosilane used, the highest surface availability of organo-functional groups was obtained when the organosilane was added 30 min after particle growth was initialized. A progressive decrease in the surface availability of primary amine groups was observed when 3-aminopropyltrimethoxysilane (APTMS) was added later than 30 min after particle formation was initiated. For each type of carboxylate-terminated organosilane used, the highest surface availability of organo-functional groups was obtained when the organosilane was added 5.5 h after particle growth was initialized.