Bouvard Hosticka

Aerogels as biosensors: viral particle detection by bacteria immobilized on large pore aerogel

Abstract A proof-of-principle study is reported in which bacteria were immobilized within macroporous, supercritically dried silica sol–gel discs and signal induction was demonstrated by aerosolized virus particles. Escherischia coli (pET-gfp) bacteria-doped gels were used as an aerosol collector to detect bacteriophage. The bacteriophage (105 and 108 plaque forming units/ml) (pfu/ml) were aerosolized through the discs for 10 min, at a flow rate of 1.75 l/min and aerosol humidity of 70%. The discs were then incubated in bacterial growth media for 4 h and green fluorescent protein (GFP) expression monitored. The induction of GFP indicated that both bacteriophage and bacteria survived the stressful desiccating conditions of the aerosol challenge. Scanning confocal laser microscopic (SCLM) analysis demonstrated that the bacteriophage contacted viable bacteria and induced expression of the GFP in 35–95% of the bacterial cells. These findings indicate that virus particles can penetrate the structure of macroporous silica gels and trigger a detectable response in immobilized bacteria. The goal is to use microorganisms immobilized within these materials to facilitate the detection of chemicals and organisms within the environment.

Cells in Sol-Gels I: A Cytocompatible Route for the Production of Macroporous Silica Gels

A novel, high hydrolysis ratio sol-gel route for the biocompatible production of macroporous silica gels is presented. This route exploits the two step nature of the gelation reaction to remove undesired alcohol by-products from an acidic aqueous sol prior to gelation. These alcohol-free sols will gel when the pH is raised to the physiologic range in a two-step, acid/base catalyzed process. Furthermore, monolithic macroporous samples can be produced in a controlled manner by introducing water-soluble organic polymers into the sol.

Gas flow through aerogels

Abstract Aerogels have an extraordinarily large internal surface area which is accessible via open pores, making them candidates for filters and gas adsorption media. The idea is frequently included in lists of potential applications, but little research has been conducted on the use of aerogels as filters or adsorption media. Consideration of aerogels for use as aerosol collection media requires knowledge of the behavior of gas flow through them. Nitrogen and helium gases at a range of pressures from 6–200 kPa were flowed through aerogel and the flow was shown to be a superposition of molecular diffusion and laminar viscous flow.

Mechanical and acoustical properties as a function of PEG concentration in macroporous silica gels

The pore size of macroporous silica aerogel can be controlled by varying the concentration of water-soluble organic polymers in the sol. These gels demonstrate a wide array of mechanical and acoustical properties in proportion to the organic polymer concentration in the sol. Presented in this paper are the resulting mechanical dependencies upon the concentration of high molecular weight polyethylene glycol (PEG) in the initial sol. Physical properties studied include density, surface area, pore structure, acoustic velocity, and mechanical strength. Most of these properties exhibited a large change when a small concentration of PEG was added to the initial sol, correlating with a strengthening of the solid matrix. Still higher concentrations of PEG progressively weakened the solid matrix. Through examination of the gels containing PEG, experiments have shown an inverse relation of acoustic velocity to PEG concentration while density remains relatively constant.

Towards a microchip-based chromatographic platform. Part 1: Evaluation of sol-gel phases for capillary electrochromatography

Silica monolithic columns suitable for implementation on microchips have been evaluated by ion‐exchange capillary electrochromatography. Two different silica monoliths were created from the alkyl silane, tetramethyl orthosilicate (TMOS), by introducing a water‐soluble organic polymer, poly(ethylene oxide) (PEO), with varying molecular weights into the prehydrolyzed sol. Silica monoliths created using 10 kDa PEO were found to have a much more closed gel structure with a smaller percentage of pores in the νm size range than gels created using 100 kDa PEO. Additionally, the size of the mesopores in the 100 kDa PEO monolith was 5 nm, while those in the 10 kDa PEO gel were only 3 nm. This resulted in a strong dependence of the electroosmotic flow (EOF) on the ionic strength of the background electrolyte, with substantial pore flow through the nm size pores observed in the 10 kDa PEO gel. The chromatographic performance of the monolithic columns was evaluated by ion‐exchange electrochromatography, with ion‐exchange sites introduced via dynamic coating with the cationic polymer, poly(diallyldimethylammonium chloride) (PDDAC). Separating a mixture of inorganic anions, the 10 kDa PEO monolithic columns showed a higher effective capacity than the 100 kDa PEO column.

An experimental investigation of aerosol collection utilizing packed beds of silica aerogel microspheres

Abstract Packed beds of silica aerogel microspheres were used as a collection medium for aerosol particles in the viral and bacterial size range (20–2000 nm). Airflow characteristics were determined by measuring the differential pressure across beds of silica aerogel microspheres as a function of flowrate. These measurements showed a permeability of 2.2×10 −7 cm 2 for the bed of aerogel microspheres. The beds were then used to capture airborne particles in the 20–2000 nm size range. The aerosol collection performance for the test beds was investigated at three flowrates corresponding to face velocities typically encountered in aerosol filtration work. As face velocity was increased from 3.4 to 20 to 40 cm/s it was determined that the minimum collection efficiency went from 93% to 76% to 64%. It was also determined that the aerosol particle size resulting in minimum collection efficiency shifted from 570 to 315 to 300 nm with increasing face velocity. The flow regime determined from the first experiment was used to explain aerosol deposition in the test beds of silica aerogel microspheres.

MICROSCALE THERMAL RELAXATION DURING ACOUSTIC PROPAGATION IN AEROGEL AND OTHER POROUS MEDIA

The longitudinal acoustic velocity in silica aerogel is presented as a function of the interstitial gas type and pressure. This was measured using air-coupled ultrasonic transducers configured for differential pulse transit time measurements. The results are interpreted in terms of the thermal relaxation of the acoustic pulse. The microscale temperature oscillations of the gas and solid phases of the aerogel due to the acoustic pulse are not identical if the rate of heat transfer between the two phases is slow compared to the period of the acoustic oscillation. The energy transferred from the gas to the solid phase is lost to the acoustic propagation and, thus, reduces the amplitude and velocity of the acoustic wave. The gas type and pressure may provide independent variables for probing these effects in aerogel.