Measurements of Acetone Fluorescence and Phosphorescence at High Pressures and Temperatures
Laser-induced fluorescence and phosphorescence signals of liquid acetone at pressures from 1 to 15 atm were measured and analyzed. Liquid acetone, which was preprocessed to minimize any dissolved oxygen, was injected as a low velocity jet into a pressurized chamber with either an air or nitrogen co-flow. The actone was excited at 266 nm. The laser-induced fluorescence intensity from the liquid was found to be invariant with pressure and co-flow conditions. The measured phosphorescence lifetimes were also found to independent of pressure, for both nitrogen and air environments. The phosphorescence lifetime for the liquid was measured to be ~1 μs, which is significantly smaller than the lifetime for acetone vapor (200 μs). This is likely due to self-quenching by acetone. The effect is further seen in the phosphorescence to fluorescence (P/F) ratio comparison between the liquid and vapor. The P/F ratio for liquid is 0.012, which is much smaller than the vapor value of 9.0. The overall phosphorescence intensities, however, were seen to decrease in the air co-flow cases compared to the nitrogen co-flow. Diffusion of oxygen into the liquid jet was observed, and the estimated concentration was found to be a few orders of magnitude less than the saturated concentration.
Investigation of laser induced phosphorescence and fluorescence of acetone at low pressure for molecular tagging velocimetry in gas microflows
Laser-induced fluorescence and phosphorescence properties of gaseous acetone in argon are measured and analyzed in a pressure ranging from 10 to 10 Pa, with the aim of analyzing by molecular tagging velocimetry gas microflows in rarefied regimes which requires operation at low pressure. Acetone is excited at a wavelength of 266 nm and immediately emits short lifetime fluorescence rapidly followed by long lifetime phosphorescence. At atmospheric pressure, the early phosphorescence intensity is more than 600 times lower than the fluorescence one. The phosphorescence signal is rapidly decreasing with time, closely following a power law. Both fluorescence and phosphorescence signals are decreasing with pressure. The systematic analysis of fluorescence and phosphorescence of acetone molecules shows that although the signal is dramatically reduced at low pressure, the on-chip integration technique and the optimization of the acquisition parameters provide an exploitable signal for molecular tagging velocimetry in rarefied microflows, in a Knudsen number range corresponding to the early slip flow regime.
Mucoadhesive Nanoparticles for Drug Delivery to the Anterior Eye
While the use of topical drops for the delivery of drugs to the anterior of the eye is well accepted, it is far from efficient with as little as 5% of the drug instilled on the eye actually reaching the target tissue. The ability to prolong the residence time on the eye is desirable. Based on the acceptability of 2-hydroxyethyl methacrylate based polymers in contact lens applications, the current work focuses on the development of a poly(2-hydroxyethyl methacrylate (HEMA)) nanoparticle system. The particles were modified to allow for degradation and to permit mucoadhesion. Size and morphological analysis of the final polymer products showed that nano-sized, spherical particles were produced. FTIR spectra demonstrated that the nanoparticles comprised poly(HEMA) and that 3-(acrylamido)phenylboronic acid (3AAPBA), as a mucoadhesive, was successfully incorporated. Degradation of nanoparticles containing N,N′-bis(acryloyl)cystamine (BAC) after incubation with DL-dithiothreitol (DTT) was confirmed by a decrease in turbidity and through transmission electron microscopy (TEM). Nanoparticle mucoadhesion was shown through an in-vitro zeta potential analysis.