Development and characterization of fluorescent pH sensors based on porous silica and hydrogel support matrices

The hydrogen ion activity (pH) is a very important parameter in environment monitoring, biomedical research and other applications. Optical pH sensors have several advantages over traditional potentiometric pH measurement, such as high sensitivity, no need of constant calibration, easy for miniaturization and possibility for remote sensing. Several pH indicators has been successfully immobilized in three different solid porous materials to use as pH sensing probes. The fluorescent pH indicator fluorescein-5-isothiocyanate (FITC) was covalently bound onto the internal surface of porous silica (pore size ~10 nm) and retained its pH sensitivity. The excited state pK* a of FITC in porous silica (5.58) was slightly smaller than in solution (5.68) due to the free silanol groups (Si-OH) on the silica surface. The pH sensitive range for this probe is pH 4.5 - 7.0 with an error less than 0.1 pH units. The probe response was reproducible and stable for at least four month, stored in DI water, but exhibit a long equilibrium of up to 100 minutes. Sol-gel based pH sensors were developed with immobilization of two fluorescent pH indicators fluorescein-5-(and-6)-sulfonic acid, trisodium salt (FS) and 8-hydroxypyrene- 1,3,6-trisulfonic acid (HPTS) through physical entrapment. Prior to immobilization, the indicators were ion-paired with a common surfactant hexadecyltrimethylammonium bromide (CTAB) in order to prevent leaching. The sol-gel films were synthesized through the hydrolysis of two different precursors, ethyltriethoxysilane (ETEOS) and 3- glycidoxypropyltrimethoxysilane (GPTMS) and deposited on a quartz slide through spin coating. The pK a of the indicators immobilized in sol-gel films was much smaller than in solutions due to silanol groups on the inner surface of the sol-gel films and ammonium groups from the surrounding surfactants. Unlike in solution, the apparent pK a of the indicators in sol-gel films increased with increasing ionic strength. The equilibrium time for these sensors was within 5 minutes (with film thickness of ~470 nm). Polyethylene glycol (PEG) hydrogel was of interest for optical pH sensor development because it is highly proton permeable, transparent and easy to synthesize. pH indicators can be immobilized in hydrogel through physical entrapment and copolymerization. FS and HPTS ion-pairs were physically entrapped in hydrogel matrix synthesized via free radical initiation. For covalent immobilization, three indicators, 6,8-dihydroxypyrene-1,3- disulfonic acid (DHPDS), 2,7-dihydroxynaphthalene-3,6-disulfonic acid (DHNDS) and cresol red were first reacted with methacrylic anhydride (MA) to form methacryloylanalogs for copolymerization. These hydrogels were synthesized in aqueous solution with a redox initiation system. The thickness of the hydrogel film is controlled as ~ 0.5 cm and the porosity can be adjusted with the percentage of polyethylene glycol in the precursor solutions. The pK a of the indicators immobilized in the hydrogel both physically and covalently were higher than in solution due to the medium effect. The sensors are stable and reproducible with a short equilibrium time (less than 4 minutes). In addition, the color change of cresol red immobilized hydrogel is vivid from yellow (acidic condition) to purple (basic condition). Due to covalently binding, cresol red was not leaching out from the hydrogel, making it a good candidate of reusable pH paper

固定床カラムの浸透モデルの改良及びそれに対応するパラメータの物理的意味の洞察

筑波大学 (University of Tsukuba)201

Screening of oleaginous yeast with xylose assimilating capacity for lipid and bio-ethanol production

Microbial oil is a promising new biodiesel resource, which have great potential in industrial-scale production. In our preliminary study, 57 oleaginous yeast with xylose assimilating capacity were isolated from 13 soil samples, 16 strains were identified as potential lipid biomass producer. Four strains which showed higher lipid content were used for further ethanol fermentation at different conditions. Strain 9-44 belonging to Pichia guillermondii showed the highest ethanol production (21.91 g/l), and the theoretical ethanol yield was 85.90%. Our study will be of great significance for coupling of lipid and bio-ethanol production, and also provide a choice of cellulocis biomass utilization.Key words: Microbial oil, oleaginous yeast, Pichia guillermondii, bio-ethanol, cellulocis biomass

Electrically empowered microcomb laser

Optical frequency comb underpins a wide range of applications from communication, metrology, to sensing. Its development on a chip-scale platform -- so called soliton microcomb -- provides a promising path towards system miniaturization and functionality integration via photonic integrated circuit (PIC) technology. Although extensively explored in recent years, challenges remain in key aspects of microcomb such as complex soliton initialization, high threshold, low power efficiency, and limited comb reconfigurability. Here we present an on-chip laser that directly outputs microcomb and resolves all these challenges, with a distinctive mechanism created from synergetic interaction among resonant electro-optic effect, optical Kerr effect, and optical gain inside the laser cavity. Realized with integration between a III-V gain chip and a thin-film lithium niobate (TFLN) PIC, the laser is able to directly emit mode-locked microcomb on demand with robust turnkey operation inherently built in, with individual comb linewidth down to 600 Hz, whole-comb frequency tuning rate exceeding $\rm 2.4\times10^{17}$ Hz/s, and 100% utilization of optical power fully contributing to comb generation. The demonstrated approach unifies architecture and operation simplicity, high-speed reconfigurability, and multifunctional capability enabled by TFLN PIC, opening up a great avenue towards on-demand generation of mode-locked microcomb that is expected to have profound impact on broad applications

Kinetic studies for nitrate adsorption on granular chitosan–Fe(III) complex

<p>In this study, a generalized kinetic equation was proposed to simulate adsorption behaviors in batch systems and several useful kinetic equations were deduced. The results indicated that the amount of nitrate uptake increased rapidly in the initial stage, followed by a slower process until adsorption equilibrium was reached after approximately 1.5 h. The rate constant was a function of the initial nitrate concentration. The adsorption and desorption rate constants quantitatively reflected the adsorption and desorption reactions at the solid/solution interface. The adsorption and desorption processes for nitrate adsorption followed identical reaction order. The kinetic parameters (adsorption and desorption rate constants, half-time and instantaneous rate) provided by these kinetic equations are of significant importance for the understanding of adsorption mechanisms.</p

Implementation of porous silicon technology for flow-through sensing using electro-osmotic phenomenon

A demonstration of pH sensing for natural waters using nanoscaled porous media and electro-osmotic flow sampling has been performed. This paper presents an innovative integration of sensing and nano-scaled fluidic actuation in the combination of pH sensitive optical dye immobilization with the electro-osmotic phenomena in polar solvents like water. Through wafer nano-scaled porous silicon and porous silica membranes have been demonstrated as porous media and template for high density fluorescence measurements on optical dyes

Susceptibility of Ureaplasma urealyticum to Methylene Blue-Mediated Photodynamic Antimicrobial Chemotherapy: An invitro Study

The aim of this study was to detect the susceptibility of Ureaplasma urealyticum to methylene blue-mediated photodynamic antimicrobial chemotherapy (PACT). Three U.urealyticum strains including the standard serotype 1 and 5, and a clinically collected strain were used in this study. Strains were first incubated in 96-well culture plates in the presence of methylene blue with decreasing concentrations (from 1 to 0.015625mgmL(-1)) for 20 or 60min, and then submitted to irradiation with a light-emitting diode laser with a power density of 100mWcm(-2) for 8, 17, 34 or 68min. Regrowth of the strains was performed soon after irradiation. A significant inactivation effect was observed after PACT. Longer incubation time induced more extensive inactivation of U.urealyticum. No difference in response to PACT was observed between the two biovars of U.urealyticum. It was concluded that PACT had a significant inactivation effect on U.urealyticum, and it might be a promising alternative treatment for resistant U.urealyticum infections