Optimisation of Sol-Gel-Derived Silica Films for Optical Oxygen Sensing

Sol-gel-derived silica films were fabricated by dip-coating onto planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence is quenched in the presence of oxygen. The structure and behaviour of sol-gel films is related to the fabrication parameters. In order to optimise the films for oxygen sensing in gaseous and in aqueous media, the quenching behaviour was monitored as a function of dip-speed and water: precursor ratio. By adjusting the above parameters, film properties can be tailored to optimise oxygen quenching in particular concentration ranges and environments.     

Optical Aspartame Biosensor Based on Bienzyme Immobilisation on Egg Shell Membrane

Aspartame is a widely used artificial sweetener in many low calorie foods and beverages. Determination of its concentration in foodstuff is important as aspartame is a relatively expensive material. A novel optical biosensor for the determination of aspartame in beverage based on a bienzyme system is presented. An aspartame biosensor was fabricated employing a bienzyme system composed of chymotrypsin and alcohol oxidase immobilised onto a egg shell membrane and an oxygen-sensitive optode membrane as the transducer. The detection schemes involve the enzymatic reactions of aspartame leading to the depletion of oxygen level of the medium with concomitant enhancement of the fluorescence intensity of the oxygen-sensitive membrane.     

Supramolecular Crowding Can Avoid Oxygen Quenching of Photon Upconversion in Water

A common challenge in chemistry that deals with photoexcited states is to avoid oxygen quenching. This is crucial for hot research fields such as photon upconversion (UC), in which oxygen-sensitive triplet excited states play pivotal roles. However, methods to avoid oxygen quenching in aqueous media are far more limited despite eagerly anticipated catalytic and biological applications. This work introduces a simple strategy to achieve air-stable triplet–triplet annihilation (TTA)-based UC in water, namely, supramolecular crowding. Amphiphilic cationic acceptor molecules and anions with long alkyl chains co-assemble in water in which hydrophobic donor molecules are molecularly dispersed. Despite the common notion that oxygen molecules diffuse readily across hydrophobic domains in water, more than 80 % of the TTA-UC emission of the obtained hydrophobic co-assemblies is maintained in air-saturated water. This work demonstrates the new promising potential of supramolecular chemistry for photophysical and photochemical functions with oxygen-sensitive species.     

Polarization-based oxygen sensor

A new approach to oxygen sensing based on the luminescence polarization observed from a novel type of sensor is described. The oxygen sensor consists of an oxygen-sensitive silicone film containing tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) chloride [Ru(dpp)3Cl2] and an oxygen-insensitive film of Styryl 7 in poly(vinyl alcohol). Polarizers are used to select orthogonally polarized emission components from Ru(dpp)3Cl2 and Styryl 7. The polarization of the combined emission was found to be highly sensitive to the partial pressure of oxygen. This method of polarization sensing is generic and can be used with any fluorophore which displays an analyte-dependent change in intensity.     

Optical oxygen sensor based on fluorescence change of pyrene-1-butyric acid chemisorption film on an anodic oxidation aluminium plate

An optical oxygen-sensing material based on the fluorescence intensity changes of pyrene-1-butyric acid (PBA) chemisorption film has been developed and characterised. The fluorescence intensity of PBA film decreased with increase of oxygen concentration. The I₀/I₁₀₀ value of PBA film is estimated to be 6.14±0.15 and large Stern-Volmer constant (K_SV=0.028±0.13 Torr⁻¹) is obtained. After irradiation for 24 h with 150 W tungsten lamp, little changes of oxygen-sensing properties were observed. These results indicate that PBA film is highly oxygen-sensitive and photostability device. The response times of the PBA chemisorption film were 10.0 s for switching from argon to oxygen, and 53.0 s for switching from oxygen to argon. Moreover, the optical sensor based on the PBA chemisorption film was applied to the measurement of oxygen concentration in aqueous solution.     

Dual optical sensor for oxygen and temperature based on the combination of time domain and frequency domain techniques

In measuring specific conditions in the real world, there are many situations where both the oxygen concentration and the temperature have to be determined simultaneously. Here we describe a dual optical sensor for oxygen and temperature that can be adapted for different applications. The measurement principle of this sensor is based on the luminescence decay times of the oxygen-sensitive ruthenium complex tris-4,7-diphenyl-1,10-phenanthroline ruthenium(III) [Rudpp] and the temperature-sensitive europium complex tris(dibenzoylmethane) mono(5-amino-1,10-phenanthroline)europium(III) [Eudatp]. The excitation and emission spectra of the two luminophores overlap significantly and cannot be discriminated in the conventional way using band pass filters or other optical components. However, by applying both the frequency and time domain techniques, we can separate the signals from the individual decay time of the complexes. The europium complex is entrapped in a poly(methyl methacrylate) (PMMA) layer and the ruthenium complex is physically adsorbed on silica gel and incorporated in a silicone layer. The two layers are attached to each other by a double sided silicone based tape. The europium sensing film was found to be temperature-sensitive between 10 and 70 °C and the ruthenium oxygen-sensitive layer can reliably measure between 0 and 21% oxygen.     

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance spectroscopy for in situ monitoring

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance (SPR) for refractive index (RI) measurements of aqueous and hydrothermal water solutions are described. Accurate measurement of RIs is essential to efficient operation and control of broad range of engineering processes. Some of these processes are carried out with harsh environments, such as high-temperature, high pressure, and chemical corrosion. These extreme physical conditions are proving a limiting factor in application of the conventional silica-based optical sensors. Single-crystal sapphire is an ideal material for sensor applications, where reliable performance is required in the extreme environment conditions. With regard to the liquid species detection, most applications of SPR sensors are designed to function near the refractive index of water (1.3330 RI). The RI changes of aqueous solution can be easily monitored by silica-fiber (RI, 1.4601 at 550 nm) based SPR sensor. However, the sapphire waveguide has a prohibitively high RI (1.7708 at 546 nm) for unmodified monitoring of the RI changes of aqueous solutions. For that purpose, a practical SPR probe geometry has been applied to the ability to tune the SPR coupling wavelength/angle pair with sapphire-fiber based SPR probe.     

乳液引起的Daniell电池中的电化学振荡

由油酸的煤油溶液与NaOH和CTAB两水溶液混合制成O/W型乳液.实验发现,此乳液的加入可使丹尼尔电池产生电池反应与电极反应的明显振荡现象.自发过程结束后,通以2 V, 50 Hz或100 Hz交流电4 h,则此电池反应可形成可逆振荡.由表面活性剂对电极表面的吸附和乳液结构变化解释了振荡机理.乳液混合能参与了此电化学反应.     

界面膜引发的乳化燃油燃烧中的振荡反应

有关小分子醇、H。和CO等易燃气体在铂催化下的高温燃烧的温度振荡及以表面活性剂为关键组分的液膜扩散振荡已有报道"－'－．但由界面膜作用而产生的乳化燃油燃烧中的振荡反应尚无其它可操作的原始研究文献,只是在前文［'j中提及过出现该现象．为了解乳化燃油燃烧过程中界面变化及其对燃烧的作用,通过静态燃烧实验配方的调节及变换以改变燃烧界面的情况．实验发现,在乳化燃油中加入一般的食用豆油,并使之水解出长链竣酸盐,则富集在燃烧界面上的长链竣酸盐所形成的界面膜对燃烧的自阻抑作用便会产生明显的振荡反应,形成火焰温度与高…     

用热聚法固定指示剂的光纤氧气传感器研究

采用热聚法将甲叉双丙烯酰胺（MBBA）聚合并共价交联在硅烷化的玻璃微珠上 ，同时将指示剂Ru（Ⅱ）-邻啡咯啉配合物物理包埋于聚合物中，研制了一种基于 荧光猝灭原理的光纤氧气传感器，采用NaHSO_3-O_2-MnSO_4体系引发MBBA水溶液热 聚合后应，通过确定NaHSO_3,MnSO_4,MBBA和Ru(phen)_3Cl_2的最佳反应浓度以及 玻璃微珠的尺寸，优化了聚合反应条件，改善了指示剂的固定效果，制备了性能较 好的传感器探头，该传感器的检测下限为5×10~(-6)(V/V)，响应时间为10s该传感 器连续工作50min,重复性标准偏差为±1%。     

Contribution to the Achievement of a New Type of Electrochemical Sensor for Oxygen,Based on Electrolyte in Non-Aqueous Medium

Abstract

A new type of amperometric sensor for oxygen, having a O. 1M solution of LiCl in ethanol as internal electrolyte, was developed

The response characteristics of this sensor have been improved in comparison with similer sensors based on internal electrolyte in aqueous media, reported in literature. Preliminary results on the response characteristics of the new sensor are reported.     

Study of mass transfer in oil-water-oil multiple emulsions by differential scanning calorimetry

A multiple emulsion of the type O1/W/O2 is studied experimentally by means of differential scanning calorimetry (DSC). The aim of this work is to characterize and measure the time-dependent changes within the emulsion. In particular, interest is focused to quantify the concentration changes in the internal and external phases of the O1/W/O2 multiple emulsion. In order to accomplish the objective, the measurement and analysis carried out by DSC are based on the crystallization behavior of the emulsion. A volume of a few mm3 is periodically removed from the O1/W/O2 multiple emulsion. The sample is submitted to steady cooling and the crystallization thermogram is recorded. The experimental data provided by the crystallization thermogram makes it possible to quantify the crystallized mass for both phases, the internal and the external. In addition, the composition in each phase can also be deduced from the thermogram. To deduce the composition, a diagram of crystallization temperatures is elaborated, employing several mixtures of known composition. In addition to the main objective previously mentioned, the influence of formulation parameters such as surfactant concentration in the aqueous phase and the mass ratio of the internal and external phases are also analyzed. The experimental results made it possible to conclude that a mass transfer took place from the internal phase toward the external phase; this transfer is caused by the composition difference on both sides of the aqueous membrane. In this work we analyzed the mass transfer in the multiple emulsion carried out by a composition gradient through the aqueous membrane. The most likely mechanism of mass transfer through the aqueous membrane is a solution-diffusion of tetradecane enhanced by the micelles of the surfactant Tween 20. The model of mass transfer confirms that the osmotic pressure difference controls the kinetics of tetradecane transfer. It is also confirmed that an increment of surfactant concentration in the aqueous phase allows a faster kinetics of the tetradecane transfer.     

含长链不饱和酯基的三官能度溶胶-凝胶薄膜制备及发光氧气传感的研究

采用溶胶-凝胶法制备了含发光三吡啶钌[Ru(bpy)₃²⁺]分子的三官能度硅氧烷预聚液,并通过旋转涂敷及凝胶处理制备了高性能的薄膜,探讨了载体的微结构和发光分子的微环境效应。与传统的四官能度正硅酸乙酯(TEOS)/Ru(bpy)₃²⁺膜体系相比,含长链不饱和酯基的甲基丙烯酸丙酯基三甲氧基硅烷(PMA-TMS)/Ru(bpy)₃²⁺体系具有成膜性能好,气体的猝灭响应值高,响应时间短等特点。     

Generation of oxygen gradients in microfluidic devices for cell culture using spatially confined chemical reactions

This paper reports a microfluidic device capable of generating oxygen gradients for cell culture using spatially confined chemical reactions with minimal chemical consumption. The microfluidic cell culture device is constructed by single-layer polydimethylsiloxane (PDMS) microfluidic channels, in which the cells can be easily observed by microscopes. The device can control the oxygen gradients without the utilization of bulky pressurized gas cylinders, direct addition of oxygen scavenging agents, or tedious gas interconnections and sophisticated flow control. In addition, due to the efficient transportation of oxygen within the device using the spatially confined chemical reactions, the microfluidic cell culture device can be directly used in conventional cell incubators without altering their gaseous compositions. The oxygen gradients generated in the device are numerically simulated and experimentally characterized using an oxygen-sensitive fluorescence dye. In this paper, carcinomic human alveolar basal epithelial (A549) cells have been cultured in the microfluidic device with a growth medium and an anti-cancer drug (Tirapazamine, TPZ) under various oxygen gradients. The cell experiment results successfully demonstrate the hyperoxia-induced cell death and hypoxia-induced cytotoxicity of TPZ. In addition, the results confirm the great cell compatibility and stable oxygen gradient generation of the developed device. Consequently, the microfluidic cell culture device developed in this paper is promising to be exploited in biological labs with minimal instrumentation to study cellular responses under various oxygen gradients.     

Dual emission probe for luminescence oxygen sensing: a critical comparison between intensity, lifetime and ratiometric measurements

The characterization of a dual emission sensing luminescence material for water-dissolved oxygen sensing is presented in this paper. The oxygen-sensitive material is based on a dual-emitting luminescent molecule immobilized onto an adequate solid support. The metal chelate formed between the 8-hydroxy-7-iodo-5-quinolinesulphonic acid (Ferron) and aluminium (Al-Ferron) was the selected oxygen-sensitive dual-emitting luminescent complex, while the anionic exchanger Dowex 1X2-200 resin was the selected solid support.When the Al-ferron metal chelate is adsorbed onto the anionic exchanger resin it displays two largely different emission bands. The first is a fluorescence emission band, possessing a decay time in the nanosecond range, and which is insensitive to the oxygen presence (the “reference” signal). The second emission is a long-lived highly sensitive oxygen-quenchable phosphorescent emission. Under some optimised experimental conditions both emissions can be simultaneously measured when the metal chelate is excited with a 390 nm light. Under these conditions, and using the same experimental set-up, oxygen concentration can be obtained by measuring the intensity of the phosphorescent emission, the triplet lifetime of the phosphorescence emission or the ratio between the intensity of the phosphorescence emission and the self-reference signal (fluorescence emission from the immobilized metal chelate).The reliability, the operational characteristics, the stability and the analytical performance characteristics for water-dissolved oxygen sensing are evaluated and critically compared for each measurement principle. Advantages and disadvantages of each measurement scheme for reliable optical sensing will be finally discussed.     

Design of double emulsions by osmotic pressure tailoring

A method was developed allowing in situ adjustment of water-in-oil-in-water double emulsion (W/O/W) morphologies by tailoring the osmotic pressure of the water phases. The control of internal droplet size is achieved by altering the chemical potential of the external and internal water phases by dissolving neutral linear polysaccharides of suitable molecular weights. As a consequence of the different chemical potentials in the two aqueous phases, transport of water takes place modifying the initial morphology of the double emulsion. Self-diffusion 1H nuclear magnetic resonance (1H NMR) was used to assess transport mechanisms of water in oil, while a numerical model was developed to predict the swelling/shrinking behavior of W/O/W double emulsions. The model was based on a two-step procedure in which the equilibrium size of a single internal water droplet was first predicted and then the results of the single droplet were extended to the entire double emulsion. The prediction of the equilibrium size of an internal droplet was derived by the equalization of the Laplace pressure with the osmotic pressure difference of the two aqueous phases, as modeled by mean-field theory. The double emulsion equilibrium morphologies were then predicted by upscaling the results of a single drop to the droplet size distribution of the internal W/O emulsion. Good agreement was found between the theoretical predictions and the measurement of double emulsion droplet size distribution. Therefore, the present model constitutes a valuable tool for in situ control of double emulsion morphology and enables new possible applications of these colloidal systems.     

Visible light induced photoelectrochemical biosensing based on oxygen-sensitive quantum dots

A visible light induced photoelectrochemical biosensing platform based on oxygen-sensitive near-infrared quantum dots (NIR QDs) was developed for detection of glucose. The NIR QDs were synthesized in an aqueous solution, and characterized with scanning electron microscopy and X-ray photoelectron spectroscopy. The as-prepared NIR QDs were employed to construct oxygen-sensitive photoelectrochemical biosensor on a fluorine-doped tin oxide (FTO) electrode. The oxygen dependency of the photocurrent was investigated at as-prepared electrode, which demonstrated the signal of photocurrent is suppressed with the decreasing of oxygen. Coupling with the consumption of oxygen during enzymatic reaction, a photoelectrochemical strategy was proposed for the detection of substrate. Using glucose oxidase (GOx) as a model enzyme, that is, GOx was covalently attached to the surface of CdTe QDs, the resulting biosensor showed the sensitive response to glucose. Under the irradiation of visible light of a wavelength at 505 nm, the proposed photoelectrochemical method could detect glucose ranging from 0.1 mM to 11 mM with a detection limit of 0.04 mM. The photoelectrochemical biosensor showed a good performance with high upper detection limit, acceptable stability and accuracy, providing an alternative method for monitoring biomolecules and extending the application of near-infrared QDs.     

Hydroxyapatite nanoparticles as stimulus-responsive particulate emulsifiers and building block for porous materials

Hydroxyapatite (HAp) nanoparticles with spherical, rod-shaped or fiber-shaped morphologies were synthesized by wet chemical method in aqueous media. Scanning electron microscopy, dynamic light scattering, helium pycnometry, and aqueous electrophoresis techniques were used to characterize the nanoparticles in terms of their particle size and morphology, density and zeta potential, respectively. Stable "Pickering-type" emulsions were prepared using the HAp nanoparticles as a particulate emulsifier and methyl myristate as an oil phase above pH 7.7, but not below pH 6.1. These emulsions were characterized in terms of their emulsion type, mean droplet diameter and morphology using electrical conductivity, light diffraction and optical microscopy. Rapid demulsification could be induced by lowering the solution pH: addition of acid led to dissolution of the HAp nanoparticles attached on oil-water interface and the emulsion was destabilized. HAp nanoparticles precipitated by addition of base to the aqueous phase after demulsification and the HAp particles precipitated worked as an effective particulate emulsifier. This emulsification-demulsification cycle was reversible. Sintering of methyl myristate-in-water emulsion stabilized with the HAp nanoparticles led to a porous HAp material.     

New Optical Sensors for Oxygen Based on Phosphorescent Cationic Water-Soluble Pd(II), Pt(II), and Rh(III) Porphyrins

A new material is proposed for optical sensors for molecular oxygen; the material is obtained by the introduction of Pd(II), Pt(II), and Rh(II) complexes of cationic water-soluble porphyrins into an MF-4SK ion-exchange polymer membrane. The phosphorescence of immobilized metal porphyrins is efficiently quenched by molecular oxygen both in the gas phase and in aqueous solutions. The Stern–Volmer relationships for phosphorescence quenching are linear over the entire range of oxygen concentrations. The new material exhibits good response times and high photochemical stability.     

Electrochemistry in blood substitutes based on perfluoro compounds

The electrochemical properties of Fluosol 43, an aqueous emulsion of perfluorotri-butylamine used as a blood substitute are reported. A saturated calomel electrode prepared in Fluosol 43 is a suitable reference system. The electroactivity ranges were determined for mercury, silver, platinum, vitreous carbon and boron carbide working electrodes; they are analogous to those observed in water under the same conditions. The diffusion coefficients of some typical cations are smaller in the emulsion than in water. The reduction of dissolved oxygen is discussed; the electrochemical procedures characterize the whole emulsion and not only the aqueous phase.