Tobias Werner

Optical chemical sensor

Optical chemical sensors have been the focus of much research attention in recent years because of their importance in industrial, environmental and biomedical applications [1]. This class of sensors combines chemical and biological recognition with advances in optoelectronic technologies. The application of solgel materials to these sensors, especially in the form of thin films, has attracted considerable interest due to the ease of fabrication and design flexibility of the process. The nature of the sol-gel process lends itself very well to the deposition of thin films using a variety of techniques such as dip-coating, spin-coating and spraying. In many sensor applications, the sol-gel film is used to provide a micro-porous support matrix in which analyte-sensitive molecules are entrapped and into which smaller analyte species may diffuse and interact [2,3]. Sol-gel films have many advantages as support matrices over polymer supports, including, for example, strong adhesion, good mechanical strength as well as excellent optical transparency. The versatility of the process facilitates tailoring of the physico-chemical film properties to optimize sensor performance. For example, films can be designed which have optimum porosity while minimizing leaching of the indicator molecules. In this chapter, the versatility of the sol-gel process with regard to the design of films for specific optical chemical sensor applications is highlighted.

Arenedicarboximide Building Blocks for Fluorescent Photoinduced Electron Transfer pH Sensors Applicable with Different Media and Communication Wavelengths

A whole family of modular photoinduced electron transfer (PET) sensors has been constructed from a single simple reaction type with commercially available materials. This family, one member of which is shown here, possesses amine receptors for protons and arenedicarboximide fluorophores addressable at different wavelengths. Its pH-sensing behaviour is examined in solution and in polymer membrane matrices, which are crucial for the use of fluorescent PET sensors as optode pH monitors.

Dual lifetime referenced optical sensor membrane for the determination of copper(II) ions

A sensor membrane has been developed for the determination of copper(II) ions that displays excellent performance due to internal referencing of luminescence intensities. The applied sensing scheme (dual lifetime referencing) makes use of the indicator lucifer yellow (LY) and an inert reference luminophore (a ruthenium complex entrapped in polyacrylonitrile beads). Both are contained in a hydrogel matrix. The copper-dependent fluorescence intensity change of LY can be converted in either a phase shift or time dependent parameter. The sensing membrane is capable of determining copper(II) with an outstanding high selectivity over a dynamic range between 1 and 1000µM in neutral or weekly acidic conditions. The advantages of the referencing method over intensity based measurementswas demonstrated by the measurement of turbid solutions. The scheme was also applied to two-dimensional measurements in the time domain. Sensor integrated microtiterplates were imaged with a CCD camera gated with square pulses in the microsecond range

Novel oxygen sensor material based on a ruthenium bipyridyl complex encapsulated in zeolite Y: dramatic differences in the efficiency of luminescence quenching by oxygen on going from surface-adsorbed to zeolite-encapsulated fluorophores

Abstract Zeolite Y was ion-exchanged with ruthenium(III) chloride, and the respective ruthenium(II) bipyridyl complex (Ru2+ (bpy)3), which is an excellent fluorescent oxygen probe, was prepared inside the zeolite supercages. In addition, a Ru2+(bipy)3 dichloride solution was used for impregnation of the zeolite surface. Both materials were characterized by X-ray diffraction and the loading with ruthenium ions determined photometrically. In order to obtain sensor materials, they were incorporated into silicone polymers and spread, as a thin layer, onto a polyester mechanical support. The resulting sensor membranes were tested with respect to luminescence intensity, quenching by molecular oxygen, response time to oxygen and long-term stability under various conditions. Oxygen can be measured over the 0–760 Torr range, with very good resolution between 0 and 200 Torr. Both the quenching efficiency and the long-term stability of the Stern-Volmer quenching constant are tremendously improved when compared to sensors where the fluorophore is absorbed onto the surface of either a zeolite or silica gel. When spread onto glass rather than polyester, the sensors lend themselves to operation at temperatures as high as 200 °C.

LED-compatible fluorosensor for measurement of near-neutral pH values

We report on an optical sensor material suitable for fluorimetric measurement of pH in the 6–9 range using a new, fully LED-compatible fluorescent dye. Its base form has a strong absorption between 580 and 630 nm that matches the emission band of conventional yellow or orange light-emitting diodes. Two kinds of dye immobilization are reported. The first is based on covalent binding to a cellulosic matrix and the resulting material is intended for use in sensing membranes. The second involves physical entrapment of the dye in a sol-gel matrix which can be used for optical fiber tip coating as well as in evanescent wave type sensors. Both kinds of sensor materials are studied with respect to dynamic pH ranges, response times, sensitivity toward ion strength, and stability.

Set of luminescence decay time based chemical sensors for clinical applications

Abstract We present a sensing scheme capable of measuring the ten parameters most important in analysis of blood gases, electrolytes and enzyme substrates. Detection is based on the variation in the decay time of the luminescence of a single class of luminophores, namely the ruthenium diimine complexes. The resulting family of sensors are operated within a limited range of modulation frequencies and are consistent in terms of spectroscopy, analytical wavelengths and opto-electronic components. Except for oxygen which directly modulates decay time, a specific receptor for each single analyte was placed in close spatial proximity to the luminophore which itself is inert to the analyte. The receptor affects both the decay time and intensity of luminescence. Sensors are presented for pH, oxygen, carbon dioxide, potassium, sodium, calcium, chloride, ammonia, urea and glucose, and the sensing schemes and respective figures of merit are discussed.

Ammonia-sensitive polymer matrix employing immobilized indicator ion pairs

A new sensor material for monitoring ammonia in aqueous solution is presented. It is based on lipophilic ion pairs consisting of an anionic pH indicator and a quaternary ammonium cation. The ion pairs are homogeneously distributed inside a layer of a silicone elastomer. Exposure of the indicators to ammonia leads to de-protonation of the hydroxy group, and this causes the strong absorbance of the basic form of the indicator. The process is fully reversible. The sensor can easily be manufactured from plastic materials and responds to ammonia over the concentration range of 0.015 to 20 mg l–1 with a detection limit of 15 µg l–1, and is not affected by pH because the silicone matrix is proton-impermeable. The sensor is intended for use as a probe to monitor ammonia in surface waters.

Optical sensor for the pH 10–13 range using a new support material

SummaryA pH-sensitive membrane has been developed consisting of a polyester support covered with a thin layer of cellulose onto which a pH-indicator is covalently immobilized. The sensor membrane is completely transparent and shows a pH-induced colour change that makes it capable of measuring pH in the 10–13 range. Its performance was studied with respect to relative signal change, reproducibility, and long-term use. The response time for 90% of the total signal change to occur was 1 min. The material has a response that is stable over hours of operation at high pHs. This is in contrast to conventional glass electrodes which tend to become unstable at high pH, but also suffer from interferences due to the so-called alkali error. Hence, this optrode sensor presents an attractive alternative for measuring the pH of highly alkaline solutions as occurring in chemical industry, scrubbers, and waste water treatment plants. The immobilization scheme is of general interest in that it allows immobilization of vinylsulfonyl dyes with a broad variety of pKa-values, thereby allowing the design of a variety of pH (and other) sensors possessing the same mechanical support.

E-LDL and Ox-LDL differentially regulate ceramide and cholesterol raft microdomains in human Macrophages†

Atherosclerosis is characterized by the generation of lipid‐loaded macrophage‐derived foam cells. To study the effect of different types of atherogenic lipoproteins, human macrophages were loaded with enzymatically degraded low density lipoprotein (E‐LDL) or oxidized LDL (Ox‐LDL). Cellular cholesterol content was increased by E‐LDL, whereas Ox‐LDL increased the ceramide content. Cell surface expression analysis by flow cytometry and confocal microscopy revealed that Ox‐LDL increased ceramide and lactosylceramide expression compared to E‐LDL loading and induced ceramide rafts, whereas loading with E‐LDL induced cholesterol‐rich microdomains. Formation of different rafts may have consequences for raft associated signaling in cholesterol homeostasis and apoptosis in human macrophages.

Highly selective optical sensing of copper(II) ions based on fluorescence quenching of immobilised Lucifer Yellow

We describe the development of an optical sensing scheme for the determination of copper(II) in drinking or waste water. It is based on static quenching of the fluorescence of Lucifer Yellow immobilised on anion exchanger particles, embedded in a hydrogel. The sensing membrane allows the determination of copper(II) in the 0.01 μM (0.63 μg l−1) to 100 μM (6300 μg l−1) concentration range with an outstanding high selectivity. The change in fluorescence on exposure to a significant concentration of 31 μM (2000 μg l−1) is −60%. The response time is concentration dependent and varies from 100 to 3 min. Selectivity was investigated by the separate solution method; mercury(II) was found to be the only interferent. The effect of pH was evaluated in the range 4.0–6.8. The application of the sensing membrane as a single shot test was demonstrated using microtitre plates for copper(II) determination in tap water samples.