Microtiter plate assay for phosphate using a europium–tetracycline complex as a sensitive luminescent probe

A new luminescent europium probe is presented for the determination of phosphate (P) in microtiter plate format. The assay is based on the quenching of the luminescence of the europium–tetracycline (EuTc) 1:1 complex by phosphate using a reagent concentration of 20.8 μmol/L. The probe is excited at 400 nm and displays a large Stokes’ shift of 210 nm. The emission maximum is located at 616 nm. The system works best at neutral pH 7 and is therefore suitable for phosphate determination in biological and biochemical systems. The linear range of the calibration plot is from 5 × 10−6 mol/L to 7.5 × 10−4 mol/L of phosphate, and the limit of detection is 3 μmol/L

Anion-lnduced Fluorescence Quenching of a New Zwitterionic Biacridine Derivative

The effect of halides and different buffer anions on the quenching of the fluorescence of the new probe 10,10′-bis(3-sulfopropyl)-9,9′-biacridine (SPBA) has been studied using fluorescence and decay time measurements. The linearity of the Stern-Volmer plot indicates that fluorescence quenching by halides can be described reasonably well by a single-exponential decay with a K of 4.06 times 10⁶M⁻¹s⁻¹for chloride, 7.83 times 10⁶M⁻¹s⁻¹for bromide and 1.12 times 10⁷M⁻¹s⁻¹for iodide. We have found that SPBA is collisionally quenched also by the buffers 3-(N-mor-pholino)propanesulfonic acid (MOPS) and N-2-hydroxy-ethylpiperazine-N′-ethansulfonic acid (HEPES). The bi-molecular rate constants are 1.67 × 10⁶M⁻¹s⁻¹for HEPES and 1.44 times 10⁶M⁻¹s⁻¹for MOPS

Hypoxia in Leishmania major Skin Lesions Impairs the NO-Dependent Leishmanicidal Activity of Macrophages

Cure of infections with Leishmania major is critically dependent on the ability of macrophages to induce the type 2 nitic oxide (NO) synthase (NOS2) that produces high levels of NO in the presence of ample oxygen. Therefore, we analyzed the oxygen levels found in leishmanial skin lesions and their effect on the NOS2-dependent leishmanicidal activity of macrophages (MΦ). When L. major skin lesions of self-healing C57BL/6 mice reached their maximum size, the infected tissue displayed low oxygen levels (pO2~21Torr). MΦ activated under these oxygen tensions failed to produce sufficient amounts of NO to clear L. major. Nos2-deficient and hypoxic wild-type macrophages displayed a similar phenotype. Killing was restored when MΦ were reoxygenated or exposed to a NO donor. The resolution of the lesion in C57BL/6 mice was paralleled by an increase of lesional pO2. When mice were kept under normobaric hypoxia, this caused a persistent suppression of the lesional pO2 and a concurrent increase of the parasite load. In Nos2-deficient mice, there was no effect of atmospheric hypoxia. Low oxygen levels found at leishmanial skin lesions impaired the NOS2-dependent leishmanicidal activity of MΦ. Hence, tissue oxygenation represents an underestimated local milieu factor that participates in the persistence of Leishmania

A Fluorescent Probe for Diacetyl Detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl

FIBRE-OPTIC SENSORS FOR CHEMICAL PARAMETERS OF INTEREST IN BIOTECHNOLOGY

Optical fibres can be used for remotely sensing chemical and physico-chemical parameters that are of interest for proper management of bio- processes as they occur, for instance, in bioreactors. Optical sensors can offer advantages over electrochemical ones because of the lack of reference cells, the immunity towards electromagnetic interferences, and the possibility of heat sterilisation. In this contribution, the principles of waveguide spectroscopy are briefly outlined, and waveguide sensors are classified according to their working principles. The most usual approach in the development of fibre-optic sensors is to provide the end of an optical fibre with a suitable indicator chemistry or a material that responds to the parameter of interest. In contact with the sample, the intensity of reflected, scattered, or re-emitted light is the analytical signal. Representative examples of fibre-optic sensors for oxygen, pH, carbon dioxide, ammonia, electrolytes, and redox status are given. Recently developed sensors for glucose and enzymes shall also be considered. Finally, potential fields of application are presented, and current trends and concepts discussed