Axel Dürkop

A Europium‐Ion‐Based Luminescent Sensing Probe for Hydrogen Peroxide

A bright idea: A 15-fold increase in fluorescence intensity occurs when the complex formed between Eu3+ and the antibiotic tetracycline binds to hydrogen peroxide at neutral pH. The complex can be used in the determination of the concentration of H2O2, the activity of oxidases, the concentration of glucose, and also in an optical sensor for H2O2.

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.

A highly K(+)-selective phenylaza-[18]crown-6-lariat-ether-based fluoroionophore and its application in the sensing of K+ ions with an optical sensor film and in cells.

Herein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K(+) ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18]crown-6 ether analogues. Probe 1 shows a high K(+)/Na(+) selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mM K(+) ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8% per 1 mM K(+) within the range 1-10 mM K(+). The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K(+) ions on both the extracellular and intracellular levels.

Set of fluorochromophores in the wavelength range from 450 to 700 nm and suitable for labeling proteins and amino-modified DNA.

We describe the synthesis, purification, and spectral properties of new dyes and reactive labels. They absorb in the visible range between 450 and 700 nm and display analytically useful fluorescence. They were made amino-reactive by esterification with N-hydroxysuccinimide (NHS). The resulting oxysuccinimide (OSI) esters were covalently linked to the amino groups of human serum albumin (HSA) or certain DNA oligomers. Except for dyes 9 and 13, they contain one reactive group only in order to avoid cross linking of biomolecules. Labeling of amino-modified biomolecules was performed by standard protocols, and the labeled proteins and oligonucleotides were separated from the unreacted dye by gel chromatography using Sephadex G25 as the stationary phase in the case of proteins, and reversed-phase HPLC in the case of DNA oligomers. The dyes also have been used as donor-acceptor pairs in fluorescence energy transfer systems and in energy transfer cascades.

Nonenzymatic direct assay of hydrogen peroxide at neutral pH using the Eu3Tc fluorescent probe.

A detailed study is presented on the use of an easily accessible probe (the europium–tetracycline 3:1 complex; referred to as Eu3Tc) for determination of hydrogen peroxide (HP). Eu3Tc undergoes a 15-fold increase in luminescence intensity on exposure to an excess of HP. Data are given on the time dependence of the reaction, on the pH dependence of the absorption and emission spectra of both the probe and its complex with HP, and on the effect of stoichiometry between Eu3+ and Tc on selectivity and signal change. HP can be quantified in aqueous solution of pH 6.9 over a 2–400 μM concentration range with a limit of detection of 960 nM. The assay is validated using standard additions, and mean recoveries are found to be between 97.0 and 101.8%. Species that interfere in concentrations below 1 mM include phosphate, copper(II), fluoride and citrate. The addition of detergents causes the response curves towards HP to shift to higher HP concentrations. The method is critically assessed with respect to other common optical methods for determination of HP.

Advanced Luminescent Labels, Probes and Beads and their Application to Luminescence Bioassay and Imaging

The design of fluorescent probes (and labels) is as challenging as it ever was. Such probes enable studies on the molecular dimensions and dynamics of even complex (bio)matter, but also bioanalytical and screening assays whose sensitivity can reach the single molecule level. The design of advanced labels for bioassays is paralleled by developments in (laser) fluorescence spectroscopy, opto-electronics and data processing. Light-emitting diodes (LEDs) and diode lasers (DLs) are particularly attractive light sources and we therefore have focused our research (a) on labels that are LED- or DL-compatible, and (b) on applications of such labels to various analytical formats.