Marina M. Lezhnina

Efficiently luminescing spherical polymer particles (beads) in the nanoscale regime of up to approximately 250 nm have become very valuable tools in bioanalytical assays. Eu³⁺- complexes imbedded in polymethacrylate and polystyrene in particular proved to be extraordinarily useful in sensitive immunochemical and multi-analyte assays, and histo- and cytochemistry. Their obvious advantages derive from both, the possibility to realize very high ratios of emitter complexes to target molecules, and the intrinsically long decay times of the Eu³⁺-complexes, which allows an almost complete discrimination against bothersome autofluorescence via time-gated measuring techniques; the narrow line emission in conjunction with large apparent Stokes shifts are additional benefits with regard to spectral separation of excitation and emission with optical filters. Last but not least, a reasonable strategy to couple the beads to the analytes is mandatory. We have thus screened a variety of complexes and ancillary ligands; the four most promising candidates evaluated and compared to each other were β-diketonates (trifluoroacetylacetonates, R-CO-CH-CO-CF₃, R = - thienyl, -phenyl, -naphthyl and -phenanthryl); highest solubilities in polystyrene were obtained with trioctylphosphine co-ligands. All beads had overall quantum yields in excess of 80% as dried powders and lifetimes well beyond 600 µs. Core-shell particles were devised for the conjugation to model proteins (Avidine, Neutravidine). Their applicability was tested in biotinylated titer plates using time gated measurements and a Lateral Flow Assay as practical examples.

The present report describes a new approach to stain bacteria by means of rare earth complexes. We demonstrate with selected Gram-negative and positive bacteria (Escherichia coli, Micrococcus luteus, Bacillus megaterium) that these microbes can be stained efficiently with derivatives of N-phenylanthranilic acid, flufenamic acid in particular, and Tb3+ ions. Hence, the inherent advantages of rare earth complexes, e.g. strong optical absorption (>50 000 L × M−1 × cm−1) due to the antenna effect, large Stokes’ shifts (~10 000 cm−1) and very long emission decay times (millisecond range), and, not least, enhanced photostability can be fully exploited in fluorescence microscopy and spectroscopy of the bacteria; foreseeably, these findings will also be useful in flow cytometry and ELISA techniques.

Rare earth ions complexes provide numerous highly beneficial optical properties ‐ unusually large Stokes shifts, very narrow line emissions and long‐lived excited states being the most prominent of them. Surprisingly few attempts have this far been reported to directly exploit them as direct microbial stains. M. Lezhnina and coworkers here describe basic staining strategies for fluorescence microscopy and outline their eventual potential in fluorescence flow cytometry.Further details can be found in the article by Marina M. Lezhnina, Weronika Rochowiak, Wolfgang Göhde, Rauni Kuczius, and Ulrich Kynast (e202000068). image

Despite an ever increasing demand for reliable and cheap methods in the detection and quantification of microbes, surprisingly few investigations have explored or utilized the luminescence of rare earths in the microbial context, neither in conventional, that is, plating and microscopic imaging techniques, nor in advanced methods like fluorescence flow cytometry. We have thus investigated the potential of some rare earth complexes and hybrid materials for microbiological analysis. We found fairly simple procedures for internal staining (dyes inside the bacterial cell) and external staining (dyes on the cell surface). The present paper is predominantly relying on microscopic imaging and luminescence spectroscopies (excitation, emission, decay times), but also evaluates model rare earth microspheres to estimate an eventual rare earth based stain for a fast and sensitive bacteria enumeration with luminescence flow cytometry.

Aromatic carboxylates of the rare earths are known for highly efficient luminescence, thus holding the promise of applicability in optical devices, but may be problematic to apply as such due to their structure, which is polymeric in nature. Therefore, means of conversion into molecular species or eventually polymer embeddings are sought, while at the same time maintaining their advantageous optical features. For these purposes, co‐ligations of rare earth p‐aminobenzoates with bidentate bipyridine and phenanthroline, tridentate terpyridine and polyurethanes, which may also be perceived as polydentate ligands, have been carried out. The materials were characterised with focus on their structure and optical performance. Brightly luminescing composites were obtained from reactions with aromatic and aliphatic diisocyanates. Prolonged UV‐irradiation of the materials proved hexamethylene diisocyanates to be superior with regard to photodegradation. Transparent polyurethane monoliths with emission quantum yields between 40 % and 55 % were eventually prepared from covalent attachement of Tb(p‐aminobenzoate)₃ and its bipyridine co‐ligated complexes to a hexamethylene diisocyanate/polyol system. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

In the recent past, numerous attempts have been made to utilize nano-, meso-, and microporous materials as hosts for luminescent guest species. The accessible spectral range now spreads from the vacuum ultraviolet to the near infrared (NIR), if sodalites are included in this scope. Although borderline materials in this context with respect to pore sizes, examples of the versatility of sodalites in accommodating small but efficient luminescent entities are discussed. In particular, optical materials whose spectral range of operation is allocated in the NIR have recently attracted our attention and will form the focus of this report.

Initially motivated by the commercial need for cheaper and environmentally friendly luminescent materials for application in fluorescent lamps and cathode ray tubes, the search for new matrices for optically active species has penetrated a scope far beyond “classical” solid-state materials. Porous matrices with voids ranging from the nano-to the microscale have become the subject of recent investigations. Crystalline, amorphous, organomorphous, nanosized matrices and matrices, which are amorphous on the atomic level but have a translational superstructure on the microscale (zeolites, sol-gel materials, polymers, nanoparticles and photonic crystals), are addressed. The optical technologies covered in this research range from mercury free discharge lamps, plasma displays, organic and polymeric light emitting diodes, and novel laser materials to biophotonics and the new generation of white emitting AlGaN solid-state light emitting diodes (LEDs). Due to their specific properties (e.g., high quantum yields, narrow line emission), rare-earth ions are indispensable components of these approaches, be it in the nanoscaling zeolites, sol-gel matrices, or as the active component in optically functional polymers. Optical properties of hybrid materials composed of either rare-earth ions as such, their complexes, or nanoparticles in these matrices, with potential application in the fields mentioned, will form the scope of the present report.