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Die Ultraschallfalle bietet eine besondere Möglichkeit zur Handhabung von Proben im Mikrolitermaßstab. Durch die akustische Levitation wird die Probe kontaktfrei in einer gasförmigen Umgebung positioniert und somit dem Einfluss fester Oberflächen entzogen. In dieser Arbeit werden die Möglichkeiten der Ultraschallfalle für den Einsatz in der Analytik experimentell untersucht. Durch die Kopplung mit typischen kontaktlosen Analysemethoden wie der Spektroskopie und der Röntgenstreuung werden die Vorteile dieser Levitationstechnik an verschiedenen Materialien wie anorganischen, organischen, pharmazeutischen Substanzen bis hin zu Proteinen, Nano- und Mikropartikeln demonstriert. Es wird gezeigt, dass die Nutzung der akustischen Levitation zuverlässig eine berührungslose Probenhandhabung für den Einsatz spektroskopischer Methoden (LIF, Raman) sowie erstmalig Methoden der Röntgenstreuung (EDXD, SAXS, WAXS) und Röntgenfluoreszenz (RFA, XANES) ermöglicht. Für alle genannten Methoden erwies sich die wandlose Probenhalterung als vorteilhaft. So sind die Untersuchungsergebnisse vergleichbar mit denen herkömmlicher Probenhalter und übertreffen diese teilweise hinsichtlich der Datenqualität. Einen besonderen Erfolg stellt die Integration des akustischen Levitators in die experimentellen Aufbauten der Messplätze am Synchrotron dar. Die Anwendung der Ultraschallfalle am BESSY konnte im Rahmen dieser Arbeit etabliert werden und bildet derzeit die Grundlage intensiver interdisziplinärer Forschung. Außerdem wurde das Potential der Falle zur Aufkonzentration erkannt und zum Studium verdunstungskontrollierter Prozesse angewendet. Die wandfreie und konzentrationsabhängige Untersuchung über einen Volumenbereich von drei Größenordnungen an derselben Probe ist eine einzigartige Möglichkeit. So konnte wesentlich zur Aufklärung von Fragestellungen der unterschiedlichen Forschungsgebiete beigetragen werden. Diese Untersuchungen sind die ersten in situ Studien der Agglomeration in einem akustisch levitierten Tropfen, angefangen von kleinen (an)organischen Molekülen über Proteine bis hin zu Nanopartikeln. Zusammenfassend eröffnen die Ergebnisse dieser Arbeit einen breiten Anwendungsbereich zur Benutzung der Ultraschallfalle als analytisches Werkzeug.
For the investigation of small sample volumes, the use of an acoustic levitator was tested as a `sample holder' for hovering droplets in a synchrotron beam. It might be advantageous to use levitated droplets instead of samples confined in solid holders, especially for the study of crystallization processes where the influence of containing walls has to be minimized. In a first experiment, the crystallization of sodium chloride in a small droplet of aqueous solution has been followed with a time resolution of 30 s. The collected diffraction peaks are compared with data in the ICSD database.
Many of todays analytical problems are characterized through small sample volumes and can only be solved through a corresponding miniaturisation of the analytical instrumentation. Handling of small sample volumes is inherently difficult due analytical blanks, contamination, and sorption processes on the walls of the containers which are employed during analytical procedures. Acoustic levitation is a powerful tool for contact-less sample handling of solid, liquid, and certain gaseous samples. In addition, levitation permits a chemical pre-treatment such as enrichment, extraction, and derivatisation as well as combination with other analytical techniques such as optical spectroscopy or mass spectrometry. Acoustically levitated liquid and solid samples are typically in a range between 0.005 - 5 µl (diameter 0.2 - 2 mm respectively) and are suspended in a gaseous environment by a stationary ultrasonic field (nodes of a standing wave). Acoustic levitation avoids sample contamination and sorption processes by container walls, but suffers from evaporation and loss of solvents. To balance evaporation and condensation on levitated drops during the experiments, techniques of contact-less droplet size monitoring and solvent and reagent supply have been developed. The advantages of acoustic levitation are demonstrated for on line analysis of crystallisation in a levitated droplet. The evaporation and formation of crystals is observed via time-resolved X-ray diffraction at BESSY. In this way, a high-throughput analysis for polymorphs seems feasible. Future work will be devoted to adaptation of a binding assay with receptors, antibodies or enzymes. Special emphasis will be on homogeneous immunoassays such as fluorescence polarisation immunoassays (FPIA) or apo-enzyme reactivation immunoassay systems (ARIS) combined with laser-induced fluorescence (LIF). This offers the opportunity to study the kinetics of the bio-macromolecule interactions without any wall effects which can have a significant influence on the apparent performance of bioanalytical assays.
Many of todays analytical problems are characterized by small
sample volumes and can only be solved through a corresponding
miniaturisation of the analytical instrumentation. Handling of
small-sample volumes is inherently difficult due to contamination
and sorption processes on the walls of containers.
Acoustic levitation is a powerful tool for contact-free sample
handling of solid, liquid, and selected gaseous samples. In addition,
levitation permits a chemical pre-treatment such as enrichment,
extraction, and derivatisation as well as combination with other
analytical techniques such as optical spectroscopy. Acoustically
levitated liquid and solid samples are typically in a range between
0.005-5 µl (diameter 0.2-2 mm respectively) and are suspended
in a gaseous environment by a stationary ultrasonic field. Acoustic
levitation avoids sample contamination and sorption processes by
container walls, but suffers from evaporation and loss of solvents.
Nonetheless, it is of great impact for the characterization of small
samples. Exact determination of volume is inherently important to
find out the resultant concentration in evaporating droplets. Levitation
is a possibility to characterise the starting conditions of crystallisation
and polymerisation. Even for spectroscopic methods the
correct information on shape, size and concentration of samples
are indispensable.
To determine the size and volume of levitated samples, different
methods of contactless droplet size monitoring were developed and
compared in detail. They give the initial values for modelling of
evaporation effects. In addition, for balancing evaporation and condensation
on levitated drops during the experiments, non-contact
techniques of solvent and reagent supply have been tested.
Here, the advantages of acoustic levitation are demonstrated for on
line analysis of crystallisation in a levitated droplet. The evaporation
and formation of crystals is observed via time-resolved X-ray
diffraction using synchrotron radiation at BESSY. Wall-free
crystallisation in an acoustic levitator gives a tool to prove existing
models concerning crystallisation processes. Furthermore the
occurrence of polymorphic modifications depending on different
conditions can be detected in situ under different and adjustable
conditions.
The impact of the ovo proteins ovalbumin and lysozyme—present in the first stage of egg shell formation—on the homogeneous formation of the liquid amorphous calcium carbonate (LACC) precursor, was studied by a combination of complementing methods: in situ WAXS, SANS, XANES, TEM, and immunogold labeling. Lysozyme (pI = 9.3) destabilizes the LACC emulsion whereas the glycoprotein ovalbumin (pI = 4.7) extends the lifespan of the emulsified state remarkably. In the light of the presented data: (a) Ovalbumin is shown to behave commensurable to the 'polymer-induced liquid precursor' (PILP) process proposed by Gower et al. Ovalbumin can be assumed to take a key role during eggshell formation where it serves as an effective stabilization agent for transient precursors and prevents undirected mineralization of the eggshell. (b) It is further shown that the emulsified LACC carries a negative surface charge and is electrostatically stabilized. (c) We propose that the liquid amorphous calcium carbonate is affected by polymers by depletion stabilization and de-emulsification rather than 'induced' by acidic proteins and polymers during a so-called polymer-induced liquid-precursor process. The original PILP coating effect, first reported by Gower et al., appears to be a result of a de-emulsification process of a stabilized LACC phase. The behavior of the liquid amorphous carbonate phase and the polymer-induced liquid-precursor phase itself can be well described by colloid chemical terms: electrostatic and depletion stabilization and de-emulsification by depletion destabilization.