Department of Pharmaceutical Technology
Fig. 1: Penetration of fluorescently labeled buffer into lipidic implants during the release of FITC-lysozym
The imaging or characterization of drug delivery systems and the detection of single molecules of an active compound are carried out both in research and diagnostics. Commonly used methods include magnetic resonance imaging (MRI), electron resonance imaging (ESR) and radioactive and fluorescence imaging. Generally, these methods demand appropriate probes (contrast agents, dyes), which are incorporated into the dosage form or linked to the drug. Fluorescence imaging via confocal laser scanning microscopy and fluorescence spectroscopy is especially prominent in research and development due to the high resolution.
Fig. 2: Distribution of quantum dots within biodegradable microparticles made of PEG-PLA Copolymer
Within several recent projects, fluorescent probes have been incorporated into drug delivery systems. Such systems, for example microparticles or hydrogels, are based on biodegradable polymers (PLGA, PEG-PLA) [1] or triglycerides [2, 3]. They are available for a wide range of applications. The use of fluorescent dyes or fluorescently labelled drugs allows the imaging of drug distribution within the delivery systems and also the determination of drug release. This permits a more detailed description of underlying mechanisms [4].
Beyond low molecular weight substances, fluorescing semiconductor nanocrystals, or quantum dots, are used. These exceptional compounds can be manifold modified and functionalized at their surface. This allows their usage as model colloids, particularly for imaging the distribution of nanoparticulate drugs within delivery systems. Additionally, they are suitable for the characterization of internal structures. Finally, due to their unique optical properties, they offer excellent potential for long-term investigations of drug release and degradation of the dosage form. With near-infrared spectroscopic techniques and infrared-emitting quantum dots or dyes, the observation of drug delivery systems in vivo may be possible.