Development of ion indicators and nanosensors
Ion concentration measurements in cells
Fluorescent ion indicators can be used as "reporters" that measure the local ion concentration. The underlying principle of this technique is that the binding of the ion of interest changes the fluorescence properties of the dyes. These changes can be monitored on the stage of a fluorescence microscope. All the "conventional" microscopic techniques depend on the quantitative measurement of the fluorescence intensity of the dye. Often, however, it is difficult to relate changes in the fluorescence intensity directly to the ion concentration since the overall magnitude of the signal is also dependent on many other factors such as the local dye concentration or the illumination intensity. Inhomogeneities in the dye distribution, photobleaching, non-uniform illumination, changing absorption within the sample or along the optical path or protein-dye interactions can invalidate the measurements.
Fluorescence lifetime based ion concentration measurements
Ratiometric indicator dyes allow correcting for many errors such as an inhomogeneous dye distribution. Ratiometric indicators are characterized by an isosbestic point in the fluorescence excitation or emission spectrum. The absorption or emission at this wavelength is independent on the concentration of the analyte and can be used to correct for changes in the indicator concentration. By forming the ratio between a wavelength at which the absorption (or emission) is dependent on the analyte concentration and the absorption (or emission) at the isosbestic point a value is obtained, which is only dependent on the analyte concentration, but not the indicator concentration.
Unfortunately, only few indicators with these properties exist. Alternatively the fluorescence lifetime can be used to determine the analyte concentration. Since the lifetime is a property of the analyte-free and analyte-bound state of the indicator it is independent on the indicator concentration.
Indicators for monovalent cations
Although a variety of indicators is available for the determination of the concentration of bivalant cations, only few indicators exist for the measurement of monovalent cations. One of the activities of the Biomolecular Photonics Group aims at synthesizing new sodium indicators.
Researchers involved in the project
Collaborations
- Prof. Dr. Rainer Beckert, Institute for Organic Chemistry and Macromolecular Chemistry, Friedrich-Schiller-University Jena
Nanosensors
The determination of the concentration of an ion - no matter if it is based on fluorescence intensity or fluorescence lifetime measurements - can be biased by the presence of proteins.
One way to overcome this problem is to incorporate the indicator dye in the polymer matrix of nanoparticles, which can be tailored to their specific task. At the same time a reference dye, which is insensitive to the analyte concentration, can be incorporated. In this way it is possible to exploit the analyte recognition capabilities of the indicator and to correct for changes in the indicator concentration by taking into account the fluorescence signal of the reference dye.
Researchers involved in the project
- Dipl.-Chem. Rainer Strathausen
- Dr. Birgit Hoffmann
- Dr. Charles Cranfield
- Dr. Sascha Dietrich
- Dr. Sarmiza Elena Stanca
Collaborations
- Prof. Dr. Rainer Beckert, Institute for Organic Chemistry and Macromolecular Chemistry, Friedrich-Schiller-University Jena
Founding
- European Union (Project: „Sensor Nanoparticles for Ions and Biomolecules“ (SNIB), Founding-ID: MTKD-CT-2005-029554)
Thuringian Ministry for Education, Science and Culture (Projekt: „NanoConSens")
Selected project-related publications
- Hornig S., Biskup C., Gräfe A., Wotschadlo J., Liebert T., Mohr G.J., Heinze T.:
Biocompatible fluorescent nanoparticles for pH-sensoring.
Soft Matter 4, 1169-1172 (2008). - Graefe A., Stanca S.E., Nietzsche S., Kubicova L., Beckert R., Biskup C., Mohr G.J.: Development and critical evaluation of fluorescent chloride nanosensors.
Anal. Chem. 80, 6526-6531 (2008). - Cywinski P.J., Moro A.J., Stanca S.E., Biskup C., Mohr G.J.:
Ratiometric porphyrin-based layers and nanoparticles for measuring oxygen in biosamples. Sens. Actuators B 135, 472-477 (2009). - Stanca S.E., Nietzsche S., Fritzsche W., Cranfield C.G., Biskup C.:
Intracellular ion monitoring using a gold-core polymer-shell nanosensor architecture.
Nanotechnology 21, 055501 (2010). - Kempe K., Vollrath A., Schaefer H.W., Poehlmann T.G., Biskup C., Hoogenboom R., Hornig S., Schubert U.S.:
Multifunctional poly(2-oxazoline) nanoparticles for biological applications.
Macromol. Rapid Comm. 31, 1869-1873 (2010). - Vollrath A., Schubert S., Windhab N., Biskup C., Schubert U.S.:
Labeled nanoparticles based on pharmaceutical EUDRAGIT S 100 polymers. Macromol. Rapid Commun. 31, 2053-2058 (2010). - Stanca S.E., Csaki A., Urban M., Nietzsche S., Biskup C. Fritzsche W.:
Simultaneous topographic and amperometric membrane mapping using an AFM probe integrated biosensor.
Biosens Biolectron 26, 2911-2916 (2011). - Babiuch K., Pretzel D., Tolstik T., Vollrath A., Stanca S., Förtsch F., Becer C.R., Gottschaldt M., Biskup C., Schubert U.S.:
Uptake of well-defined, highly glycosylated, pentafluorostyrene-based polymers and nanoparticles by human hepatocellular carcinoma cells.
Macromol. Biosci. 12, 1190-1199 (2012).