Fluorescence imaging is widely used in biomedical sciences for a large spec- trum of applications ranging from the morphological analysis of anatomical struc- tures to time-resolved measurements of intracellular molecular events.
It enables noninvasive probing of biological processes with high spatial resolution in ex vivo tissue preparations as well as in whole organisms.
A powerful application of this technique is the ability to monitor in real- time the complex intracellular fluxes of ions and metabolites that underlie many essen- tial physiological functions. But some ions such as Cl-, Na+, K+ are difficult to measure. Sodium imaging, in particular, is an attrac- tive way of assessing many fundamental cellular processes, from the transport of small molecules through epithelial barriers to the integration of complex signals in the brain, that depend on the transmembrane Na+ gradient. However, the poor characteristics of available Na+ probes have rendered Na+ imaging an uneasy task. Many strategyes have been developed, but they are limited in the size of the cell that can be sensed.
Dendrimers are branched poly- mers with well-defined sizes and geometry. After several layers of branching, they make spheres that contain solvent-filled cavities. These structural features endow them with the ability to encapsulate small guest molecules and act as nanocontainers. Dendrimer nanocontainers have been extensively used for drug and gene delivery applications. However, this property has not been used in molecular imaging yet. In this study, they ested whether a Naþ dye such as CG could be encapsulated in a dendrimer in order to prolong its intracellular half- life while maintaining its Naþ response characteristics.They also assessed whether a Naþ nanoprobe built on this principle could be used to probe cell functions in thick tissue preparations without disturbing baseline physiological parameters.
They obtained a sensitive molecule, that can sense even small concentrations of Na+.
To read more about this work, search in ACS:
Lamy, Christophe; Sallin, Oliver. Sodium sensing in Neurons with a dendrimer-based nanoprobe. ACS NANO Vol 6. No 2. 1176-1187. 2012.