title: Ratiometric pH-nanosensors based on rhodamine-doped silica nanoparticles functionalized with a naphthalimide derivative.
abstract: This paper describes the preparation of two-dye-doped silica nanoparticles for ratiometric pH measurements in the biologically relevant pH-range. While a rhodamine derivative is embedded in a silica core and used as the reference, a pH-sensitive naphthalimide dye is immobilized on the previously amino-functionalized core through two different approaches. Either the naphthalimide's carboxylic group is activated to a succinimidyl-ester to form an amide bond or the system can be built up via solid-phase organic synthesis in only two steps. Both types of nanosensors are characterized in terms of morphology (dynamic light scattering, transmission electron microscopy) and optical properties (steady-state fluorescence spectroscopy). In terms of application, e.g. reproducibility and handling of the synthesis, the first approach gave very good results with respect to size and size distribution and a pK(a) value of 6.55 was found that is comparable to the free indicator dye in solution. The solid-phase organic synthesis method proves the possibility of covalent immobilization of naphthalimides to amino-functionalized surfaces, showing the stability of the polymeric substrate and achieving comparable results for pH sensing.
authors.affiliation: Institute of Physical Chemistry, Friedrich Schiller University Jena, Lessingstrasse 10, 07743 Jena, Germany. tristan.doussineau@uni-jena.de
authors.forename: Tristan
authors.initials: T
authors.lastname: Doussineau
authors.forename: Sabine
authors.initials: S
authors.lastname: Trupp
authors.forename: Gerhard J
authors.initials: GJ
authors.lastname: Mohr