Ratiometric pH-nanosensors based on rhodamine-doped silica nanoparticles functionalized with a naphthalimide derivative

• Published in: Journal of colloid and interface science 2009-11, Vol.339 (1), p.266-270
• Main Authors: Doussineau, Tristan, Trupp, Sabine, Mohr, Gerhard J.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Derivatives; Dyes; Dynamics; Exact sciences and technology; General and physical chemistry; Nanoparticles; Nanostructure; Naphthalimide dyes; pH sensor; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Ratiometric measurements; Silica nanoparticles; Silicon dioxide; Surface immobilization; Surface physical chemistry; Synthesis
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2009.07.044

A naphthalimide derivative has been successfully immobilized on the outer surface of rhodamine-doped silica nanoparticles yielding pH-nanosensors able to monitor proton concentration in the biologically relevant pH-range. 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 p K 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.