Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 339, Issue 1, Pages 266-270Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2009.07.044
Keywords
pH sensor; Silica nanoparticles; Naphthalimide dyes; Ratiometric measurements; Surface immobilization
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Funding
- EU [MRTN-CT-2006-033873]
- Deutsche Forschungsgemeinschaft [MO 1062/5-1, MO 1062/6-1]
- [PIEF-GA-2008-220775]
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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. (C) 2009 Elsevier Inc. All rights reserved.
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