Calcium phosphate nanoreactor sensors

In this dissertation, the calcium phosphate nanoreactor with encapsulation of fluorescenet dye was developed for high resolution and accuracy of pH sensing. The nanoreactor was made of a calcium phosphate shell covering egg phosphatidylcholine liposomes that were filled with a pH sensitive dye. The coating of calcium phosphate protects the lopsome-encapsulated fluorescent dyes from interference with surrounding molecules and provides a biocompatible interface for the nanoreactor device. Various synthesis conditions were examined to establish an optimized recipe for the production of stable and reproducible nanreactors. The mean diameter of synthesized nanoreactors was measured to be around 100 nm with dynamic light scattering, the shell thickness was determined to be about 15 nm with TEM, and calcualtions were used to estimate about 10 dyes/particle. The dual wavelength emission pH sensitive dye, carboxySNARF-1, was encapsulated into the nanoreactor to build a pH responsive nanosensor and shown to provide accurate pH measurements even in complex biological media, where the unprotected pH responsive dyes have failed. The nanoreactor's response time to pH change nearly equals that of the dye in solution. Its pH titration curves at two different wavelengths are equivalent to those of the dye in solution, and fluorescence intensity ratio dependent pH analysis is possible using the modified Henderson-Hasselbalch equation. In addition, the fluorescence emission and photodegradation properties of the fluorescent dye fluorescein inside nanoreactors were studied in detail. Flurescein dye molecules tend to from stable./ -assregates inside the nanoreactors. The molecular collision rate constants between the dye aggregates and between the dyes and soluble quenchers were found to be greatly reduced inside the nanoreactors and this is thought to be responsible for the observed resistance to photodegradation and reduced emission quenching of the dye at high internalized dye concentration. Nanoreactors were concentrated to a high suspension concentration, yielding exceptionally strong luminescence affected only by inner filter effects absent particle-particle crosstalk. These results suggest that the interference to the dye for the pH analyses with the environmental molecules may be reduced or prohibited by usage of dye encapsulated nanoreactors.