Preparation and photophysics of HPTS-based nanoparticle-assembled microcapsules

In this paper we introduce a methodology to encapsulate hydroxy pyrene trisulfonate (HPTS) inside the microcapsules and carry out spectroscopic and fluorescence lifetime studies of these encapsulated HPTS. The synthesis of microcapsule encapsulating HPTS was achieved using poly-L-lysine, trisodium citrate and silica sol and characterized by scanning electron microscopy (SEM), confocal and optical microscopy. The spectroscopic evaluation of encapsulated HPTS showed completely different but more-stable optical properties by lowering the energy gap between the excited and ground state. A single-exponential prolonged fluorescence lifetime upon encapsulation of probe inside the microcapsule compared to pyrene was obtained, by improving de-quenching by molecular oxygen in the solution. Based on a solvatochromic study, a higher polarizability was recorded inside the microcapsule. Temporal evolution under continuous irradiation indicates that the probe present inside the silica microcapsule is highly photostable compared to pyrene in solution, suggesting that the microcapsule can provide extra photochemical stability to not only the probe molecule during molecular sensing, but also the guest (drug) molecule while applied as drug delivery system.