Here, we report that a mesoporous silica nanoparticle
(MSN) coated
with a fluoresceine-labeled bovine serum albumin (F-BSA) hydrogel
layer works as a temperature-responsive nanocarrier for tetrakis-N-methylpyridyl porphyrin (TMPyP) and as a fluorescence
ratiometric pH probe. F-BSA hydrogel–coated MSN containing
TMPyP (F-BSA/MSN/TMPyP) was synthesized by thermal gelation of denatured
F-BSA on the external surface of MSN. The F-BSA hydrogel layer was
composed of an inner hard corona layer and an outer soft layer and
was stable under physiological conditions. F-BSA/MSN/TMPyP exhibited
temperature-dependent exponential release of TMPyP. In this release
profile, the MSN was found to be a suitable host for stable encapsulation
of tetracationic TMPyP by electrostatic interactions, and the F-BSA
hydrogel layer mediated the diffusion of TMPyP from the MSN pore interior
into the solution phase. Increasing temperature promoted partitioning
of TMPyP from the pore interior to the F-BSA hydrogel layer, from
where it was spontaneously released into the bulk solution phase by
cation exchange. F-BSA/MSN/TMPyP also gave a linear ratiometric fluorescence
response (1.3 per pH unit) in the pH range from 6.1 to 8.9.