Local pH tracking in living cells.

Continuous and simultaneous 3D single-particle movement and local pH detection in HeLa cells were demonstrated for the first time by combining fluorescent mesoporous silica nanoparticles (FMSNs) and a single-particle tracking (SPT) technique with a precision of ∼10 nm. FMSNs, synthesized by the co-condensation of both pH-sensitive and reference dyes with a silica/surfactant source, allow long-term reliable ratiometric pH measurements with a precision better than 0.3 pH unit because of their excellent brightness and stability. pH variation in the surrounding area of FMSNs during endocytosis was monitored in real-time. Acidification and low mobility of FMSNs were observed at the early endocytic stage, whereas basification and high mobility of FMSNs were observed at the late stage. Our results indicate that it is possible to monitor local pH changes in the environments surrounding nanoparticles during the cellular uptake process of FMSNs, which provides much needed information for designing an efficient drug delivery nanosystem.

A broad range fluorescent pH sensor based on hollow mesoporous silica nanoparticles, utilising the surface curvature effect.

In this study, a broad range pH sensor was synthesized by loading the pH sensitive dye, fluorescein isothiocyanate (FITC), and a reference dye, rhodamine B isothiocyanate (RITC), into the mesostructure of hollow mesoporous silica nanoparticles (HMSNs) synthesized using a co-condensation method. Compared to a pH sensor based on the same pair of dyes on conventional mesoporous silica nanoparticles (MSNs), this dual-labeled pH sensor based on HMSNs shows a larger pH sensitive range, between 4.5 and 8.5, because of its broad surface curvature distribution which has a strong effect on the apparent pKa values of the FITC dye. The hollow mesoporous silica-dye nanoparticles were used to monitor intracellular pH via a ratiometric fluorescence method. The confocal images demonstrated the capacity of this broad range sensor which can differentiate simultaneously the local pH between various environments, for example, in the medium (pH = 7.2), cytosol (pH ∼ 7) and the endosome-lysosome pathway (pH = 4-5.5).

Collapsed (kippah) hollow silica nanoparticles.

Novel collapsed kippah-like mesoporous silica nanoparticles were synthesized using an O/W microemulsion system. The oil (hexadecane) can escape from the core while water could not enter through the surfactant filled nanopores of the soft shell during synthesis.