Ratiometric pH sensing at the nanoscale for biochemical applications

B. Demosthene, J. Pereira, E. Davidson, S. Santra, L Tetard
University of Central Florida,
United States


The ability to probe pH at the microscale and nanoscale is highly sought after in the life sciences and in chemistry applications. Existing pH probes are suitable for large scale measurements, and only a few studies have proposed nanoscale pH probes to date. These involved the development of a tip with embedded electrodes for electrochemical-based measurements. However, some living systems, such as plant leaves, are not amenable to electrochemical measurements.Here we present the development of a fluorescence-based nanoscale pH probe based on novel dual dye-doped nanoparticles. Two dyes are selected to obtain a self-calibrated ratiometric pH reading: pyranine, a pH sensitive dye, and tris (bipyridine) ruthenium (II), a pH insensitive dye. We show that the two dyes can be successfully encapsulated in silica nanoparticles using a water-in-oil microemulsion method. The synthesized nanoparticles are characterized by electron microscopy, dynamic light scattering (DLS), Zeta potential, UV-Visible and fluorescence spectroscopy. The encapsulation of the two dyes in the silica nanoparticles is demonstrated. The performance of the nanoparticles as a pH sensor are evaluated for pHs between 5.5 and 8.5, relevant to conditions in living systems. Initial applications of the pH sensor are demonstrated.