Søndergaard, Rikke Vicki1; Henriksen, Jonas Rosager4; Andresen, Thomas Lars1
1 Department of Micro- and Nanotechnology, Technical University of Denmark2 Colloids and Biological Interfaces, Department of Micro- and Nanotechnology, Technical University of Denmark3 Center for Nanomedicine and Theranostics, Center, Technical University of Denmark4 Department of Chemistry, Technical University of Denmark5 Physical and Biophysical Chemistry, Department of Chemistry, Technical University of Denmark
Particle-based nanosensors offer a tool for determining the pH in the endosomal-lysosomal system of living cells. Measurements providing absolute values of pH have so far been restricted by the limited sensitivity range of nanosensors, calibration challenges and the complexity of image analysis. This protocol describes the design and application of a polyacrylamide-based nanosensor (∼60 nm) that covalently incorporates two pH-sensitive fluorophores, fluorescein (FS) and Oregon Green (OG), to broaden the sensitivity range of the sensor (pH 3.1-7.0), and uses the pH-insensitive fluorophore rhodamine as a reference fluorophore. The nanosensors are spontaneously taken up via endocytosis and directed to the lysosomes where dynamic changes in pH can be measured with live-cell confocal microscopy. The most important focus areas of the protocol are the choice of pH-sensitive fluorophores, the design of calibration buffers, the determination of the effective range and especially the description of how to critically evaluate results. The entire procedure typically takes 2-3 weeks.
Nature Protocols, 2014, Vol 9, Issue 12, p. 2841-2858