Lysosomal pH and temperature are two crucial physiological parameters that are involved in regulating intracellular homeostasis, and their precise measurements are extremely important in understanding this process and diseases diagnosis. A lysosome-targeting nanosensor has been designed for simultaneous imaging of pH values and temperature in HeLa cells. Three dyes were covalently immobilized either inside or on silica nanoparticles. The nanosensors have an average diameter of 95 nm. The large surface area of these nanomaterials provides abundant sites for multi-functionality. The surface of nanosensors has been modified with positively-charged amino groups in order to facilitate endocytosis and targeting lysosome. Fluorescein is used as the indicator probe for pH measurement, rhodamine B is the probe for temperature, and a europium complex acts as the reference dye. The dual nanosensor responds to pH values in the range from 3.0 to 9.0, and to temperature in the range from 20 to 60 °C. Owing to its good biocompatibility and good sensitivity, the dual nanosensor has been used to monitor changes in local pH values and temperature in the lysosome of HeLa cells. Graphical abstract A dual nanosensor for simultaneously imaging of pH values and temperature inside the lysosome of HeLa cells was constructed by labelling three luminophores in/on silica nanoparticles. It shows high sensitivity and selectivity, good photostability, and good biocompatibility.
Keywords: Core-shell; Europium complex; Fluorescein; Intracellular sensing; Ratiometric measurement; Rhodamine B; Silica nanoparticle; Temperature response; pH response.