Cover picture

Andrew Burns, Prabuddha Sengupta, Tara Zedayko,Barbara Baird, and Ulrich Wiesner*

The cover picture illustrates quantitative chemical imaging of pH in mast cells fa-cilitated by core/shell silica nanoparticle sensors incorporating two fluorescent dyespecies. These 70-nm particles maximize the exposure of the sensor dye in theouter silica shell, while sequestering the reference dye within the particle core tominimize perturbations. Ratiometric comparison of the sensor and reference fluo-rescence allows the pH to be measured down to the single-particle scale. Confocalfluorescence images of the red and green channels are shown superimposed on abright-field image of the cell under investigation (inset) and were analyzed to yieldthe false-spectrum image of pH in various intracellular vesicles. For more informa-tion, please read the Communication “Core/Shell Fluorescent Silica Nanoparticlesfor Chemical Sensing: Towards Single-Particle Laboratories” by U. Wiesner and co-workers on page 723 ff.