Preview: Small 5/2006

The cover picture illustrates quantitative chemical imaging of pH in mast cells facilitated by core/shell silica nanoparticle sensors incorporating two fluorescent dye species.These 70-nm particles were designed to maximize the exposure of the covalently bound sensor dye (FITC) in the outer silica shell, while sequestering the reference dye (TRITC) within the particle core to minimize perturbations.Ratiometric comparison of the sensor and reference fluorescence allows the pH to be measured down to the single-particle scale.Confocal fluorescence images of the red and green channels are shown superimposed on a bright-field image of the cell under investigation (inset) and were analyzed to yield the false-spectrum image of pH in various intracellular vesicles.For more information, please read the Communication "Core/Shell Fluorescent Silica Nanoparticles for Chemical Sensing: Towards Single-Particle Laboratories" by U. Wiesner and co-workers in Issue 6/2006 of Small.