| Abstract
| - This article describes two complementary techniques,single-particle tracking and correlation spectroscopy, foraccurately sizing nanoparticles confined within picolitervolume aqueous droplets. Single-particle tracking workswell with bright particles that can be continuously illuminated and imaged, and we demonstrated this approach for sizing single fluorescent beads. Fluorescencecorrelation spectroscopy detects small intensity burstsfrom particles or molecules diffusing through the confocalprobe volume, which works well with dim and rapidlydiffusing particles or molecules; we demonstrated FCS forsizing synaptic vesicles confined in aqueous droplets. Incombination with recent advances in droplet manipulations and analysis, we anticipate this capability to sizesingle nanoparticles and molecules in free solution willcomplement existing tools for probing cellular systems,subcellular organelles, and nanoparticles.
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