  A single levitated nanoparticle is used as a nano-reactor for studying
surface chemistry at the nanoscale. Optical levitation under controlled
pressure, surrounding gas composition, and humidity provides extreme control
over the nanoparticle, including dynamics, charge, and surface chemistry. Using
a single nanoparticle avoids ensemble averages and allows to study how the
presence of silanol groups at its surface affects the adsorption and desorption
of water from the background gas with unprecedented real time, spatial, and
temporal resolution. Here, we demonstrate the unique potential of this
versatile platform by studying the Zhuravlev model in silica particles. In
contrast to standard methods, our system allowed the first observation of an
abrupt and irreversible change in scattering cross section, mass, and
mechanical eigenfrequency during the dehydroxylation process, indicating
changes in density, refractive index and volume.
