<p></p><p></p><p>Optical
microresonators have widespread application at the frontiers of nanophotonic
technology, driven by their ability to confine light to the nanoscale and
enhance light-matter interactions. Microresonators form the heart of a new
method for single-particle photothermal absorption spectroscopy, whereby the
microresonators act as microscale thermometers to detect the heat dissipated by
optically pumped, non-luminescent nanoscopic targets. However, translation of
this technology to chemically dynamic systems requires a platform that is
mechanically stable, solution compatible, and visibly transparent. We report
microbubble absorption spectrometers as a new and versatile platform that meets
these requirements. Microbubbles integrate a two-port microfluidic device within
a Whispering Gallery Mode (WGM) microresonator, allowing for the facile
exchange of chemical reagents within the resonator’s interior while maintaining
a solution-free environment on its exterior. We first leverage these qualities to
investigate the photo-activated etching of single gold nanorods by ferric
chloride, providing a new method for rapid acquisition of spatial and
morphological information about nanoparticles as they undergo chemical
reactions. We then demonstrate the ability to control nanorod orientation within
a microbubble through optically exerted torque, a new route toward the
construction of hybrid photonic-plasmonic systems. Critically, the reported
platform advances microresonator spectrometer technology by permitting
room-temperature, aqueous experimental conditions, opening a regime of time-resolved
single-particle experiments on non-emissive, nanoscale analytes engaged in
catalytically and biologically relevant chemical dynamics.</p><p></p><p></p>
A quantitative nanoparticle extraction method for microsecond time resolved single-particle ICP-MS data in the presence of a high background
