Toward Real-Time Monitoring and Control of Single Nanoparticle Properties with a Microbubble Resonator Spectrometer

20 June 2019, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


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.


single-particle spectroscopy
gold nanorod
absorption spectroscopy

Supplementary materials

Microbubble SI ChemRxiv v2


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