Abstract
The dynamics of nanosystems in solution contain a wealth of information with relevance for diverse fields ranging from materials science to biology and biomedical applications. When nanosystems are marked with fluorophores or strong scatterers, it is possible to track their position and reveal internal motion with high spatial and temporal resolution. However, markers can be toxic, expensive, or change the object’s intrinsic properties. Here, we simultaneously measure dispersive frequency shifts of three transverse modes of a high-finesse microcavity to obtain the three-dimensional path of unlabeled SiO2 nanospheres with 300 μs temporal and down to 8 nm spatial resolution. This allows us to quantitatively determine properties such as the polarizability, hydrodynamic radius, and effective refractive index. The fiber-based cavity is integrated in a direct-laser-written microfluidic device that enables the precise control of the fluid with ultra-small sample volumes. Our approach enables quantitative nanomaterial characterization and the analysis of biomolecular motion at high bandwidth.
Highlights
The dynamics of nanosystems in solution contain a wealth of information with relevance for diverse fields ranging from materials science to biology and biomedical applications
We have introduced the simultaneous measurement of several cavity transverse modes to achieve 3D particle tracking inside the cavity, which is an important step to combine the exceptional sensitivity of cavity-based sensors with spatial imaging
We have used this to demonstrate the quantitative characterization of the nanoparticle size and effective refractive index
Summary
The dynamics of nanosystems in solution contain a wealth of information with relevance for diverse fields ranging from materials science to biology and biomedical applications. We simultaneously measure dispersive frequency shifts of three transverse modes of a highfinesse microcavity to obtain the three-dimensional path of unlabeled SiO2 nanospheres with 300 μs temporal and down to 8 nm spatial resolution. This allows us to quantitatively determine properties such as the polarizability, hydrodynamic radius, and effective refractive index. Other approaches which enable single nanoparticle detection are evanescent biosensors using, e.g., nanoplasmonics[11,12], tapered fibers[13], or whispering gallery mode resonators such as microspheres[14,15], which enable the real-time detection, e.g., of adsorption events[16,17,18,19] and quantitative particle sizing[20] Those sensors are limited to the evanescent near-field. Particle tracking adds a central functionality to cavity-based sensing, opening up prospects for studies of diffusion dynamics and accurate characterizations of unlabeled nanosystems
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