Combined scattering and fluorescence sensing of single nanoparticles confined in an anti-Brownian electrokinetic trap

Biomolecular nanoparticles are increasingly prevalent in health and sustainability sciences, but they show complexity in their composition and dynamics. Therefore, it is important to extract multiple types of measurements from individual nanoparticles such as their sizes, electrostatic properties, and chemical dynamics. Anti-Brownian electrokinetic trapping has provided a useful platform to study single fluorescent nanoparticles with a high level of detail, though photobleaching and blinking prematurely end particle detection. To remedy this, we developed an interferometric scattering anti-Brownian electrokinetic (ISABEL) trap, where a particle is localized through the universal mechanism of scattering and active feedback on the particle's Brownian motion is applied by electric fields. We show that single nanoparticles can be localized and trapped with this scheme, that internalized fluorescent biosensors can measure chemical environment within biological nanoparticles, and that positional fluctuations in the trap provide access to the particle's diffusion coefficient, leading to a single-particle radius estimate. These combined capabilities place the ISABEL trap in a distinct position in the ecosystem of solution-phase trapping experiments.