REACTMIN: Reactive Scanning Based Single Particle Tracking using a Minimum of Light

Real-time feedback-driven single particle tracking is an emerging method of measuring the state and dynamics of individual molecules and particles at the nanometer scale as they move inside living cells. Two problems limit current performance: the photon budget of fluorescent labels, and the control temporal budget. REACTMIN overcomes these challenges by reactively scanning a minimum of light to track diffusing particles and molecules. It is comprised of a non-holonomic based extremum seeking controller and structured illumination using a laser with a central minimum. The controller allows for estimationless tracking, addressing the control temporal budget, and the structured illumination enables information rich measurements, addressing the photon budget. We use two metrics of performance, Fisher information and tracking duration, to characterize the system and find optimal settings for one of the dominant controller parameters, the steady state orbital radius. We demonstrate a trade-off between tracking duration and localization precision and discuss how to select this parameter in the context of specific experimental aims.