Abstract
The use of optical tweezers to measure forces acting upon microscopic particles has revolutionised fields from material science to cell biology. However, despite optical control capabilities, this technology is highly constrained by the material properties of the probe, and its use may be limited due to concerns about the effect on biological processes. Here we present a novel, optically controlled trapping method based on light-induced hydrodynamic flows. Specifically, we leverage optical control capabilities to convert a translationally invariant topological defect of a flow field into an attractor for colloids in an effectively one-dimensional harmonic, yet freely rotatable system. Circumventing the need to stabilise particle dynamics along an unstable axis, this novel trap closely resembles the isotropic dynamics of optical tweezers. Using magnetic beads, we explicitly show the existence of a linear force-extension relationship that can be used to detect femtoNewton-range forces with sensitivity close to the thermal limit. Our force measurements remove the need for laser-particle contact, while also lifting material constraints, which renders them a particularly interesting tool for the life sciences and engineering.
Highlights
We recently showed [1] how an optically generated flow field, which adaptively pushes a particle towards a target position, is sufficient to counteract the particle’s diffusion on timescales longer than the feedback time
As the flow velocity at the position of the particle was independent from its radial displacement, we concluded that this hydrodynamic trap was not suitable for force measurements
Analysis revealed that the profile of the trapping potential is symmetric, confirming that the magnitude of the restoring force achieved by dynamic optical rotation of the laser scan paths
Summary
We recently showed [1] how an optically generated flow field, which adaptively pushes a particle towards a target position, is sufficient to counteract the particle’s diffusion on timescales longer than the feedback time. As the flow velocity at the position of the particle was independent from its radial displacement, we concluded that this hydrodynamic trap was not suitable for force measurements. We present a novel optically induced hydrodynamic trap that effectively relies on the passive self-centring of a particle in a quasi-1D flow field. This field is characterised by a linear force–displacement relationship that enables the measurement of external forces. To this end, we transitioned from a flow dipole. The reduction to one dimension renders this new trap inherently stable and isotropic, and mitigates the need to stabilise particle dynamics along an extensional axis via the adaptive repositioning of this stagnation point
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
