Abstract
Anti-Brownian electrokinetic trapping is a method for trapping single particles in liquid based on particle position measurements and the application of feedback voltages. To achieve trapping in the axial direction, information on the axial particle position is required. However, existing strategies for determining the axial position that are based on measuring the size of the first diffraction ring, theory fitting, advanced optical setups or pre-determined axial image stacks are impractical for anisotropic particles. In this work, axial electrokinetic trapping of anisotropic particles is realized in devices with planar, transparent electrodes. The trapping algorithm uses Fourier-Bessel decomposition of standard microscopy images and is learning from the correlation between applied voltages and changes in the particle appearance. No previous knowledge on the particle appearance, theory fitting or advanced optical setup is required. The particle motion in the trap and the influence of screening of the electric field on this motion are analyzed. The axial trapping method opens new possibilities for measuring properties of anisotropic or isotropic particles and forces acting on such particles.
Highlights
In recent years anti-Brownian electrokinetic trapping has become a valuable tool in the study of individual particles and inter-particle interactions in liquid[1,2,3,4,5,6,7,8,9]
For the case of standard microscopy images, one approach is to extract specific features from the images such as the distance from the particle center to the first bright diffraction ring and to create a calibration curve relating this distance to the axial position[6,10,11]
To achieve robust axial electrokinetic trapping of anisotropic particles an algorithm is developed with two key features
Summary
In recent years anti-Brownian electrokinetic trapping has become a valuable tool in the study of individual particles and inter-particle interactions in liquid[1,2,3,4,5,6,7,8,9]. Www.nature.com/scientificreports diffraction limit, it may not be possible to use a look-up-table, to fit the images with theory sufficiently fast to achieve real-time trapping or to use laser scanning schemes. For these cases the question arises if a more general algorithm can be developed to achieve electrokinetic trapping based on standard microscopy images. Axial electrokinetic trapping of anisotropic particles such as doublets and triplets as well as spherical particles in water is demonstrated without requiring look-up-tables, theory fitting or other particle-specific methods. The presented method opens new possibilities for trapping and characterizing particles in lab-on-a-chip devices with microscale electrode geometries, for measuring forces on anisotropic particles and for characterizing electrokinetics and Faradaic reactions at the water-electrode interface
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