Microfluidic Droplet dynamics Actuated by Light-Induced Virtual Electrodes - µDrop ALIVE

• Applicant: Riccardo Zamboni, Ph.D.
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Experimental Condensed Matter Physics ; Microsystems ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512630344

This project aims to develop and study an optically induced electric field to manipulate microfluidic droplets confined in micrometer-sized channels. The limited reconfigurability of the electrical potential by miniaturized electrodes within microfluidic platforms will be overcome by the introduction of purely optically shaped electrodes. Reconfigurable and flexible electrodes will allow the introduction of a bottom-up approach to assemble groups of droplets on demand, controlling the individual trajectory and position of each droplet within a microfluidic platform. A localized electric field will be applied within the microfluidic channels by means of the integration of iron-doped lithium niobate crystals, exhibiting the bulk photovoltaic effect. Upon illumination with light patterns, photoinduced evanescent electric fields will be generated near the surfaces of these crystals and within the microfluidic droplet device, thereby tailoring the potential for electrical interaction with femto- and nanoliter droplets via light structures. A soft lithography fabrication protocol will be used for the integration of this crystal into droplet microfluidic devices, while maintaining the wettability for droplet flow within the channels (WP1). Unlimited spatial control of the virtual electrode shape will be achieved by means of light shaping techniques. The high spatial flexibility provided by the optically shaped electrode makes this approach unique for custom manipulation of individual droplets. Among the wide range of shapes that can be generated, strip- and ring-shaped light patterns will be used to control the movement and position of droplets in Poiseuille flows (WP2), trapping them or forcing them to follow specific trajectories. The ability of the system to perform different and consecutive operations on the droplets will depend on the reconfigurability of the systems and, thus, the reorganization of the charge within the crystal and the temporal response of the microfluidic part of the system. The reconfiguration frequency will be measured by means of specific experiments, aimed at analyzing the different contributions to the temporal response of the virtual electrode systems (WP3). Finally, this light-based electrical interaction will be exploited to manipulate droplets in order to create droplet ensembles, such as crystal-like structures, as well as functional droplet clusters, in a bottom-up approach (WP4). Among the different configurations that can be achieved, the dynamics of droplet assembly in a customizable 2d and 1d electrical potential landscape will be observed, as well as hybrid manipulation will be addressed by nano- and microparticle-based electrical encapsulation within the droplet.

• DFG Programme: WBP Position