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: from 2022 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512630344

• Final Report Year: 2025

Final Report Abstract

This project aimed to develop and study an optically induced electric field to manipulate microfluidic droplets. The limited reconfigurability of electrical potentials using miniaturized electrodes within microfluidic platforms was overcome by introducing purely optically shaped electrodes. Localized electric fields were generated by integrating iron-doped lithium niobate crystals taking advantage of its strong bulk photovoltaic effect. When illuminated, spatial charge distributions are induced in these crystals by light acting as virtual electrodes. Such a configuration enabled unlimited spatial control over the electrode shape through advanced light-shaping techniques. The high spatial flexibility offered by optically shaped electrodes makes this approach uniquely suited for custom droplet manipulation using the evanescent electric field outside the crystal. Various experimental configurations were explored, including tailoring the wetting properties of micropatterned surfaces, photovoltaic dispensing of pending droplets, and manipulating microfluidic droplets within micrometer-sized channels. The latter is particularly significant for broadening the range of applications involving closed microfluidic channels and circuits, which are gaining a lot of interest for their potential as lab-on-a-chip, biomedical and chemical devices. The integration of the crystal into conventional soft lithography fabrication was achieved by replacing the glass layer in traditional two-layer devices (e.g., PDMS bonding), maintaining the microfluidic device's performance. Notably, the change in wettability within the channels was negligible, enabling the realization of microfluidic generator configurations using the photovoltaic crystal as a substrate. Furthermore, the introduction of surfactants commonly used in droplet microfluidics was found to influence the virtual electrodes' working mechanism, leading to novel interactions with droplets. Specifically, a wide variety of coalescence regimes were observed and investigated in large droplet ensembles. By precisely controlling the light exposure for the virtual electrodes, the number of droplets involved in coalescence could be tailored on demand. Throughout this project, several collaborations were established, one of which led to the discovery of a novel technique for printing the virtual electrodes investigated in the project on dielectric materials. This breakthrough paves the way for future applications where the crystal's properties could enhance device functionality, such as flexible substrates and disposable platforms for biomedical applications.

Publications

• XXVII Young Researchers Meeting poster presentation, poster presentation: “Photovoltaic charge lithography on passive dielectric substrates using active Fe:LiNbO3 stamps”
  Riccardo Zamboni
  
• Light‐Induced Virtual Electrodes for Microfluidic Droplet Electro‐Coalescence. Advanced Functional Materials, 34(13).
  Zamboni, Riccardo; Sebastián‐Vicente, Carlos; Denz, Cornelia & Imbrock, Jörg
  
• MüSIM23: 2nd Münster Symposium on Intelligent Matter, 2 poster presentation: “Light-Driven Patterning of Electric Charge on Passive Dielectric Substrates using Fe:LiNbO3 Photovoltaic Stamps”
  Riccardo Zamboni
  
• MüSIM23: 2nd Münster Symposium on Intelligent Matter, 2 poster presentation: “Manipulating Matter using Light-Induced Virtual Electrodes Based on Lithium Niobate"
  Riccardo Zamboni
  
• NanoBioTech-Montreux Conference 2023, poster presentation: “Virtual electrodes in photovoltaic crystals: new opportunities in droplet manipulation”
  Riccardo Zamboni
  
• Optoelectric‐Driven Wetting Transition on Artificially Micropatterned Surfaces With Long‐Range Virtual Electrodes. Advanced Materials Interfaces, 12(1).
  Zamboni, Riccardo; Ray, Debdatta; Denz, Cornelia & Imbrock, Jörg
  
• Photorefractive Photonics and Beyond 2024 - PR’24, oral presentation: “Photovoltaic opto-electrowetting using Fe:LiNbO3 on artificially micropatterned surfaces”
  Riccardo Zamboni
  
• Photovoltaic Charge Lithography on Passive Dielectric Substrates Using Fe:LiNbO3 Stamps. Advanced Electronic Materials, 11(2).
  Sebastián‐Vicente, Carlos; Zamboni, Riccardo; García‐Cabañes, Angel & Carrascosa, Mercedes
  
• Photo‐Induced Electric Field Effects on Water Droplets Generated in a LiNbO3 Opto‐Microfluidic Platform. Advanced Materials Interfaces, 11(12).
  Bragato, Giovanni; Zaltron, Annamaria; Zanardi, Michele; Zamboni, Riccardo; De Ros, Maddalena & Sada, Cinzia
  
• All‐Optically Driven Optofluidic Light Modulator. Advanced Optical Materials, 13(14).
  Zamboni, Riccardo; Altin, Margherita; Bragato, Giovanni; Lucchetti, Liana; Sada, Cinzia & Zaltron, Annamaria
  
• Hybrid Microfluidic Chip Design with Two‐Photon Polymerized Protein‐Based Hydrogel Microstructures for Single Cell Experiments. Advanced Materials Technologies, 10(9).
  Dzikonski, Dustin; Bekker, Elena; Zamboni, Riccardo; Ciechanska, Dominika; Schwab, Albrecht; Denz, Cornelia & Imbrock, Jörg
  
• Lab-on-a-chip device for microfluidic trapping and TIRF imaging of single cells. Biomedical Microdevices, 27(1).
  Dzikonski, Dustin; Zamboni, Riccardo; Bandyopadhyay, Aniket; Paul, Deepthi; Wedlich-Söldner, Roland; Denz, Cornelia & Imbrock, Jörg
  
• Transition between light-induced attraction and repulsion of nanoparticles on a lithium niobate surface. Physical Review B, 111(5).
  Asché, E.; Zamboni, R.; Denz, C. & Imbrock, J.