Electrostatic Manipulation and Measurement of Liquid Transport Properties of Diatoms via In Situ Optical Microscope

Diatoms, a type of phytoplankton, inhabit diverse aquatic environments such as oceans, lakes, and rivers. These unicellular organisms are encased in complex, silica-based shells known as frustules. Diatom frustules are characterized by intricate, multi-level hierarchical pore patterns, with the smallest pores measuring just a few nanometers. Such sophisticated structures are beyond the capabilities of modern cleanroom fabrication techniques. Consequently, diatom frustules have garnered significant interest for various applications in nanotechnology and biotechnology, including drug delivery, wastewater treatment, and the development of bio and gas sensors.<br/>To advance these applications, a deep understanding of the principles governing liquid transport within diatom frustules is crucial. However, studying liquid transport through the hierarchical pores of individual diatom frustules, which are only tens of micrometers in size, presents substantial challenges. To address these issues, we have developed a microfluidic test rig that incorporates high-resolution optical microscopy. This device can not only detect liquid propagation from multiple perspectives with high spatial resolution and frame rate but is also capable of lifting and placing diatoms at desired positions using an electrostatic manipulator. Using the diatom species Coscinodiscus Wailesii as a case study, we identified the key microscopic features influencing liquid transport in diatom frustules and, for the first time, determined critical liquid transport properties. Additionally, the electrostatic manipulation of these organisms can be achieved and is explained by theoretical calculations.<br/>This research illuminates the fundamental mechanisms of manipulation and liquid transport in diatom frustules. The optical metrology-based test rig created for this study offers a versatile platform for various microfluidic analyses. This work was supported by the Air Force Office of Scientific Research under Award Number FA9550-23-1-0055.