Imaging and Quantitative Analysis on the Etching of Diatom Frustules via Digital Holographic Microscopy.

Frustules, whose length spans from a few micrometers to more than a hundred micrometers, have been the subject of various modifications to improve their physical properties because of their complex porous silica structure. However, three-dimensional measurements of these changes can be challenging because of the complex 3D architecture and limitations of known methods. In this study, we present a new method that applies digital holographic microscopy (DHM) to analyze controlled etched frustules and observe real-time degradation of frustules at the single-cell level. Frustules obtained from Craspedostauros sp. diatoms were etched in 1 N NaOH for 5 min at 25 and 60 °C, respectively, and the frustule's valve was analyzed using DHM. DHM uses a combination of holography and tomography to reconstruct a 3D refractive index image of the frustule. Measurements of the width, volume, and surface area are achieved. Results showed that at 60 °C of etching, a significant difference with the unetched frustule was observed for all measurements but with high fluctuation values. Finally, real-time observation of the degradation of the frustule is observed when immersed in a high concentration of NaOH. This is the first time the real-time etching of the frustule is observed at the single-cell level. This research provides an easy estimation of the 3D measurements of frustules that may provide new fundamental information and applications.

λ-like transition in the dynamics of ratchet gears in active bath.

To what extent the orientational order of self-propelling particles affects the dynamics of active bath-immersed ratchet devices remains unclear. We report experimental results of an inverse λ-like transition of the angular velocity of two ratchet gears in an active bath of self-propelling granular rods (SPRs) at different gear distances. The transition is caused by the phase transition in the orientational order of those SPRs located in the space between the gears. Brownian dynamics simulation of confined SPRs supports these observations. Thus, conditions for the upper bound efficiency of systems of active ratchet gears were obtained.