Laser-patterned thin-film electrodes: Imaging ion accumulation and trapped nanoparticles

This study introduces a straightforward electrode design featuring sharp edges with a curvature of a few hundred nanometers in radius, with which both ion accumulation and nanoparticle deposition can be observed under an alternating electrical potential. The electrodes, termed “shark-teeth electrodes,” are fabricated using a laser ablation technique optimized for facile nanostructure creation. This method involves successive, overlapping ablated disks in a thin-film of gold, producing sharp tips that generate strong electric fields. When electrically polarized in an electrolyte solution, these sharp tips form a screening layer, facilitating the observation of ion and nanoparticle behavior. A total-internal reflection microscope is employed to monitor ion accumulation on these electrodes, demonstrating their capability in iontronic microscopy. In addition, the same electrodes are used to track nanoparticle trapping under high-frequency alternating potentials. This dual functionality allows for the investigation of electrochemical and physical interactions between ions and colloidal nanoparticles, which provide valuable insights into soft matter systems, including biological systems such as cells, where similar interactions play a crucial role.