Seungbin Yoon

Microelectrodes are widely used for neural signal analysis because they can record high-resolution signals. In general, the smaller the size of the microelectrode for obtaining a high-resolution signal, the higher the impedance and noise value of the electrodes. Therefore, to improve the signal-to-noise ratio (SNR) of neural signals, it is important to develop microelectrodes with low impedance and noise. In this research, an Au hierarchical nanostructure (AHN) was deposited to improve the electrochemical surface area (ECSA) of a microelectrode. Au nanostructures on different scales were deposited on the electrode surface in a hierarchical structure using an electrochemical deposition method. The AHN-modified microelectrode exhibited an average of 80% improvement in impedance compared to a bare microelectrode. Through electrochemical impedance spectroscopy analysis and impedance equivalent circuit modeling, the increase in the ECSA due to the AHN was confirmed. After evaluating the cell cytotoxicity of the AHN-modified microelectrode through an in vitro test, neural signals from rats were obtained in in vivo experiments. The AHN-modified microelectrode exhibited an approximate 9.79 dB improvement in SNR compared to the bare microelectrode. This surface modification technology is a post-treatment strategy used for existing fabricated electrodes, so it can be applied to microelectrode arrays and nerve electrodes made from various structures and materials.

Oblique submicron-scale structures are used in various aspects of research, such as the directional characteristics of dry adhesives and wettability. Although deposition, etching, and lithography techniques are applied to fabricate oblique submicron-scale structures, these approaches have the problem of the controllability or throughput of the structures. Here, we propose a simple X-ray-lithography method, which can control the oblique angle of submicron-scale structures with areas on the centimeter scale. An X-ray mask was fabricated by gold film deposition on slanted structures. Using this mask, oblique ZEP520A photoresist structures with slopes of 20° and 10° and widths of 510 nm and 345 nm were fabricated by oblique X-ray exposure, and the possibility of polydimethylsiloxane (PDMS) molding was also confirmed. In addition, through double exposure with submicron- and micron-scale X-ray masks, dotted-line patterns were produced as an example of multiscale patterning.

Abstract Electrospun fibrous membranes are widely used for water‐oil separation. However, achieving effective separation often requires post‐processing to enhance membrane wettability or modify pore size, which can reduce productivity. In this study, a simple method is proposed for pore size control via mechanical compression of electrospun membranes. Polystyrene (PS) fibrous membranes (PFMs) are fabricated through electrospinning and subsequently compressed using a hand tool, reducing the membrane thickness by ≈87%. The proportion of pores smaller than 10 µm in diameter increase from 4.8% before compression to a maximum of 45.6% after compression. While the uncompressed membrane allowes sub‐10‐µm water droplets to pass through, the compressed membrane effectively blocked them. Due to the oleophilic nature of PS, oil permeation occurres rapidly via capillary action, while water droplets are retained within the membrane's internal pores, facilitating continuous demulsification. By combining electrospinning with mechanical compression, the optimized compressed PS fibrous membrane (CPFM) successfully separated water‐in‐oil emulsions under gravity, achieving a separation flux of 606 L m −2 h −1 with an oil purity of over 99.85%. This approach provides a simple, cost‐effective, and highly efficient method for water‐in‐oil emulsion separation.