arXiv subjects

Michio Niwano

Publications and source records attributed to Michio Niwano.

4 recordsLinked to original sources

arXiv2025

Genesis of a Horizontal Electric Field within the Lipid Bilayer: A Bilayer-Embedded Actuation Platform

The electric field of biological membranes has long been treated as a one-dimensional quantity, defined solely by the component normal to the bilayer (E_VERT). Here, we present a bioelectronic platform that enables controlled generation of a horizontal electric field within the hydrophobic core of a lipid bilayer (E_HORZ). The device incorporates micrometer-scale electrodes embedded within the bilayer torus, allowing sustained E_HORZ actuation. Applied E_HORZ selectively and reversibly accelerates slow inactivation of a voltage-gated potassium channel while leaving activation essentially unchanged. Physical considerations further indicate that E_HORZ arises naturally wherever membrane potential varies spatially, including at action potential wavefronts, suggesting broader physiological relevance. This platform provides experimental access to vector-resolved membrane electric fields and establishes a generalizable strategy for multidirectional electrical control of soft-matter biointerfaces.

physics.bio-ph↗

arXiv2020

Optical transport of sub-micron lipid vesicles along an optical nanofibre

Enhanced manipulation and analysis of bio-particles using light confined in nano-scale dielectric structures has proceeded apace in the last several years. Small mode volumes, along with the lack of a need for bulky optical elements give advantages in sensitivity and scalability relative to conventional optical manipulation. However, manipulation of lipid vesicles (liposomes) remains difficult, particularly in the sub-micron diameter regime. Here we demonstrate the optical trapping and transport of sub-micron diameter liposomes along an optical nanofiber using the nanofiber mode's evanescent field. We find that nanofiber diameters below a nominal diffraction limit give optimal results. Our results pave the way for integrated optical transport and analysis of liposome-like bio-particles, as well as their coupling to nano-optical resonators.

physics.bio-ph↗

arXiv2020

Characterization of bulk nanobubbles formed by using a porous alumina film with ordered nanopores

Gaseous nanobubbles (NBs), with their unique physicochemical properties and promising applications, have become an important research topic. Generation of monodispersed bulk NBs with specified gas content remains a challenge. We developed a simple method for generating bulk NBs, using porous alumina films with ordered straight nano-scaled holes. Different techniques, such as nanoparticle tracking analysis (NTA), atomic force microscopy (AFM), and infrared absorption spectroscopy (IRAS), are used to confirm NB formation. The NTA data demonstrates that the minimum size of the NBs formed is less than 100 nm, which is comparable to the diameter of nanoholes in the porous alumina film. By generating NBs with different gases, including CO2, O2, N2, Ar, and He, we discovered that the minimum size of NBs negatively correlated with the solubility of encapsulated gases in water. Due to the monodispersed size of NBs generated from the highly ordered porous alumina, we determined that NB size is distributed discretely with a uniform increment factor of sqrt(2). To explain the observed characteristic size distribution of NBs, we propose a simple model in which two NBs of the same size are assumed to preferentially coalesce. This characteristic bubble size distribution is useful for elucidating the basic characteristics of nanobubbles, such as the long-term stability of NBs. This distribution can also be used to develop new applications of NBs, for example, nano-scaled reaction fields through bubble coalescence.

physics.app-ph↗

arXiv2019

A Teflon-based system for applying multidirectional voltages to lipid bilayers as a novel platform for membrane proteins

Artificial bilayer lipid membranes (BLMs), along with patch-clamped membranes, are frequently used for functional analyses of membrane proteins. In both methods, the electric properties of membranes are characterized by only one parameter, namely, transmembrane potential. Here the construction of a novel BLM system was reported, in which membrane voltages can be controlled in a lateral direction in addition to conventional transmembrane direction. A microaperture was fabricated in a Teflon film and Ti electrodes were evaporated around the aperture. BLMs were reproducibly formed in the aperture without being affected by the presence of the electrodes. The application of a lateral voltage induced no significant changes in the electric properties of the BLMs, such as baseline current, transmembrane resistance, and transmembrane capacitance. In contrast, lateral voltages clearly affected the activities of biological ion channels, suggesting that the lateral voltage might be a useful parameter for analyzing channel activities. The present Teflon-based system in which multidirectional voltages can be applied to BLMs represent a promising platform for the analysis of underlying functional properties of membrane proteins.

physics.bio-ph↗