Shigeru Amemiya

Our studies are focused on electrochemistry and analytical applications of charge- and molecular-transport processes at liquid/liquid interfaces, such as water/organic solution, water/polymer membrane, and biomembrane interfaces. Especially, our projects are directed toward (1) understanding membrane transport phenomena of chemical and biological importance and (2) developing electrochemical sensors based on the interfacial transport processes. In addition to conventional electrochemical techniques, we use scanning probe microscopy, such as scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM), in order to investigate the interfacial transport processes with high spatial resolutions. We also use computational simulation approaches to quantitatively understand these transport processes.

Chemical Imaging of Biomembranes by SECM

It is well known that biomembrane surface is laterally highly heterogeneous in nanometer scale. Thus, high-resolution imaging of membrane structure and function is urgently required in various biological contexts. We will develop very small electrochemical sensors for studying the ion- and molecular-transport processes through biomembrane nanostructures, e.g., ion-channel pores (0.2-10 nm) and lipid domains (100-500 nm). A scanning electrochemical microscope is used to position the sensors very close to a biomembrane surface and measure their response simultaneously. As the response indicates how fast the transport processes are at the local position, a plot of the response against the x,y-positions gives a chemical image of the membrane surface.

Electrochemical Sensors Based on Interfacial Molecular Recognition

In our second project, electrochemical sensors with high selectivity and sensitivity will be developed on the basis of molecular recognition (or host-guest chemistry) at liquid/liquid interfaces. Interfacial transfer of an analyte ion from a sample solution into a sensor membrane can be facilitated selectively by a receptor (ionophore) that forms complexes with the analyte in the membrane phase. This process can be directly detected as electrical signals, i.e., potential and current, allowing for simple construction of ion sensors, so called potentiometric and voltammetric ion-selective electrodes (ISEs), respectively. We are interested in miniaturization of the sensors for biomembrane studies (Figure 1) and in improving and understanding their response properties for clinical and environmental analysis. For both purposes, we will try to widen the range of detectable analytes by applying different types of receptors and by sophisticating detection principles.

Computational Simulations of Electrochemical Problems

We use PC-based numerical simulation methods to quantitatively understand important processes in the above-mentioned projects and more generally those in electrochemical problems, which have not been accessible analytically or numerically within reasonable computation time. A special emphasis will be on comprehensive understanding of diffusion and other kinetic processes at microenvironments such as intra- and extracellular spaces, biomembrane surfaces, and microelectrodes.