Hiroko Someya

Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

Spin-Seebeck thermoelectric converter

Thermoelectric conversion (TEC) technologies, which convert heat into electricity, have received a great attention, because they are expected to be a powerful approach to utilize wasted thermal energy. Here we present novel thermoelectric converters based on the spin Seebeck effect (SSE), and show their scaling law which is largely different from that of conventional TEC devices. We experimentally demonstrate that the TEC output signals straightforwardly increase with the size of the converters. This scaling law enables us to implement simple-structured thermoelectric converters by using productive film-coating methods. Such coating-based TEC techniques may pave the way for a wide range of applications using a variety of heat sources.

Label-free immunosensor using a gold electrode covered with conductive self-assembled monolayer

This paper describes an electrochemical immunosensor for the detection of target molecules without the use of labeled antibodies. The sensor is based on the combination of a gold electrode covered with a conductive self-assembled monolayer (SAM) of mixed thiols and a permeability measurement of an antibody layer anchored on the SAM. The permeability was measured by the square wave voltammetry (SWV) of ferrocyanide added in a measurement solution. The conductive SAM allows constant electron transfer between the electrode and ferrocyanide, providing a stable signal during repeated SWV measurements in contrast to immunosensors using conventional SAM techniques. We demonstrate that our sensor using the Anti-human chorionic gonadotropin (hCG) antibody selectively detects hCG in a minute without any washing process. The presented label-free immunosensor technology is fundamentally suited for easy-to-use assays for biological molecules such as hormones and drugs.