Force detection of high-frequency electron paramagnetic resonance spectroscopy of microliter solution sample

Force detection of magnetic resonance is now able to attain extremely high spin sensitivity. In these setups, microcantilevers were usually used as a sensitive force sensor and, in most cases, have been applied to solid-state samples such as paramagnetic impurities in solids. On the other hand, there are now growing demands for their applications to liquid-state samples in the research areas of life science because many proteins and enzymes are biofunctionally active only in solutions, where they interact with the surrounding water molecules. In this letter, we present an electron paramagnetic resonance (EPR) technique for solution samples using a SiNx nanomembrane and report high-frequency EPR spectroscopy of a microliter-volume frozen solution sample of hemin and myoglobin at multiple frequencies up to 350 GHz. This technique would be particularly useful to obtain more detailed insight into the electronic structure of metalloproteins/metalloenzymes under biologically active conditions.This study was partly supported by a Grant-in-Aid for Scientific Research (A) (No. JP17H01184) to Y.M., a Grant-in-Aid for Scientific Research (B) (No. JP26287081) to E.O., a Grant-in-Aid for Challenging Exploratory Research (No. JP26610104) to H.O., and a Grant-in-Aid for JSPS Research Fellow (No. JP18J11268) to T.O. from the Japan Society for the Promotion of Science (JSPS), the Asahi Glass Foundation to E.O., the Casio Foundation to E.O., and the Shimadzu Foundation to H.T.