@article{oai:repo.qst.go.jp:00076859,
 author = {Fujisaku, Takahiro and Tanabe, Ryotaro and Onoda, Shinobu and Kubota, Ryou and F. Segawa, Takuya and So, Frederick and Ohshima, Takeshi and Hamachi, Itaru and Shirakawa, Masahiro and Igarashi, Ryuji and Takahiro, Fujisaku and Shinobu, Onoda and So, Frederick and Takeshi, Ohshima and Masahiro, Shirakawa and Ryuji, Igarashi},
 issue = {10},
 journal = {ACS Nano},
 month = {Sep},
 note = {Nanoscale measurements provide insight into the nano world. For instance, nanometric spatiotemporal distribution of intracellular pH is regulated by and regulates a variety of biological processes. However, there is no general method to fabricate nanoscale pH sensors. Here, we, to endow pH-sensing functions, tailor the surface properties of a fluorescent nanodiamond (FND) containing nitrogen-vacancy centers (NV centers) by coating the FND with an ionic chemical layer. The longitudinal relaxation time T1 of the electron spins in the NV centers inside a nanodiamond modified by carboxyl groups on the particle surface was found to depend on ambient pH between pH 3 and pH 7, but not between pH 7 and pH 11. Therefore, a single particle of the carboxylated nanodiamond works as a nanometer-sized pH meter within a microscopic image and directly measures the nanometric local pH environment. Moreover, the pH dependence of an FND was changed by coating it with a polycysteine layer, which contains a multitude of thiol groups with higher pKa. The polycysteine-coated nanodiamond obtained a pH dependence between pH 7 and pH 11. The pH dependence of the FND was also observed in heavy water (D2O) buffers. This indicates that the pH dependence is not caused by magnetic noise induced by 1H nuclear spin fluctuations, but by electric noise induced by ion exchanges. Via our method, the
sensitive pH range of the nanodiamond pH sensor can potentially be controlled by changing the ionic layer appropriately according to the target biological phenomena.},
 pages = {11726--11732},
 title = {pH Nanosensor Using Electronic Spins in Diamond},
 volume = {13},
 year = {2019}
}