pH Nanosensor Using Electronic Spins in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2019-09-20 |
| Journal | ACS Nano |
| Authors | Takahiro Fujisaku, Ryotaro Tanabe, Shinobu Onoda, Ryou Kubota, Takuya F. Segawa |
| Institutions | Kyoto University, ETH Zurich |
| Citations | 115 |
Abstract
Section titled âAbstractâNanoscale 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 <i>T</i><sub>1</sub> 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 p<i>K</i><sub>a</sub>. 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 (D<sub>2</sub>O) buffers. This indicates that the pH dependence is not caused by magnetic noise induced by <sup>1</sup>H nuclear spin fluctuations, but by electric noise induced by ion exchanges. <i>Via</i> 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.