Sensor Measures Protons, Polarity

A two-for-one sensor that can simultaneously detect local proton concentration and polarity could lead to a tool that can measure the proton gradients across biological membranes involved in the production of adenosine triphosphate, the cell's energy currency. A. Prasanna de Silva at Queen's University, in Belfast, and his collaborators built a small molecule that possesses an amine proton receptor and a polarity-sensitive aromatic fluorophore (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200801516). Proton concentration is measured by the intensity of the light emitted by the fluorophore. Polarity is measured by tracking shifts in the wavelength of the emitted light caused by changes in local dielectric constant. The sensor also has three sites (red) that can be tailored to position the sensor within a membrane or other system. The researchers used the sensor shown to measure how deep into micelles protons can penetrate, and they are now developing a molecule that can sense other ions such as sodium. Such sensors are "nanoscale versions of robotic vehicles that go to humanly inaccessible spaces, map local properties, and send information back to us," de Silva notes.