The detection of real changes in the membrane potential across a human fat cell was monitored by measuring the electrochemical potential at the single cell membrane/ZnO nanorod surface interface in the intracellular environment. The probe was positioned within a sub-micrometer of the membrane surface. As the ZnO nanorods probe moved between the intracellular near-membrane and intracellular far from the membrane positions the electrochemical potential difference signal was detected. This electrochemical potential is caused by binding of biomolecular species onto the surfaces of the ZnO nanoprobe due to the high isoelectric point of ZnO. The response time is of critical interest for our physiological experiment. Other challenges include the insertion of intracellular electrodes and the ability to follow slowly changing events.

ZnO nanorods are minimally invasive tools appropriate for intracellular measurements in single living cells. The penetration of the ZnO nanorods electrode into the membrane of a single cell does not visibly seem to affect cellular viability in our experiment. But it was used to obtain only one measurement at a time and was not reused, resulting from the strong association of cell materials with the electrode. ZnO nanorods electrodes deliver remarkable sensitivity and they can be equally applied to measure the pH gradient and cell-membrane potential as well as acting as an electrochemical pH sensor. This experiment allows for measurements around the surface of cells and localized to particular points.

The researchers presented their work in Nanotechnology.