Functionalized ZnO nanorod-based selective magnesium ion sensor for intracellular measurements.

ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 μm in tip diameter) and used as selective potentiometric sensor of intracellular free Mg(2+). To functionalize the ZnO nanorods for selectivity of Mg(2+), a polymeric membrane with Mg(2+)-selective ionophores were coated on the surface of the ZnO nanorods. These functionalized ZnO nanorods exhibited a Mg(2+)-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode within the concentration range from 500 nM to 100 mM. Two types of cells, human adipocytes and frog oocytes, were used for the intracellular Mg(2+) measurements. The intracellular concentration of free Mg(2+) in human adipocytes and frog oocytes were 0.4-0.5 and 0.8-0.9 mM, respectively. Such type of nanoelectrode device paves the way to enable analytical measurements in single living cells and to sense other bio-chemical species at the intracellular level.