Separate Detection of Sodium and Potassium Ions with Sub-micropipette Probe

A novel method of detecting sodium and potassium ions separately with a sub-micropipette probe of approximately 100 nm inner diameter has been demonstrated. A poly(vinyl chloride) film containing crown ether ligands in sub-micropipettes filtered the ions. Sodium ions were trapped with bis(12-crown-4), whereas potassium ions were trapped with bis(benzo-15-crown-5). Alternate and direct bias voltages were applied to the counter electrode in the sub-micropipette so that the local ion concentrations could be observed as current signals after conversion to milivolt output signals with our low-current detection system prepared for this study.