Detection of clinically important cations by a pillar[5]arene-modified electrochemical sensor

1,4-Dimethoxypillar[5]arene (1,4-DMP[5]A) was incorporated into graphite-epoxy composite electrodes and shown to give an enhanced response to clinically important Na+ and K+ over other simple cations. Electrode selectivity, sensitivity, stability and reproducibility were determined. The mechanism behind selectivity was investigated using computational simulations which indicated that Li+, Rb+ and Cs+ exist as solvated cations outside, or at the opening to, the macrocycle whereas Na+ and K+ are bound within the macrocyclic cavity. Simulations suggest that 1,4-DMP[5]A has a higher binding affinity for K+ over Na+. This was confirmed experimentally by stripping cations from the electrodes; Na+ was released in 6 s and K+ in 36 s. Accurate K+ detection by the composite electrodes was only possible above 8 mM but Na+ could be detected across the entire physiologically relevant concentration range.