Ion-selective detection of non-intercalating Na+ using competitive inhibition of K+ intercalation in Prussian blue nanotubes sensor

A nanotubes sensor for Na+ is fabricated using electrodeposition of iron hexacyanoferrate polymer within the nanochannels of a nanoporous metal-coated membrane. The sensing signal is derived from the influence of Na+ on the cathodic peak potential of the voltammetric response of the Prussian blue (PB) nanotubes immersed in a background solution containing K+, giving a 2K+:1e− Nernstian response, instead of the usual 1K+:1e− process in the absence of Na+. A competitive-inhibition reaction scheme is proposed which gives excellent agreement of theoretical values derived from equilibrium consideration, with experimental data obtained under reversible, slow scan rate conditions. A wide linear range over three orders of magnitude for Na sensing can be achieved by simple adjustment of background K+ levels. Specific and accurate detection of Na+ using the PB nanotubes sensor is demonstrated in a solution containing potential interfering ions: K+, Mg2+, Ca2+.