Amperometric tape ion sensors for cadmium(II) ion analysis
This paper describes a novel tape platform ion sensing methodology specific to the detection of cadmium(II) ions in aqueous solution based on assisted ion transfer reactions across a polarized water | organic gel micro-interface. The tape ion sensors were constructed to incorporate the microwater | polyvinylchloride-2-nitrophenylethyl ether (PVC–NPOE) gel interfaces referred to as ionodes. The sensors have overall thicknesses less than $300\mu m$, allowing their packaging in a disposable tape format. The detection methodology is based on the selective assisted transfer of the cadmium ion in aqueous phase by ETH 1062 present in the PVC–NPOE gel layer and was first investigated using cyclic voltammetry. Quantitative analysis of cadmium(II) ions in aqueous solution using the tape sensors was then conducted under stop-flow conditions. Detection limits as low as 20 ppb (178 nM) for Cd(II) ions in very small volumes as low as a single 20ul droplet without any sample preconcentration was achieved in an analysis time of approximately 20 s, which could be easily employed for the direct measurement of Cd(II) ion levels in various field applications. The tape ion sensor can also be used in a flow-cell geometry to preconcentrate Cd(II) ions from aqueous samples and further improve the detection limit.