Nanopore-Based Detection of Trace Concentrations of Multivalent Ions When Impurity Ions Are Present.

The feasibility of detecting a trace concentration of multivalent ions based on the ionic current rectification (ICR) of a nanopore when impurity ions might present is assessed. Adopting a bullet-shaped nanopore surface modified with tannic acid as an example, the detection of trace concentrations of Cu 2+ (target ion) when Fe 3+ (impurity) is present with K + as background ions under various conditions is simulated. In particular, the influence of the reaction order of the association of target ions and tannic acid on the nanopore performance is examined. We show that the lower the background concentration the better the detection performance. For the examined background concentrations of 1, 10, 100, and 1000 mM, the optimal detection ranges are [0.5, 1000 μM] and [1, 1000 nM] for Cu 2+ and Fe 3+ , respectively. The detection limits, 0.5 μM for Cu 2+ and 1 nM for Fe 3+ , are lower than those that can be obtained from conventional instruments, suggesting the potential of applying the present nanopore-based approach. In addition, we also consider the presence of multiple ions, which can occur, for example, in detecting Cu 2+ (target ion) when Fe 3+ (impurity) might present or vice versa with K + as background ions. The competitive adsorption of these three kinds of ions can yield complicated ICR behaviors.