Simultaneous stochastic sensing of divalent metal ions

Stochastic sensing is an emerging analytical technique that relies upon single-molecule detection. Transmembrane pores, into which binding sites for analytes have been placed by genetic engineering, have been developed as stochastic sensing elements(1-3). Reversible occupation of an engineered binding site modulates the ionic current passing through a pore in a transmembrane potential and thereby provides both the concentration of an analyte and, through a characteristic signature, its identity(1-3). Here, we show that the concentrations of two or more divalent metal ions in solution can be determined simultaneously with a single sensor element. Further, the sensor element can be permanently calibrated without a detailed understanding of the kinetics of interaction of the metal ions with the engineered pore.