Simultaneous stochastic sensing of divalent metal ions

Stochastic sensing is an emerging analytical technique that relies upon sin gle-molecule detection. Transmembrane pores, into which binding sites for a nalytes have been placed by genetic engineering, have been developed as sto chastic sensing elements(1-3). Reversible occupation of an engineered bindi ng site modulates the ionic current passing through a pore in a transmembra ne 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 de termined simultaneously with a single sensor element. Further, the sensor e lement can be permanently calibrated without a detailed understanding of th e kinetics of interaction of the metal ions with the engineered pore.