Stochastic sensing of TNT with a genetically engineered pore

Engineered versions of the transmembrane protein pore a-hemolysin (alpha HL) can be used as stochastic sensing elements for the identification and quantification of a wide variety of analytes at the single-molecule level. Until now, nitroaromatic analytes have eluded detection by this approach. We now report that binding sites for nitroaromatics con be built within the lumen of the alpha HL pore from simple rings of seven aromatic amino acid side chains (Phe, Tyr or Trp). By monitoring the ionic current that posses through a single pore at a fixed applied potential, various nitroaromatics con be distinguished from Ton the basis of the amplitude and duration of individual current-blocking events. Rings of less than seven aromatics bind the analytes more weakly; this suggests that direct aromatic-aromatic interactions are involved. The engineered pores should be useful for the detection of explosives and, in combination with computational approaches and structural analysis, they could further our understanding of non-covalent interactions between aromatic molecules.