Department of Medical Biochemistry & Genetics, The Texas A&M University System Health Science Center, College Station, TX 77843-1114, U.S.A.
Sensor elements are being made in our laboratory by engineering transmembrane protein pores. Analyte molecules modulate the ionic current driven through the engineered pores by a transmembrane potential. Stochastic sensing, which uses currents from single pores, is an especially attractive prospect. This approach yields both the concentration and identity of an analyte, the latter from its distinctive current signature. Further, several analytes can be detected simultaneously with a single sensor element. In one example of stochastic sensing, the bacterial pore-forming protein staphylococcal alpha-hemolysin has been altered to permit the detection of divalent metal cations by using mutagenesis to place a cation-binding site within the conductive pathway. In a second example, the hemolysin pore has been modified with cyclodextrins, which act as non-covalent molecular adapters, to allow the detection of a variety of small organic molecules. Finally, ligands have been covalently attached to the hemolysin pore, either directly or through polymer tethers, permitting the detection of proteins and DNA.