Amplification of single molecule translocation signal using β-strand peptide functionalized nanopores.

Changes in ionic current flowing through nanopores due to binding or translocation of single biopolymer molecules enable their detection and characterization. It is, however, much more challenging to detect small molecules due to their rapid and small signal signature. Here we demonstrate the use of de novo designed peptides for functionalization of nanopores that enable the detection of a small analytes at the single molecule level. The detection relies on cooperative peptide conformational change that is induced by the binding of the small molecule to a receptor domain on the peptide. This change results in alteration of the nanopore effective diameter and hence induces current perturbation signal. On the basis of this approach, we demonstrate here the detection of diethyl 4-nitrophenyl phosphate (paraoxon), a poisonous organophosphate molecule. Paraoxon binding is induced by the incorporation of the catalytic triad of acetylcholine esterase in the hydrophilic domain of a short amphiphilic peptide and promotes β-sheet assembly of the peptide both in solution and for peptide molecules immobilized on solid surfaces. Nanopores coated with this peptide allowed the detection of paraoxon at the single molecule level revealing two binding arrangements. This unique approach, hence, provides the ability to study interactions of small molecules with the corresponding engineered receptors at the single molecule level. Furthermore, the suggested versatile platform may be used for the development of highly sensitive small analytes sensors.