Aptamer-Studded Nanopore Detects Ricin

A quantity of ricin smaller than a grain of sand can kill a person, so researchers are trying to develop sensitive detection methods for this potent bioterrorism threat. Now, Li-Qun Gu and colleagues at the University of Missouri, Columbia, report an aptamer-studded glass nanopore that detects single molecules of ricin protein (Anal. Chem., DOI: 10.1021/ac9006705). The team attached copies of a ricin-specific aptamer—a short RNA sequence that recognizes ricin—to the surface of a glass nanopore. When a ricin molecule binds to an aptamer at the narrow opening of the wineglass-shaped nanopore, the ionic current through the pore changes. The researchers detect sequential molecules of aptamer-captured ricin as a series of stepwise current blocks. Unlike antibodies, aptamers are much smaller than their targets, so the method is more sensitive than antibody-coated synthetic nanopores. It also distinguishes between transient current blockades caused by nonspecific molecules passing through the nanopore and longer blocks resulting from ricin binding. In principle, the technique could be used to detect any molecule for which an aptamer has been identified.