Fine-Tuning Chemical Sensors

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Science  12 May 2000:
Vol. 288, Issue 5468, pp. 929
DOI: 10.1126/science.288.5468.929d

Non-destructive, real-time detection of small molecules can be achieved via recognition of the target by a larger receptor molecule, such as a fluorophore whose emission spectrum changes in the occupied state. In most cases, binding occurs at a single site.

Glass has explored the use of cooperative binding of ligands, which is more typical of biological receptors, with the goal of sacrificing some of the operating concentration range in return for greater affinity and selectivity. He designed a metal-ion sensor in which two halves of a recognition element join to form a metal binding site. Three such elements are attached in a pinwheel arrangement, and two such pinwheels are linked by a rigid carbon spacer, which serves as an axle. The unoccupied sensor adopts the lower energy or “staggered” configuration in which the recognition element halves are not properly juxtaposed. Binding of the first ion not only aligns these halves, but also brings the two empty sites into register (the “eclipsed” configuration), increasing the binding affinity. For silver ions, the single-site sensor operates over a larger dynamic range (10 to 900 μM), but the cooperative pinwheel sensor is more responsive and more sensitive (0.6 to 6 μM, with a Hill coefficient of 2.9).—PDS

J. Am. Chem. Soc., in press.

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