Unexpected enrichment of DNA aptamers for Zn 2+ ions from an insulin selection.

We serendipitously discovered Zn 2+ -binding DNA aptamers when selecting insulin aptamers. The Zn-1 aptamer binds to Zn 2+ with a dissociation constant ( K d ) of ∼1 μM, and has 450-fold higher selectivity for Zn 2+ over Cd 2+ . A strand-displacement based fluorescent sensor achieved a limit of detection of 0.2 μM Zn 2+ .