title: Selective Aptamers for Detection of Estradiol and Ethynylestradiol in Natural Waters.
abstract: We used in vitro selection to identify new DNA aptamers for two endocrine-disrupting compounds often found in treated and natural waters, 17β-estradiol (E2) and 17α-ethynylestradiol (EE). We used equilibrium filtration to determine aptamer sensitivity/selectivity and dimethyl sulfate (DMS) probing to explore aptamer binding sites. The new E2 aptamers are at least 74-fold more sensitive for E2 than is a previously reported DNA aptamer, with dissociation constants (Kd values) of 0.6 μM. Similarly, the EE aptamers are highly sensitive for EE, with Kd of 0.5-1.0 μM. Selectivity values indicate that the E2 aptamers bind E2 and a structural analogue, estrone (E1), equally well and are up to 74-fold selective over EE. One EE aptamer is 53-fold more selective for EE over E2 or E1, but the other binds EE, E2, and E1 with similar affinity. The new aptamers do not lose sensitivity or selectivity in natural water from a local lake, despite the presence of natural organic matter (∼4 mg/L TOC). DMS probing suggests that E2 binding occurs in relatively flexible single-stranded DNA regions, an important finding for rational redesign of aptamers and their incorporation into sensing platforms. This is the first report of aptamers with strong selectivity for E2 and E1 over EE, or with strong selectivity for EE over E2 and E1. Such selectivity is important for achieving the goal of creating practically useful DNA-based sensors that can distinguish structurally similar estrogenic compounds in natural waters.
authors.affiliation: †Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
authors.forename: Spurti U
authors.initials: SU
authors.lastname: Akki
authors.affiliation: †Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.|‡Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, 301 East Dean Keeton Street, Austin, Texas 78712, United States.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Werth
authors.affiliation: §Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States.
authors.forename: Scott K
authors.initials: SK
authors.lastname: Silverman
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry*; D004958:Estradiol / Q000032:analysis* / Q000737:chemistry; D004997:Ethinyl Estradiol / Q000032:analysis* / Q000737:chemistry; D005374:Filtration; D007700:Kinetics; D013463:Sulfuric Acid Esters / Q000737:chemistry; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D052157:Aptamers, Nucleotide; D013463:Sulfuric Acid Esters; D014874:Water Pollutants, Chemical; D014867:Water; D004997:Ethinyl Estradiol; D004958:Estradiol; C007482:dimethyl sulfate