Quinclorac　is　an　herbicide　widely　used　in　rice　production,　and　its　residue　in　water　and　soil　poses　significant　threats　to　aquatic　organisms　and　subsequent　crops.　We　herein　isolated　a　group　of　aptamers　with　high　binding　affinity　to　quinclorac　using　library-immobilized　SELEX.　Notably,　one　of　these　aptamers　(Apt.Q1)　demonstrated　excellent　specificity　and　affinity　to　quinclorac,　with　dissociation　constant　(Kd)　of　8.7　±　2.4　µM　and　no　interference　from　structurally　similar　pesticides.　Molecular　dynamics　simulations　identified　the　G-rich　loop　in　Apt.Q1　as　the　potential　binding　domain,　and　circular　dichroism　analysis　revealed　the　conformational　transition　from　hairpin　to　G-triplex　structure　upon　quinclorac　interaction.　Moreover,　a　one-step,　label-free　colorimetric　biosensor　was　developed　based　on　quinclorac-mediated　displacement　of　Cy7　dye　and　Apt.Q1　for　detecting　quinclorac　within　1　min　with　a　detection　limit　of　237　nM　and　RSD　©　2023　Elsevier　B.V.