Abstract: The present invention relates to sensors including artificial receptors and methods of using them. In an embodiment, the present invention includes an artificial receptor as a component of a receptor system including a ligand permeable interface that isolates the artificial receptor from certain components of the surrounding environment. In an embodiment, the present invention includes an artificial receptor and a competitor against a ligand of interest. In an embodiment, the present invention includes a competitive artificial receptor as a component of a detector system including a semipermeable membrane that isolates the competitive artificial receptor from certain components of the surrounding environment. This embodiment also includes the competitor and a detector operatively coupled to the competitive artificial receptor. The detector produces a signal indicating binding of the competitor and/or the ligand of interest to the artificial receptor.