Bistable devices are constructed using a polynucleotide platform for the sensing of molecular events such as binding or conformational changes of target molecules. Uses include measurement of target concentration, measuring the effect of environmental condition (such as heat, light, or pH) on the target, or screening a library for molecules that bind the target or modulate its biological function. Devices comprise three regions: a top lid, bottom lid, and flexible linker or hinge between them. A device has an open configuration in which the top and bottom lid are separated, and a closed configuration they are bound close together. Binding domains or variations of the target molecule are fixed to a device so that when the molecular event occurs, the device switches from open to closed, or vice versa, which generates a signal. Devices carry DNA tags to enable separation of open and closed devices, as well as barcoding for multiplexed detection.