One aspect of the invention relates to an ultrathin micro-electromechanical chemical sensing device which uses swelling or straining of a reactive organic material for sensing. In certain embodiments, the device comprises a contact on-off switch chemical sensor. For example, the device can comprises a small gap separating two electrodes, wherein the gap can be closed as a result of the swelling or stressing of an organic polymer coating on one or both sides of the gap. In certain embodiments, the swelling or stressing is due to the organic polymer reacting with a target analyte.