Out-of-equilibrium sensing with a chemically fueled molecular machine

Adaptive sensing underpins many biological processes. We present a strategy for artificial sensors that exploits the heightened responsiveness possible with out-of-equilibrium systems. We incorporate a Zn(II) allosteric binding site into a chemically fueled rotaxane information ratchet that catalyzes diisopropylcarbodiimide (DIC) hydration. Zn(II) coordination shifts the macrocycle distribution on the rotaxane axle, and this redistribution changes the catalytic rate of fuel-to-waste conversion. This couples Zn(II) binding to the nonequilibrium steady-state (NESS) macrocycle distribution produced by catalysis. As a result, the rate of catalysis can be used to measure the concentration of Zn(II) over a range that is inaccessible to titration experiments carried out at equilibrium. The strategy may prove useful for developing broad-range sensors that function through chemically fueled adaptive sensing.