A new biosensor design is demonstrated, in which a protein conformational change is used as a trigger mechanism for a low-cost, solid-state sensor (see also the cover). The figure illustrates the principle: an enzyme (hexokinase, large white shape) immobilized on a lipid polydiacetylene (PDA) layer undergoes a conformational change when glucose (dark shape) binds to it. The resulting stress in the PDA layer produces a color change.