In some examples, a device includes first and second electrodes separated from one another by a space; a particle coupled to the first electrode via a first plurality of bonds, and coupled to the second electrode via a second plurality of bonds; and a polymerase coupled to the particle. In some examples, a composition includes first and second electrodes separated from one another by a space; a fluid including a first electrically conductive label having a length at least as long as a length of the space; and detection circuitry to generate a first signal responsive to transient formation, using the first electrically conductive label, of a first electrically conductive bridge between the first and second electrodes.