Reservoir-based medical devices are provided. In one embodiment, the medical device comprises a substrate; at least two discrete, microfabricated reservoirs provided in spaced positions across at least one surface of the substrate; discrete reservoir caps covering the at least two reservoirs; and control circuitry for selectively disintegrating the reservoir caps to open the reservoirs. The reservoirs of the device can include a diagnostic reagent or other molecules useful in medical diagnostics. In one embodiment, the reservoir cap comprises an anode and the control circuitry comprises a cathode and a power source for creating an electric potential between the cathode and the anode. Application of the electric potential causes the reservoir cap to disintegrate, thereby opening the reservoir.