A cartridge reader for carrying out a diagnostic test on a sample contained in a fluidic cartridge comprising a mechanical valve for isolating the sample within the cartridge, the cartridge reader comprising a system for actuating the mechanical valve comprising: an actuation member configured to move the mechanical valve from an open position to a closed position; an armature connected to the actuation member, configured to engage an electromagnet, wherein the electromagnet can be switched between an active state in which it electromagnetically holds the armature and an inactive state in which it does not electromagnetically hold the armature; first biasing means, disposed between the actuation member and a bearing surface, wherein the first biasing means is configured to bias the actuation member into a first position in which it actuates a mechanical valve in a fluidic cartridge inserted into the reader; wherein the actuation member is held in a second position against the bias of the first biasing means by the electromagnet when the electromagnet is in its active state, and is moved into its first position by the first biasing means when the electromagnet is in its inactive state; and further comprising processing means for controlling operation of the cartridge reader and configured to determine when a diagnostic test carried out by the reader has been completed, and to switch the electromagnet to its inactive state at the end of the diagnostic test so as to move the mechanical valve from an open position to a closed position to isolate the sample within the cartridge; wherein the cartridge reader further comprises: an upper clamp having a fixed position relative to the reader and a lower clamp, movable relative to the upper clamp, wherein the upper clamp and the lower clamp are configured to receive the fluidic cartridge therebetween, and wherein the armature is comprised in the upper clamp; a gantry, fixedly connected to the lower clamp by at least one alignment shaft which passes through at least one aperture in the upper clamp such that at least a portion of the gantry extends above the upper clamp; and wherein the electromagnet is connected to the gantry and the bearing surface is comprised in the upper clamp. an actuation member configured to move the mechanical valve from an open position to a closed position; an armature connected to the actuation member, configured to engage an electromagnet, wherein the electromagnet can be switched between an active state in which it electromagnetically holds the armature and an inactive state in which it does not electromagnetically hold the armature; first biasing means, disposed between the actuation member and a bearing surface, wherein the first biasing means is configured to bias the actuation member into a first position in which it actuates a mechanical valve in a fluidic cartridge inserted into the reader; wherein the actuation member is held in a second position against the bias of the first biasing means by the electromagnet when the electromagnet is in its active state, and is moved into its first position by the first biasing means when the electromagnet is in its inactive state; and further comprising processing means for controlling operation of the cartridge reader and configured to determine when a diagnostic test carried out by the reader has been completed, and to switch the electromagnet to its inactive state at the end of the diagnostic test so as to move the mechanical valve from an open position to a closed position to isolate the sample within the cartridge; wherein the cartridge reader further comprises: an upper clamp having a fixed position relative to the reader and a lower clamp, movable relative to the upper clamp, wherein the upper clamp and the lower clamp are configured to receive the fluidic cartridge therebetween, and wherein the armature is comprised in the upper clamp; a gantry, fixedly connected to the lower clamp by at least one alignment shaft which passes through at least one aperture in the upper clamp such that at least a portion of the gantry extends above the upper clamp; and an upper clamp having a fixed position relative to the reader and a lower clamp, movable relative to the upper clamp, wherein the upper clamp and the lower clamp are configured to receive the fluidic cartridge therebetween, and wherein the armature is comprised in the upper clamp; a gantry, fixedly connected to the lower clamp by at least one alignment shaft which passes through at least one aperture in the upper clamp such that at least a portion of the gantry extends above the upper clamp; and