A device for measuring a change in flow characteristics in a liquid sample, wherein the change in flow characteristics arises from a specific binding interaction between an analyte and an analyte-specific binding reagent, comprising: (a) a first substrate; (b) a second substrate; (c) a spacer layer (2, 3) disposed between the first and second substrates (1,4), said spacer layer having an opening formed therein defining a sample receiving chamber, a vented sink chamber, and an elongated reservoir forming a conduit for liquid movement between the sample receiving chamber and the sink chamber; (d) a first electrode disposed on the first substrate, said first electrode being exposed through the reservoir portion of the opening in the spacer layer (2,3); (e) a second electrode disposed on the second substrate, said second electrode being exposed through the reservoir portion of the opening in the spacer layer (2,3) such that an electrical signal can be detected between the first and second electrodes when a conductive liquid sample is disposed in the reservoir, at least one of the electrodes being electrically insulated from the sample receiving chamber and from the sink chamber, (f) first and second contact leads extending from the first and second electrodes, respectively, for connection of the device to an apparatus for measuring an electrochemical signal between the first and second electrodes through a sample in the reservoir, wherein the reservoir comprises a constriction separating a main portion of the reservoir from the sink chamber, the constriction being arranged to control the flow rate from the reservoir such that the time required for emptying sample from the reservoir into the sink chamber to occur in the absence of a change in flow characteristics arising from reaction of the analyte with the analyte-specific binding reagent is greater than the time required for the reaction of the analyte with the analyte-specific binding reagent to occur, and (g) an analyte-specific binding reagent disposed to react with an analyte in the sample and change the flow characteristics of the liquid sample. (a) a first substrate; (b) a second substrate; (c) a spacer layer (2, 3) disposed between the first and second substrates (1,4), said spacer layer having an opening formed therein defining a sample receiving chamber, a vented sink chamber, and an elongated reservoir forming a conduit for liquid movement between the sample receiving chamber and the sink chamber; (d) a first electrode disposed on the first substrate, said first electrode being exposed through the reservoir portion of the opening in the spacer layer (2,3); (e) a second electrode disposed on the second substrate, said second electrode being exposed through the reservoir portion of the opening in the spacer layer (2,3) such that an electrical signal can be detected between the first and second electrodes when a conductive liquid sample is disposed in the reservoir, at least one of the electrodes being electrically insulated from the sample receiving chamber and from the sink chamber, (f) first and second contact leads extending from the first and second electrodes, respectively, for connection of the device to an apparatus for measuring an electrochemical signal between the first and second electrodes through a sample in the reservoir, wherein the reservoir comprises a constriction separating a main portion of the reservoir from the sink chamber, the constriction being arranged to control the flow rate from the reservoir such that the time required for emptying sample from the reservoir into the sink chamber to occur in the absence of a change in flow characteristics arising from reaction of the analyte with the analyte-specific binding reagent is greater than the time required for the reaction of the analyte with the analyte-specific binding reagent to occur, and (g) an analyte-specific binding reagent disposed to react with an analyte in the sample and change the flow characteristics of the liquid sample.