A Fill-and-Flow Biosensor

An alternative design for an amperometric biosensor for lactate is described in which the analyte flows through a rectangular duct without the aid of external pumping or a flow system. With this deviation from the traditional "stacked layers" of the biosensor geometry, the biorecognition matrix is located upstream of the detector electrode rather than directly over the electrode; this general design is reminiscent of the "dipstick" technology of the home test kits, but in the latter case the "flow" is a function of the nature of the wicking material rather than the dimensions of the channel. A droplet of analyte, l-lactate, is placed in the inlet well of the channel which flows through the cell and reacts with an immobilized lactate oxidase surface matrix zone, and the coproduct, hydrogen peroxide, is swept downstream to the monitoring electrode, where it is detected. The flow through the channel biosensor is shown to be laminar, and the biosensor response varies with the rate of flow of the analyte, which could be controlled by the outlet porosity; the sensitivity was observed to increase, but the dynamic range decreased with an increase in flow rate until a threshold loading, where the biosensor response became independent of the enzyme loading.