Designing the 'fill and flow' (bio) sensor to give stable measurements from a dynamic system

A laminar 'fill and flow' channel containing band electrodes is presented w ith a redesigned sample reservoir. The channel allows well-defined electroa nalytical currents to be measured at the electrodes, so that it is suitable for inclusion as part of a total analysis system. The goal in the use of t he channel is an electroanalytical system which operates by 'gravity-feed' without pumping, but the measured electrochemical current is a function of sample flow rate within the channel, which varies according to the height o f sample in the reservoir and may be influenced by device to device variati on or the nature of the sample. In this paper, a method is explored whereby the sample flow rate can be extracted automatically from features in the r ecorded electrode current. Two designs for the sample reservoir are present ed involving step constrictions in their internal profile. Equations are de rived to correct the current readings for varying flow Fate, using the mark ers generated by the sample meniscus passing these steps. The design with t wo step constrictions in the reservoir is shown to give results where corre ction for flow rate can be made independent of the current or the sample. T he technique is also shown to provide an opportunity to determine and hence to correct for the viscosity and, by taking a two-point reading within cur rent markers provided by discontinuities created by the step constrictions of the reservoir design, the data may also be corrected to eliminate the ef fects of tilt of the channel and device-to-device variation. (C) 2000 Elsev ier Science S.A. All rights reserved.