Structural development of a minimally invasive sensor chip for blood glucose monitoring

Our newly developed glucose sensor chip has the world smallest blood sample volume, as small as 200 nL, which makes lancing with less pain possible. Forming the inside walls of the cavity, where the blood is collected, by screen printing of the adhesive ink instead of the conventional adhesive sheet placing drastically reduced the cavity thickness, to less than 50 microm, and the blood sample volume. On this thin-cavity type sensor, the cavity thickness was proven to have the strong influence on the sensor response. This means that thinner cavity requires more accurate printing, in terms of thickness control. The printing conditions were adjusted to minimize the dispersion in the cavity geometry. One of the challenges was how to print patterns without saddles, which was achieved by selecting proper ink. After the adjustment, the contribution of the dispersion in the cavity thickness and the electrode area to the dispersion in sensor responses was estimated, respectively, which indicated the contribution of the cavity thickness still existed. Finally, the sensor was evaluated using whole sheep blood containing glucose of from 60 to 493 mg dL(-1). Irrespective of the influence relating to the cavity thickness, the coefficients of variation of the sensor responses were from 4.4 to 7.6. In addition, the correlation curve showed linearity in this blood glucose range, and the coefficient of determination r2 was 0.98. That is, the sensor was verified to have sufficient performance for practical use.