Fig. 5. Phosphatidyl choline self-assembled monolayers minimize the drift seen in whole blood in vitro. E-AB sensors fabricated using hydroxyl-terminated monolayers drift significantly (typically of order 10 to 15% per hour) when deployed directly in undiluted whole blood.^15,25. (Left hand column) As shown here, however, sensors fabricated using a phosphatidyl choline-terminated monolayer are much more resistant to this drift. Shown are the absolute currents produced by both the MB and AQ reporters on our cocaine, ATP and aminoglycoside sensors. (Right hand column) The ratio of the output currents likewise resists drift (less than 0.5% per hour).