Prior to the spin-coating of PEDOT–PSS and GOx, the substrate
was subjected to O2 plasma for 60 s to hydrophobize and clean the
photoresist residue from the channel region of the patterned surface.
After spin-coating PEDOT–PSS, the samples were annealed
for 2min at 75◦C in air, to improve the polymer film morphology
and firmness. This step was followed by spin-coating of the GOx layer. The total film thickness was measured to be about
50nm (using a Tencor Profilometer). Finally, the substrate was
dip coated in a cellulose acetate solution, 2.5% (w/v) of cellulose
acetate in Tetrahydrofuran (THF) (60%) and acetone (40%) solution,
to form a protecting membrane thatwould prevent PEDOT–PSS and
GOx from dissolving into glucose solution. The individual sensor
devices were then wire bonded for electrical measurements. For
testing, the sensor device was placed on a stage andwas connected
to source/measure unit (Keithley 238) for measuring transistor
characteristics. Several control measurements were taken such as
before exposing (dry state) the device to glucose or DIwater (buffer
used tomix glucose). In addition, control measurementswere taken
to measure the effect of DIwater on the device. For glucose sensing
measurements, drop of glucose solution was placed on the channel
(with PEDOT–PSS and GOx) and resulting change in current
between source and drain was measured.