The reactive paper is made of cellulose filter
paper dipped into bromothylmol blue and
acetylcholine chloride. Bromothymol blue is
used as color indicator and acetylcholine chloride
as a substrate for cholinesterase enzyme.
It takes 7 minutes to complete the determination
of cholinesterase activity at 25◦C ± 1◦C
and 70% relative humidity. The cholinesterase
activities determined by the Biggs method23 and
the reactive-paper method have no significant
difference (P < .01). There is also a correlation
coefficient of .56 when the cholinesterase
activity is in the 20–120 units/mL range.