The extracted filter paper was dried at room
temperature in a fume hood, and then cut into 4.0 cm × 2.5 cm
strips. 1.2 ml of 5% gelatin, 0.25 ml enzyme (16.2 mg glucose oxidase
and 1.2 mg peroxidase per 10 ml in double distilled water,
denoted as CEM), 1.05 ml of citric acid buffer solution, 2.0 ml of
TBHBA (5 mg/ml), 0.5 ml 4-APP (20 mg/ml) were mixed in a 50-
ml glass vial to make a soaking solution