Agarose solution (4.5 %) was prepared in 10 ml of distilled water by heating in a microwave oven for 30 s. Five ml of indicator solution (anthocyanin) was added to the solution just before solidification, and the mixture was shaken well to completely mix the indicator solution with agarose. The mixture was then poured into a petri dish of 100 mm diameter and allowed to solidify at refrigeration temperature. A 2 cm 9 2 cm strip was cut and packed in cling film to prepare indicator sensor (gel type). Another type of indicator sensor using filter paper as carrier was also prepared. Filter paper no. 42 was made into strips having dimensions of 1.5 cm 9 5 cm and centrifuged in indicator solution at 3000 rpm for 15 min and dried overnight at 60 C. It was packaged in cling film and sealed to make indicator sensor (strip type).