doi:10.1038/nindia.2016.21 Published online 15 February 2016
By using filter paper, researchers have fabricated a sensitive sensor that can measure increased levels of the enzyme amylase in human blood serum1. Since acute pancreatitis, pancreatic cancer, salivary gland infection and kidney damage all cause amylase levels to increase, the sensor will be potentially useful for diagnosing these diseases.
The pancreas and salivary glands secrete the enzyme amylase, which converts edible starch into simple sugars such as glucose, maltose and dextrin.
To develop a simple and efficient amylase sensor, the researchers coated filter paper with starch and iodine, which turned the paper blue. This colour faded on adding drops of amylase solution to the coated filter paper.
Amylase broke starch down into simple sugars and these chemical reactions generated heat, which evaporated the iodine. This, in turn, caused the colour of the paper to fade.
The coated filter paper was exposed to light from a light-emitting diode, both before and after the addition of amylase. The scientists found that the paper’s ability to reflect and transmit light changed before and after amylase addition. They detected this change by using a photoresistor to measure resistance differences.
Fading of the paper on amylase addition increased the intensity of reflected light to the photoresistor, lowering its resistance. Thus, increased amylase levels decreased the resistance of the photoresistor. The sensor could also detect amylase levels in human serum samples.
It is possible to convert the photoresistor’s analogue data into digital data and so display the amylase level, the researchers say.
1. Dutta, S. et al. Paper-based α-amylase detector for point-of-care diagnostics. Biosens. Bioelectron. 78, 447–453 (2016)