GUWAHATI: IIT- Guwahati (IIT-G) researchers have developed a paper-based sensor that can test the freshness of milk.

A research team led by Pranjal Chandra, assistant professor of the department of biosciences and bioengineering at IIT-G, along with research scholar Kuldeep Mahato developed a simple visual detection technique to detect the quality of milk, without the need of specialised equipments and instruments. Their work was recently published in the journal Biosensors and Bioelectronics.

The paper-based sensor assesses the presence of microbes in milk to test how fresh it is. Bacteria and other microbes that grow in milk products not only affect the taste and freshness but also cause health problems. "It would be useful if the quality of milk can be tested at the point of collection itself," said Chandra, adding that such testing require easy-to-operate and portable detection kits.

Alkaline Phosphatase (ALP), a metalloprotein found naturally in raw milk samples, is considered an important marker to test the quality of milk. On pasteurisation, this component gets destroyed. High amounts of ALP in milk samples may mean that the milk is derived from animals with infection in the mammary glands. Pasteurisation tends to kill these microbes to make the milk healthy.

"The multi-step nature and requirement of sophisticated bulky analytical instruments and trained personnel to detect ALP limit their use as a sensor in remote settings and in home kitchens. Our sensor takes merely 13 minutes to detect ALP and hence it can be applied for quick on site analysis," Chandra said.

The researchers successfully tested milk obtained from villages and commercial outlets using their paper-based sensor kit and found that they could detect up to 0.87 units of ALP per millilitre of milk. Noting an accuracy of 91-100 per cent, the sensors made it possible to discriminate raw milk (containing as high as 191 U/mL of ALP) from pasteurized or boiled milk which contains ALP in ultra-trace amounts.

Coming to the specifics of the device, the researchers chemically modified filter paper and loaded it with a recognition element that can detect ALP. Upon testing, a complex form of ALP would leave behind a blue-green coloured precipitate which would be absent if the milk did not contain any ALP. The researchers said that the intensity of the colour indicates the amount of ALP present.

"We plan to extend the sensing platform we have developed for ALP towards the detection of various molecules in different matrices. In fact, we have developed another sensor for ALP detection using a label-free bio-electronic chip. This new sensor has been developed by Kuldeep Mahato, Ashutosh Kumar and Buddhadev Purohit. The chip is an advanced version of the paper-based kit with improved accuracy", Chandra said while divulging their plans to commercialize both testing kits.