Research Highlight

How fresh is your milk? 

This colour-changing paper device can tell.

doi:10.1038/nindia.2019.148 Published online 13 November 2019

Researchers from the Indian Institute of Technology in Guwahati have developed a paper-based kit and a bio-electronic chip that can instantly assess the freshness of raw milk1, 2.

They say that the devices can detect the presence of bacteria and microbes usually found in raw milk.

Existing tests for monitoring the freshness of milk are complex and time-consuming. To devise a rapid and simple test, the scientists, led by Pranjal Chandra, developed the paper-based kit using a chemically modified filter paper. The paper was loaded with an element that can capture alkaline phosphatase (ALP), a marker protein naturally found in raw milk.

This protein, destroyed during boiling, is found in higher amounts in raw milk of animals with infection in their mammary glands.

The detection kit.

© Mahato, K. et al.

When exposed to ALP-containing milk samples, the paper-based kit formed a blue-green precipitate. This kit, however, doesn’t display any colour in the absence of ALP. It detects ALP within 13 minutes, making it suitable for quick onsite analysis.

The researchers used a smartphone to capture the image of the colour and a specific filter in the phone to profile the obtained colour. This colour could be correlated to the concentrations of ALP present in different milk samples.

Based on this detection principle, they then developed another sensor for ALP detection using a bio-electronic chip. The chip, already patented, is an advanced, higher-accuracy version of the paper-based kit and is suitable for testing milk quality at the point of collection or in home kitchens, says Chandra.


1. Mahato, K. et al. Paper-based miniaturized immunosensor for naked eye ALP detection based on digital image colorimetry integrated with smartphone. Biosens. Bioelectron. 128, 9-16 (2019)