Research Highlight

A mobile app to measure pH 

doi:10.1038/nindia.2019.170 Published online 22 December 2019

Researchers have developed a sensing tool that can detect a wide range of pH levels, making it potentially useful for measuring the acidity or alkalinity of various solutions and of water resources such as rainwater and tap water1.

Gold nanostructures exhibit the colour pink in a solution. A change in pH or temperature of this solution causes the nanostructures to coalesce. Such aggregation also changes their colour from pink to blue-purple. Such properties are widely exploited to make various sensors.

Scientists from the National Institute of Technology in Durgapur, India, invented the sensing tool, using gold nanostructures of various shapes and a smartphone app. They then tested this tool’s efficiency to measure pH levels of a solution.

The researchers, led by Pathik Kumbhakar, found that the tool could measure acidity or alkalinity of the solution. It was able to detect a wide range of pH levels from 2 to 12.

When the pH levels of a solution containing nanostructures change, it exhibits various colours. The researchers developed a mobile app using specific software that can capture images of such colour changes due to variations in pH levels. 

The combination of the nanostrutcures and the app successfully measured the pH levels of rainwater, municipality tap water and drinking beverages. The efficiency of the pH-sensing tool was found to be as good as a commercial pH meter.

The researchers say that the app could run in offline mode, making it suitable for use in real-life environments in remote locations.


1. Biswas, S. et al. Gold nanostructures for the sensing of pH using a smartphone. RSC. Adv.9, 34144 (2019) doi: 10.1039/c9ra07101f