Faster, cheaper food pathogen testing

Janus droplets consist of two equally sized hemispheres, one a fluorocarbon and one a hydrocarbon. When the droplets sit on a surface the hydrocarbon hemisphere, being less dense, is always at the top. When oriented like this the droplets are transparent, but if their orientation changes the droplets become opaque.

Researchers decided to utilise this fact in creating some sensors. They designed a surfactant molecule containing mannose sugar to self-assemble at the hydrocarbon–water interface. These molecules can bind to a protein called lectin, which is found on the surface of some strains of E. coli. When E. coli is present, the droplets attach to the proteins and become clumped together. This knocks the particles off balance, so that light hitting them scatters in many directions and the droplets become opaque when viewed from above.

This change in transparency is so obvious that it can be seen with the naked eye or using a smartphone. In a demonstration the researchers put the droplets’ Petri dish atop a QR code that can be scanned with a smartphone. When E. coli were present, the droplets clumped together and the QR code couldn’t be read.

This novel approach to food pathogen testing could ultimately result in cheaper, faster testing for food manufacturers.

The research team included scientists from MIT, the Max Planck Institute of Colloids and Interfaces and the Max Planck Institute, and has been published in ACS Central Science.