Supermarkets are filled with delicious and fresh food products everyday thanks to continuous innovations in the agrifood industry. However, for products that spoil fast – think of seafood, fish, meat, fresh vegetables, etc. – ‘best before’ and ‘use-by’ dates are kept as short as possible to minimize the risk of public health issues. Unfortunately, this causes a lot of perfectly edible foods to be wasted.
The Terafood project aims to tackle this issue by developing an ultra-sensitive food packaging sensor that can measure the freshness of the product in real time without having to open the protective food packaging environment. To do so, the Terafood partners from France and Belgium created a method that relies on the interaction of the product’s environment with terahertz (THz) light. A foodstuff that is going bad will produce characteristic aromatic and gaseous compounds, so called Volatile Organic Compounds or VOCs. Each type of these molecules absorbs THz light in a specific way, allowing a chemical fingerprint of the gaseous content of the package. This is a unique property of THz light: being able to "see-through" package materials while at the same time exhibiting very specific molecular absorption.
To be able to use this method in a packaging sensor, one of the major challenges is to make this small interaction detectable. Terahertz light is relatively low in energy, which on the positive side avoids that the light degrades the food material (as for instance with X-rays), but on the downside is not powerful enough to be detected by an optical sensor. This is where micro fabrication comes in.
Unique peek in the cleanroom and micro-fabrication center of IEMN (joint CNRS research lab)
After one year of development, the consortium has now managed to bring together a platform of different structures on a single silicon chip, smaller than a thousandth of a millimeter. These structures are then linked very precisely and efficiently, allowing it to collect all light coming from a THz light source and to guide that light with minimal loss towards an area of analysis, where the interaction with the atmosphere takes place and a large part of the optic power is concentrated. In this way, this miniscule chip becomes a complete sensor that allows sensitive and correct analysis of its environment. Part of this microfabricated sensor acts as a tiny microphone (only one hundredth of a square millimeter!) that will amplify the vibrations of the gas molecules that have absorbed the THz light. This microphone generates an electrical signal that acts as a readout for the sensor.
All of this is only feasible thanks to the use of photolithography techniques and plasma engraving, techniques coming from the micro-electronics industry. These methods are only realizable in an extremely neat environment, called the cleanroom. The industrial partner of the project – Vmicro –
operates its equipment in the cleanroom of the Institute of Electronics, Microelectronics and Nanotechnology (IEMN), located at the University of Lille’s Science campus.
The partners now have a modular platform in order to create and optimize the sensors according to the specific needs of the food packaging industry. The platform has made it possible to already realize two generations of prototypes. These prototypes have allowed the partners to prove that that THz light can indeed be trapped in a tiny volume (of the order of 0,001 mm³ ) without losing any of its power. These tiny hole-‘traps’ are visible in frame C of the images below. In a next step these holes will be covered with very thin microphone membranes to complete the principles of the sensor. As such, the Terafood partners are very close to "listen to the freshness of your food"!
A: Wafer in silicon consisting of different prototypes. B: Sensors detached from the wafer and ready to use. C: Close-up of the resonator structure in the sensor. The holes have a diameter of 50µm, with a precision in the order of 1 µm (1 thousandth of a millimeter).
Source and more information
- More information on the project can be found on the project website: https://terafood.iemn.fr/
- If you want more information on the project, do not hesitate to contact the project coordinator Mathias Vanwolleghem - firstname.lastname@example.org
- If you are interested to become a member of the advisory board of this project, you can contact Sofie Verdoodt – S.Verdoodt@UGent.be
With support of the European Regional Development Fund and the province of East-Flanders.