British and Arab scientists have developed a new laser method for printing nanostructured holograms onto dried corn syrup films.
According to the team from University of Birmingham, University of Warwick, Imperial College London and Abu Dhabi’s Khalifa University of Science and Technology, these edible holograms could someday be used to ensure food safety, label a product, or indicate sugar content.
Holograms can be found in a number of items we use today – driver’s licenses, credit cards and even product packaging.
However, they are imprinted with lasers onto metal surfaces – such as aluminum, and are thus not edible.
Holograms made with nanoparticles have been proposed for foods, but these tiny particles can generate reactive oxygen species that are harmful for people to eat.
Food scientists have previously molded edible holograms onto chocolate; this process only works for certain types of the confection, and a different mold is needed for each hologram design.
Now a team led by Birmingham’s Bader AlQattan and Khalifa’s Haider Butt has proposed a safer, faster and versatile way for patterning edible holograms onto a variety of foods.
To develop their method, the researchers made a solution of corn syrup, vanilla and water and dried it into a thin film. They then coated the film with a fine layer of non-toxic black dye.
Following this, the scientists used a technique called Direct Laser Interference Patterning (DLIP) to etch off most of the dye, leaving behind raised, nanoscale lines that formed a diffraction grating.
When struck by light, the nanostructure diffracted the light into a rainbow pattern, with different colors appearing at different angles of viewing.
The team also succeeded in controlling the intensity and range of colors by varying the spacing between lines in the grating or the sugar content of the corn syrup film.
AlQattan and his colleagues are currently working on adapting the method to a food-grade dye that could replace the synthetic black dye used in these pilot experiments.
Image and content: ACS Nano