Beer-brewing ‘biobots’ could boost the drinks industry by speeding up fermentation. Researchers in Czechia encapsulated yeast and iron oxide nanoparticles in a biocompatible polymer to create self-propelling biobots, which can be retrieved from beer samples magnetically – eliminating the need for filtration steps.
The biobots have a two-sided design with one hemisphere made porous to allow gas release. The researchers first synthesised the nanostructured biobots by combining sodium alginate, yeast cells and iron oxide nanoparticles and inducing alginate crosslinking by dropping the mixture into an iron chloride solution. They then exposed the resulting beads to the middle of an electrochemically generated pH gradient, creating pores in the alginate matrix through precipitation on the alkaline-exposed hemisphere.
Beer fermentation typically takes a couple of days up to a couple of weeks, but the new biobots speed up the process, transforming sugars into alcohol faster than free yeast due to their mixing action. During fermentation, the biobots constantly move due to a catalytically controlled buoyancy shift mechanism. As the yeast produces carbon dioxide, the biobots rise upwards to the surface and release the gas before sinking again in a repeating cycle.
When fermentation is complete, the biobots can be easily retrieved using an external magnetic field, allowing beer production without additional filtration steps. After removal, the biobots can be reused, retaining their biocatalytic activity for up to four fermentation cycles.
R Maria-Hormigos et al, ACS Nano, 2023, DOI: 10.1021/acsnano.2c12677