The Acer iSeed in the field. Credit: G.Berretta, Istituto Italiano di Tecnologia.
Scientists in Italy and Germany have drawn inspiration from nature to develop a new kind of compact flying thermometer. Mimicking the size, shape and aerodynamics of maple seeds, multiple copies of this biocompatible device could be deployed to measure top-soil temperature over broad areas and in future might also record changes in humidity and carbon dioxide levels.
Researchers to date have developed a variety of sensors linked by wireless networks to monitor certain physical and chemical parameters. However, these devices rely on heavy and expensive electronics that must be retrieved once their task is complete, to avoid polluting the environment.
In the latest work published in Science Advances1, Kliton Cikalleshi, Barbara Mazzolai and colleagues at the Italian Institute of Technology (IIT), in Genoa, along with researchers at the INM-Leibniz Institute for New Materials in Saarbrücken, Germany, have instead shown the feasibility of a small biocompatible sensor that could be self-deployed and then left in the field. The 3cm "I-SeedSam" consists of a dense nut and longer, thinner wing, which, just like those from the tree Acer campestre, enable it to rotate and fall slowly to the ground, drifting some distance when dropped from height in windy conditions.
The device, which degrades over several years, relies on particles containing ions of erbium and ytterbium that are embedded within a matrix of polylactic acid. When exposed to infrared light from a laser, the ytterbium absorbs the radiation and excites the erbium, which then emits green light at two slightly different wavelengths. It is the relative intensity of these two shades of green that reveals the temperature of the seed's surroundings.
Cikalleshi and colleagues produced the artificial seeds by mixing the fluorescent and matrix materials, extruding them into a long filament and then feeding the filament into a 3D printer. They found that the seeds continued to emit as expected after 30 hours of infrared exposure and that they were able to correctly measure temperatures to within half a degree centigrade.
The researchers' next step is to try and reproduce these results in the field, using drones to deploy, irradiate and then read out the sensors. Mazzolai says that the scheme must work in all weather, and on soil with or without vegetation. She adds that different fluorescent particles could target other environmental parameters or pollutants.
