As the repercussions of climate change worsen, threatening global food security and food supply chains, accurate and real-time monitoring of crop health becomes an absolute necessity for farmers to avoid crop losses and direct irrigation operations intelligently.
In this context, a research team from Tufts University in the United States succeeded in developing a promising innovation: a hybrid sensing system that attaches directly to plants and operates without the need for traditional batteries, deriving its energy from the moisture of the plant itself and its natural evaporation process, scientifically known as transpiration.
This innovative system, detailed in a recent study in the journal ACS Applied Materials and Interfaces, consists of two innovative components: a smart paper tattoo that touches the surface of the plant's leaves to monitor temperature and humidity levels, and a rubber band inspired by the Japanese art of kirigami that wraps around the stem to track its growth and changes in diameter.
Harvesting energy from plant breath
“We wondered: if we use wearable devices to monitor our health, why not make the same for plants? It takes time for visible signs of stress to appear on a plant, and we wanted a way to communicate directly with it,” said Samir Sonkosali, a professor of computer and electrical engineering who participated in the study, in exclusive statements to Al Jazeera Net. “Our tattoos allow us to monitor water vapor pressure deficits, a crucial indicator of stress, and track stem growth to know exactly how the plants are doing before they are damaged.”
But for those sensors to work, it requires generating energy, and this is where different aspects of innovation lie, as the researchers relied on the phenomenon of transpiration, which is the natural process by which plants release water vapor through their microscopic pores known as stomata, and it differs from the well-known biochemical respiration process.
Scientists have incorporated into tattoos a thin nanofilm made of a special material called "vanadium pentoxide". Samir explains: "We use stacked nanochannels that break down moisture into positive and negative ions thanks to their catalytic properties."
The ions are separated across the channels into two electrodes, just like a battery. The generated charge is not large, but we accumulate it over time to use in wirelessly transmitting information to a central station, which is a very acceptable time delay in agriculture."
According to the researchers, this work represents the first integrated sensing platform that is placed inside the plant and operates entirely on self-moisture power, allowing the monitoring of leaf thirst indicators and changes in stem circumference simultaneously without the need for chemical batteries that may harm the environment and are difficult to dispose of or recycle in vast fields.
The second part of the system, designed for the leg, is inspired by kirigami, a traditional Japanese art form that involves cutting and stretching paper with remarkable flexibility. Researchers designed a flexible, engineered sensor, known as a stretch and elasticity sensor, that wraps around the leg like a stretchy bandage without compressing it or hindering its natural growth.
This strip is coated with an innovative type of smart gel specifically designed to withstand extreme dryness and heat without drying out or freezing, unlike traditional water-based gels whose water evaporates quickly under direct sunlight.
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