Tufts University plant wearable sensors draw power from plant moisture to spot stress early

Smartwatches log your pulse and can flag up a poor night’s sleep. Until now, plants have had nothing remotely similar.

On farms, problems are often spotted only once they show themselves: leaves begin to curl, growth slows, and the stress may already have been accumulating for several days.

A new type of sensor aims to shift that timeline. Worn directly on the plant, it can register stress signals well before any obvious harm appears.

Detecting plant damage before it’s visible

Engineers at Tufts University have created two separate gadgets designed to be fitted to a living plant.

The first is an ultra-thin, tattoo-style patch that adheres to a leaf; the second is a flexible band that sits around the stem and stays put even when it is windy.

Working as a pair, they keep an eye on two key “vital signs”. The patch measures temperature and humidity just beneath the surface of the leaf, while the band checks whether the stem continues to widen as the plant develops.

There is also an unexpected feature: the setup does not need an external battery. Instead, it harvests energy from the moisture evaporating from the plant itself.

“Other plant sensors exist, but their ability to track multiple stressors and growth-related parameters is limited, and the technology often relies on external batteries, which complicate field deployment,” said Nafize Hossain at Tufts.

Beyond the technology

Farmers already use tools that observe crops from above, with satellites and drones collecting visible, infrared, and microwave information across whole fields.

Those images can chart greenness, patchy development, temperature variation, pest impacts, and soil moisture. In the ground, soil probes contribute their own measurements for moisture, temperature, pH, and certain nutrient levels.

Weather stations then complete the picture by recording air temperature, humidity, rainfall, wind, and sun exposure.

Although these technologies are valuable, they largely describe a plant’s surroundings-or document damage after it has occurred.

By contrast, the leaf-mounted sensor focuses on how the plant is managing right now.

Early warning signs

“The leaf sensor is more of an early warning system showing how the plant is responding in the moment, before visible signs appear,” said Hossain.

“The larger promise is not merely that one plant can wear one sensor. It is that fields could one day contain networks of plant-level monitors, each reporting early signs of thirst, salt stress, disease or nutrient imbalance.”

Professor Sameer Sonkusale is an electrical engineer at Tufts University.

“While satellites and drones already give farmers a bird’s-eye view, plant wearables could offer a more intimate perspective of a plant’s-eye view,” said Professor Sonkusale.

Catching water stress

The leaf patch concentrates on the vapour pressure deficit, or VPD, which describes how strongly the surrounding air is drawing water out of the plant.

When VPD is high, the air is dry and it pulls moisture from leaves. In response, plants protect themselves by closing their stomata-tiny pores that regulate gas exchange and water loss.

That protective move helps prevent dehydration, but it also reduces photosynthesis and slows growth.

Power from the plant

The moisture-sensing element is where the approach becomes particularly inventive. It uses vanadium pentoxide crystals separated into extremely thin nanosheets.

Inside a membrane, those nanosheets stack into layers. A graphene film-made of carbon atoms-then acts like a sieve, allowing plant moisture to pass through to the layered sheets.

As water enters, ions form and move across the nanosheets, generating an electric current. As a result, the patch functions both as a sensor and as a small battery at the same time.

The size of the current corresponds to how much moisture the leaf is exchanging with the air.

The resulting power is modest-on the order of microwatts. Even so, when combined with low-power electronics and a small amount of energy storage, it can still support routine measurements.

Tracking the stem

The stem-worn device takes inspiration from kirigami, the Japanese craft of cutting paper so it can stretch and bend. The pattern of cuts allows the band to expand and contract with the stem rather than fighting against its movement.

The sensor is coated with a soft, ion-conducting gel known as a eutectogel, whose electrical resistance changes as the stem thickens or becomes narrower.

Under normal conditions, stems generally widen from one day to the next; under stress, that widening may slow, or the stem may even contract.

Sensors and timescales

Using both devices together is important because plants display stress across more than one timescale.

Leaves respond quickly to the immediate conditions that affect water loss, while the stem reflects a slower biological process playing out over time.

In other words, one sensor captures what is happening now, and the other follows the longer-term trajectory. Interpreted together, they provide a more complete picture than either could deliver on its own.

Tested on bell peppers

The researchers installed the system on bell pepper plants and used it to distinguish healthy specimens from those affected by water shortage or salt stress.

In healthy plants, VPD rose and fell in a regular rhythm matching the normal daily cycle of air moisture.

Plants under water stress drove VPD upwards in a steady climb, whereas salt-stressed plants showed the opposite pattern, with VPD lower than the controls.

That reduction is likely linked to shifts in water uptake and stomatal behaviour. The stem measurements supported the same conclusion from another angle.

Plants in good condition continued to grow, but stressed plants either stopped widening or shrank.

Built for the field

Because farm conditions are tough on electronics, the leaf patch is designed to flex and stretch without tearing, while still allowing the leaf to ‘breathe’.

This pliability helps it keep contact on a real leaf’s uneven surface as it moves. The stem sensor relies on its kirigami structure to distribute strain across the material.

That layout enables it to withstand sudden shocks-such as a strong gust-without losing the signal.

Wireless plant networks

At present, the team is developing a complete wireless link for the sensors, evaluating LoRa (a long-range standard) alongside Bluetooth-based alternatives.

With wireless communication, sensors spread across a field could send updates back automatically, removing the need for anyone to walk the rows.

The approach could also expand beyond water and heat. Later versions may monitor nutrients, plant hormones, and the earliest disease responses across roots, leaves, stems, and fruit.

Image Credit: Nafize Hossain