Integrated
flexible device attached onto the lower epidermis of the leaf to monitor
transpiration processes. Credit: Lu et al. ACS Nano (2020), DOI:
10.1021/acsnano.0c03757
The
emergence of biotic and abiotic stresses poses potential impairment on plant
growth and yield. Accurate monitoring and assessment of plant health status is
therefore highly important; however, conventional bulky and heavy sensors are
usually restricted to centralized climate conditions or perform measurements in
gas exchange chambers.
One
strategy relies on intelligently interfacing plants with flexible sensors.
However, it is challenging to tap into physiological information in plants due
to their relatively complex signaling pathways. Additionally, synchronous
detection of abiotic stress factors demands a perdurable, flexible,
multifunctional sensor system for prolonged monitoring without performance
degradation and signal cross-talk.
In a
recent study published in ACS Nano titled "Multimodal Plant Healthcare
Flexible Sensor System," researchers from Osaka Prefecture University
(OPU) report an integrated multimodal flexible sensor system comprising a room
humidity sensor, a leaf humidity sensor, an optical sensor and a temperature
sensor that can tap into potential physiological health issues on plants.
Significantly, dehydration conditions are visually recorded in a Pachira
macrocarpa over a long-term monitoring (>15 days) based on such
plant-machine biointerfaces by leveraging the plant transpiration process.
Using
stacked ZnIn2S4 (ZIS) nanosheets as the kernel sensing media, the ZIS
nanosheets-based flexible sensor can not only perceive light illumination at a
fast response (~4 ms), but also monitor the humidity with a perdurable steady
performance. As the ZIS nanosheets are applied in humidity sensor for the first
time, theoretical and experimental investigations of humidity sensing mechanism
were carried out in detail. Three primary abiotic stresses (i.e. humidity,
light and temperature) that govern the transpiration of plants are measured
without signal cross-coupling effect in real time.
"Most
of the flexible sensors have been applied to human health monitoring and/or
human-machine interfaces. The proposed concept of the multimodal flexible
sensor system for the plant health status monitoring may open up a pathway
toward intelligent agriculture," said Prof. Dae-Hyeong Kim, an expert on
soft electronics.
Prof.
Kuniharu Takei, the leader of this project, said, "By rationally selecting
the active sensing materials and electrodes, we have addressed the perdurable
sensor performance for long-term tracking of abiotic stresses on plants as well
as multichannel signals' collection without crosstalk."
Future
tasks include further reducing the thickness and weight of flexible sensor
systems, increasing sensor functionalities in response to other biotic and
abiotic stresses, and improving capabilities to decode plant chemical signals
in spatiotemporal patterns. The influence of environmental gas, such as CO2,
O2, or NOx, on the sensor output should be considered as well.