Micromechanical Switch-Based Zero-Power Chemical Detectors for Plant Health Monitoring

Abstract

In this paper, for the first time we demonstrate zero-power volatile-organic-chemical (VOC) detectors based on micromechanical switches suitable for plant health monitoring. Differently from state-of-the-art active chemical sensors, the device presented here exploits a completely passive, chemically-sensitive switch based on a bimaterial microcantilever and a passive switch-based readout mechanism to detect VOCs exceeding a predetermined concentration released by unhealthy plants. When exposed to target VOCs, the polymer/metal bimaterial beam bends downward and trigger the switch due to the stress induced from the absorption of chemicals in the polymer layer. Here we show experimental demonstrations of detecting toluene, hexenol (cis-3-Hexen-1-ol, a chemical released from plants under attack by pests) and ethanol, respectively, with our fabricated prototypes. The demonstrated high sensitivity to ethanol (∼ 8 nm/ppm) and hexenol (∼ 3.3 nm/ppm) was achieved by the optimization of device geometries showing a great promise of the proposed technology to ultimately achieve 10s ppm detection limit (with a sub-micron contact gap and voltage bias) which is required for the device operation in close proximity to a plant in an open environment.

Emerging Wearable Sensors for Plant Health Monitoring

“…[40] Therefore, several wearable chemical sensors have been developed to analyze plant VOC emissions or toxic chemicals and monitor plant health noninvasively (Table 3). [58][59][60][61][62][63] Li et al reported a wearable nitrogen dioxide (NO 2 ) chemiresistive sensor array by employing hybrid nanostructures consisting of silver nanoparticles (AgNPs) and all-carbon materials, including CNTs and reduced graphene oxide (rGO) [58] (Figure 4a). This sensor was directly spray-coated on various target objects, while the AgNPs-decorated rGO was used as the sensing layer to detect the change of NO 2 concentrations around the leaf surface.…”

“…Reproduced with permission. [ 63 ] Copyright 2020, IEEE. d) Left: A schematic diagram of the fluorescence modulation of the G‐SWNT sensor following H 2 O 2 binding.…”

“…Calisgan et al. reported a micromechanical switch‐based chemical detector, integrating a bimaterial microcantilever and a passive switch‐based readout mechanism [ 63 ] (Figure 5c). When exposed to the target VOCs, poly(methyl methacrylate)/gold bimaterial cantilever bent downward to the bottom gold electrode, due to the chemical absorption in the active polymer layer.…”

“…Gas sensing on the plant VOC sensor [63] rGO/ligand-modified AuNP Resistance change Screen printing, drop-casting, spin-coating, laser cutting Fast response (< 20 s), classification of 13 VOCs Plant health monitoring VOC sensor [64] Gold/PMMA Resistance change Chemical vapor deposition (CVD), photolithography, spin-coating, oxygen plasma High sensitivity (≈8 nm ppm −1 )…”

“…Right: The measured current of a device in response to ethanol while a 9.5 V bias voltage is being applied. Reproduced with permission [63]. Copyright 2020, IEEE.…”