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Our traditional manufacturing, fabrication, and electronics have been centered around synthetic and completely artificial techniques. Coming from an industrial revolution, this is not surprising. However, in recent years, the progress in material science has enabled us to work at a deeper substrate level, much beyond the chip-layer. This has helped us rethink form/structure, sources of power and "hosts" of future electronics.
A new emergent field is hybridization with the real world, wherein artificial techniques are intertwined processes with natural systems. In a series of recent projects [1, 2, 3], we have projected such natural systems to be living plants—partly because of micro-capabilities of plants such as physiological signals, water uptake, light energy harvesting, etc. Such micro-capabilities coupled with self-repairing, self-powered properties of plants could be a boon to our own electronics (manufacturing, sensing, response) techniques. An auxiliary sensing system can be powered by placing it in conjunction with a plant’s natural system. In this vein, we present Argus—a living plant with nanosensors inside its leaves that can monitor for water quality/toxicity.
Argus is a living plant with DNA nanosensors inside it that detects lead (Pb2+ Heavy Metal). Irregularities in industrial waste management has lead to depletion of water quality in rivers in many regions. Current processes of monitoring the water quality are not realtime (taking a week or longer) or require special systems that are not off-the-shelf.
Through Argus, we propose a novel water monitoring method where plants provide an optical readout of lead in water. A DNAZyme is used as sensor assay—double stranded DNA that breaks into single stranded on contact with Pb2+ and binds to single walled carbon nanotubes. This sensor assay can be injected inside the leaf of a plant and stays within the intercellular space.
The precedents follow from agricultural biotechnology and nanomaterials to make plants resistant to diseases, enhance their nutrient absorption, and more. Several nanomaterials and their effects have been studied on plants [23]. Carbon-based material such as Carbon Nanotubes (CNTs) have been shown to penetrate the seeds [25] and plant cells [26]. We prepare chemical sensors that can reside inside the leaf of a plant and stay within its intercellular space. A needleless syringe (Fig 7b) was used to do infusion of the above CNT chemical sensors [21] through the abaxial side of the leaf. The leaf was cleaned of any remaining assay on the surface.
For our sensors, we use the DNA cleavage approach by Yao et al. [24] but modify it for in-vivo detection in plants. We prepare ‘8-17 DNAZyme’ turn-off assay where 5'-end of strand is labelled with a quencher and 3'-end with a flourophore. We use "8-17 DNAzyme" for turn-off assay where 5'-end of strand is labelled with a quencher and 3'-end with a flourophore, modified for in-vivo detection. In presence of Pb2+, the dsDNA is cleaved to ssDNA which binds more strongly to SWNT walls thus quenching the flourophore. The reduction in fluorescence is proportional to the lead (II) concentration.
Following introduction of Pb2+ ions, the fluorescence output is quenched due to release of ssDNA and its binding with the CNT walls. The following pictures show the time resolved output. When the blob is visible, the output is interpreted as heavy-metal free. Following introduction of Pb2+, the laser output is quenched inside the plant
Traditional Pb2+ sensing isn’t an easy off-the-shelf electronic sensor work. Sophisticated instrumentation and a number of days are required for such analysis. To interface our plant-based Lead detection with the digital world, we built a non-specialized setup. The "in-vivo" rapid detection is interfaced with the digital world, with the vision of a greater detection palette and bidirectional relay channel with the plants. Such an approach can be useful at home interfacing with the activities we usually do at home. Watering a house plant regularly could tell us about the chemical levels in water. Sensors for detecting other elements can also be deployed in industrial or nuclear towns for continuous monitoring.
References:
[1] Sareen, Harpreet, and Pattie Maes. "Cyborg Botany: Exploring In-Planta Cybernetic Systems for Interaction." Extended Abstracts of the 2019 CHI Conference on Human Factors in Computing Systems. ACM, 2019.
[2] Sareen, Harpreet, Jiefu Zheng, and Pattie Maes. "Cyborg botany: augmented plants as sensors, displays and actuators." Extended Abstracts of the 2019 CHI Conference on Human Factors in Computing Systems. ACM, 2019.
[3] Sareen, Harpreet. “Project Overview ‹ Elowan: A Plant-Robot Hybrid.” MIT Media Lab, www.media.mit.edu/projects/elowan-a-plant-robot-hybrid/overview/.