Robust, Long-Term, and Exceptionally Sensitive Microneedle-Based Bioimpedance Sensor for Precision Farming.

Abdullah Bukhamsin,Ikram Blilou,Gilles Lubineau,Ran Tao,Jürgen Kosel,Khalil Moussi,Khaled Nabil Salama

doi:10.1002/advs.202101261

Abstract

Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open‐air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming.

Highlights

The miscibility of chloroform in ethanol allows it to remain in a unique phase that does not mix with water in solution
In summary, a novel micromolding and release strategy has been demonstrated for high fidelity replication of MNs for the fabrication of impedimetric plant sensors
The utility of the method is demonstrated via the reproduction of MNs composed of either photocurable or thermosetting polymers

Summary

Fabrication and Characterization

The robust mechanical properties and biocompatibility of these polymers allow for their use to penetrate the cuticle of living plants without triggering any cytotoxic effects.[28,29] More importantly, the low viscosity of the chosen formulations for SU-8 and polyimide coupled with a relatively high solid content enables more flow into the conical cavities of the PDMS mold with little shrinkage after crosslinking or polymerization. As both polymers are dielectrics, they can be subsequently patterned with the use of shadow masks and direct metal sputtering. Minimizing the weight of the sensor is crucial to mitigate triggering the thigmomorphogenetic response in the plant, which is initiated under mechanical stimulation to protect the tissue from damage.[31]

Plant Impedance Testing

Conclusion

Experimental Section

Data Availability Statement