A chemical switch for detecting insect infestation.

Plants emit phytochemicals as a defensive mechanism against herbivores. A small sensor switch that responds to these chemicals could be used to stop insect infestation at early stages. Polyethylene-co-vinyl acetate was chosen as the best polymer for this particular application, based on its swelling response to plant volatiles. When the carbon concentration of the active layer was low enough to be near the percolation threshold, the sensor could be used as a 'chemical switch'. The resistance of the sensor increased significantly, mimicking a 'switch-off' response when exposed to the analyte vapor. When the analyte vapor was no longer present, the sensor returned back to its original condition, showing a 'switch-on' response. The percolation point was obtained when the carbon concentration of the polymer/carbon composite was kept at 2.5 wt%. A low-mass-fraction carbon composite sensor has been designed and fabricated to detect γ-terpinene, α-pinene, p-cymene, farnesene, limonene and cis-hexenyl acetate. The sensor is inexpensive, easy to fabricate and highly stable in air.