Highly sensitive terahertz spectroscopy of residual pesticide using nano-antenna

In this report, a novel type of highly sensitive small molecule sensing tool has been employed to detect residual pesticide molecules including e. g. methomyl using terahertz (THz) time-domain spectroscopy (TDS) system with nano-slotantenna array. Enhance THz wave by the nano-slot-antenna array induces strong THz field enhancement around nano antenna and thus increases an absorption cross section leading to the detection sensitivity upto ppm level even in solution state. Measured spectrums in transmission and reflection show an excellent performance in both sensitivity and selectivity. We also tested the performance of our nano-antenna array in reflection imaging geometry to simply detect the contained residual pesticide at the real fruit surface as it is, without any extraction or sampling preprocess. The clear difference in the obtained THz reflection image distinguishes the stained area with methomyl from the bare area. Our observation can offer the possibility for further application as a prompt and an accurate small molecule monitoring tool in real time. A quantitative analysis tool for such small molecule can be also developed by this method.

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