Ultrasensitive Detection of Residual Pesticides Using THz Near-Field Enhancement

We present a novel type of highly sensitive and selective detection method for residual pesticide molecules including, e.g., methomyl using nanoscale metamaterials based terahertz (THz) time-domain spectroscopy (TDS) system. Nanoscale slot-antenna-based metamaterials were designed for the strong THz resonance at a certain frequency, where the specific molecule has intramolecular or intermolecular collective vibrational mode. Enhanced THz near-field via a nano-antenna metamaterial strongly increases absorption cross section, and this leads to the detection sensitivity up to parts-per-billion level even in a solution state of pesticide sample. Measured transmittance and reflectance spectrum results show excellent performances in both sensitivity and selectivity. We also imaged reflected THz signals though our THz nano-metamaterials in a nondestructive manner to simply detect the contained residual pesticide at the surface of an apple as it is, without any treatment. This observation can offer the possibility for further various applications as prompt and accurate molecule sensing tools in real time.