A High-Sensitivity Microwave Resonator for Triclosan and Glyphosate Detection in Water

This work presents the design, fabrication, and testing of a circular split ring resonator (Cir-SRR) with an embedded interdigital capacitor (IDC) for emerging contaminant detection. The IDC attached to the outer ring gap of the Cir-SRR concentrates the electric field and improves the sensitivity of the resonator. According to measurements, the IDC/Cir-SRR resonates at 1.77 GHz and achieves a quality factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of 295. The simulation reported a hot spot of 115.9204 dBV/m in the IDC detection zone. The resonant frequency shifts approximately 400 MHz when the liquid sample changes from water to ethanol. The sensitivity was studied using ethanol in deionized water. An average sensitivity of 1.53% was achieved in the relative permittivity range of 18–79. Triclosan and glyphosate were selected as emerging contaminants and were tested by dissolving them in a 50% ethanol-water mixture and water, respectively. Linear relationships between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> transmission parameter and concentration were found in the selected ranges of 0–50 μg/mL and 0–35 μg/mL for triclosan and glyphosate, respectively. A sensitivity of 6.87×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> dB/(μg/mL) and a limit of detection (LOD) of 1.83 μg/mL were obtained with glyphosate solutions. In contrast, the values of 1.47×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> dB/(μg/mL) and 1.18 μg/mL were obtained with triclosan solutions. The results suggest that this technology offers a viable approach for the rapid detection of emerging water contaminants.