A wireless and passive RFID tag sensor for the detection of Pb in soil combining chemiresistive sensing and impedance mismatch: A new method for onsite detection of hazardous metals.

In this work, a wireless and passive radio frequency identification (RFID) tag sensor, which integrated a reduced graphene oxide/ion-selective membrane (rGO/ISM) chemiresistive sensing component, was developed for the onsite detection of Pb in soil. Additionally, a new detection method combining impedance mismatch and spectral sensing technique for Pb was proposed. Furthermore, the sensing mechanism of the RFID tag sensor was investigated in terms of the field-effect transistor (FET) transfer curve and antenna reflection coefficient. The charge density in the sensing component was altered by Pb, reducing resistance and modifying the tag antenna impedance. Impedance mismatch between the antenna and RFID chip was thereby induced, with varying degrees of mismatch directly altering the light-emitting diode (LED) luminous intensity on the tag sensor. Rapid detection (<2 s) via luminous intensity monitoring eliminated a vector network analyser (VNA), achieving a detection limit of 1.96 μg/L. Ultimately, the sensing performance of the RFID tag sensor was verified through the detection of Pb in real soil samples (recovery rates of 99-101 %, and RMSEs of 2.08-7.32 μg/kg), indicating that the tag sensor offers a simple and effective solution for rapid and onsite detection of hazardous heavy metals in soil, with potential for practical application.