A Novel Miniaturized THz PPCPs’ Metasensor

At present, the residues and potential risks of pharmaceuticals and personal care products (PPCPs) in water surface, groundwater, and drinking water sources have attracted extensive attention. The concentration of PPCPs in the environment is usually at the level of ng/L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~\mu $ </tex-math></inline-formula>g/L. In this study, we designed a novel terahertz (THz) graphene metasensor (GMS) for determining and quantifying PPCPs. Taking five common PPCPs for example, the GMS can enhance the sensing performance at low concentrations due to strong interaction between the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula>-bond electrons from PPCP molecules and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi - \pi $ </tex-math></inline-formula> stacking from graphene, that is, the initial Fermi level of p-doped graphene (slightly off the Dirac point and in the valence band) gradually shifts from the valence band to the Dirac point with increased concentration. However, at high concentrations, the Fermi level moves away from the Dirac point to the conduction band, and the sensing performance decreases until it reaches a minimum. In addition, five PPCPs can show different sensing performances regarding to their <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> electrons number of PPCPs by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi -\pi $ </tex-math></inline-formula> stacking with proposed GMS. The limit of detection (LOD) can achieve 21.19 fg/mL, which reaches the standard of actual sample concentration. The GMS has the advantages of high sensitivity, fast time, and label-free detection, which has potential applications for the detection of trace pollutants in the field of environment.