Functionalized Gold Nanoparticles as an Active Layer for Mercury Vapor Detection at Room Temperature

Nanomaterials such as gold nanoparticles employed as solid-state sensors have attracted attention in recent years due to their ability to detect poisonous elements in the indoor/outdoor environment. Herein, chemoresistive sensors based on gold nanoparticles (AuNPs) functionalized with mixed thiol ligands were tested as sensing materials. Specifically, the electrical response of gold nanoparticles-based sensors was tested against Hg-vap(0), H2S, SO2, NH3, and relative humidity (RH) at room temperature. Gold nanoparticles samples were synthesized by the wet reduction method and then deposited as thin films on suitable interdigitated transducers. Electrical conductivity measurements allowed evaluating a semiconducting behavior of the colloids. A selective and reproducible sensing behavior toward Hg-vap(0) was observed in the range 0.1-1.0 ng/mL, allowing simple and reliable resistive devices to be obtained. An irreversible interaction mechanism, based on formation of an Au-Hg direct bond, was observed in the case of isolated AuNPs samples. Interconnected AuNPs exhibited a reversible behavior as assessed by Micro Raman, XRD, XPS, AFM, SEM, and UV-vis and FTIR spectroscopies together with DLS measurements. Broadening of the plasmonic band and an increase in the mean particle size upon contact with Hg-vap(0) was observed. Morphological characterization revealed the formation of aggregates after interaction between Hg-vap(0) and AuNPs. XRD and Micro Raman measurements collected on the nonexposed and Hg-exposed nanoparticles suggest their structural rearrangement at the surface and formation of an Au-Hg alloy with Hg mechanically trapped within the bulk material. The simple and cost-effective fabrication of these sensors has prospect in the future as nanodevices for real-time outdoor air quality monitoring.