The rapid maturing of nanotechnology and its wide range of applications not bring benefits only, so the downsides are worth noting. Nanopollutants, generally undetectable, are often found as byproducts involved in various chemical or physical reactions. Many nanopollutants are concerned and suspected of causing negative impact on human health due to their unpredictable existence in the environment. Unlike the traditional sensing systems which can detect select gaseous molecules, effective nanoparticle sensing methods are still lacking in the literature. In this paper, sensing of Mercury(II)-containing nanopollutants suspended in N2 with a room-temperature ionic liquid (RTIL) ([C4 mim][PF6 ] (1-butyl-3-methyl imidazolium hexafluorophosphate)) has been studied. The sensitivities (RIL /Rnano ) obtained by determination of the RTIL resistance to the absorbed phosphor fly ash (<200 nm) is 7.0, while the RTIL has higher sensitivity of 11 and 10, respectively, to HgO and HgS nanoparticles By component- fitted X-ray absorption near edge structure (XANES) spectroscopy, it seems that the N-methyl imidazole (mim) complexes are formed during sensing of the phosphor fly ash, HgO and HgS nanoparticles with the RTIL. The 1 H and 31 P NMR observations also suggest that the (mim) behaves as a carrier during sensing of nanopollutants with the RTIL.