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We report an excellent anisotropic Au nanoparticle-based colorimetric probe for the detection of Hg 2+ ions with higher detection ability and selectivity. The manifestation of different morphologies of Au nanoparticles including round, triangular, rectangular, pentagonal, and hexagonal has been realized by the dimethylenebis-(tetra-decyldimethylammonium bromide) (14-2-14 Gemini surfactant) assisted one-step thermal reduction method where the average size of Au nanoparticles was 54.65 ± 44.3 nm. The growth and frequency of Au nanoparticles were enhanced as a function of Gemini surfactant's concentration. The detection limit as low as 1.8 nM was efficaciously achieved and was considerably lower than the required world standards defined the maximum allowable level of Hg 2+ ions for health hazards. Notably, the Au nanoparticles showed visible detection for 100 μM Hg 2+ ion by means of the change in the solution color from red to tarnish blue within 180 s followed by saturation in the absorption ratio ( A LSPR / A TSPR ). These results provide novel insight into the detection of the heavy metal ion using Gemini surfactant-assisted grown anisotropic metal nanoparticles. On the basis of obtained results, it is concluded that the size of metal nanoparticles is no longer critical for preparation of efficient selective chemoprobe; rather, growth of more number of edges provides a large number of sights for incoming moieties and plays an important role in improving the detection capability of the anisotropic metal nanoparticle irrespective of their large sizes. We believe that this work provides valuable insight into researchers working in the area of chemosensor applications., Competing Interests: The authors declare no competing financial interest.

Surface-area-controlled porous TiO 2 thin films were prepared via a simple sol-gel chemical route, and their gas-sensing properties were thoroughly investigated in the presence of typical oxidizing NO 2 gas. The surface area of TiO 2 thin films was controlled by developing porous TiO 2 networked by means of controlling the TiO 2 -to-TTIP (titanium isopropoxide, C 12 H 28 O 4 Ti) molar ratio, where TiO 2 nanoparticles of size ∼20 nm were used. The sensor's response was found to depend on the surface area of the TiO 2 thin films. The porous TiO 2 thin-film sensor with greater surface area was more sensitive than those of TiO 2 thin films with lesser surface area. The improved sensing ability was ascribed to the porous network formed within the thin films by TiO 2 sol. Our results show that surface area is a key parameter for obtaining superior gas-sensing performance; this provides important guidelines for preparing and using porous thin films for gas-sensing applications.