Functionalized TiO2 Nanorods on a Microcantilever for the Detection of Organophosphorus Chemical Agents in Air.

We report the fabrication of nanostructured microcantilevers employed as sensors for the detection of organophosphorus (OPs) vapors. These micromechanical sensors are prepared using a two-step procedure first optimized on a silicon wafer. TiO2 one-dimensional nanostructures are synthesized at a silicon surface by a solvothermal method and then grafted with bifunctional molecules having an oxime group known for its strong affinity with organophosphorus compounds. The loading of oxime molecules grafted on the different nanostructured surfaces was quantified by UV spectroscopy. It has been found that a wafer covered by vertically aligned rutile TiO2 nanorods (NRs), with an average length and width of 9.5 μm and 14.7 nm, respectively, provides an oxime function density of 360 nmol cm-2. The optimized TiO2 nanorod synthesis was successfully reproduced on the cantilevers, leading to a homogeneous and reproducible TiO2 NR film with the desired morphology. Thereafter, oxime molecules have been successfully grafted on the nanostructured cantilevers. Detection tests were performed in a dynamic mode by exposing the microcantilevers to dimethyl methylphosphonate (a model compound of toxic OPs agents) and following the shift of the resonant frequency. The nanostructure and the presence of the molecules on a TiO2 NR surface both improve the response of the sensors. A detection limit of 2.25 ppm can be reached with this type of sensor.