Detection of Organophosphorous Chemical Agents with CuO-Nanorod-Modified Microcantilevers.

Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand on the surface of the sample. The oxidation is performed in an alkaline solution containing a mixture of Na(OH) and (NH4)2S2O8. The synthesis procedure was first optimized on a silicon wafer, then transferred to optical cantilever-based sensors. This transfer requires specific synthesis modifications in order to cover all the cantilever with nanorods. A masking procedure was specially developed and the copper layer deposition was also optimized. These nanostructured cantilevers were engineered in order to detect vapors of organophosphorous chemical warfare agents (CWA). The nanostructured microcantilevers were exposed to various concentration of dimethyl methylphosphonate (DMMP) which is a well-known simulant of sarin (GB). The detection measurements showed that copper oxide is able to detect DMMP via hydrogen interactions. The results showed also that the increase of the microcantilever surface with the nanostructures improves the sensors efficiency. The evolution of the detection performances of the CuO nanostructured cantilevers with the DMMP concentration was also evaluated.

Cu(OH)2 and CuO Nanorod Synthesis on Piezoresistive Cantilevers for the Selective Detection of Nitrogen Dioxide.

Self-controlled active oscillating microcantilevers with a piezoresistive readout are very promising sensitive sensors, despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper hydroxide (Cu(OH)2) or with copper oxide (CuO) nanorods. The Cu(OH)2 rods were grown, on a homogeneous copper layer previously evaporated on the top of the cantilever. The CuO nanorods were further obtained by the annealing of the copper hydroxide nanostructures. Then, these copper based nanorods were used to detect several molecules vapors. The results showed no chemical affinity (no formation of a chemical bond) between the CuO cantilevers and the tested molecules. The cantilever with Cu(OH)2 nanorods is selective to nitrogen dioxide (NO2) in presence of humidity. Indeed, among all the tested analytes, copper hydroxide has only an affinity with NO2. Despite the absence of affinity, the cantilevers could even so condensate explosives (1,3,5-trinitro-1,3,5-triazinane (RDX) and pentaerythritol tetranitrate (PETN) on their surface when the cantilever temperature was lower than the explosives source, allowing their detection. We proved that in condensation conditions, the cantilever surface material has no importance and that the nanostructuration is useless because a raw silicon cantilever detects as well as the nanostructured ones.

Chip calorimetry for the sensitive identification of hexogen and pentrite from their decomposition inside copper oxide nanoparticles.

Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.

Double side nanostructuring of microcantilever sensors with TiO2-NTs as a route to enhance their sensitivity.

We reported a new strategy to enhance the sensing performances of a commercial microcantilever with optical readout in dynamic mode for the vapor detection of organophosphorus compounds (OPs). In order to increase significantly the surface area accessible to the molecules in the vapor phase, we nanostructured both sides of the microcantilever with ordered, open and vertically oriented amorphous titanium dioxide nanotubes (TiO2-NTs) in one step by an anodization method. However, due to the aggressive conditions of anodization synthesis it remains a real challenge to nanostructure both sides of the microcantilever. Consequently, we developed and optimized a protocol of synthesis to overcome these harsh conditions which can lead to the total destruction of the silicon microcantilever. Moreover, this protocol was also elaborated in order to maintain a good reflection of the laser beam on one side of the microcantilever towards the position sensitive photodiode and limit the light diffusion by the NTs film. The results related to the detection of dimethyl methylphosphonate (DMMP) showed that TiO2 and the nanostructuring on both sides of the microcantilever with NTs indeed improved the response of the sensor to vapors compared to a microcantilever nanostructured on only one side. The dimensions and morphology of NTs guaranteed the access of molecules to the surface of NTs. This approach showed promising prospects to enhance the sensing performances of microcantilevers.

Synthesis of zinc oxide nanorods or nanotubes on one side of a microcantilever.

Cantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with zinc oxide (ZnO) nanorods or nanotubes having a diameter of approximately 100 nm and a length of 1 µm. The nanostructure growth was first optimized on a silicon wafer and then transferred to the cantilevers. The ZnO nanorods were grown in an autoclave. The centre of the nanorods was dissolved in order to obtain nanotubes. The dissolution conditions were optimized in order to have the longest etching depth. After 1.25 h in a dissolution solution containing 0.75 wt% of NH3(aq) and 0.75 wt% of cetyltrimethyl ammonium bromide, the longest etching depth was obtained. After the transfer of the syntheses to the cantilevers, nanorods/nanotubes grew on both sides of the cantilever, which prevents the reflection of the laser allowing the resonance frequency measurement. A masking procedure was developed in order to avoid the growth on one face of the cantilever of zinc oxide nanostructures. As far as the authors are concerned, for the first time, zinc oxide nanotubes were synthesized on only one face of cantilevers with optical readout.

A new zinc hydroxy acetate hydrogen carbonate lamellar phase for growing large and clean ZnO nanorod arrays.

A novel zinc hydroxy acetate hydrogen carbonate Zn5(OH)8.2(CH3COO)(HCO3)0.8·1.9H2O, isomorphous to Zn5(OH)8(CH3COO)2·xH2O, has been obtained by the reaction of zinc acetate dihydrate in aged ethylenediamine. This phase allows the growth of large arrays of oriented and crystallized nanorods up to 8 µm in length on a substrate, without crystallization of additional particles.

Effect of ball-milling and Fe-/Al-doping on the structural aspect and visible light photocatalytic activity of TiO2 towards Escherichia coli bacteria abatement.

Escherichia coli abatement was studied in liquid phase under visible light in the presence of two commercial titania photocatalysts, and of Fe- and Al-doped titania samples prepared by high energy ball-milling. The two commercial titania photocatalysts, Aeroxide P25 (Evonik industries) exhibiting both rutile and anatase structures and MPT625 (Ishihara Sangyo Kaisha), a Fe-, Al-, P- and S-doped titania exhibiting only the rutile phase, are active suggesting that neither the structure nor the doping is the driving parameter. Although the MPT625 UV-visible spectrum is shifted towards the visible domain with respect to the P25 one, the effect on bacteria is not increased. On the other hand, the ball milled iron-doped P25 samples exhibit low activities in bacteria abatement under visible light due to charge recombinations unfavorable to catalysis as shown by photoluminescence measurements. While doping elements are in interstitial positions within the rutile structure in MPT625 sample, they are located at the surface in ball milled samples and in isolated octahedral units according to (57)Fe Mössbauer spectrometry. The location of doping elements at the surface is suggested to be responsible for the sample cytotoxicity observed in the dark.