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Abstract: A numerical model has been developed to predict the sensitivity of QCM (Quartz Crystal Microbalance) sensors. Such device is coated with a spray-deposited polymer, which has a specific affinity for a given family of molecules: here, nitro aromatic compounds are the target as they are key compounds for explosives trace detection in gas phase. The model is tested by a set of initial measurements performed on several target and interfering molecules. Physico- chemical characterizations are used to validate the model assumptions. The main goal of our approach is twofold: (i) to improve the choice of sensing material for chemical sensor development with a small number of experimental detection tests and (ii) to predict the response of a given material to other analytes. [Copyright &y& Elsevier]

Abstract: As of lately, the demand for developing artificial sensors with improved capabilities for the detection of explosives, toxics or drugs has increased. Ideally, sensor devices should provide high sensitivity and give a response that is specific to a given target molecule without being influenced by possible interfering molecules in the atmosphere. These properties strongly depend on the structure of the chemical compound used as a sensitive material. It is thus crucial to select the right compound and this step would be facilitated with the aid of predictive tools. The present investigations have been focused on a family of functionalized polysiloxane polymers deposited on a QCM device, producing only weak interactions compatible with reversible sensors. The quartz frequency variation at equilibrium has been linked to the partition coefficient that was evaluated using a thermodynamic description of the adsorption process. We have shown that the relative responses of two polymers can be directly determined from the Gibbs free enthalpy of mixing as determined from NMR measurements performed on neat liquid mixtures. An equivalence of this term—including both enthalpy and entropy contributions—to the energy interaction term calculated using Hansen solubility coefficients, has been demonstrated previously. These results constitute a basis for the development of a numerical program for calculating equilibrium sensor responses. For small molecules, the adsorption kinetics can be easily accounted for by a Fick diffusion coefficient estimated from the Van der Waals volume. [Copyright &y& Elsevier]

Abstract: By functionalising gold samples, planar wafers or AFM tips, with an acid- or an amino acid-terminated thiols, mercaptoundecanoic acid (MUA) and homocystein (H-Cyst) respectively, we were able to differentiate the interactions with ammonium perchlorate (AP) and starch (S), two components of a nanocomposition mixture. To do so, the interaction between gold functionalized surfaces and the two targeted compounds have been characterized and quantified by several complementary techniques. Polarisation modulation-infrared spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS), providing chemical analyses of gold surfaces after contacting S or AP, proved that both compounds were retained on MUA or H-Cyst-modified surfaces, but to various extents. Quartz crystal microbalance on-line measurements enabled to monitor the kinetics of interaction and showed distinct differences in the behaviour of MUA and H-Cyst-surfaces towards the two compounds. Having observed that only H-Cyst-modified surfaces enables to get a contrast on the chemical force microscopy (CFM) images, this new result could be well explained by examining the data obtained by combining the above-mentioned surface characterisation techniques. [Copyright &y& Elsevier]

Abstract: Adsorption of thiols of varying structures bearing amine, acid or aromatic functionalities was characterised by Polarisation Modulation Infrared Absorption Spectroscopy (PM-IRRAS). The so functionalised surfaces were then submitted to atmospheres containing traces of 2,4-dinitrotrifluoromethoxybenzene and gas capture was evaluated by Quartz Crystal Microbalance (QCM). The selectivity of these new sensors was also evaluated thanks to exposures to solvents: ethanol, methylethylketone, toluene and dichloromethane. The QCM response appeared to be the best one, high and specific to the nitroaromatic, for aromatic amine functions. [Copyright &y& Elsevier]

A new type of sensor was built by synthesizing a long-chain thiol functionalized with an aromatic head group and grafting it onto a gold surface. The synthesis route is here described, together with the IR, MS, and RMN analysis of the new product. Adsorption of the latter onto gold was assessed by a combination of RAIRS and XPS data. Those reveal that a monolayer of thiol is adsorbed and oriented with the benzene groups toward the external part of the layer. Detection tests were performed in various atmospheres by QCM. The response shows good sensitivity to 2,4-dinitrotrifluoromethoxybenzene as a model of nitroaromatic compound. [Copyright &y& Elsevier]