Effect of Viscoelasticity on Quality Factor of Microcantilever Chemical Sensors: Optimal Coating Thickness for Minimum Limit of Detection

Microcantilevers with polymer coatings hold great promise as resonant chemical sensors. It is known that the coated cantilever sensitivity increases with coating thickness; however, the drawback of increasing the coating thickness is the increase of the frequency noise and thus the deterioration of the sensor\u27s limit of detection. In this paper, an analytical expression for the viscoelastic losses in the coating, hence the quality factor is established and is used to explain the observed increase of the frequency noise with the polymer thickness. This result is then used to demonstrate that an optimum coating thickness exists that minimise the limit of detectio

Study of Viscoelastic Effect on the Frequency Shift of Microcantilever Chemical Sensors (proceedings)

Microcantilevers coated with a chemically sensitive layer are increasingly being used in chemical detection systems. The sensitive coating, often a polymer, absorbs specific molecules, which can be detected by monitoring the shift in the mechanical resonant frequency. Usually, the frequency shift resulting from molecular absorption is interpreted as a mass loading effect. However, mass loading is not the only effect that has an impact on the frequency shift; the viscoelastic properties of the sensitive coating are also affected by the sorption process. Sorption-induced modulus changes are typically difficult to characterize. However, it is known that the sorption of analyte molecules in a polymer coating results in the plasticization of the coating. In most cases, the polymer becomes more rubbery with increasing concentration of analyte molecules, i.e., the coating becomes softer with increasing loss modulus while the storage modulus decreases. Using a new analytical model developed for the resonant frequency expression of a hybrid microcantilever (elastic base and viscoelastic layer), the effects of the modification of the storage and loss moduli of the sensitive layer on the resonant frequency are examined. The main conclusion of this analytical study is that, even if the sensitive coating moduli are small compared to the base cantilever\u27s Young\u27s modulus, the effect of the change in the viscoelastic coating properties could contribute significantly to the overall frequency shift (8-23% in the simulations depending on the coating thickness, with even higher contributions for other sets of problem parameters)

Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry

While 17O NMR is increasingly being used for elucidating the structure and reactivity of complex molecular and materials systems, much effort is still required for it to become a routine analytical technique. One of the main difficulties for its development comes from the very low natural abundance of 17O (0.04%), which implies that isotopic labeling is generally needed prior to NMR analyses. However, 17O-enrichment protocols are often unattractive in terms of cost, safety, and/or practicality, even for compounds as simple as metal oxides. Here, we demonstrate how mechanochemistry can be used in a highly efficient way for the direct 17O isotopic labeling of a variety of s-, p-, and d-block oxides, which are of major interest for the preparation of functional ceramics and glasses: Li2O, CaO, Al2O3, SiO2, TiO2, and ZrO2. For each oxide, the enrichment step was performed under ambient conditions in less than 1 h and at low cost, which makes these synthetic approaches highly appealing in comparison to the existing literature. Using high-resolution solid-state 17O NMR and dynamic nuclear polarization, atomic-level insight into the enrichment process is achieved, especially for titania and alumina. Indeed, it was possible to demonstrate that enriched oxygen sites are present not only at the surface but also within the oxide particles. Moreover, information on the actual reactions occurring during the milling step could be obtained by 17O NMR, in terms of both their kinetics and the nature of the reactive species. Finally, it was demonstrated how high-resolution 17O NMR can be used for studying the reactivity at the interfaces between different oxide particles during ball-milling, especially in cases when X-ray diffraction techniques are uninformative. More generally, such investigations will be useful not only for producing 17O-enriched precursors efficiently but also for understanding better mechanisms of mechanochemical processes themselves

The use of calix[6]arene molecules for actinides analysis in urine: an alternative to current procedures

Individual monitoring of workers exposed to a risk of internal contamination with actinides is achieved through in vivo measurements (anthroporadiametry) and in vitro measurements (urine and feces). The procedures currently used for analyzing actinides in urine require lengthy separation associated with long counting times by alpha spectrometry due to low activity levels. Their main drawback is thus that they are time-consuming, which limits the frequency and flexibility of individual monitoring. In this context, the aim of this work, carried out by the Radiochemistry Laboratory at the Institute for Radiological Protection and Nuclear Safety (IRSN), is to propose alternative radiochemical procedures for the analysis of actinides U, Pu and Am in urine. In order to selectively extract actinides from urines, it is of interest to use calix[n]arene molecules. Indeed, the preorganized structure of these macrocyclic molecules is suitable for the complexation of ions and they can be easily functionalized to be more specific. Thus, the p-tertbutylcalix[6]arenes bearing three carboxylic acid groups or three hydroxamic acid groups are excellent extractants for uranium, and they have also a very good affinity for plutonium and americium. The extraction of actinides by these calixarene has been studied experimentally, and also by computational study for uranium. From these results, a new radiochemical procedure has been proposed for U, Pu, Am analysis in urine. For an application to bioassays laboratories, it was decided to immobilize the calix[6]arene molecules on an inert solid support, for implementation with a chromatographic column. This technique makes it possible to combine the extraction performances of the calix[6]arenes with the practical advantages of the chromatographic column. Consequently, this new radiochemical is well suited for routine analysis. Furthermore, the actinides separation is quantitative and reproducible, and is faster and easier than the current procedures

An alternative procedure for uranium analysis in drinking water using AQUALIX columns: Application to varied French bottled waters

The general population is chronically exposed to uranium (234U, 235U, and 238U) and polonium (210Po) mainly through day-to-day food and beverage intake. The measurement of these naturally-occurring radionuclides in drinking water is important to assess their health impact. In this work the applicability of calix[6]arene-derivatives columns for uranium analysis in drinking water was investigated. A simple and effective method was proposed on a specific column called AQUALIX, for the separation and preconcentration of U from drinking water. This procedure is suitable for routine analysis and the analysis time is considerably shortened (around 4 h) by combining the separation on AQUALIX with fast ICP-MS measurement. This new method was tested on different French bottled waters (still mineral water, sparkling mineral water, and spring water). Then, the case of simultaneous presence of uranium and polonium in water was considered due to interferences in alpha spectrometry measurement. A protocol was proposed using a first usual step of spontaneous deposition of polonium on silver disc in order to separate Po, followed by the uranium extraction on AQUALIX column before alpha spectrometry counting. © 2013 Elsevier B.V

Calixarene-entrapped nanoemulsion for uranium extraction from contaminated solutions

Accidental cutaneous contamination by actinides such as uranium occurring to nuclear power plant workers can lead to their dissemination in other tissues and induce severe damages. Until now, no specific emergency treatment for such contamination has been developed. The aim of the present work was to formulate a tricarboxylic calix[6]arene molecule, known to exhibit good affinity and selectivity for complexing uranium, within a topical delivery system for the treatment of skin contamination. Since calixarene was shown to reduce oil/water interfacial tension, we have designed an oil-inwater nanoemulsion, taking advantage of the small droplet size offering a high contact surface with the contaminated aqueous medium. Characterization of the calixarene nanoemulsion was performed by determination of the oily droplet size, zeta potential and pH, measured as a function of the calixarene concentration. The obtained results have confirmed the surface localization of calixarene molecules being potentially available to extract uranyl ions from an aqueous contaminated solution. In a preliminary experiments, the calixarene nanoemulsion was used for the removal of free uranium from an aqueous contaminated solution. Results showed that the calixarene nanoemulsion extracted up to 80 ± 5% of uranium, which demonstrates the potential interest of this delivery system for uranium skin decontamination. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association

The use of calix[6]arene molecules for actinides analysis in urine and drinking water: An alternative to current procedures

In this work the applicability of calix[6]arene columns for actinides analysis in urine samples and drinking water was investigated. A radiochemical procedure has been developed for U, Pu, Am analysis in urine. A simple and effective method has also been proposed on a specific column named AQUALIX, for the separation and preconcentration of U from drinking water. These procedures are suitable for routine analysis and require a considerably reduced number of steps of sample treatment as compared to current procedures. © 2009 Akadémiai Kiadó, Budapest, Hungary