RESUMEN
Gas chromatography is a reference method for gas analysis. As part of efforts to miniaturize gas chromatography systems, the miniaturization of detectors is essential. In this work, we report a new integrated photonic platform for gas chromatography analyte detection. The fabricated silicon die integrates Mach-Zehnder interferometers into low dead volume microfluidic channels, with coherent cost-effective detection scheme with a fixed 850 nm wavelength laser. A proof of concept is demonstrated with the separation and detection of three volatile organic compounds: heptane, octane, and toluene. Peaks' widths at half height range from 1 to 5 s. Peaks are very well resolved by our system, which acquires more than 100 points per second. From a heptane dilution range, we evaluate the limit of detection of our system to be the headspace of a 0.26 % heptane concentration solution. To our knowledge, these are the first integrated Mach-Zehnder interferometers reported for gas chromatography detection. This work could open new strategies for fast low cost and low limit of detection specific gas chromatography silicon micro-detectors.
RESUMEN
Metal-organic frameworks are a class of porous materials that show promising properties in the field of microelectronics. To reach industrial use of these materials, gas phase techniques are often preferred and were recently introduced. However, the thicknesses achieved are not sufficient, limiting further development. In this work, an improved gas phase process allowing ZIF-8 layer formation of several hundreds of nm using cyclic ligand/water exposures is described. Then, by a combination of in-depth surface analyses and molecular dynamics simulations, the presence and role of hydroxyl defects in the ZIF-8 layer to reach this thickness are established. At the same time, this study unveils an inherent limit of the method: thickness growth is consubstantial with defect repairing upon the crystallites ripening; such defect repairing eventually leads to the decrease of the pore window below the diffusion radius of the incoming linker, thus apparently capping the maximum MOF thickness observable for this type of material topology through this growth method.
RESUMEN
This study presents the impregnation in supercritical carbon dioxide (scCO2) of nanocellulose-based structures with thymol as a natural antimicrobial molecule to prepare bioactive, biosourced materials. First, cellulose nanofibrils (CNFs) were used to produce four types of materials (nanopapers, cryogels from water or tert-butyl alcohol suspensions, and aerogels) of increasing specific surface area up to 160 m2·g-1, thanks to the use of different processes, namely, vacuum filtration, freeze-drying, and supercritical drying. Second, these CNF-based structures were impregnated with thymol in the scCO2 medium using a relatively low temperature and pressure of 40 °C and 100 bar during 1 h. The amount of impregnated thymol in the different CNF materials was investigated by fluorescence spectroscopy, 13C NMR analysis, and gas chromatography. All three methods consistently showed that the amount of impregnated thymol increases with the specific surface area of the material. The antimicrobial activity of the impregnated CNF-based materials was then measured against three reference strains of microorganisms: the Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis bacteria, and the yeast Candida albicans using the disk diffusion test method. The latter revealed the leaching of thymol in sufficient amounts to generate antimicrobial activity against the three strains in the case of the cryogel derived from a tert-butyl alcohol suspension and the aerogel, which are the two materials exhibiting the highest specific surface areas. The proposed strategy, therefore, enabled us to precisely steer the amount of active molecule loading and the related antimicrobial activity by adjusting the specific surface area of the biosourced material impregnated in green supercritical conditions. These results are very promising and confirm that supercritical impregnation of active molecules onto nanocellulose three-dimensional (3D) structures can be an interesting solution for the design of active medical devices such as wound dressings.
RESUMEN
This work presents the performances of silicon micro-preconcentrators chips for breath sampling. The silicon chips were coupled to a handheld battery powered system for breath sampling and direct injection in a laboratory gas chromatography mass spectrometry system through thermal desorption (TD). Performances of micro-preconcentrators were first compared to commercial TD for benzene trapping. Similar chromatographic peaks after gas chromatographic separation were observed while the volume of sample needed was reduced by a factor of 5. Repeatability and day to day variability of the micro-preconcentrators were then studied for a 500 ppb synthetic model mixture injected three times a day four days in a row: 8% and 12% were measured respectively. Micro-preconcentrator to micro-preconcentrator variability was not significant compared to day to day variability. In addition, micro-preconcentrators were tested for breath samples collected in Tedlar® bags. Three analyses of the same breath sample displayed relative standard deviations values below 16% for eight of the ten most intense peaks. Finally, the performances of micro-preconcentrators for breath sampling on a single expiration were illustrated with the example of volatile tobacco markers tracking. The signals of three smoking markers in breath, benzene, 2,5-dimethylfuran, and toluene were studied. Concentrations of benzene and toluene were found to be 10 to 100 higher in the breath of smokers. 2,5-dimethylfuran was only found in the breath of smokers. The elimination kinetics of the markers were followed as well during 4 h: a fast decrease of the signal of the three markers in breath was observed 20 min after smoking in good agreement with what is described in the literature. Those results demonstrate the efficiency of silicon chips for breath sampling, compared to the state of the art techniques. Thanks to miniaturization and lower sample volumes needed, micro-preconcentrators could be in the future a key technology towards portable breath sampling and analysis.