Characterization of Nano-Gravimetric-Detector Response and Application to Petroleum Fluids up to C34.

A nano-gravimetric detector (NGD) for gas chromatography is based on a nanoelectromechanical array of adsorbent-coated resonating double clamped beams. NGD is a concentration-sensitive detector and its sensitivity is analyte-dependent based on the affinity of the analyte with the porous layer coated on the NEMS surface. This affinity is also strongly related to the NGD temperature (NGD working temperature can be dynamically set up from 40 to 220 °C), so the sensitivity can be tuned through temperature detector control. An adsorption-desorption model was set up to characterize the NGD response on a large set of n-alkanes from C10 to C22 at different NGD temperatures. For fast identification of petroleum mixture based on chromatogram fingerprint, a general strategy for NGD temperature program design was developed leading to a constant relative response factor between 0.96 and 1.03 for all the alkanes, and then chromatograms are very similar to those obtained with a flame ionization detector (FID). The analysis of a real petroleum fluid was also performed and compared to FID results: quantitative results obtained for all the analytes were satisfactory according to precision (<5%) and accuracy (average relative error = 4.3%). Based on such temperature control strategy, NGD sensitivity and the dynamic linear range can be adjusted and detection limits at a picogram level can be easily achieved for all n-alkanes.

A new generation of scanners for DNA chips.

Today, most of the DNA chips are used with fluorescent markers. Associated with fluorescence confocal scanners, this technology achieves remarkable performances in terms of sensitivity and accuracy. The main technical issues related to these scanners have already been reviewed. However, these scanners are costly, especially when high density chips are used. In this case, a mechanical precision of 1 microm or less is required to achieve the measurement precision required. This cost level prevents the spread of this technology in the diagnostic market. We will present a new concept for scanners with equivalent or superior performances, with a cost cut of 5-10. This concept is inspired from the field of optical disk and reader. Basically, an optical format is added to the chip, before DNA deposition. This format contains tracks which are superimposed to the DNA features. These tracks define the path that an optical head of a CD player must follow in order to scan the surface of the DNA chip. Such a head is a very cheap component, and has a precision of less than 100 nm thanks to real-time focus and tracking. These functions are fulfilled by electromagnetic actuators mounted on the support of the frontal lens. We show here that it is possible to use such a head to build a fluorescence confocal scanner with equivalent or even better performances than conventional scanners.