Development of a Sub-ppb Resolution Methane Sensor Using a GaSb-Based DFB Diode Laser near 3270 nm for Fugitive Emission Measurement.

A challenge for mobile measurement of fugitive methane emissions is the availability of portable sensors that feature high sensitivity and fast response times, simultaneously. A methane gas sensor to measure fugitive emissions was developed using a continuous-wave, thermoelectrically cooled, GaSb-based distributed feedback diode laser emitting at a wavelength of 3.27 µm to probe methane in its strong ν3 vibrational band. Direct absorption spectra (DAS) as well as wavelength-modulated spectra (WMS) of pressure-broadened R(3) manifold lines of methane were recorded through a custom-developed open-path multipass cell with an effective optical path length of 6.8 m. A novel metrological approach was taken to characterize the sensor response in terms of the linearity of different WMS metrics, namely, the peak-to-peak amplitude of the X2f component and the peak and/or the integrated area of the background-subtracted quadrature signal (i.e., Q(2f - 2f0)) and the background-subtracted 1f-normalized quadrature signal (i.e., Q(2f/1f - 2f0/1f0)). Comparison with calibration gas concentrations spanning 1.5 to 40 ppmv indicated that the latter WMS metric showed the most linear response, while fitting DAS provides a traceable reference. In the WMS mode, a sensitivity better than 1 ppbv was achieved at a 1 s integration time. The sensitivity and response time are well-suited to measure enhancements in ambient methane levels caused by fugitive emissions.

Pressure-dependent sensitivity of a single-pass methane detection system using a continuous-wave distributed feedback laser at 3270 nm.

A single-pass, compact, and low-power-consumption methane sensing system is presented, and its sensitivity is examined for a set of reference cells with pressures of 7.4, 74, and 740 Torr and the same methane concentration at laboratory temperature of 23°C. A GaSb-based continuous-wave distributed feedback tunable diode laser at 3270 nm and wavelength modulation spectroscopy were employed to collect 2f spectra in the ν3, R3 band of CH412. The collected 2f spectra were fitted to a modulated Voigt line profile model. An Allan-Werle variance analysis shows that the best detectivity, 4 ppbm, is obtained for the highest pressure cell. At pressures of 74 and 7.4 Torr the detectivities are 16 and 28 ppbm, respectively. For these low-pressure cells, further sensitivity improvements were achieved using a large modulation depth (m>2.2) at the expense of spectral resolution.

Priming and testing silicon patch-clamp neurochips.

We report on the systematic and automated priming and testing of silicon planar patch-clamp chips after their assembly in Plexiglas packages and sterilization in an air plasma reactor. We find that almost 90% of the chips are successfully primed by our automated setup, and have a shunt capacitance of between 10 pF and 30 pF. Blocked chips are mostly due to glue invasion in the well, and variability in the manual assembly process is responsible for the distribution in shunt capacitance value. Priming and testing time with our automated setup is less than 5 min per chip, which is compatible with the production of large series for use in electrophysiology experiments.

Capacitance-derived dielectric constants demonstrate differential preinitiation complexes in TBP-independent and TBP-dependent transcription.

The electronic properties of proteins and DNA may change dramatically upon complex formation, yet there are not many experimental methods which can be used to measure these properties. It has been previously shown that measuring the capacitance of a solution containing interacting DNA and protein species can yield information about changing dipole moments. The measured dielectric constant relates directly to the dipole moment of the complexes in solution. Here, we apply this method to partial transcription initiation complexes in order to investigate the changing electronic properties in the transcriptional preinitiation complex. These experiments are the first reported observations relating to the overall dipole moment and its changes in preinitiation complex formation. Comparing results from TBP-independent and TBP-dependent transcriptional systems shows a divergence in the electronic properties of built-up transcription complexes, suggesting that they initiate transcription by significantly different electronic and structural pathways.

YY1 is regulated by O-linked N-acetylglucosaminylation (O-glcNAcylation).

YY1 is a zinc finger DNA-binding transcription factor that influences expression of a wide variety of cellular and viral genes. YY1 is essential for the development of mammalian embryos. It regulates the expression of genes with important functions in DNA replication, protein synthesis, and cellular response to external stimuli during cell growth and differentiation. How YY1 accomplishes such a variety of functions is unknown. Here, we show that a subset of the nuclear YY1 appears to be O-GlcNAcylated regardless of the differentiation status of the cells. We found that glucose strongly stimulates O-linked N-acetylglucosaminylation (O-GlcNAcylation) on YY1. Glycosylated YY1 no longer binds the retinoblastoma protein (Rb). Upon dissociation from Rb, the glycosylated YY1 is free to bind DNA. The ability of the O-glycosylation on YY1 to disrupt the complex with Rb leads us to propose that O-glycosylation might have a profound effect on cell cycle transitions that regulate the YY1-Rb heterodimerization and promote the activity of YY1. Our observations provide strong evidence that YY1-regulated transcription is very likely connected to the pathway of glucose metabolism that culminates in the O-GlcNAcylation on YY1, changing its function in transcription.

YY1-DNA interaction results in a significant change of electronic context as measured by capacitance.

The detailed mechanism behind the processes of DNA-dependent RNA transcription initiation is largely unknown. When transcription initiation factors bind DNA, a significant change in the electrostatic state of the complex can result. Using electrical capacitance measurements of solutions of the YY1 zinc finger transcription initiation factor and the adeno-associated viral P5 promoter DNA, we observed a specific dielectric change when a protein-DNA complex was formed. We propose that complexation results in electrostatic changes that may trigger the markedly different electrical behavior, and offer a possible explanation for our results.