Gradient microarray

Fig. 3.27 KAMINA gas sensor chip with gradient microarray mounted in its housing.

However, in addition to its low production costs and excellent gas analytical features, the gradient microarray chip offers further advantages over the classical arrays consisting of separate gas sensors of different chemistry. Since all sensor ele-... 

Fig. 3.31 The KAMINA demonstrator. The lifted device head shows the gradient microarray which receives ambient air by a fan. The complete microprocessor-controlled electronics is contained in the lower part of the device.

Fig. 3.32 A complete electronic nose based on gradient microarray technology does not even take up the space of a credit card and is thus applicable in intelligent user products.

One important issue concerning fire prevention is the early detection of overheated wire insulation, a common source of smoldering fires. Therefore model experiments were performed to examine how far early indications of overheated insulation could be recognized by the gradient microarray and its simple sampling arrangement. The tests were carried out in a closed box with KAMINA placed next to a cable overheated by a current overload. The experiments were performed... 

In order to investigate the discrimination power of the gradient microarray regarding the changes in air composition, a signal pattern analysis was performed... 

Sysoev, V. V, Goschnick, J., Schneider, T, Strelcov, E. and Kolmakov, A. (2007) A Gradient Microarray Electronic Nose Based on Percholating SnQ2 Nanowire Sensing Elements, NonoZeff., 7,3182. 

Figure 10.1 Experimental schemes for microarray analysis. All experimental schemes start with a separation step of the cell lysate by velocity sedimentation in a sucrose gradient (top scheme). Collection of the desired fractions is assisted by a continuous ultraviolet (UV) reading of the gradient (an example of such UV reading is shown in each section). This allows determination of the sedimentation position of the 40S, 60S, 80S, and polyribosomal complexes (2,3, and more).Three general ways for fraction collection and analysis are presented (sections A, B, and C) (A) Collection of two fractions (free and polysomes) and direct comparison between them, with the free mRNA fraction labeled with green dye and the polysome fraction labeled with red dye. (B) Collection of two fractions and indirect comparison between them by utilizing an unfractionated reference RNA. (C) Collection of multiple fractions (four in this case), where each fraction is compared to an unfractionated reference sample. The blue arrows indicate the addition of spike-in RNA to each fraction and to the reference RNA.

There are numerous protocols for polysomal gradients preparations that differ mainly at the step for harvesting the cells, and the gradient composition and separation times. The protocol presented later was optimized for isolation of polysomal mRNA from the yeast Saccharomyces cerevisiae, yet many steps will be similar to other eukaryotes and the procedure can easily be modified for other organisms. We will use this protocol as a template on which we will indicate and highlight points that are critical for the microarray analysis. Generally, the RNA isolated by this protocol can be used for analysis by DNA microarray, Northern blot, or RT-PCR. 

The amount of mix to add depends on the experimental setting and the number of fractions collected. We typically add 70 pi of spike-in mix into an entire sucrose gradient, where each fraction receives the relative share from that amount. For example, 35 pi of the spike-in mix will be added to each fraction of a gradient that was divided into two, and 7 pi of this mix will be added to each fraction of a gradient that was divided into 10fractions. The added amounts should consider losses during purification steps and that a minimum of 0.2 ng of each spike is needed to yield sufficient signal in the microarray hybridization. 

Koizumi, Y. Kelly, J.J. Nakagawa, T. Urakawa, H. El-Fantroussi, S. Al-Muzaini, S. Fukui, M. Urushigawa, Y. Stahl, D.A. Parallel characterization of anaerobic toluene- and ethylhenzene-degrading microhial consortia hy PCR-denaturing gradient gel electrophoresis, RNA-DNA membrane hybridization, and DNA microarray technology. Appl. Environ. Microbiol. 2002, 68, 3215-3225. 

Sysoev, V. V. Kiselev, I. Frietsch, M. Goschnick, J., Temperature gradient effect on gas discrimination power of a metal-oxide thin-film sensor microarray, Sensors 2004,... 

Each pixel in the heatmap is colored, where a color gradient scale is used to represent gene expression intensity. Typically green to red, or more recently blue to yellow, is used to represent increasing gene expression. These plots are effective visualizations and have been widely used in microarray literature. These plots are often referred to as Eisen plots. 

Tallman et al. (1984) presented data to suggest that microelectrodes further enhance response by remixing between electroactive zones on the surface. As discussed earlier, in the case of continuous planar electrodes, the diffusion layer increasingly extends out in the cell volume as flow moves down the length of the electrode. In a microarray. significant areas are inactive, and diffusion layers dwindle in thickness over these relaxation zones before moving on to the next active area. The net effect is to maximize the concentration gradient over the entire macroscopic electrode area. This... 

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