Surface multiplexed

These two transducer pairs are activated alternating. For this purpose an ultrasonic instrument is combined with a two channel multiplexer. Figure 8 presents a modified standard instrument USN52 which also implies a modified software. This system performs four measurements per second - alternating the velocity and the thickness are determined. The probe can be scanned over the surface and in every position both, the velocity and the wall thickness are indicated Using the serial interface of the instrument finally a two-dimensional map of velocity or thickness can be generated. 

A variation on depth profiling that can be performed by modern scanning Auger instruments (see Sect. 2.2.6) is to program the incident electron beam to jump from one pre-selected position on a surface to each of many others in turn, with multiplexing at each position. This is called multiple point analysis. Sets of elemental maps acquired after each sputtering step or each period of continuous sputtering can be related to each other in a computer frame-store system to derive a three-dimensional analysis of a selected micro volume. 

Thermal desorption spectroscopy and temperature programmed reaction experiments have provided significant insight into the chemistry of a wide variety of reactions on well characterized surfaces. In such experiments, characterized, adsorbate covered, surfaces are heated at rates of 10-100 K/sec and molecular species which desorb are monitored by mass spectrometry. Typically, several masses are monitored in each experiment by computer multiplexing techniques. Often, in such experiments, the species desorbed are the result of a surface reaction during the temperature ramp. 

The most common use of protein microarrays is in immunoassays. In particular, antibody-based immunoassays are the main stream of diagnostic assays due to their specificity. The assay usually runs in a multiplexed mode where the antibodies or other capture agents are immobilized and then exposed to a biological sample. There are four immunoassay formats direct binding, sandwich (ELISA), competitive, and displacement. Direct-binding and sandwich assays are the most common. There are some reports on the use of competitive assays and displacement assays, which are usually associated with high surface area/volume systems [72-76],... 

An approach to multiplexing analysis was presented by Min et al. [23], who de-velopped a SAMDI-based assay scheme to screen for the activity of different kinases. In this assay scheme, peptide substrates were used that are specific for one type of kinase. A mixture of four substrates was immobilized on the SAM. After incubation with an appropriate kinase, the target surface was rinsed, thus stopping the reaction. Matrix was deposited on the surface and MALDI-MS analysis was carried out (Fig. 8.13). By monitoring the signal intensities for the substrates... 

Fig. 8.13 A multiplexing SAMDI-MS assay. In this case, a mixture of three substrates is immobilized on the SAM. After incubation with appropriate enzyme solutions, the enzymatic reaction is quenched by rinsing the surface. Subsequently, matrix is deposited on the surface and MALDI-MS is carried out. Consumption of all three substrates can thus be determined in parallel.

In this approach, NAs are directly deposited onto a glass support using a robot able to deliver with high precision a sample to a specific x y programmed location. The NA sample is loaded into a spotting pin (highly miniaturized stainless-steel fountain-pen nibs with a gap) by capillary action, and small volumes are transferred to a solid surface, such as a microscope slide, by direct physical contact between the pin and the solid substrate. Spot size depends on the acceleration of the pen towards and away from the slide, and the surface tension of the slide. After the first spotting cycle, the pin is washed and a second sample is then transferred to an adjacent address. A robotic control system and multiplexed print heads allow the automated immobilization of many different probes simultaneously onto the slide [29]. 

We have shown in the past few years that due to their finite size (comparable to an average protein), CdSe-ZnS core-shell nanocrystals capped with a thin layer of dihydrolipoic acid ligands provide excellent nanoscale scaffolds ( nanoscaffolds ) for attaching several proteins on their surfaces. QD-protein conjugates were used to design multiplexed immunoassays to detect soluble toxins. 

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