Array sensing

Here also lies one major difference between a sensor array and a separation experiment. In the latter, the advancing front of the already separated sample always encounters the pristine stationary column phase and interacts accordingly, whereas in a chemical sensor array all components of the sample interact with the sensing layers at once. The direct sensing and the separation experiments are not directly comparable but are complementary. In summary, increasing the order of the sensor 

Information obtained from the array is much more than the sum of information obtained from the individual sensors. This additional information accrues from analyzing and understanding the group behavior of chemical sensors. There are many excellent texts covering this topic in detail. Reviews by Hierlemann et al. (1996) and Jurs et al. (2000) are particularly recommended. A large section of this chapter follows, and in some spots paraphrases (in abbreviated form), those two reviews. 

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Figure 13. Schematic lay-out of compact optical sensor chip without need of external optical apparatus with 4 different sets of sensing arrays. LED broad band source, for example Light Emitting Diode, MR-F microresonator used as optical filter, MR-S microresonator used as optical sensor, PD Photo Diode.

Cross-reactive sensing arrays were developed to detect odors and vapors in an artificial nose manner. Solvatochromic dyes such as Nile Red are adsorbed on the surface or embedded into various polymeric or porous silica beads. The beads respond to analyte vapor by a change in fluorescence maxima or/and intensity due to changes of polarity inside the bead. A portable instrument and preliminary field test for the detection of petroleum products was recently described [106]. 

LaFratta CN, Walt DR (2008) Very high density sensing arrays. Chem Rev 108 614-637... 

N.O. Savage, S. Roberson, G. Gillen, M.J. Tarlov, and S. Semancik. Thermolithographic patterning of sol-gel metal oxides on micro hot plate sensing arrays using organosUanes , Analytical Chemistry 75 (2003), 4360-4367. 

Vacuum deposition techniques, such as sputtering, electron beam evaporation, and plasma deposition are common. Photopolymerization and laser-assisted depositions are used for preparation of specialized layers, particularly in the fabrication of sensing arrays. Most commercial instruments have thickness monitors (Chapter 4) that allow precise control of the deposition process. 

Fig. 9.29 Randomly ordered, addressable, high-density optical sensing array (see text for description of steps adapted from Michael et al., 1999)...

Table 10.1 Examples of static and dynamic modes of sensing arrays and their uses...

Spatial Information Obtained with Sensing Arrays... 

Fig. 10.19 (a) Experimental dependence of coherence spectra on distance (10-120 cm) between the modulation source and the sensing array, (b) Ratios of intensities ao/ai at fundamental frequency and at its first harmonic, plotted as the function of distance. The breaks indicate disappearance of the higher harmonics with distance. They indicate softening of plume edges with distance due to diffusion... 

LaFratta CN, Walt DR (2008) Very high density sensing arrays. Chem Rev 108 614—637 Wadkins RM, Golden JP, Pritsiolas LM et al (1998) Detection of multiple toxic against using a planar array immunoassay. Biosens Bioelectron 13 407 15... 

Recycling of this MTP confined sensing array was also studied, and it was found that the complexation of metal ions at the surface is reversible, and the surface can be easily recycled for further analysis upon rinsing the surface with a metal chelate agent. 

To automate the process of SAM synthesis in the microchannels for the generation of sensing arrays, a multichannel chip suitable for continuous flow of reagents was designed. A microchannel chip (4 x 2.2 cm2) with five parallel channels confined in an area of 200 pm was fabricated. Each channel can be individually addressed and... 

Computational methods cannot generally produce the level of confidence in sensor performance that can be found with experimental data however, initial screening with computational methods could be used to reduce the time and effort necessary to optimize the materials selected for a sensing array. Once a set of possible materials has been selected, optimizing the array with the best set must be done using computational-experimental methods. 

A chemical sensing array is achieved by obtaining multiple parameter measurements from one information channel in addition to using multiple channels. The information obtained then comes from information space. This approach is similar to hyphenated techniques, such as gas chromatography-mass spectrometry, which separates components and then finds further information about those components with the second technique. 

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