Chemical sensing arrays

Asher, S. A., Crystalline colloidal array chemical sensing devices, In ACS PRF summer school on nanoparticle materials, June 6 18, 2004. Eastern Michigan University, Ypsilanti, MI, 2004... 

Asher, S., Peteu, S., Reese, C. et al.. Polymerized crystalline colloidal array chemical-sensing materials for detection of lead in body fluids. Anal. Bioanal. Chem., 373, 632, 2002. 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

Variations of semiconductor PL and EL intensities resulting from analyte adsorption are promising techniques for chemical sensing. When coupled with films such as MIPS, the selectivity of such structures may be improved. Integrated devices in which forward- and reverse-biased diodes are juxtaposed using microelectronics fabrication methods provide an opportunity to create completely integrated sensor structures on a single chip and to prepare arrays of such structures. 

The main advantage of piezoelectric devices is that, in principle, any process that results in a mass change at an interface can be measured. However, this very nonselective transduction process is also a major disadvantage in that it mandates the use of even more selective surface chemistries than are required for other types of chemical transducer systems. This will make the implementation of piezoelectric chemical sensing devices for ocean measurements rather difficult, but by no means impossible. Indeed, the coupling of pattern recognition techniques with an array of marginally selective piezoelectric transducers may, in the future, make these devices more useful for quantitative ocean measurements. 

Keywords Nanohole array Surface plasmon resonance Optical sensing Chemical sensing Biosensing Microfluidic Nanofluidic Extraordinary optical transmission... 

Based on these considerations, a great deal of current research on SERS has focused on the controlled and reproducible fabrication of metallic nanostructures that produce hot spots in which the molecules are appropriately and predictably located for large Raman enhancement. Several strategies have been proposed for engineering such hot structures for chemical sensing applications in a reproducible and controllable manner. These include structures such as triangular nanoparticle array [30], silver nano wire bundles [31, 32], Ag nanoparticle-assembled silica... 

Array-based sensing, in which an array of several semiselective chemical sensors is used to characterize selected analytes, has given rise to electronic noses, which focus on detecting and characterizing vapor phase chemical species in air. In electronic... 

Use of computational methods in designing, selecting, and ultimately in optimizing chemical sensing materials and sensor sets for arrays is a growing field, which will assist in development of sensing devices for various applications. 

The artificial intelligence systems to which sensor arrays are coupled supply the closest likeness to the human olfactory system. Some of the recent theories on olfaction require that the human nose has only relatively few types of receptor, each with low specificity. The activation of differing patterns of these receptors supplies the brain with sufficient information for an odour to be described, if not recognized. As a consequence of this belief, the volatile chemical-sensing systems commercially available only contain from 6 to 32 sensors, each having relatively low specificity. Statistical methods such as principal component analysis, canonical discriminant analysis and Euclidian distances are used for mapping or linked to artificial neural nets as an aid to classification of the odour fingerprints . 

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. 

Higher-order chemical sensing can alleviate some inherent problems of chemical sensors. For example, a sensor array can mathematically correct for systematic drift. It also provides cross selectivity for elimination of interference. 

Sensor arrays are produced by microfabrication. Because different portions of the array have different fabrication requirements, convenience dictates that the sensors be fabricated in two parts the chemical sensing chip with the transducer... 

There are also some potentially useful agent-sensing technologies that do not rely on biological sensors. These new devices may offer more rapid analysis and simpler, continuous measurement. One kind of new sensor is the electronic (or artificial) nose. An array of semiselective, cross-reactive sensors produces a response pattern characteristic of a chemical (Gardner and Bartlett, 1999 Albert and Walt, 2000). The patterns are preprogrammed mathematically so that upon exposure, the patterns are matched to the chemicals sensed. There are two main groups of electronic noses ... 

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