Molecule-receptor binding chemical detection

The ability to detect molecnle-receptor binding events is a critical aspect for chemical detection methods based on molecular recognition. Currently, fluorescence is a primary means by which these events are detected. (4-6) However, this often requires modification of the receptor to incorporate the fluorescent center and/or immobilization of the receptor molecule onto a surface. Far more desirable would be a means to directly detect the molecule-receptor interaction in solution without the need to modify the naturally occurring receptor. In the absence of any receptor modification, however, there are no signatures stemming from the molecule-receptor interaction that are... 

The mechanism of olfaction has many theories but is not fully understood and is still the subject of research. The nose is the human organ that detects smell (Fig. 5.9). It extends from the face to the end of the palate. In its simplest explanation the two nasal cavities are lined with a mucous membrane, kept moist by the secreted substance mucus. Chemicals in the air entering the nose must dissolve in this mucus before they can be detected. A small area - about the size of a small postage stamp - in the upper part of the nasal cavity contains olfactory cells, which are sensitive to the chemicals in the mucus solution. For a molecule to be detected it must bind specifically to the sensitive cells that act as sensory receptors. The sensory receptors situated in the olfactory epithelium (epithelium is the name given to the outer layer of covering cells) are believed to bind specifically with substances according to the shape of their molecules. 

When combined with tandem mass spectrometry, capable of selectively detecting a few analytes from the many that could be present, this approach provides for unsurpassed analytical selectivity for difficult chemical problems such as the study of drug—receptor binding [36] or the separation of complex mixtures of proteins or peptides [37]. The detection approach can be implemented in either on- or off-line formats. Alternatively, the purified antibody can be immobilized on a matrix-assisted laser-desorption ionization probe to allow direct application and characterization of a liquid sample containing the target molecule [38]. 

The key to achieving chemical selectivity using microcantilevers is the ability to functionalize one surface of the microcantilever with receptive molecules so that explosive molecules will preferentially bind to the treated surface. Choosing receptor molecules that can provide highest affinity, therefore, can control the selectivity of detection. Another important requirement for a sensor system is fast regeneration (recovery), so that the sensor can be used repetitively. 

For the detection of ionic species other than protons, it is necessary to introduce receptor molecules which can selectively bind guest species on top of the gate of the ISFET. Direct attachment of ion-selective moieties to the surface, e.g. by silylation with (3-cyanopropyl)dimethyl(dimethylamino)silane resulted in some sensitivity towards Ag+ ions (20 mV decade" ), but the sensor was still sensitive towards protons (15 mV decade" ) [10]. Chemical grafting with ammonium phosphonate (1-3) and phosphate sites (4) (Figure 2) or with phthalocyanine-based ionophores bearing crown-ether moieties resulted in a sensitivity towards alkaline (earth) ions, but the pH dependency remained [11,12]. 

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