Analytical detection systems, enzyme-probe

In this presentation we will discuss analytical detection systems composed of enzyme and probe molecular components working in tandem, with the enzymes serving the role of the signal-generating mechanism linked to ligand-specific biomolecular probes. In general, we will draw a distinction between the enzyme and the probe components. 

The development of analytically useful enzyme electrodes is limited by the availability of purified and stable enzyme preparations. In an effort to extend the range of measurable species using ISE devices further, Rechnitz and co-workers (Rl) recently introduced bacterial- and tissue-based bio-selective electrode systems. These sensors are prepared in much the same manner as the enzyme probes except that whole intact cells are utilized as the immobilized reagents. There are several potential advantages to this novel approach, including (1) no need to extract and purify the enzymes involved, i. e., low cost (2) enzymes which are unstable when extracted from the cell may be used in situ to maximize and preserve their activity (3) if desired enzyme reactions require cofactors, these co ctors need not be added to the assay mixture because they are already present in the intact cell and (4) analytical reactions involving multistep enzyme sequences already present in the cells may be used to detect given analytes. 

A similar type of biotin-dendritic multimer also was used to boost sensitivity in DNA microarray detection by 100-fold over that obtainable using traditional avidin-biotin reagent systems (Stears, 2000 Striebel et al., 2004). With this system, a polyvalent biotin dendrimer is able to bind many labeled avidin or streptavidin molecules, which may carry enzymes or fluorescent probes for assay detection. In addition, if the biotinylated dendrimer and the streptavidin detection agent is added at the same time, then at the site of a captured analyte, the biotin-dendrimer conjugates can form huge multi-dendrimer complexes wherein avidin or streptavidin detection reagents bridge between more than one dendrimer. Thus, the use of multivalent biotin-dendrimers can become universal enhancers of DNA hybridization assays or immunoassay procedures. 

Frerichs et al. [128] developed and validated a method for the quantitation of omeprazole and hydroxyomeprazole from one 250 [A sample of human plasma using HPLC coupled to tandem mass spectrometry. The method was validated for a daily working range of 0.4-100 ng/ml, with limits of detection between 2 and 15 pg/ml. The interassay variation was less than 15% for all analytes at four control concentrations and the samples were stable for three freeze-thaw cycles under the analysis conditions and 24 h in the postpreparative analysis matrix. The method was used to analyze samples in support of clinical studies probing the activity of the cytochrome P-450 enzyme system. 

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