Biomedical Engineering Reference
In-Depth Information
study basic biological properties like examining protein interactions with other ligands
such as proteins, peptides, lipids or other molecules. In addition, functional microar-
rays are also used to determine enzyme activity and substrate specifi city. These bio-
chips are typically produced by printing the proteins or other molecules of interest on
the array surface using various methods to maintain their integrity and activity, which
allows hundreds to thousands of target proteins to be simultaneously screened for
function [68]. For example, Espejo et al. [47] proved that protein interaction domains
would retain function and specifi city when interacting with their corresponding lig-
ands by arraying several kinds of proteins onto nitrocellulose coated microarrays.
Hall et al . [69] probed yeast protein microarrays with dye-labeled genomic single and
double-stranded DNA probes and identifi ed more than 200 proteins that bound DNA.
Fang et al. [70] demonstrated specifi c binding of small molecule ligands to G-protein-
coupled receptors, indicating that receptors in model membranes retain membrane-like
properties on the slide. Except for the reported results, the potential applications of
such microarrays are still large. An array of a particular class of enzymes could be
screened with a candidate inhibitor to examine binding selectivity. Protein interaction
networks, including the assembly of multiprotein complexes, could shed light on bio-
chemical pathways. Eventually, it may even be of great possibility to use these high
density microarrays as a MELDI source for mass spectrometry, allowing the possibil-
ity to probe complex samples for binding partners to many proteins simultaneously.
In addition, molecular profi les of cell types provided by tissue microarrays and the
layered expression scanning technique are relevant in understanding biological proc-
esses. Many other types of experiments performed on microchips from assays to mim-
icking cellular migration in tissues and neuronal behavior in vivo give new insight into
processes relevant in cellular biology and medicine. From running the DNA arrays to
profi ling proteins encoded by differentially expressed cDNA clones requires a high
throughput approach to parallel protein expression analysis. This implies expressing a
large number of cDNA clones simultaneously, having the appropriate vector system to
do this, and arraying the resulting proteins rapidly [71].
11.3.3.2 Clinical diagnostics
The most common use of protein microarrays is in immunoassays. In particular, anti-
body-based immunoassays are the main stream of diagnostic assays due to their spe-
cifi city. 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 dis-
placement. 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].
Apart from immunoassays, enzyme assays can also be used to detect certain sub-
strates in a clinical diagnostic setting. The benefi ts of performing enzymatic assays on
microchips are the analytical power and minimal reagent use in microfl uidic systems
combined with the selectivity and amplifi cation factors that come with biocatalysis.
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