DNA arrays brought multiplexed assays to molecular biology. DNA arrays contain tens of thousands to few millions of DNA probes spatially arranged on a surface (Affymetrix and Nimblegen) or on beads (Illumina). These arrays for the first time allowed large number of analytes to be measured in a single sample and revolutionized the field of genetic assays. Not surprisingly, protein arrays followed soon after-though their commercial successes have been less than stellar. The feature that made these technologies attractive is their miniaturization and multiplexing capabilities enabling huge amount of data to be generated from miniscule amount of samples. Although assays are multiplexed they are not necessarily high-throughput- means very large number of analytes can be detected in a single sample but numbers of samples that can be processed at same time are rather limited.
Enter the encoded micro/nao-particle arrays-they allow several analytes to be measured simultaneously in multiple samples. Moreover the microparticle handling can be automated making this technology perfect for automation using robotic platforms. In theory idea is simple-
A) Make micro/nano particles that are encoded so that they can be identified individually. Encoding can be optical, electronic or just physical shape or patterns.
B) Attach unique biological recognition
element to individually encoded particle. Biological recognition elements can be DNA/RNA, proteins, antibodies, etc.
C) Add mix of encoded particles to sample(s) of interest. Analytes of interest (if present) binds to their specific particles
D) Separate encoded particle and see if the analyte of interest is attached to it or not
The most commercially successful encoded microparticle based multiplexed assays are offered by Luminex. Luminex optically encodes 5.5um polystyrene particles with two different dyes to make 100 different colored particles. Particles can be loaded with DNA, proteins or antibodies. Specific binding to the encoded particles can be detected using green fluorescent labeled dye. After particles bind their specific analyte the encoded particles and the bound analytes are detected using combination of lasers that excite both the particles and attached analytes.
This platform is now one of the most commercially successful multiplexed assay platforms exploiting the encoding technology. But the platform is currently limited to 100 individual assays and exciting new technologies are under development to increase the number of assays to thousands or even more.
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