Technology

Beads are homogenous microspheres produced from polymer by special synthesis techniques. The most common material used is polystyrene and available bead sizes range from 0.4 to 200 mm. In order to function as carriers for binding interactions, beads have to be ''sensitized'' by attaching biological ligands such as antibodies or single-stranded nucleic acids to their surface. The first bead-based assay was reported in 1956, when Singer and Plotz introduced their rheumatoid factor agglutination test.[1] Later, beads were introduced in flow cytometry, which is a powerful combination, because here, like cells, several hundreds of beads can be discriminated by fluorescence intensity and spectral diversity in a couple of seconds. As a large number of each distinct species are measured, a mean signal with high precision is obtained. The increasing request for the simultaneous determination of complex parameter profiles in small sample volumes brought up the idea of multiplexing with microspheres as carriers for tests and assays, which can be analyzed and discriminated by flow cytometry. First, attempts to use microspheres of different size have been made, then beads were impregnated with fluorescent dyes, to make them spectrally distinctable. The maximum number of such populations depends on the availability of fluorescent dyes, the technologies to impregnate the beads, and the number of suitable fluorescent channels available in a flow cytometer. By color-coding beads with a blend of different amounts of only two fluorescent dyes, a set of 100 distinct bead populations can be generated (Fig. 1), which are commercially available as LabMAP Beads (Luminex Corporation, Austin, TX). Numerous companies have licensed the LabMAP technology as platform for the development of their bead-based assays especially in immunology and microbiology. Now that the conquest of bead-based assays over the traditional microtiter plate ELISA has begun, beads have been discovered as carriers for nucleic acid testing. Here, like antigens or antibodies, oligonucleotides of interest can be attached to beads using simple chemical reactions. Thus each bead population corresponds to a specific oligonucleotide. In a suspension hybridization, amplicons that carry another fluorescence can be immobilized to the beads by hybridization. Analysis is performed in the flow cytometer, where this additional fluorescence, that was brought to the bead by successful hybridization, is also detected. A conventional flow cytometer with three fluorescence channels measures two dyes that specify the bead population and a reporter dye that specifies hybridization events. By using more sophisticated flow cytometers with additional fluorescent channels (e.g., FACSCalibur, BD Biosciences, San Diego, CA), it would be possible to use more dyes for

Fig. 1 By impregnating beads with a blend of two fluorescent dyes, a set of 100 color-coded species can be generated, which can be discriminated in a flow cytometer.

amount of one fluorescent dye

Fig. 1 By impregnating beads with a blend of two fluorescent dyes, a set of 100 color-coded species can be generated, which can be discriminated in a flow cytometer.

color-coding of beads or more colors for the test reaction. However, flow cytometers are expensive and their capabilities exceed what is required for bead-based analysis. With the Luminex100 (Luminex), a low-cost flow cytometer is available that is specifically adapted to the measurement of color-coded beads.[2'3]

which can cause cystic fibrosis. A set of 10 bead populations, each carrying a sequence-specific oligonu-cleotide for 10 common mutations, and 10 bead populations, each carrying the according wild-type sequence, were used. The relevant DNA segments were amplified by PCR using labeled primers prior to hybridization to the beads.[6]

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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