LiquiChip System Fluid
For use with the LiquiChip Reader
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For antibody-mediated direct detection, use of 10–50 ng labeled antibody per assay point is recommended. For indirect detection, 10 ng primary antibody and 50–200 ng labeled secondary antibody per assay point deliver optimal results.
The LiquiChip Applications Handbook contains protocols for immunoassay and subsequent detection using both direct and indirect methods.
The detection of the green reporter signal is triggered by the detection of the red classification fluorescence. Therefore, a specific sample value is only recorded if a red bead classification signal and a green reporter signal are measured simultaneously.
In addition, the assay mixture is covered by the LiquiChip System Fluid for the measurement in the capillary, so that only a small amount of assay mixture is around the beads during measurements. Further information can be found online on the product page for the LiquiChip System.
A homogeneous LiquiChip Assay is an xMAP assay with no requirement to separate free fluorophores from bead-bound fluorophores.
Since reporter fluorescence is only registered when the measured bead can be recognized as belonging to a defined bead set and as having a defined size, reporter fluorescence is derived from a bead only, and not from unbound fluorophores free in solution. Thus, there is no need to perform wash steps.
Using the LiquiChip System, thousands of beads can be interrogated in seconds, allowing a 96-well microplate to be measured in 35–60 minutes, depending on assay set up (bead concentration per assay, total assay volume). Approximately 20-60 seconds are needed per well (including wash procedure). Using a 100-plex assay, up to 9600 data points can be measured in 1 hour.
Only one reporter dye can be used, because only a single laser (green reporter laser) is available to read the reporter signal using the LiquiChip Workstation. However, since multiplexing is not done via the reporter dye, but instead by using different color-coded beads identified by a red classification laser, multiplexing on this instrument is possible. QIAGEN supplies Kits performing 10-plexes for the LiquiChip System. In theory, a 100-plex is possible using this system.
This is difficult to determine as the sensitivity highly depends on assay set-up, quality of the interactions, or antibodies used. In general, we can detect in the low pg/ml range using high affinity antibodies.
An example for the high assay sensitivity can be found on the LiquiChip System page.