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Figure 1. Overlaid binding response curves for interaction of CBS with immobilized carbonic anhydrase.

Multiplex bead assays allow simultaneous analysis of multiple targets within one reaction, providing more information and higher sensitivity while using less sample than traditional ELISA assays. As the samples are bound to free-floating microspheres as a solid support, it can be tricky to wash and remove liquid from the microplates using traditional methods. These assays are dependent on supporting equipment in order to deliver the best quality results; inferior equipment can lead to inaccurate data, low bead recovery, or require additional testing.

Washing polystyrene beads
Vacuum technologies for polystyrene beads require the use of special filter-bottomed microplates. A vacuum is applied to the microplate to remove liquid while retaining the beads in each well. The vacuum pressure should be carefully regulated to remove all liquid residue while avoiding trapped beads within the filter membrane or other membrane clogs. Additionally, regulation of vacuum pressure prevents contaminating aerosols or splashing of any liquid residue.

Although manual vacuum processes exist, ideal results are obtained with an automated instrument. A filter microplate washer provides equivalent or better wash performance (Figure 1) without the technical difficulties and variable results associated with manual vacuum manifold methods, especially when working with fluids of varying viscosity. Additionally, integrated aspiration and dispensing of liquids using a filter microplate washer provides convenient operation with consistent performance by consolidating the overall number of steps in the washing process; integrating this washer into an automated system can boost performance even further.

Washing biomagnetic beads
On the other hand, biomagnetic beads require use of a rare-earth magnet to immobilize the beads so that liquid can be removed. Ideally, the beads are superparamagnetic, which means that once removed from an external magnetic field, the beads will not retain any magnetism that could lead to clumping.

A manual system for biomagnetic bead washing can consist of little more than a magnet and a pipette, although this is a cumbersome and inefficient process. Inconsistency within the microplate wells and between microplates is inevitable and could significantly impact assay results. A better option is a magnetic bead washer, where washing and dispensing are consistent and accurate, and human error is greatly reduced.

A rare-earth magnet within the washer rapidly immobilizes the biomagnetic beads in a specific arrangement, allowing liquid to be efficiently removed. Ideally, the magnet is removable so that the user can perform magnetic bead assays and traditional ELISAs on the same instrument, thus reducing cost and clutter in the laboratory. Gentle and thorough aspiration and dispensing are highly repeatable through numerous wash cycles and a biomagnetic bead washer can be further enhanced through integration into an automated system. A benefit of using magnetic bead washers over filter microplate washers for washing biomagnetic beads is that the magnetic bead washer delivers consistently lower CV levels and demonstrates no high CV data points (Figure 2) consistent with filter clogging.

Summary
Multiplex assays in either form can yield a wealth of data, and with dependable washing equipment, costly and timely errors can be prevented.

This article was published in Drug Discovery & Development magazine: Vol. 13, No. 1, January/February, 2010, pp. 22-23.

 

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