I've got microspheres at approx 1.5µm diameter, these undergo several coating steps, one step is to coat with silver and another with polyelectrolytes. These steps cause aggregation and I'm left with many clumps of several spheres mixed with single spheres.
What I would like to be able to do, is somehow filter out the larger aggregates and retain the 1.5µm spheres. I have tried some filtering before but was left with caked filters and the sample was barely recoverable.
Any help in this matter would be greatly appreciated.
Try sonication to break clusters apart, then filtration. Try membrane filter (not fibrous). You can buy various types of "track membranes" of well defined pores and flat filtering surface.
i would agree with tomasz sir, also other methods are there but they are more tedious and not precise output .....
1) Sonication
Although a probe sonicator will provide the most ultrasonic energy, be autious about using this. An unclean probe tip can contaminate the microsphere suspension, and an old tip can shed metal, even if it is clean. A better option might be a bath type sonicator. To achieve maximum efficiency, it is best to work with a small volume (or a large volume dispersed in a larger container), so that the relative microsphere concentration is reduced as much as possible. This allows the ultrasonic energy to reach all of the microspheres effectively, increasing the likelihood of breaking the aggregates. Also, glass seems to be a better conductor of ultrasonic energy than plastic, and therefore working in glass is recommended if at all possible. It should be noted that extended exposure, even in a mild ultrasonic bath, can heat the microspheres to an undesirable level. Therefore, the temperature should be monitored, and ice can be added to the bath to ensure that the microspheres do not overheat.
2) Vortexing
The ruggedness of all of microspheres makes vortexing a suitable approach to reducing aggregation. Working with small volumes and vortexing in repeated short pulses (perhaps 5 seconds) seems to be the most effective. A case in which this is not recommended is when unwanted aggregation is present after passively adsorbing ligand to the surface of non-functionalized microspheres. The shear forces involved in vortexing can dislodge some of the protein adsorbed at the microsphere surface.
3) Pipetting
Much like vortexing, the shear forces created by rapid pipetting of a suspension of microspheres through a fine tip pipet are often enough to reduce or eliminate aggregation caused by hydrophobic interactions, and should be avoided if ligands have been adsorbed at the microsphere surface.
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