Mixing of Bio-buffer reagents with Magnetic Beads on Dropbot Chip


I am using magnetic beads on dropbot chip. For making a proper mixing/mixture of bio-reagent buffers with Magnetic Beads, I have tried different ways/pattern of mixing on dropbot chip (like clock-wise mixing, anti-clock wise mixing, both clock-wise and anti clockwise mixing, horizontal and vertical way of mixing by selecting some electrodes in ‘+’ shape) with a delay of 1500ms, 700ms. All the mixing experiments had a minimum of 10 rounds of mixing. But I haven’t get a proper ‘mixture’. The Magnetic Beads were placed in one ‘corner’ inside the droplet after mixing.

The specifications of Magnetic Beads which we are using includes :

‘The grain size of the magnetic particle is about 70 nm. Magnetic particle aggregated by some granule and its average diameter is about 100-500 nm.’

Is there any better way for making a Mixture of Buffer while using Magnetic Beads ?

Thanks in advance.


It looks to me like the beads have aggregated, in which case there’s probably no magic “mixing pattern” that will break them up. I’m not a chemist, but I suspect you will need to adjust the composition of your beads.

Not sure if it’s helpful, but as a reference, you can look at the bead preparation used for our measles assay (amine-terminated 3.07-um-diameter paramagnetic particles from Bangs Laboratories).


Hi anandbabyalias,

The beads you are using are very small, unfortunately I do not have experience with such beads.
In our lab we often use beads in the range 2-5 um.
As Ryan mentioned you can look at our bead preparation procedure (measles assay). Note that after we functionalize the beads, we use PBS with BSA and Tween-20 to wash the beads and then block them overnight using superblock.

You may also want to take a look at this thread from Research Gate and this FAQ compilation: Ask “The Particle Doctor®”, on page 16 there is a section for handling very small beads.

A few suggestions:

  • Depending on the type of the beads, there might be an additional quenching step after the functionalization to cap any unreacted sites on your beads (e.g. Carboxyl Beads), make sure you don’t skip this step. This might be included in your bead conjugation protocol.
  • Consider adding small amounts of Tween-20 in your working solution. Tween-20 is a very common surfactant used with beads, it may help preventing the aggregation of your beads. Be careful, high amounts of Tween-20 may interfere with your assay.

I hope this helps.