Measuring nanoparticle aggregates

[kurite]

Hello,
I am currently working with magnetic nanoparticles that aggregate and can be measured on the micro scale. Part of the project involves measuring their velocity as it move through vrious liquids. My current set up is simply timing their distance traveled. Does anyone know of a more precise way of measuring this?
Thank you

 

[Baluncore]

Welcome to PF.
Is this a ferrofluid or are the particles permanent magnets ?
https://en.wikipedia.org/wiki/Ferrofluid

Do the particles aggregate in the liquid and then begin to fall through the liquid ?
How many aggregations do you have moving through the liquid at one time ?

You might consider moving the liquid at a rate that holds the particles in a steady position. Over time the flow rate would give the velocity. It might be possible to measure bulk position of aggregates in a column with an LVDT made from three coils wound around the column.
https://en.wikipedia.org/wiki/Linear_variable_differential_transformer