Measuring the flow in a FluidFM probe
There are no direct methods available to measure the typical flows present in FluidFM probes of a few pL/s down to fL/s. Nevertheless, here we present a particle tracking method which was used to validate the flow-rates predicted by physics models.
A method to measure the flow through the FluidFM probe is presented in the references (Dörig et al., 2013), where single fluorescent nanobeads were tracked through the channel of a FluidFM probe with pressure variations. The video below shows the nanobeads flowing through the FluidFM channel. The stabilization pillars in the channel of the probe are clearly visible as well.
Parameter influencing the flow rate
Generally speaking the flow through a FluidFM probe depends of several parameters:
- Applied pressure: A higher pressure means higher flow.
- Properties of the liquid in the probe: High viscosity liquids decrease the flow.
- Opening of the probe: Only openings below 500nm have an influence on the flow, before that the flow is dominated by the resistance of the probe channel.
- Surface tension: Due to the surface tension, a large offset pressure is required to dispense water in air, or even oil in water.
Typical water flow through a FluidFM probe
The water flow through a FluidFM cantilever in liquid buffer is determined by the probe type and the application, which gives an additional resistance to the flow and hence reduce it significantly:
Probe Application Flow FluidFM Micropipette Free flow/Lithography ~160 fL/(s mbar) FluidFM Nanopipette Free flow ~20 fL/(s mbar) FluidFM Nanopipette Lithography with tight contact <4 fL/(s mbar) FluidFM Nanosyringe Injection <1 fL/(s mbar)
More information about the measurement of the flow through a FluidFM cantilever can be found in next file:
Dörig, P., Ossola, D., Truong, A. M., Graf, M., Stauffer, F., Vörös, J. & Zambelli, T. Exchangeable Colloidal AFM Probes for the Quantification of Irreversible and Long-Term Interactions (2013). Biophysical Journal, 105 (2): 463-472. doi:10.1016/j.bpj.2013.06.002