Fluid Force Microscopy or FluidFM
FluidFM is a unique combination of atomic force microscopy (AFM) and closed micro-channels for liquid delivery. It gives you a precisely controlled nanopipette which is 100 times thinner than a human hair.
FluidFM scheme based on FluidFM: Meister & Gabi et al., Nano Lett. 9, 2009
Like a record player, an AFM scans surfaces with a needle - the so called cantilever or probe. This probe is so sensitive to forces (pN!) it can register a single atom in its way, hence the name.
The force detection is based on the deflection of a laser beam. Any forces exerted on the probe bend it. This in turn changes the reflection of a laser focused on the probe. The laser reflection is then registered with a ultra-sensitive photodiode and allows to deduce the acting forces.
A very small pyramid can be placed at the apex of the probe, allowing the determination of forces in the pN range. It is possible to measure both attractive and repulsive forces.
With the FluidFM technology we introduce closed microchannels into AFM probes. This allows to handle fL fluid volumes in air and liquid. It also allows to gently manipulate microscopic objects while grasping them with underpressure.
FluidFM is now used by top-universities around the world for applications in physics, material sciences and diverse disciplines in the field of biology.
The flow through a FluidFM probe is 1000 times below the detection limit of even the best flow-sensors. The flow depends on several parameters:
- The applied pressure: A higher pressure means higher flow.
- The property of the liquid in the cantilever: High viscosity fluids have a reduced flow.
- The opening of the probe: Small openings below 500 nm reduce the flow.
- The surface tension: Due to the surface tension, a large offset pressure is necessary to dispense water in air or even oil in water.
Assortment of FluidFM probes. The channel height of 1 um can be seen in the lower image. SEM images courtesy D. Ossola, ETH.
Many details on the FluidFM probes can be found in the hardware section. They include geometrical, mechanical and fluidic properties.