Exchangeable Colloidal AFM Probes for the Quantification of Irreversible and Long-Term Interactions

Abstract

An original method is presented to study single-colloid interaction with a substrate in liquid environment. Colloids, either in solution or adsorbed on a surface, are fixed by suction against the aperture of a microchanneled atomic force microscopy cantilever. Their adhesion to the substrate is measured, followed by their release via a short overpressure surge. Such colloid exchange procedure allows for 1), the quick variation of differently functionalized colloids within the same experiment; 2), the investigation of long-term interactions by leaving the colloids on a surface for a defined time before detaching them; and 3), the inspection of irreversible interactions. After validation of the method by reproducing literature results obtained with traditional colloidal atomic force microscopy, the serial use of colloids with different surface functionalization was shown on a micropatterned surface. Finally, concanavalin A-coated colloids were allowed to adsorb on human embryonic kidney cells and then detached one by one. The adhesion between cells and colloids was up to 60 nN, whereas individual cells adhered with 20 nN to the glass substrate. A cellular elastic modulus of 0.8 kPa was determined using the attached colloid as indenter.

A new strategy to measure intercellular adhesion forces in mature cell-cell contacts

“…Micropipette cantilevers with nominal spring constant of 0.2 N/m and an aperture of 4 μm in diameter were used. As an indenter, a polyethylene glycol coated polystyrene bead of 10 μm in diameter (Micromer #01-54-104, Micromod Partikeltechnologie GmbH, Germany) was immobilised at the aperture of the cantilever as follows54: beads at a density of 5 μg/mL were added into a petri dish containing culture medium. A bead was grabbed by applying a suction pressure of 700 mbar and the deflection sensitivity was calibrated.…”

Writing with Fluid: Structuring Hydrogels with Micrometer Precision by AFM in Combination with Nanofluidics

“…For the FluidFM cantilevers used here, one finds a hydrodynamic resistance of R tot ≈ 5 × 10 17 (cf. calculation in Section S4 in the Supporting Information) . The volumetric flow rate Q through the aperture is Q = Δ p / R tot = V sol /Δ t .…”

Elasticity Spectra as a Tool to Investigate Actin Cortex Mechanics

“…5. In particular, the microfluidics of FluidFM can be exploited to pick-up the sphere, and release it after few indentations (in case of contamination), without the need of gluing the sphere on the cantilever in advance, or changing the cantilever for every experiment [54,71]. On a different note, the interferometric read-out of the Chiaro nanoindenter results in a very quick and practical calibration and set-up of the experiment, without any special requirement for the sample holder (see for example the arrangement pictured in Fig.…”

“…The spring constant was determined in air by thermal tuning and the Sader's method [77] and the channel was filled with physiological solution containing 0.1 mg/ml of the blue fluorescent dye AMCA (7-amino-4-methylcoumarin, Sigma-Aldrich, USA) for blockage detection. Green fluorescent beads (Phosphorex Inc, USA) with 3µm to 4µm diameter were placed next to the confluent cell layer and attached to the cantilever tip by applying 800mbar suction pressure through the microchannel [71,78]. Indentations were performed at 1µm/s approach speed and up to 100nN force setpoint in grids of 5x5 points with 25µm pitch.…”