The Next Generation of Colloidal Probes: A Universal Approach for Soft and Ultra‐Small Particles

Abstract

The colloidal probe technique, which is based on the atomic force microscope, revolutionizes direct force measurements in many fields, such as interface science or biomechanics. It allows for the first time to determine interaction forces on the single particle or cell level. However, for many applications, important “blind spots” remain, namely, the possibility to probe interaction potentials for nanoparticles or complex colloids with a soft outer shell. Definitely, these are colloidal systems that are currently of major industrial importance and interest from theory. The here‐presented novel approach allows for overcome the aforementioned limitations. Its applicability has been demonstrated for 300 nm sized carboxylate‐modified latex particles as well as sub‐micron core–shell particles with a soft poly‐N‐isopropylacrylamide hydrogel shell and a rigid silica core. For the latter, which until now cannot be studied by the colloidal probe technique, determined is the temperature dependency of electrosteric and adhesion forces has been determined on the single particle level.

Translating Therapeutic Microgels into Clinical Applications

“…Suitable models needed for evaluation NMR [131][132][133][134] Molecular scale Chemical composition Quantification of chemical groups, diffusivity of guest molecules Sensitivity → Broad signals AFM [135][136][137] Nanometer to sub-nanometer scale Mechanical properties, interaction forces 3D surface profile Individual measurement imaged. [125] TEM additionally gives information about the "inner" morphology of microgel with a resolution of up to 1 Å in high resolution transmission electron microscopy (HRTEM).…”

“…To investigate the mechanical properties of individual microgels, colloidal probe nanoindentation and atomic force microscopy (AFM) have to be employed. [135,136] In colloidal probe AFM, a tip is modified with a micron-sized colloidal particle, with a diameter of up to 15 μm, which is used to deform and indent the microgel. [137,146] Bending of the cantilever during contact with the microgel is detected using a laser diode and a split photodetector, which gives information about tip-microgel displacement and the associated interaction force, thus allowing the calculation of Young's moduli for individual microgels.…”

Electrokinetics in Micro-channeled Cantilevers: Extending the Toolbox for Reversible Colloidal Probes and AFM-Based Nanofluidics

“…Moreover, the new capability to access the state of the aperture, i.e . ‘open’ vs. ‘blocked’, will be critical for direct force measurements with reversible colloidal probes, and in particular when working with sub-μm colloidal particles 25,60 . Here, we presented a method that allows for an in-situ monitoring the state of the aperture.…”

“…Core-shell particles with a silica core and a poly(N-isopropylacrylamide) (PNIPAM) shell were synthesized according to a previously published protocol 61 . Further details are given also elsewhere 60 .…”

Producing Plant Virus Patterns with Defined 2D Structure

“…[22,24] Applying an overpressure to the microchanneled cantilever leads to the deposition of the desired material (liquids or nanoparticles), while the feedback of the scanning force microscope regulates the contact between the nanopipette respectively nanosyringe with the substrate. (In addition to the here-utilized mode of spotting, FluidFM can also be used for a variety of applications, such as immobilizing soft colloidal particles [25,26] or cells [27,28] at the tip for single-particle or single-cell force spectroscopy by an underpressure, producing DOI: 10.1002/pssa.202100259…”