Colloid Probe Measurements

Colloidal systems play a significant role in our daily lives, with substances such as milk, paint, cosmetics, and smoke all falling into this category. Therefore, it is not surprising that a great deal of research has been driven by a desire to understand, and ultimately control, such common systems. To this end, force balance instruments such as the AFM have been utilised along with a range of other techniques which allow the study of interacting surfaces in confined geometries. By attaching colloidal particles to the end of a cantilever, we can modify both the surface chemistry and the interaction geometry, allowing investigation of the nature of colloidal interactions on the single particle-particle level. Many studies have been conducted using this technique to study the stability of simple systems which are theoretically described by DLVO theory.

The ability to readily modify the interacting surfaces in AFM has lead to it becoming the instrument of choice in the study of a wide variety of colloidal phenomena. Such applications include the study of

  • Tissue nanomechanics

  • Interaction of oil drops

  • Direct measurement of cell mechanics

  • Ligand-receptor interaction studies of cell membranes

The versatility of this technique also allows for the study of non-eqillibrium interactions. The understanding of the dynamic behaviour of fluids at the nanoscale and their role in governing the behaviour of colloidal systems and cell interactions represents an exciting area of research which is currently receiving much attention. We have applied the FM-AFM technique to the study of colloidal interactions. The advantage of this technique is that it allows for the simultaneous measurment of conservative interaction forces (e.g. DLVO, Figure 2(a)) and dissipative interaction forces (e.g. hydrodynamics, Figure 2(b)) in a single measurement. The enhances sensitivity afforded by FM-AFM when using stiff cantilevers has allowed us to reversibly measure colloidal interactions in the near surface reigime without suffering from a 'jump to contant' which usually limits the application of colloid probe AFM techniques.

Figure 1: A 5um colloidal sphere attached to a tipless cantilever

Figure 1: A 5um colloidal sphere attached to a tipless cantilever

Figure 1: (a) Completely reversible force measurement of DLVO interactions between mica and a borosilicate glass sphere. Solid and dashed lines are calculated values assuming constant surface potential and constant surface charge (b) The recovered d…

Figure 1: (a) Completely reversible force measurement of DLVO interactions between mica and a borosilicate glass sphere. Solid and dashed lines are calculated values assuming constant surface potential and constant surface charge (b) The recovered damping coefficent due to hydrodynamic interactions. Both force and damping coeficient are measured simultaneously using FM-AFM.

Project collaborators

  • Assistant Professor Stephen Thorpe, UCD

  • Assistant Professor David MacManus, UCD

References

  1. Direct Measurement of Colloidal Forces Using an Atomic Force Microscope, Ducker, W. A., Senden, T. J., and Pashley, R. M., Nature, 353, 239-241, (1991).

  2. Measuring electroscatic, van der Walls, and hydration forces in electrolyte solutions with an atomic force microscope, Butt, H. J., Biophysical Journal, 60, 1438-1444, (1991).

  3. Theory of Stability of Highly Charged Lyophobic Sols and Adhesion of Highly Charged Particles in Solutions of Electrolytes, Derjaguin, B. V., and Landau, L., Acta Physicochim URSS, 14, 633-652, (1941).

  4. Theory of the Stability of Lyophobic Colloids, Verwey, E. J. W., and Overbeek, J. T. G., Elsevier, Amsterdam, (1948).

  5. Forces between two oil drops in aqueous solution measured by AFM, Dagastine, R., R., Stevens Geoffrey, W., Chan, D. Y. C., and Grieser, F., Journal of Colloid and Interface Science, 273, 339-342, (2004).