The rotating particles probe: A new technique to measure interactions between particles and a substrate

We demonstrate a new probing technique to measure physicochemical interactions between particles and a substrate in a fluid. The technique is based on the measurement of field-induced rotation of individual magnetic particles in contact with the substrate. The parallel measurement of many particles with single-particle resolution gives reliable statistics in a short time. Using this technique, the interaction between streptavidin-coated magnetic particles and a glass substrate is measured for various buffer conditions. Increased binding is quantified for increasing ionic strength and decreasing pH. The results are found to be in agreement with calculations of electrostatic interactions. We also apply the technique to study how binding is reduced by blocking the substrate with albumin.

Graphical abstract. The interactions between particles and a glass surface are measured using a new technique based on measuring the rotational behavior of individual magnetic particles upon excitation with rotating magnetic fields.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ We developed a new technique to probe interactions between particles and substrates. ▶ We measured the field-induced rotation of many magnetic particles in parallel. ▶ The interaction between streptavidin-coated particles and glass is measured. ▶ Binding between particles and glass is highly dependent on buffer conditions. ▶ Binding increases with increasing ionic strength and decreasing pH.