Nanoscale Interparticle Distance within Dimers in Solution Measured by Light Scattering

Abstract

We demonstrate a novel approach to quantify the interparticle distance in colloidal dimers using Mie scattering. The interparticle distance is varied in a controlled way by changing the ionic strength of the solution and the magnetic attraction between the particles. The measured scaling behavior is interpreted using an energy–distance model that includes the repulsive electrostatic and attractive magnetic interactions. The center-to-center distances of particles with a 525 nm radius can be determined with a root-mean-square accuracy of 12 nm. The data show that the center-to-center distance is larger by 83 nm compared to perfect spheres. The underlying distance offset can be attributed to repulsion by charged protrusions caused by particle surface roughness. The measurement method accurately quantifies interparticle distances that can be used to study cluster formation and colloid aggregation in complex systems, e.g., in biosensing applications.

Multivalent weak interactions enhance selectivity of interparticle binding

“…20). Within the magnetic dimers, it is not trivial to model the surface-to-surface distance of the particles, because the interparticle distance results from the sum of several interparticle forces with different signs and length ranges, for example the Hamaker force, electrostatic forces, the magnetic force, entropic forces such as the hydrophobic effect and steric repulsion, and the depletion force; in addition, surface roughness can be important (28). To enable a calculation starting from the basic force equations, one would need to know the underlying particle parameters with high precision, which is not the case for the particles used in this study.…”

Rotating magnetic particles for lab-on-chip applications – a comprehensive review

“…38 With a detection angle of the scattered light at 90 degrees, Ranzoni et al 43 demonstrated that the concentration of PSA in undiluted blood plasma could be measured in the low picomolar range, by recording the amplitude of the 2f signal (at twice the driving frequency). Vliembergen et al 124,125 have extended the optical detection method by analyzing the rotation-angle dependent scattering signals. Sharp peaks in the spectrum allowed them to measure nanometer-scale inter-particle distances within the clusters.…”