(591a) Reversible Adsorption Kinetics of Dimer Colloids

We use micron-sized colloidal dimers as an experimental model system to investigate the effect of shape on adsorption kinetics using near a solid interface. The colloid-interface interaction strength is tuned using electrostatic, depletion, and gravitational forces to be comparable with nanoscale systems such as proteins.  Kinetics are measured by tracking individual colloids as they transition between an entropically trapped adsorbed state and a desorbed states through Brownian motion. The dimers are further categorized into side-on, end-on, and desorbed states. A light emitting diode (LED) based total internal reflection microscopy (TIRM) setup is used to measure the height of each colloid relative to the glass surface, while the lateral position of the colloids are determined using epifluorescence. This approach allows us to gather statistics from long-duration tracking of a single particle.  The TIRM images are processed using a deconvolution approach that can isolate the height of each side of the dimer.  We first analyze the accuracy of this measurement method and investigate the influence of secondary scattering effects. The interfacial kinetics of the dimer colloid are compared with single isolated colloids to infer the effects of colloid shape. The observed kinetics are also compared to theoretical predictions based on the measured interaction potential and diffusivity. Dimers display enhanced adsorption probabilities once the one side of the dimer has adsorbed but longer timescales for those transitions to occur. The model system demonstrates how particle shape may alter the adsorption kinetics of nonspherical molecules such as proteins.