Protein-Ligand Mediated Aggregation of Nanoparticles: A Study of Synthesis and Assembly Mechanism

Two difunctional, asymmetric PEG linkers were synthesized and utilized to prepare water-soluble, biotinylated CdS@SiO2 particles with various surface contents of the biotin groups. Aqueous dispersions of these particles were prepared, and upon addition of avidin, aggregation was observed using DLS, TEM, and SEM analysis. The resulting aggregates were dense but also had fractal shapes. It was shown that singleangle DLS measurements at 90 were sufficiently accurate for quickly measuring the size of the aggregates as it evolved with time. Initial aggregation rates were measured as a function of surface biotin content of the nanoparticles and initial avidin concentration. The initial rates displayed bell-shaped curve responses to variations in the avidin-to-particle ratio and biotin-to-avidin ratio, the shapes of which were attributed to the stoichiometric balance/imbalance of the avidin-tobiotin ratio in the system and to intraparticle and interparticle bridges that could sterically block avidin from reaching some biotin sites. The growth mechanism was postulated to be a step-growth process.