Following our initial imaging of 1D fiber formation, we next focused on 2D platelet growth, where the characteristic morphology and fast controllable assembly of platelets might be used to assess the capabilities of iSCAT for CDSA measurement. Seeds were deposited on glass coverslips at a surface density of ∼0.16 µm -2 . Following the addition of 150 µL of 0.35 µM (3.33 µg/mL) PCL 45 :PCL 45 -b-PDMA 348 unimer mixtures, hexagonal platelets appear on the surface and uniformly grow in size as the reaction proceeds (Fig. , Movie S2; 637 nm, 4 µW µm -2 , 400 µs exposure time, 1.5 s -1 per frame time-lapse). We selected a PCL 45 :PCL 45 -b-PDMA 348 unimer mixture with the concentration of 0.35 µM (3.33 µg/mL) to ensure slow growth of well isolated platelets. Keeping the seed surface density fixed, increasing the unimer concentration results in faster kinetics. Further details are provided in the Experimental Methods section below. Control experiments without the presence of seeds show no characteristic fast growth (Fig. ). We also explored the effect of changing the core chemistry: Platelets prepared with a poly(η-octalactone) (POL)-based core-forming block exhibited less uniform morphology and size compared to the PCL-based system (Fig. ). Furthermore, we observed changes in platelet morphology with solvent (Fig. ), however, iSCAT was able to resolve CDSA assemblies under a wide range of solution conditions (Fig. ).