Taken together, our results demonstrate the potential of using iSCAT microscopy as a labelfree tool for the in-situ reporting the morphological and dimensional information of CDSA assemblies, ranging from 1D fiber formation to 3D thickness information of multi-annulus structures. With its excellent sensitivity and sub-millisecond temporal resolution, iSCAT successfully provides detailed insights into the CDSA process, including early-stage growth and high-resolution imaging of the growth dynamics.