This preprint shows that intracellular TDP-43 amyloid — the pathological aggregate central to ALS and frontotemporal dementia — nucleates from nascent condensates whose maturation is arrested, and that co-expressing an oligomeric binder in cells can halt this CTD amyloid formation. Flow Induced Dispersion Analysis (FIDA) was used to quantify the residual soluble monomer fraction after urea-induced disassembly of differentially seeded TDP-43 CTD amyloids, providing a measure of their chemical depolymerization and thermodynamic stability directly from cell lysate. It is an example of using FIDA to quantify soluble monomer and assess the stability of protein amyloid aggregates in complex biological samples.