Herein, we have studied the self-assembly and the spontaneous growth of microassemblies of the plant polyphenol ellagic acid for HeLa cancer cell imaging and therapy. The growth of the assemblies was studied at varying pH over time. It was found that initially microspheres were formed which gradually transformed into microfibers via nucleation and polymerization process. The optimum growth of microfibers was found to be in the pH range of 6-8. We have shown that the microfibers successfully adhered to the HeLa cell membranes and inhibited their proliferation. This biological approach, using assemblies derived from plant polyphenols, may be used for direct cellular drug delivery and may potentially help develop a simple and economical method to create building blocks with desired properties for a new generation of sensors, bioimaging and drug delivery systems.