Core-Shell Nanostructured Fe₃O₄-Poly(styrene- co-vinylbenzyl chloride) Grafted PPI Dendrimers Stabilized with AuNPs/PdNPs for Efficient Nuclease Activity

Four different novel magnetic core-shell nanocomposites stabilized with Au/Pd nanoparticles (NPs) were prepared by a simple procedure and demonstrated their catalytic activity for effective cleavage of pBR322 DNA. Initially, the Fe₃O₄-poly(styrene-divinylbenzene-vinylbenzyl chloride) (ST-DVB-VBC) matrix functionalized with 3-aminobenzoic acid was prepared and grafted with PPI-G(2) and PPI-G(3) dendrimers. Each core-shell matrix was immobilized with AuNPs and PdNPs separately. The resulting composites were characterized by FT-IR, UV-vis, SEM, TEM, XRD, VSM, XPS, Raman, and TGA. The magnetic core-shell nanocomposites at concentrations from 30 to 50 μM were employed separately to study DNA cleavage by agarose gel electrophoresis. Among the four magnetic core-shell nanocomposites, Fe₃O₄-poly(ST-DVB-VBC)-PPI-G(3)-AuNPs showed higher activity than others for DNA cleavage, and formed Form-II and -III DNA. When the concentration of Fe₃O₄-poly(ST-DVB-VBC)-PPI-G(3)-AuNPs was increased from 40 to 45 and 45 to 50 μM, Form-III (linear) DNA was observed with 10 and 22%, respectively, in addition to Form-II. This observation suggests formation of linear DNA from the supercoiled DNA via nicked DNA-intermediated consecutive cleaving process. The magnetic core-shell nanocomposites were stable and monodispersed, and exhibited rapid magnetic response. These properties are crucial for their application in biomolecular separations and targeted drug-delivery in the future.