Spherical Nucleic Acid Mediated Functionalization of Polydopamine-Coated Nanoparticles for Selective DNA Extraction and Detection

Magnetic nanoparticles have been widely used for the separation of biomolecules for biological applications due to the mild and efficient separation process. In previous studies, core-shell magnetic nanoparticles (NPs) were designed for DNA extraction without much sequence specificity. In this work, to achieve highly selective DNA extraction, we designed a core-shell magnetic structure by coating polydopamine (PDA) on Fe3O4 NPs. Without divalent metal ions, PDA does not adsorb DNA at neutral pH. The Fe3O4@PDA NPs were then functionalized with spherical nucleic acids (SNA) to provide a high density of probe DNA. Fe3O4@PDA@SNA was also compared with when a linear SH-DNA was covalently attached to the NPs surface, showing a higher density of the probe SNA than SH-DNA can be loaded on the NPs in a remarkably shorter time. Nonspecific DNA extraction was thoroughly inhibited by both probes. DNA extraction by the Fe3O4@PDA@SNA was more effective as well as 5-fold faster than by the Fe3O4@PDA@SH-DNA, probably due to the favorable standing conformation of DNA strands in SNA. Moreover, extraction by Fe3O4@PDA@SNA showed high robustness in fetal bovine serum, and the same design can be used for selective detection of DNA. Finally, the method was also demonstrated on silica NPs and WS2 nanosheets for coating with PDA and SNA. Altogether, our findings revealed an interesting and general surface modification strategy using PDA@SNA conjugates for sequence-specific DNA extraction.