pH-Regulated Conformation of Oligonucleotides Immobilized on PEI-Coated Nanoparticles

DNA-nanoparticle conjugates have been extensively exploited in drug delivery and biosensing, in which DNA conformation serves as a critical determinant of drug release rate and sensing sensitivity. However, it is difficult to regulate DNA conformation because DNA tends to extend in upright conformation at high packing density but may adopt a lying-down conformation at low packing density. We herein report pH-regulated conformation of oligonucleotides immobilized on nanoparticles with low surface density by coating polyethylenimine (PEI) on nanoparticle surface. The theoretical results suggest oligonucleotides are immobilized in significantly more shrunken and compact conformation at low pH and in more extended and loose conformation at high pH than oligonucleotides on bare nanoparticles, which is dominated by the surface coverage of protonated PEI monomers and influenced by oligonucleotide density and length. The pH-dependent oligonucleotide conformation on PEI-coated nanoparticles may be exploited in drug delivery and biosensing regulation.