Theoretical Study on Enhancement of Sensing Capability of Plasmonic Dimer Au Nanoparticles with Amphiphilic Polymer Brushes

Au nanoparticle (Au-NP) sensors need a high surface plasmon resonance intensity and a low steric effect for efficient labeling in sensors. Since dimers meet these requirements, we have theoretically studied the self-assembly of monomer and dimer Au-NPs by considering influential factors such as Au-NP size, polymer thickness, and gap distance between dimer Au-NPs. In order to control the monomerization and dimerization of spherical Au-NPs and their sizes via self-assembly, two polymers (hydrophilic PEG and hydrophobic PMMA) were grafted on the Au-NPs as amphiphilic brushes. Computational methods of dissipative particle dynamics and discrete dipole approximation were employed for virtual self assembly and theoretical analyses of plasmons related to sensing properties, respectively. We found that the bigger Au-NPs were obtained when the amounts of each polymer were roughly identical and the gap distance between Au-NPs in the dimer was shorter when the amount of PMMA was reduced within the condition of dimerization. This theoretical study revealed an optimal near-contact distance for Au-NPs@PMMA/PEG, where the electron tunneling effect was minimized, and reported unseen roles of polymers and plasmons, which consequently allowed achieving a highly efficient Au-NP dimer sensor.