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

Abstract

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.