Optimal Inter‐distance of Dimer Au Nanoparticles with Amphiphilic Polymer Brushes for Plasmonic Senso

Abstract

Gold nanoparticle (Au-NP) sensor needs to have high intensity of surface plasmon resonance and less steric effect for the efficient labeling of sensing. Since dimer satisfies the specified conditions, we have explicitly studied self-assembled monomer and dimer Au-NPs by considering significantly influential factors such as the size of Au-NP, the thickness of polymers, and the gap distance of inner Au-NPs. To control monomerization and dimerization of Au-NPs and their sizes, two polymers, hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(methyl methacrylate) (PMMA) as amphiphilic brushes, were grafted on Au-NPs via self-assembly simulation. Computational methods of dissipative particle dynamics (DPD) and discrete dipole approximation (DDA) were employed for virtual self-assembly and theoretical analyses of plasmon characteristics related to sensing property, respectively. We found that the same amount of the amphiphilic polymers induced the largest Au-NP monomer and the optimal growing condition of dimer was achieved with 54.3-64.3 vol % of PMMA. The gap distance between Au-NPs also controlled by the number of PMMA, which demonstrated that the amounts of hydrophobic polymers may significantly affect the sensing capability of the dimer. Moreover, the gap distance was suggested to be good when the distance is about 0.2-0.4 nm considering sensitivity and detection accuracy. This study unveiled an optimal near-contact Au-NPs@PMMA/PEG with high sensing capability, where the sensitivity and the detection accuracy were high and the electron tunneling effect was minimized, by reporting unseen roles of polymers and plasmons, which consequently allowed achieving a highly efficient Au-NP dimer sensor.