Polyethylenimine-mediated gold nanoparticle arrays with tunable electric field enhancement for plasmonic applications

Localized surface plasmon resonance (LSPR) technologies are used in some of the most effective optical biosensors and can be used for the detection of biomolecules at ultralow concentrations. The construction of ordered nanoparticle arrays is important for LSPR and biosensing applications. The main challenge in the development of LSPR-based sensors is optical instability, which mainly originates from the detachment or aggregation of the gold nanoparticles (AuNPs) on the plasmonic surfaces. In this study, highly monodisperse and stable AuNPs with a particle size from 20.39 ± 1.2 to 106.17 ± 1.6 nm were synthesized by using the Turkevich and seed-and-growth methods. Here, we aimed to control the construction of plasmonic AuNPs by using the electrostatic assembly of oppositely charged polycationic polymer. For this purpose, we used positively charged polyethylenimine (PEI) to immobilize AuNPs on the disposable polystyrene surface and designed a model for plasmonic sensing. Our results confirmed that the 1-mg/mL PEI concentration efficiently prevented the aggregation or detachment of immobilized AuNPs. LSPR peak wavelengths were adjustable in the range from 530 ± 2.0 to 548 ± 1.5 nm. In addition, we theoretically showed that electric field enhancement within the gaps of nanoparticle arrays could enhance the sensitivity of the plasmonic surfaces. Such nanoplasmonic surfaces could be important in fabricating facile sensing devices and could be easily integrated into bioelectronics and microfluidic devices.