Fabrication Of A Large-Scale Plasmonic Nanojunction For Chemical Sensing
Ministry of Science and Technology, Taiwan, Grant 108-2218-E-006-056-MY3
Plasmonic coupling between nanojunctions showed potential applications in bio/chemical sensing. The most common method of fabricating large-scale ordered arrays was using direct-writing techniques, such as lithography. There were some drawbacks to this approach: it is complicated and expensive, and sub-nanoscale spacing between nanocrystals was poorly controlled. Here, we demonstrated that layer-by-layer deposition and polymer-directed assembly of nanocrystals can be integrated to fabricate large-scale dimer nanojunctions with controllable spacing, conformations, and quantity of dimer nanojunctions. When silver nanocube (AgNC) is used as building blocks to fabricate high-quality dimer nanojunctions in the polymer matrix, the thickness of the polymer matrix played an important role in tuning the interplane and intraplane interactions between nanocrystals, resulting in different conformational dimer nanojunctions: vertical dimers (face-to-face assembly) and horizontal dimers (edge-to-edge assembly). The optical properties of large-scale dimer nanojunctions strongly depended on their conformations, which were caused by electromagnetic field coupling, also known as hot spots, between the nanocrystals. Hot spots in both types of dimer nanojunctions can be used to amplify chemical signals in the Raman spectrum with an enhancement factor (EF) of about 103 compared with the pure polymer film. This high EF in the Raman spectrum made these dimer nanojunctions suitable for sensing applications. This fabrication technique can produce high-quality and quantitatively controllable dimer nanojunction structures with highly sensitive sensing applications in the fields of biology, biomedicine, and chemistry.