Metal nanograil arrays with tunable multiple dipolar plasmon modes in integrated optofluidic devices for ultrasensitive sensing of biomolecules

Abstract

Biomolecular detection using Localized Surface Plasmon Resonances (LSPR) has been extensively investigated because these techniques enable label-free detection. The high-density metal nanopatterns with tunable LSPR characteristics have been used as refractive index sensing because LSPR property is highly sensitive to refractive index change of surroundings. Meanwhile, Colloidal lithography is a robust method for fabricating regularly ordered nanostructures in a controlled and reproducible way using spontaneous assembly of colloidal particles. In this study, nanopatterns on UV-curable polymer were prepared via colloidal lithography. Then, metallic nanograil arrays with high density were fabricated by sputtering noble metals such as gold and subsequent removal of residual polymers and colloidal particles. From Finite-Difference Time-Domain Method (FDTD) simulations and reflectance spectra, we found that multiple dipolar plasmon modes were induced by gold nanograil arrays and each mode was closely related with structural parameters. LSPR characteristics of gold nanograil arrays could be tuned by varying the fabrication conditions to obtain optimal structures for LSPR sensing. Sensing behavior of gold nanograil arrays was tested by applying various solvents with different refractive indices and measuring the variations of LSPR dips. Finally, gold nanograil arrays as LSPR sensors were integrated in optofluidic devices and used to achieve real-time label-free monitoring of biomolecules.