Thermal nanoimprint lithography based plasmonic nanogratings for refractive index sensing of polar solvents

Abstract

This work illustrates a facile approach for the design of flexible plasmonic sensors using gold nanograting. The fabrication of surface plasmon resonance (SPR) coupled refractive index (RI) sensor is proposed to sense the various known RIs of polar solvents. Thermal nanoimprint lithography (T-NIL) is used to transfer the nanograting of the processed digital versatile discs (DVDs) through polydimethylsiloxane (PDMS) stamp to thermoplastic polymer coated flexible polyethylene terephthalate (PET) substrate. The gold nanograting sample was obtained after the subsequent deposition of the gold thin film of thickness 60 nm on top of polymer nanograting. The surface plasmon resonance (SPR) modes excited on gold-encrusted polymer nanograting appeared as a dip in the reflectance spectra measured at normal incidence under white light in air and liquid medium. We use refractive index calibration polar solvents [methanol (1.331), water (1.333), acetone (1.359), ethanol (1.361) and isopropanol (1.382)] to determine the refractive index sensitivity of our gold nanograting arrays. This produces a bulk refractive index sensitivity of 535 ± 47 nm/RIU. The real-time kinetic response demonstrates the stability of the sensor with respect to the time and reusability of the sensing chip for multiple measurements. Thus, we envisaged that our proposed sensor can be a potential candidate for the development of highly sensitive plamonic device.