In this paper, gold asymmetric-split ring resonators (A-SRRs) are used for proteins sensing in the mid-infrared
(IR) spectral region. Self-assembled monolayers (SAMs) of octadecanethiol (ODT) in ethanolic solution were
deposited on the resonator surfaces to immobilise protein molecules for their detection. Different diameters ASRRs
were fabricated on zinc selenide (ZnSe) substrates using electron-beam lithography technique. Their
plasmonic responses appear in the mid-IR spectral region and match with the vibrational responses of many
organic molecules. After the formation of SAMs layer, one sample was immersed in bovine serum albumin
(BSA) solution for proteins adsorption while other sample was immersed in hydroxyl terminated hexa-ethylene
glycol (EG6-OH) solution to modify SAMs surfaces to resist immobilisation of proteins. The vibrational
responses of these organic molecules, all samples were excited using an incident broadband mid-IR light
source and their reflectance spectra were measured at normal incidence using a microscope coupled Fourier
Transform Infrared (FTIR) spectrometer. This study highlights the capability of plasmonic structures (A-SRRs)
fabricated on transparent and high refractive index ZnSe substrates allows the detection of BSA proteins with
enhanced detection in the mid-IR spectral range, demonstrating their potential for a wide range of sensing
applications, e.g. in biomedical engineering and food industries.
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