Detection of Estrogenic Hormones Using Plasmonic Nanostructures
By optimising the geometry of asymmetric split-H (ASH) resonators fabricated on zinc selenide, we have produced a total of four distinct plasmonic resonances that could be matched with six molecular vibration wavelengths (for O-H, C-H, C=O, C=C, CºC-H and C-C bonds) which are relevant to the detection of four estrogenic hormones: estrone (E1), 17β-estradiol (E2), estriol (E3) and synthetic estrogen; 17α-ethinyl estradiol (EE2). Specifically, sensitivities of 363 nm/RIU and 636 nm/RIU were achieved from the deposition of E2 on ASH1 (2 μm and 4 μm) and ASH2 (5 μm and 8 μm) respectively. A Fourier transform infrared (FTIR) spectrometer was used to measure the transmittance resonances of the fabricated ASH arrays. The amplitudes of the molecular vibrational resonances were also around 500 times greater when matched with the plasmonic resonances of the ASHs as compared with deposit on on bulk ZnSe substrates. Finally, when mixtures of two hormones were deposited on the nanoantennas, the molar ratio for each of the hormones could also be calculated by using the peak intensities for the different molecular vibration wavelengths. By engineering the spectral response of ASH resonators to match specific estrogenic fingerprints, the work paves the way for the development of metamaterial sensors with better specificity and enhanced functionalities.