We propose the use of gold nanoparticles grown on the surface of nanoporous TiO2 films as surface-enhanced Raman scattering (SERS) sensors for the detection of 17β-estradiol. Gold deposition on top of a TiO2 surface leads to the formation of nanoparticles the plasmonic properties of which fulfil the requirements of a SERS sensor. The morphological and optical properties of the surface were investigated. Specifically, we demonstrate that the TiO2 background pressure during pulsed laser deposition and the annealing conditions offer control over the formation of Au nanoparticles with different sizes, shapes and distributions, yielding a versatile sensor. We have exploited the surface for the detection of 17β-estradiol, an emerging contaminant in environmental waters. We have found a limit of detection of 1 nM with a sensitivity allowing for a dynamic range of five orders of magnitude (up to 100 µM).

In this paper, we report on arrays of asymmetric split H-shape (ASH) nanostructures tuned to produce two distinct resonances at wavelength that range from 3 µm to 7 µm. The electric-field of the incident wave has been both polarized parallel to the vertical asymmetric dipole arms and polarized across the 50 nm gap in the asymmetric horizontal bar. We have produced resonance quality factors as large as 26 in the MIR region.

We propose the use of gold nanoparticles grown on the surface of nanoporous TiO2 films as Surface Enhanced Raman Scattering (SERS) sensors for the detection of 17β-estradiol. Gold deposition on top of TiO2 surfaces leads to the formation of nanoparticles, which plasmonic properties fit the requirements of a SERS sensor well. The morphological and optical properties of this surface were investigated. Specifically, we demonstrated that the TiO2 background pressure during pulsed laser deposition and annealing conditions enabled the formation of a variety of Au nanoparticles with controlled size, shape and distribution thus resulting in a versatile sensor. We have exploited this surface for the detection of 17β-estradiol, an emerging contaminant in environmental waters. We have found a limit of detection of 10 nM with a sensitivity allowing dynamic range of five orders of magnitude (up to 100 µM).

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<div> <div> <div> <p>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.</p> </div> </div> </div>