Abstract
We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm2 is also discussed.
Highlights
Optical biosensors are of fundamental role in their field of label-free characterization of various processes related to biomolecules due to the outstanding sensitivity and non-destructive characteristic [1, 2]
Fabrication and characterization of the Bragg45 mirror structure (BMS) and surface plasmon resonance (SPR) structures BMS was fabricated by electron beam evaporation on a fused silica (FS) glass slide
Three pairs of SiO2 and ZrO2 layers were evaporated on FS slides to create a multilayer structure with a sharp (FWHM=3-4 nm) absorption feature in 415 surface-enhanced internal reflection Kretschmann-Raether configuration for spectroscopic ellipsometry (SE)
Summary
Optical biosensors are of fundamental role in their field of label-free characterization of various processes related to biomolecules due to the outstanding sensitivity and non-destructive characteristic [1, 2]. Biological changes are accompanied with a change in the optical properties and biological processes can be studied in SPR approach 10 by measuring the reflectance of a p-polarized probe light. With the help of the so-called Kretschmann-Rather configuration [5] propagating surface plasmon oscillation can be excited by incident light at the interface of Au layer and aqueous ambient. The exact wavelength (λ) value of this dip is highly dependent on the thickness (d) and optical properties of the Au layer [6], the angle of incidence (θ) of the light beam, the optical properties of the configuration and most importantly the optical properties of the investigated ambient near the Au surface. 25 The combination of SE and SPR spectroscopy can be realized reasonably [10] This combined configuration is usually referred in the literature as total internal reflection ellipsometry (TIRE) [11]. Compared to the biological 30 measurements through the liquid ambient with SE, TIRE is far more sensitive as well as the available λ range is wider since the absorbance of the aqueous ambient is not present anymore
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