Abstract
High sensitivity biosensors based on the coupling of surface plasmon polaritons on titanium nitride (TiN) and a planar waveguide mode were built; they were proved by sensing three different media: air, water and dried egg white; sensors described here could be useful for sensing materials with a refractive index between 1.0 and 1.6; in particular, materials of biological interest with a refractive index in the range 1.3–1.6, like those containing biotin and/or streptavidin. They were built by depositing Nb2O5/SiO2/TiN multilayer structures on the flat surface of D-shaped sapphire prisms by using the dc magnetron sputtering technique. Attenuated total reflection (ATR) experiments in the Kretschmann configuration were accomplished for the air/TiN/Prism and S/Nb2O5/SiO2/TiN/Prism structures, S being the sample or sensing medium. ATR spectra for plasmons at the TiN/air interface showed a broad absorption band for angles of incidence between 36 and 85°, with full width at half maximum (FWHM) of approximately 40°. For the S/Nb2O5/SiO2/TiN/Prism structures, ATR spectra showed a sharp reflectivity peak, within the broad plasmonic absorption band, which was associated with Fano resonances. The angular position and FWHM of the Fano resonances strongly depend on the refractive index of the sensing medium. ATR spectra were fitted by using the transfer-matrix method. Additionally, we found that angular sensitivity and figure of merit increase with increasing the refractive index of the sensing medium.
Highlights
Surface plasmon polaritons (SPPs) are electromagnetic waves, in the infrared or visible frequency-range, simultaneously propagating in the two adjacent media of a dielectric–metal interface, producing collective oscillations of the electronic plasma on the metal surface and dissipation of electromagnetic energy
We reported and discussed the experimental and fitted attenuated total reflectance (ATR) spectra of the S/H/L/titanium nitride (TiN)/Prism multilayer structures, which were proposed here as prototypes of high sensitivity biosensors; from the data of fitted spectra, we obtained the angular sensitivity and the figure of merit for some sensors
Three prototypes of high sensitive biosensors were built by sputtering H/L/TiN multilayer structures on the flat surface of sapphire D-shaped prisms; the titanium nitride layer was approximately
Summary
Surface plasmon polaritons (SPPs) are electromagnetic waves, in the infrared or visible frequency-range, simultaneously propagating in the two adjacent media of a dielectric–metal interface, producing collective oscillations of the electronic plasma on the metal surface and dissipation of electromagnetic energy. A very detailed discussion of electromagnetic modes propagating at the boundaries of a thin metallic film with two semi-infinite dielectric media at both sides of the film is given by J.J. Burke et al [1]; book by S.A. Maier [2] is an excellent reference to review dispersion relations and conditions which have to be satisfied by the refractive indices of the media, as well as, to review experimental techniques of excitation and detection of SPPs. A very common experimental set up for producing and detecting SPPs was first suggested by Kretschmann [3] in 1971. A very common experimental set up for producing and detecting SPPs was first suggested by Kretschmann [3] in 1971 In this technique, the very well known experiment of total reflection is slightly modified by placing a thin film of a noble metal (gold or silver) on the flat surface of a D-shaped prism; SPPs are excited by evanescent waves traveling at the interface when angles of incidence are greater than the critical angle.
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