In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor
structure based on silicon nanosheet and two-dimensional transition metal
dichalcogenides. This configuration contains six components: SF10 triangular prism,
gold thin film, silicon nanosheet, two-dimensional
MoS2/MoSe2/WS2/WSe2 (defined as
MX2) layers, biomolecular analyte layer and sensing medium. The
minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR
curve are systematically examined by using Fresnel equations and the transfer matrix
method in the visible and near infrared wavelength range (600 nm to
1024 nm). The variation of the minimum reflectivity and the change in
resonance angle as the function of the number of MX2 layers are presented
respectively. The results show that silicon nanosheet and MX2 layers can
be served as effective light absorption medium. Under resonance conditions, the
electrons in these additional dielectric layers can be transferred to the surface of
gold thin film. All silicon-MX2 enhanced sensing models show much better
performance than that of the conventional sensing scheme where pure Au thin film is
used, the highest sensitivity can be achieved by employing 600 nm
excitation light wavelength with 35 nm gold thin film and
7 nm thickness silicon nanosheet coated with monolayer
WS2.
The extreme anisotropic permittivity of hyperbolic metamaterials (HMMs) represent a unique opportunity to realize effective bulk metastructures with extraordinary optical properties over a broad frequency range from visible to terahertz. [1] HMMs are artificial uniaxial materials that exhibit hyperbolic dispersion because the out of plane dielectric constant (ε zz = ε ⊥ ) has an opposite sign to the in-plane dielectric constants (ε xx = ε yy = ε ll ). HMMs can be classified into two types based on the sign of their dielectric components, i.e., type I (−ε ⊥ and ε ll ) and type II (ε ⊥ and −ε ll ). In comparison to isotropic materials showing elliptical dispersion, HMMs support propagation of optical modes across the structure with infinitely large momentum (high-k modes) in the effective medium limit, [2,3] irrespective of Hyperbolic metamaterials (HMMs) have emerged as a burgeoning field of research over the past few years as their dispersion can be easily engineered in different spectral regions using various material combinations. Even though HMMs have comparatively low optical loss due to a single resonance, the noble-metal-based HMMs are limited by their strong energy dissipation in metallic layers at visible frequencies. Here, the fabrication of noble-metal-free reconfigurable HMMs for visible photonic applications is experimentally demonstrated. The low-loss and active HMMs are realized by combining titanium nitride (TiN) and stibnite (Sb 2 S 3 ) as the phase change material. A reconfigurable plasmonic biosensor platform based on active Sb 2 S 3 -TiN HMMs is proposed, and it is shown that significant improvement in sensitivity is possible for small molecule detection at low concentrations. In addition, a plasmonic apta-biosensor based on a hybrid platform of graphene and Sb 2 S 3 -TiN HMM is developed and the detection and real-time binding of thrombin concentration as low as 1 × 10 −15 m are demonstrated. A biosensor operating in the visible range has several advantages including the availability of sources and detectors in this region, and ease of operation particularly for point-of-care applications.
Atomically thin transition metal dichalcogenide nanomaterials have shown superior optical and electronic properties in the two-dimensional (2D) scale. They are considered as promising alternative materials to graphene. Here, we have precisely engineered a plasmonic sensing substrate with four types of two-dimensional transition metal dichalcogenide nanomaterial to achieve significant phase sensitivity improvement. Phase modulation is currently the most sensitive interrogation method among all the plasmonic detection approaches. The tuning of the substrate thickness in an atomic scale with a step less than 1 nm allows the efficient modulation of phase signals. More importantly, the optical absorption rate for each of these nanomaterials is different and can be tuned by changing the number of 2D layers, where perfect absorption and interrogation of the plasmonic signal can be obtained. Through systematically optimizing the parameters of the transition metal dichalcogenide structured plasmonic substrate, we can balance the optical absorption efficiencies and the electron losses at the plasmonic resonance condition. All of the calculations were based on the transfer matrix method and Fresnel equations. A very low minimum reflectivity of 3.2560 × 10 −8 was demonstrated with an excitation wavelength of 1024 nm, showing a complete transfer (∼100%) of the light energy into the plasmon resonance energy. The ultradark singularity at the resonance dip leads to an ultrahigh plasmonic sensitivity of 1.1 × 10 7 deg/RIU, which is 3 orders of magnitude higher than those with bare metallic sensing substrates used in commercial plasmonic sensors. The resolution is also improved by at least 3 orders of magnitude compared with conventional substrates.
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