Surface plasmon resonance detections based on phase changes have demonstrated superior sensitivities over the intensity, spectral and angular methods due to the singularity effect (abrupt change of phase value) observed at resonance. The Goos–Hänchen effect, a higher first order derivative of the phase, can be observable as a lateral displacement of the reflected wave at total internal reflection and magnified by the surface plasmons. The GH sensitivity can be further improved through the addition of a phase change material nanolayer beneath the gold. Vanadium dioxide (VO2) belongs to the family of phase change materials that exhibit reversible insulator-metal behavior when heated above 68℃. Adding a thin layer of VO2 below the metal proved to theoretically enhance the sensitivity of a conventional gold-based surface plasmon biosensor (up to 28 times of improvement in comparison with the bare gold configuration).
Plasmonic biosensing is an optical technique that based on refractive index change when the target molecules interact with the sensing surface. Main plasmonic material used in this type of biosensors is gold. Our work is dedicated to design a novel sensing SPR chip with vanadium dioxide (VO2) nanolayer, known for its unique insulator-to-metal phase transition in the near-infrared region. VO2 thin film is deposited using Cross-Beam Pulsed Laser Deposition (CB-PLD) method and gold layer deposition is performed by sputtering. By employing the VO2 nanolayer, we create a highly responsive biosensing interface (with a much-improved sensitivity and also a wide dynamic measurement range). The VO2 layer's ability to modulate the refractive index enables precise control of the excited plasmon resonance. This interaction results in enhancing sensitivity and the capability to detect low-concentration analytes with high accuracy.
The development of biochemical sensing devices that can achieve simple and fast detection with high sensitivity and specificity would significantly facilitate the efficiency for environmental monitoring. Optical sensors based on surface plasmon resonance (SPR) effect can provide several advantages that other sensors are difficult to achieve such as real-time and label-free sensing. Current SPR approaches are incapable of detecting small particles with toxins (bacteria and heavy metal ions) at a low concentration level. In this context, we will aim at the use of phase singularity enhanced optical signal to achieve a compact and more sensitive detection. By taking up this challenge, it would allow us to engineer the sensing chips in a resolution of sub-nanometer and realize an efficient and compact sensor for environmental monitoring for small pollutants.
In this paper, we have designed and fabricated an atomically thin plasmonic sensing substrate based on two-dimensional phase change material Ge2Sb2Te5 and silver (Ag-GST). This substrate offers an ultra-low reflection in the SPR curves and a strong optical phase singularity. A custom-built SPR setup was developed here to directly measure the phase-singularity-induced lateral position shift. We have obtained a SPR sensitivity regarding the lateral position shift of 9.9577 x 10^7 μm/RIU, which is 3 orders of magnitudes higher than current position shift sensing scheme based on hyperbolic metamaterial. Due to the ultra-high SPR sensitivity, the binding processes between peptide and integrins directly from un-purified liposomes were real-time monitored. The concentrations of Mn2+ ions ranging from 1 fM to 1 mM on the binding dynamics have been systematically monitored with our developed phase-sensitive surface plasmon resonance biosensors.
In this study, we report the design of a 2D nanomaterial-enhanced biosensor by integrating both the 2D nanomaterials and immunoassay sensing techniques. A phase interrogation surface plasmon resonance (SPR) system was used for detecting antigen with a concentration ranging from nanomolar to femtomolar level. Our work has shown that the evanescent field generated from the Au film to 2D perovskite could lead to a significant sensitivity improvement. This specially antibody-functionalized sensing substrate, embedded with plasmonic metasurface structure, exhibited strong plasmonic coupling effect. And this optimized nanostructure could be engineered as a powerful and ultrasensitive platform for cancer diagnostics. The thickness of the sensing substrate is tuned in an atomic scale and optimized to obtain an enhanced sensing effect. More specifically, a sharp phase signal change and phase-related Goos-Hänchen signal shift was achieved that results from the strong resonance. The improved sensitivities of 2D Perovskite nanostructures were investigated. It is worth noting that the atomic layer design led to the sensing substrate optimized with a tuning scale less than 1 nm. Through a precise engineering of the metasurface substrates, 3 orders of magnitude improvement of the sensitivity (800,000 um/RIU) were demonstrated compared to the one with pure gold sensing substrate (300 um/RIU). This hybrid 2D nanomaterial-based metasurfaces would provide a good opportunity for the development of integrated cancer theranostic devices.
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