Degeneracy Breaking of Wood’s Anomaly for Enhanced Refractive Index Sensing

Abstract

We introduce an ultrasensitive detection technique for refractive index (RI) sensing based on an array of nanometer scale slot-antennas milled in a thin gold layer using a single lithographic step. Our experimental figures of merit (FOMs) of 140-210 in the telecom wavelength range approach the fundamental limit for standard propagating SPR sensors (~250).The underlying mechanism enabling this is the combination of a narrowband resonance of the slot-antennas with degeneracy breaking of Wood's anomaly under slightly non-perpendicular illumination. In addition, we explore the sensitivity of the device to the depth of the analyte layer. This concept can be easily tuned to any desired wavelength and RI range by modifying the slot dimensions and the array spacing, thus rendering it highly useful for numerous sensing applications.

High aspect ratio titanium nitride trench structures as plasmonic biosensor

“…The measured S b = 430 nm/RIU is comparable to the previously reported sensitivities for periodic metallic (plasmonic) nanostructures for biosensing with 300 -600 nm/RIU in the visible to near infrared wavelength range including sensors based on the RWAs principle [12]. Reported sensitivities over 1000 nm/RIU were achieved for telecommunication wavelengths around λ = 1500 nm [14] with a larger grating period as the BRIS of RWAs-based sensors scales with their pitch [13]. Moreover, the sensitivity our structure is also comparable and even slightly outperforming those of all-dielectric structures in the near-infrared wavelengths, such as dielectric photonic crystal biosensing platform with 310 nm/RIU for HIV virus detection [44,45], Si resonators with 227 nm/RIU for cancer biomarker detection of prostate specific antigen (PSA, limit of detection, LOD: 0.87 ng/ml) [51], high-contrast grating resonator with 418 nm/RIU for label-free detection of cardiac disease biomaker, serum cardiac troponin I (LOD: 0.1 ng/ml) [46].…”

“…Various applications range from telecomunnication [2,3] to solar energy harvesting [4,5]. Nevertheless, one of the most promising applications of plasmonics is sensing (biosensing) [6][7][8][9][10][11][12][13][14][15][16]. Such sensing devices have been developed utilizing plasmons properties to concentrate and enhance electric fields in very confined volumes close to the metal surfaces, thus tracing very small amounts of analytes in label-free biosensors, which may lead to point-of-care (POC) devices for swift, facile, and inexpensive diagnosis in future health care [17].…”

“…Here, we demonstrate surface sensitivity of high aspect ratio TiN trench structures towards the refractive indices of different ambient liquids for potential biosensing applications. The sensitivity of our sensing unit, 430 nm/RIU, originates from the Rayleigh-Woods anomalies (RWAs) on plasmonic grating, which changes the relevant reflection peaks with different refractive indices of surrounding media [8,13,14]. Our TiN-based trench structures were realized by the combination of ALD with advanced deep reactive ion etching (DRIE).…”

Plasmon drag effect with sharp polarity switching

“…According to equations (1) and (2), a change in the dielectric constant of the environment results in a shift of the SPP resonance angle. This effect is commonly used in plasmonic-based sensing applications [27][28][29][30][31]. As one can see in figure 4, adding a polystyrene layer (with a refractive index of 1.6 and thickness of ∼800 nm) on the top of the Ag/DVD structure, results in a shift of the switching point to higher angles, while the switching phenomenon occurs in both air and polymer environments.…”

Fano resonance and tunability of optical response in double-sided dielectric gratings

“…12(a). Recently, some groups have published experimental results of plasmonic sensors with substantially higher sensitivities and FOM [32,33]. However, both of the methods are still limited for the detection of lossless solutions.…”