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We have designed and investigated a three-band refractive index (RI) sensor in the range of 550–900 nm based on the metal nanoslit array with gain-assisted materials. The underlying mechanism of the three-band and enhanced characteristics of the metal nanoslit array with gain-assisted materials, have also been investigated theoretically and numerically. Three resonant peaks in transmission spectra are deemed to be in different plasmonic resonant modes in the metal nanoslit array, which leads to different responses for the plasmonic sensor. By embedding the structure into the CYTOP with proper gain-assisted materials, the sensing performances can be greatly enhanced due to a dramatic amplification of the extraordinary optical transmission (EOT) resonance by the gain medium. When the gain values reach their corresponding thresholds for the three plasmonic modes, the ultrahigh sensitivities in three bands can be obtained, and especially for the second resonant wavelength (λ2), the FOM=128.1 and FOM* = 39100 can be attained at the gain threshold of k =0.011. Due to these unique features, the designing scheme of the proposed gain-assisted nanoslit sensor could provide a powerful approach to optimize the performance of EOT-based sensors and offer an excellent platform for biological sensing.

Transmission surface plasmon resonance (TSPR) is an unusual extraordinary optical transmission that is more transparent at certain wavelengths than expected by classical theory. The three main plasmonic structures that providing this phenomenon are nanohole arrays, diffraction gratings, and nanoslit arrays. This extraordinary optical transmission phenomenon is produced as a result of surface plasmon excitations. The shifting in TSPR responses upon changing of dielectric environment at the surface of a metallic film was observed. After TSPR was discovered from metallic nanohole arrays in 1998, the number of papers about this topic rapidly increased. In the 20 years since, TSPR has been utilized to improve the detection limits, sensitivity, selectivity, and dynamic range of biosensing devices, resulting in them having greater potential for commercialization. This review gives a broad overview of the TSPR phenomenon, the development of this technique, and the typical experimental setups used to acquire TSPR signals; it also describes how they are applied in the field of research into biosensors. [ABSTRACT FROM AUTHOR]

A novel spatial and spectral selective plasmonic sensing based on the metal nanoslit arrays has been proposed and investigated theoretically, which shows a high performance in the multiplexing biomolecular detections. By properly tuning the geometric parameters of metal nanoslit arrays, the enhanced optical fields at different regions can be obtained selectively due to the excitation of SPP, cavity mode (CM), and their coupling effects. Simulation results show that the resonances of the metal nanoslit arrays at different spatial locations and different wavelengths can be achieved simultaneously. A relative bigger red-shift of 57 nm can be realized when a layer of biomolecular film is adsorbing at the slit walls, and the corresponding total intensity difference will be enhanced near 10 times compared to that at the top surface. In addition, when a BSA protein monolayer is adsorbing at slit walls with different slit widths, the corresponding wavelength shifts can reach to more than 80 nm by modulating the widths of the slit. The simulated results demonstrate that our designed metal nanoslit arrays can serve as a portable, low-cost biosensing with a high spatial and spectral selective performance. [ABSTRACT FROM AUTHOR]

Label-free biosensing based on extraordinary optical transmission (EOT) through metallic nanoaperture arrays is a highly promising application of nanoplasmonics. The optical properties of these nanostructures, however, are complex due to the coupling between propagating and localized plasmon resonances, and some important features of the sensing mechanism have not been fully exploited. In this paper, in contrast to most previous studies that focused on the optimization of sensor response to bulk refractive index changes, we investigate the sensor response upon biomolecule bindings at different sensor positions inside or outside the nanoapertures. By properly tuning the geometric parameters of a gold nanoslit array, we show that the enhanced optical field in this EOT-based sensor can be spatially tailored to increase its interaction volume with the binding target biomolecules and improve the sensor performance. The results presented deepen the current understanding of the EOT-based sensor properties and open up new opportunities to further optimize their sensing performance. [ABSTRACT FROM PUBLISHER]