Lung cancer is the most frequently life-threatening disease and the prominent cause of cancer-related mortality among human beings worldwide, where poor early diagnosis and expensive detection costs are considered as significant reasons. Here, we try to tackle this issue by proposing a novel label-free and low-cost strategy for rapid detection and distinction of lung cancer cells relying on plasmonic toroidal metasurfaces at terahertz frequencies. Three disjoint regions are displayed in identifiable intensity-frequency diagram, which could directly help doctors determine the type of lung cancer cells for clinical treatment. The metasurface is generated by two mirrored gold split ring resonators with subwavelength sizes. When placing analytes on the metasurface, apparent shifts of both the resonance frequency and the resonance depth can be observed in the terahertz transmission spectra. The theoretical sensitivity of the biosensor over the reflective index reaches as high as 485.3 GHz/RIU. Moreover, the proposed metasurface shows high angular stability for oblique incident angle from 0 to 30°, where the maximum resonance frequency shift is less than 0.66% and the maximum transmittance variation keeps below 1.33%. To experimentally verify the sensing strategy, three types of non-small cell lung cancer cells (Calu-1, A427, and 95D) are cultured with different concentrations and their terahertz transmission spectra are measured with the proposed metasurface biosensor. The two-dimensional fingerprint diagram considering both the frequency and transmittance variations of the toroidal resonance dip is obtained, where the curves for different cells are completely separated with each other. This implies that we can directly distinguish the type of the analyte cells and its concentration by only single spectral measurement. We envisage that the proposed strategy has potential for clinical diagnosis and significantly expands the capabilities of plasmonic metamaterials in biological detection.
Metasurfaces have been increasingly used in wireless communication applications, such as vortex beam generators, [14][15][16][17][18] lens antennas, [19][20][21][22][23] and asymmetric transmissions, as they present advantages including strong EM manipulation, a low profile, minimal loss, and easy processing. [24,25] Currently, most electronic devices are becoming miniaturized and highly integrated. Therefore, research on multifunctional metasurfaces has received considerable attention. In general, metasurfaces are constructed by arranging the different amplitudes and phases of each minimum pixel on a surface by changing the sizes or geometries of each meta-atom to meet preset conditions and obtain desired field distribution for specific characteristics. [26][27][28][29][30][31][32] Another feasible method to construct multifunctional metasurfaces is to load tunable devices such as graphene, [33] diodes, [34,35] or microelectromechanical systems. [36] However, compared with passive metasurfaces, some limitations still exist, including complicated design, high insertion loss, and poor robustness. Extending the function of passive metasurfaces is crucial in terms of economics and design difficulty. In general, the use of the independent characteristics of frequency and polarization for guiding the design of passive metasurfaces to achieve additional functionalities is feasible. [37][38][39][40] However, metasurface operations are limited to a half-space, transmission, or reflection mode without effectively manipulating the EM wave of full space. Recently, some full-space metasurfaces were used to achieve two spatial mode control of a linear polarized (LP) wave with a multilayer structure; [41][42][43][44][45] however, little information is available on the full-space work for a circular polarized (CP) wave with a two-layer structure. For many applications, such as antennas, circularly polarized radiation may present many advantages, including improved immunity to multipath distortion, polarization mismatch losses, and Faraday rotation effects caused by the ionosphere. [46][47][48] In this study, we proposed a strategy to design multifunctional metasurfaces with high-efficiency CP wave control in full-space by using an ultra-thin single board, for which the key was to engineer almost completely suppressed crosstalk among three substructures for the individual control of the triple sets of Pancharatnam-Berry (PB) phases in both transmission and reflection modes. To prove the concept, we arbitrarily integrated Full-space manipulation of electromagnetic waves with a thin flat plate is particularly intriguing for large-angle scanning, functionality integration, and data capacity applications. However, majority of the designs to date are confined to linearly-polarized wave operations; these render the versatile full-space device operating under circularly-polarized waves unaddressed due to the critical issue of the geometric phase being hardly decoupled among reflections and transmissions. Herein, a strategy for a helici...
self-healing, and accelerating [3-9] properties. Airy beams are described by light waves that do not diffract, and have shapepreserving features along continuous curved trajectories formed by the peak intensity when the waves propagate in free-space. Numerous studies have demonstrated that Airy beams have great potential for use in many applications such as particle manipulation, [3,4] highresolution light-sheet microscopy, [5] and light bullet generation. [6,7] Traditional ways to produce Airy beams rely on the use of phase masks formed by spatial light modulators, or diffractive optical elements and an extra Fourier-transform lens. [8,9] Such methods are bulky, and not compatible with on-chip integration of nanophotonic systems. Moreover, the pixel sizes of these methods are typically larger than the operation wavelengths, limiting the performance and accuracy. Therefore, generating high-performance Airy beams with subwavelength pixel size, compact footprint, and low cost is challenging, but of great importance for compact and integrated systems. Metasurfaces are planar versions of metamaterials, and have shown unprecedented ability to arbitrarily manipulate light wavefronts, [10-17] providing efficient solutions to generate desired accelerating beams. Metasurfaces are composed of subwavelength-scale dielectric or metallic building blocks that alleviate some challenges of bulky metamaterials, such as volumetric loss, fabrication requirements, and compatibility with on-chip photonic devices. By locally tailoring the amplitude, polarization, and phase of light, recent studies have demonstrated various uses of metasurfaces in many practical applications, including beam shapers, [18,19] focusing lenses, [20,21] multifunctional devices, [22,23] invisibility cloaks, [24,25] etc. In particular, metasurfaces can achieve simultaneous phase and amplitude modulations by absorbing, reflecting, or polarizationconverting the unwanted amplitude components, while using geometric rotating or scaling operations to obtain the desired phase response. [26-29] Based on these metasurfaces, free-space Airy beam generation has been successfully realized with the metasurfaces implemented as orthogonal gold nanorods, [30] C-aperture arrays, [31] etc. However, such techniques have low efficiency and limited bandwidth. To circumvent the high
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