DNA methylation is one of the earliest known modification pathways, and it regulates gene expression, which in turn influences many biological processes. Direct, label-free detection of DNA methylation with high sensitivity remains a great challenge. Surface-enhanced Raman scattering (SERS), a non-invasive and label-free vibration spectroscopy technique, offers sensitive intrinsic chemical information that makes it an attractive option for DNA analysis. In this study, we employed iodide-modified silver nanoparticles to generate highly consistent SERS signals of DNA at micromolar concentrations in aqueous solutions. This enabled the acquisition of single-base sensitive DNA fingerprint details pertaining to base methylations (such as 5-methylcytosine). As a proof of concept, the SER spectra of a DNA and its methylated counterpart were compared and analyzed, resulting in an obvious identification of DNA methylation. In particular, we first designed two DNA sequences, the sole change being that one of the nucleotides, cytosine, is replaced with a 5-methylcytosine. Further SERS experimental study revealed that methylating a single cytosine in the DNA strand caused a subtle but evident alteration in the SERS spectrum. A new Raman peak emerged at 760 cm-1 the Raman peak at 792 cm-1 moved to 790 cm-1, and there was a noticeable drop in the peak intensity ratio between 1572 cm-1 and 1634 cm-1. This approach may provide a novel and easy-to-use tool for the label-free identification of single-molecule DNA mutations or modifications, furthering the advancement of ultra-sensitive genomic research in the future.
Non-reciprocal devices are essential in many field that require unidirectional wave transmission, such as communications, sensor technology and quantum computing. However, most existing devices are constrained by factors including power supply, external magnetic field, efficiency, and bandwidth. We demonstrated an all-passive, broadband and high efficient nonreciprocal metasurface based on vanadium dioxide (VO2). The electromagnetic thermal coupling simulation results show that when the incident light power density is 40-55 kW/cm2, the transmittance is 90% in one direction and nearly 20% in the other direction. Moreover, benefiting from the non-resonant structure of the metasurface, the device can be used at a broadband wavelength of 7-12 μm. Thus, the demonstrated device has the advantages of broadband and high efficiency, offering a simple but effective scheme of all-passive unidirectional devices.
Catenary metasurface has been widely used in fields such as wild-angle imaging, spectral detection, and broadband absorbers, due to its advantages of high efficiency and broadband. In our previous studies, perfect wavefront control of catenary metasurface is achieved via field-driven optimization (FDO). However, the proposed method focuses solely on the performance of catenary metasurfaces at a specific wavelength. Here, considering the broadband and multifunctional of the catenary and catenary-like metasurfaces, multi-objectives FDO is proposed. With 30 iterations, the average diffraction efficiency of the catenary metasurface increases to ~96% at the wavelength of 9-13 μm. In addition, considering the functionality, the catenary and catenary-like metasurfaces are optimized with a pair of orthogonal polarized light incidences. The optimization process preserves the chiral nature of the catenary metasurface. After 30 iterations, the diffraction efficiency of the catenary metasurface is improved from 96.4% to 99.2%. For catenary-like metasurfaces, the diffraction efficiencies exceed 90% for both left-handed and right-handed elliptically polarized light incidences. Our work provides a methodology for designing multifunctional complex continuous metasurfaces, which may further promote catenary optics.
As an important means of contactless manipulation of targets, optical force has significant application prospects in areas such as light sail propulsion and orbital intervention of space debris. Precise measurement of the optical force generated by spatial targets in complex optical fields is crucial for establishing their spatial dynamics model. The torsion balance can be used to measure the optical torque. We use a 5 μm tungsten fiber to build a torsion balance system to measure the extremely weak optical torque less than 1×10-15 Nm, which can help to establish an accurate model of the interaction between objects and optical forces. At the same time, it provides experimental data for the study of spacecraft orbit control and light sail navigation.
Simultaneously achieving a large field of view (FOV) and high-resolution imaging has always been the goal in the design of optical systems. Although traditional optical systems can switch from large-FOV to high-resolution imaging by adjusting the focal length, this method relies on complex mechanical structures and multi-lens combinations, leading to slow switching speed and bulky volume. Planar metasurfaces composed of subwavelength structures can achieve arbitrary wavefront manipulation, but their phase distributions are usually fixed once fabricated. In this paper, we propose a strategy for large-scale pixel-level active control of local phase on demand via cascaded bilayer metasurfaces. This method enables fast switching between the quadratic phase and hyperbolic phase by globally translating one of two layers at a one-lattice interval. Simulation results indicate that the full FOV for the quadratic phase exceeds 80°, and the point spread functions for the hyperbolic phase at various focal lengths closely approach the diffraction limit. Such multifunctional metalenses may find many potential applications, such as surveillance, unmanned vehicles, and medical science.
The geometric phase concept has profound implications in many branches of physics, from condensed matter physics to quantum systems. Although geometric phase has a long research history, novel theories, devices, and applications are constantly emerging with developments going down to the subwavelength scale. Specifically, as one of the main approaches to implement gradient phase modulation along a thin interface, geometric phase metasurfaces composed of spatially rotated subwavelength artificial structures have been utilized to construct various thin and planar meta-devices. In this paper, we first give a simple overview of the development of geometric phase in optics. Then, we focus on recent advances in continuously shaped geometric phase metasurfaces, geometric–dynamic composite phase metasurfaces, and nonlinear and high-order linear Pancharatnam–Berry phase metasurfaces. Finally, conclusions and outlooks for future developments are presented.
We designed a broadband achromatic multilevel diffractive lens which is using the nanoparticle composite. Nanoparticle composite is a new artificial material, which has both pattern-transfer capability and high refractive index requirements. The device has good achromatic performance and good focusing performance at the focal plane in the visible band. The simulated average focusing efficiency is over 85% at the visible frequency.
We design a simple catenary metasurface with high efficiency, which could obtain both the degree of circular polarization and the wavelength of incident polarized light by measuring the diffraction intensity and the deflection angle. The catenary decomposes the incidence into left and right circularly polarized light and diffracts them to different predesigned directions with different deflection angles that present the wavelength information. The diffraction efficiency of the designed catenary exceeds 94%, the average diffraction efficiency is up to 97.6% at the wavelength of 8-14μm, and angular dispersion is 0.078°/nm. Moreover, the degree of circular polarization for various incident polarization states can be characterized by diffraction intensities. This work may provide extensive applications for biosensing, DNA structural analysis, stereochemistry, etc.
Super-oscillation phenomenon provides an effective solution for realizing far-field non-invasive super-resolution imaging. However, most super-oscillatory lenses are challenging to balance the working bandwidth and working efficiency, which greatly limits the practical applications of super-oscillation lenses in optical systems. In this work, a broadband high-efficiency super-oscillatory metalens for sub-diffraction focusing about 0.75 times the diffraction limit based on the reflective metasurface is proposed for super-resolution imaging in the visible ranging from 400 nm to 700 nm. Moreover, another metalens with a sub-diffraction focusing spot equal to 0.6 times of the diffraction limit is also designed to prove the universal applicability of the proposed method. The proposed method provides an effective pathway for the development of microscopy, holography, and machine vision.
In this paper, we propose an ultra-thin metasurface to achieve simultaneous thermal infrared camouflage and 1.06 μm laser scattering with thermal management. First, the metasurface has an average absorptivity/emissivity of 0.04 in the band of 8~14 μm and a emission peak at 5.62 μm with nearly 100% emissivity. Therefore, camouflage against thermal infrared detectors and effective thermal management can be achieved. Second, the chessboard-like square patches on the top of the meatsurface make it possible to reduce the specular reflection at the laser wavelength of 1.06 μm to less than 2% by redirecting the reflected light to non-normal angles. These excellent simulated results indicate that our proposed metasurface has promising applications in the fields of multi-band infrared camouflage.
Multispectral imaging technology plays an important role in lots of domains, but traditional systems are limited by large volumes and complex constructions. Here, we propose a high-efficiency multispectral integrated imaging system based on metasurfaces, with its spectral range covering two important infrared windows of 3-5 μm and 8-12 μm. This system is composed of the microlens, metasurface, and filter array, hence its volume, weight, and complexity can be greatly decreased. The average efficiencies of the aforementioned two bands are over 96.47% and 97.43%, respectively. The bandwidth of each spectral channel can be tuned flexibly according to realistic requirements, which makes the system more applicable to various circumstances. The proposed design method is universally applicable and has potential applications in many aspects, such as remote sensing, epidemic monitoring, and archeology.
Dielectric metasurfaces is a plane optical device to achieve the desired function by modulating amplitude and phase, polarization for the incident light, and its transmission efficiency is higher than other metasurfaces, these advantages lead to dielectric metasurfaces will be used widely in the future. Nevertheless, the majority of metasurfaces are planar singlelayered structure, which limit seriously the view field and effect of monochromatic imaging. Here, we demonstrate a composed dielectric meta-lens doublet by the electromagnetic simulation can achieve perfectly diffraction-limited monochromatic focus for the polarization-insensitive incident lights at a wavelength of 375 nm, which has the view field of 60°, the numerical aperture of 0.5, and a focal length of 380μm. Due to the dielectric meta-lens doublet has the scaling of subwavelength at ultraviolet light, and the devices have high distinguishability, it can be used widely in nanolithography, imaging with large view field, and other optical domains.
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