Observation of spatiotemporal optical vortices enabled by symmetry-breaking slanted nanograting.

Providing additional degrees of freedom to manipulate light, spatiotemporal optical vortex (STOV) beams carrying transverse orbital angular momentum are of fundamental importance for spatiotemporal control of light-matter interactions. Unfortunately, existing methods to generate STOV are plagued by various limitations such as inefficiency, bulkiness, and complexity. Here, we theoretically propose and experimentally demonstrate a microscale singlet platform composed of a slanted nanograting to generate STOV. Leveraging the intrinsic topological singularity induced by C2 symmetry and z-mirror symmetry breaking of the slanted nanograting, STOV is generated through the Fourier transform of the spiral phase in the momentum-frequency space to the spatiotemporal domain. In experiments, we observe the space-time evolution of STOV carried by femtosecond pulses using a time-resolved interferometry technique and achieve a generation efficiency exceeding 40%. Our work sheds light on a compact and versatile platform for light pulse shaping, and paves the way towards a fully integrated system for spatiotemporal light manipulation.

Wearable intelligent sweat platform for SERS-AI diagnosis of gout.

For the past few years, sweat analysis for health monitoring has attracted increasing attention benefiting from wearable technology. In related research, the sensitive detection of uric acid (UA) in sweat with complex composition based on surface-enhanced Raman spectroscopy (SERS) for the diagnosis of gout is still a significant challenge. Herein, we report a visualized and intelligent wearable sweat platform for SERS detection of UA in sweat. In this wearable platform, the spiral channel consisted of colorimetric paper with Ag nanowires (AgNWs) that could capture sweat for SERS measurement. With the help of photos from a smartphone, the pH value and volume of sweat could be quantified intelligently based on the image recognition technique. To diagnose gout, SERS spectra of human sweat with UA are collected in this wearable intelligent platform and analyzed by artificial intelligence (AI) algorithms. The results indicate that the artificial neural network (ANN) algorithm exhibits good identification of gout with high accuracy at 97%. Our work demonstrates that SERS-AI in a wearable intelligent sweat platform could be a feasible strategy for diagnosis of gout, which expands research on sweat analysis for comfortable and noninvasive health monitoring.

Robust temporal adiabatic passage with perfect frequency conversion between detuned acoustic cavities.

For classical waves, phase matching is vital for enabling efficient energy transfer in many scenarios, such as waveguide coupling and nonlinear optical frequency conversion. Here, we propose a temporal quasi-phase matching method and realize robust and complete acoustical energy transfer between arbitrarily detuned cavities. In a set of three cavities, A, B, and C, the time-varying coupling is established between adjacent elements. Analogy to the concept of stimulated Raman adiabatic passage, amplitudes of the two couplings are modulated as time-delayed Gaussian functions, and the couplings' signs are periodically flipped to eliminate temporal phase mismatching. As a result, robust and complete acoustic energy transfer from A to C is achieved. The non-reciprocal frequency conversion properties of our design are demonstrated. Our research takes a pivotal step towards expanding wave steering through time-dependent modulations and is promising to extend the frequency conversion based on state evolution in various linear Hermitian systems to nonlinear and non-Hermitian regimes.

Superwavelength self-healing of spoof surface sonic Airy-Talbot waves.

Self-imaging phenomena for nonperiodic waves along a parabolic trajectory encompass both the Talbot effect and the accelerating Airy beams. Beyond the ability to guide waves along a bent trajectory, the self-imaging component offers invaluable advantages to lensless imaging comprising periodic repetition of planar field distributions. In order to circumvent thermoviscous and diffraction effects, we structure subwavelength resonators in an acoustically impenetrable surface supporting spoof surface acoustic waves (SSAWs) to provide highly confined Airy-Talbot effect, extending Talbot distances along the propagation path and compressing subwavelength lobes in the perpendicular direction. From a linear array of loudspeakers, we judiciously control the amplitude and phase of the SSAWs above the structured surface and quantitatively evaluate the self-healing performance of the Airy-Talbot effect by demonstrating how the distinctive scattering patterns remain largely unaffected against superwavelength obstacles. Furthermore, we introduce a new mechanism utilizing subwavelength Airy beam as a coding/decoding degree of freedom for acoustic communication with high information density comprising robust transport of encoded signals.

Sound non-reciprocity based on synthetic magnetism.

Synthetic magnetism has been recently realized using spatiotemporal modulation patterns, producing non-reciprocal steering of charge-neutral particles such as photons and phonons. Here, we design and experimentally demonstrate a non-reciprocal acoustic system composed of three compact cavities interlinked with both dynamic and static couplings, in which phase-correlated modulations induce a synthetic magnetic flux that breaks time-reversal symmetry. Within the rotating wave approximation, the transport properties of the system are controlled to efficiently realize large non-reciprocal acoustic transport. By optimizing the coupling strengths and modulation phases, we achieve frequency-preserved unidirectional transport with 45-dB isolation ratio and 0.85 forward transmission. Our results open to the realization of acoustic non-reciprocal technologies with high efficiency and large isolation, and offer a route towards Floquet topological insulators for sound.

Early-stage oral cancer diagnosis by artificial intelligence-based SERS using Ag NWs@ZIF core-shell nanochains.

Surface-enhanced Raman spectroscopy (SERS) has great potential in the early diagnosis of diseases by detecting the changes of volatile biomarkers in exhaled breath, because of its high sensitivity, rich chemical molecular fingerprint information, and immunity to humidity. Here, an accurate diagnosis of oral cancer (OC) is demonstrated using artificial intelligence (AI)-based SERS of exhaled breath in plasmonic-metal organic framework (MOF) nanoparticles. These plasmonic-MOF nanoparticles were prepared using a zeolitic imidazolate framework coated on Ag nanowires (Ag NWs@ZIF), which offers Raman enhancement from the plasmonic nanowires and gas enrichment from the ZIF shells. Then, the core-shell nanochains of Ag NWs@ZIF prepared with 0.5 mL Ag NWs were selected to capture gaseous methanethiol, which is a tumor biomarker, from the exhalation of OC patients. The substrate was used to collect a total of 400 SERS spectra of exhaled breath of simulated healthy people and simulated OC patients. The artificial neural network (ANN) model in the AI algorithm was trained with these SERS spectra and could classify them with an accuracy of 99%. Notably, the model predicted OC with an area under the curve (AUC) of 0.996 for the simulated OC breath samples. This work suggests the great potential of the combination of breath analysis and AI as a method for the early-stage diagnosis of oral cancer.

Plasmon-driven catalytic reactions in optoplasmonic sandwich hybrid structure.

As an interesting phenomenon in the field of surface enhanced Raman spectroscopy (SERS), the plasmon-driven catalytic reaction (PDSC) induced by plasmonic hot electrons has great value in the research of novel properties of surface plasmons and accuracy of SERS applications. In this work, an optoplasmonic sandwich hybrid structure is proposed for studying PDSC of p-aminothiophenol (PATP) molecules, which is composed of Au film, metal organic frameworks (MOFs) nanoparticles, zeolithic imidazolate (ZIF-8), and single S i O 2 microsphere (Au f i l m@M O F s@S i O 2). In order to analyze the novel, to the best of our knowledge, phenomenon of the PDSC in this micro-nano structure, the hot electron generation in the MOF without the plasmonic core is carried out by combining the plasmonic enhancement of gold film with the light concentration of microspheres. Experimental data show that the PDSC reactions is dependent on the size of the MOFs nanoparticle and the size of the S i O 2 microsphere, which is confirmed by the electromagnetic field simulation of the finite-difference time-domain method (FDTD). Our work not only strengthens the understanding of surface plasmon in optoplasmonic hybrid structures but also has broad application prospects in the SERS and plasmon-driven catalytic fields.

Near-Infrared Light-Responsive Size-Selective Lateral Flow Chip for Single-Cell Manipulation of Circulating Tumor Cells.

Accurately obtaining information on the heterogeneity of CTCs at the single-cell level is a very challenging task that may facilitate cancer pathogenesis research and personalized therapy. However, commonly used multicellular population capture and release assays tend to lose effective information on heterogeneity and cannot accurately assess molecular-level studies and drug resistance assessment of CTCs in different stages of tumor metastasis. Herein, we designed a near-infrared (NIR) light-responsive microfluidic chip for biocompatible single-cell manipulation and study the heterogeneity of CTCs by a combination of the lateral flow microarray (LFM) chip and photothermal response system. First, immunomagnetic labeling and a gradient magnetic field were combined to distribute CTCs in different regions of the chip according to the content of surface markers. Subsequently, the LFM chip achieves high single-cell capture efficiency and purity (even as low as 5 CTCs per milliliter of blood) under the influence of lateral fluid and magnetic fields. Due to the rapid dissolution of the gelatin capture structure at 37 °C and the photothermal properties of gold nanorods, the captured single CTC cell can be recovered in large quantities at physiological temperature or released individually at a specific point by NIR. The multifunctional NIR-responsive LFM chip demonstrates excellent performance in capture and site release of CTCs with high viability, which provides a robust and versatile means for CTCs heterogeneity study at the single-cell level.

Enhanced response of titanium doped iron(ii) oxalate under electric field.

Electrorheological (ER) fluid, containing polarized particles within an insulating liquid, represents a smart material, the mechanical properties of which can be altered mainly by an electric field. In this work, ER fluids based on cauliflower iron(ii) oxalate doped titanium particles show excellent rheological and wetting properties by the sample co-precipitation method. The morphology of the particles is observed by SEM and the molecular structure within the particles is obtained via XRD and FTIR. The distribution of elements within the particles is obtained by EDS. Owing to a lower current density than pure iron(ii) oxalate, the SEM and optical images show an obvious chain-like structure within the ER fluids with 2 wt% and 5 wt%, respectively, under 2 kV mm-1. Then, the rheological properties of these ER fluids are tested up to 3 kV mm-1 and the results show a gratifying property of resisting shear with different shear rates (0.1-100 s-1), which is attributed to the appearance of a stable chain-like structure. At the same time, the ER efficiency and the switching performance are obtained and the static yield stress fits the relevant electric field strength well. Ultimately, an excellent sedimentation ratio is obtained from 0 h to 600 h.

Mxenes-Au NP Hybrid Plasmonic 2D Microplates in Microfluidics for SERS Detection.

Combined with microfluidics, surface-enhanced Raman spectroscopy (SERS) exhibits huge application prospective in sensitive online detection. In current studies, the design and optimization of plasmonic enhanced structures in microfluidics for SERS detection could be an interesting challenge. In this work, hybrid plasmonic 2D microplates composed of Mxenes (Ti3C2Tx) microplates and in-situ synthesized Au nanoparticles (Au NPs) are fabricated in a microchannel for enhanced structures in SERS microfluidics. Benefiting from the 2D Mxenes microplates with complex distributions, the enhanced areas generated by Au NPs are quite enlarged in a microchannel, which exhibits high sensitivity in SERS detection at 10-10 M for Nile blue (NB) molecules in microfluidics. The mechanism of electromagnetic enhancement (EM) and chemical enhancement (CM) is analyzed. The experimental data indicate the ultrasonic times of Mxenes and the concentration of Au3+ play important roles in the sensitivity of SERS detection, which is confirmed by the simulated electric field distributions. Furthermore, a typical pesticide (thiram) at 100 ppm in water is detected on these SERS microfluidics with hybrid plasmonic enhanced structures, which demonstrates that our work not only strengthens the knowledge of plasmonics but also enlarges the application of SERS.

Efficient nonreciprocal mode transitions in spatiotemporally modulated acoustic metamaterials.

In linear, lossless, time-invariant, and nonbiased acoustic systems, mode transitions are time reversible, consistent with Lorentz reciprocity and implying a strict symmetry in space-time for sound manipulation. Here, we overcome this fundamental limitation by implementing spatiotemporally modulated acoustic metamaterials that support nonreciprocal sound steering. Our mechanism relies on the coupling between an ultrathin membrane and external biasing electromagnetic fields, realizing programmable dynamic control of the acoustic impedance over a motionless and noiseless platform. The fast and flexible impedance modulation of our metamaterial imparts an effective unidirectional momentum in space-time to realize nonreciprocal transitions in k-ω space between different diffraction modes. On the basis of these principles, we demonstrate efficient nonreciprocal sound steering, showcasing unidirectional evanescent wave conversion and nonreciprocal upconversion focusing. More generally, our metamaterial platform offers opportunities for generation of nonreciprocal Bloch waves and extension to other domains, such as non-Hermitian topological and parity-time symmetric acoustics.

Landau-Zener Transition in the Dynamic Transfer of Acoustic Topological States.

Topological notions in physics often emerge from adiabatic evolution of states. It not only leads to fundamental insight of topological protection but also provides an important approach for the study of higher-dimensional topological phases. In this work, we first demonstrate the transfer of topological boundary states (TBSs) across the bulk to the opposite boundary in an acoustic waveguide system. By exploring the finite-size induced minigap between two TBS bands, we unveil the quantitative condition for the breakdown of adiabaticity in the system by demonstrating the Landau-Zener transition with both theory and experiments. Our results not only serve as a foundation of future studies of dynamic state transfer but also inspire applications leveraging nonadiabatic transitions as a new degree of freedom.

Tailoring entanglement through domain engineering in a lithium niobate waveguide.

We propose to integrate the electro-optic (EO) tuning function into on-chip domain engineered lithium niobate (LN) waveguide. Due to the versatility of LN, both the spontaneously parametric down conversion (SPDC) and EO interaction could be realized simultaneously. Photon pairs are generated through SPDC, and the formation of entangled state is modulated by EO processes. An EO tunable polarization-entangled photon state is proposed. Orthogonally-polarized and parallel-polarized entanglements of photon pairs are instantly switchable by tuning the applied field. The characteristics of the source are theoretically investigated showing adjustable bandwidths and high entanglement degrees. Moreover, other kinds of reconfigurable entanglement are also achievable based on suitable domain-design. We believe tailoring entanglement based on domain engineering is a very promising solution for next generation function-integrated quantum circuits.