Light-controlled soft bio-microrobot

Micro/nanorobots hold exciting prospects for biomedical and even clinical applications due to their small size and high controllability.However,it is still a big challenge to maneuver micro/nanorobots into narrow spaces with high deformability and adaptability to perform complicated biomedical tasks.Here,we report a light-controlled soft bio-microrobots(called“Ebot”)based on Euglena gracilis that are capable of performing multiple tasks in narrow microenvironments including intestinal mucosa with high controllability,deformability and adaptability.The motion of the Ebot can be precisely navigated via light-controlled polygonal flagellum beating.Moreover,the Ebot shows highly controlled deformability with different light illumination duration,which allows it to pass through narrow and curved microchannels with high adaptability.With these features,Ebots are able to execute multiple tasks,such as targeted drug delivery,selective removal of diseased cells in intestinal mucosa,as well as photodynamic therapy.This light-controlled Ebot provides a new bio-microrobotic tool,with many new possibilities for biomedical task execution in narrow and complicated spaces where conventional tools are difficult to access due to the lack of deformability and bio-adaptability.

On-chip readout plasmonic mid-IR gas sensor

Gas identification and concentration measurements are important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change.Here a novel mid-IR plasmonic gas sensor with on-chip direct readout is proposed based on unity integration of narrowband spectral response,localized field enhancement and thermal detection.A systematic investigation consisting of both optical and thermal simulations for gas sensing is presented for the first time in three sensing modes including refractive index sensing,absorption sensing and spectroscopy,respectively.It is found that a detection limit less than 100 ppm for CO2 could be realized by a combination of surface plasmon resonance enhancement and metal-organic framework gas enrichment with an enhancement factor over 8000 in an ultracompact optical interaction length of only several microns.Moreover,on-chip spectroscopy is demonstrated with the compressive sensing algorithm via a narrowband plasmonic sensor array.An array of 80 such sensors with an average resonance linewidth of 10 nm reconstructs the CO2 molecular absorption spectrum with the estimated resolution of approximately 0.01 nm far beyond the state-of-the-art spectrometer.The novel device design and analytical method are expected to provide a promising technique for extensive applications of distributed or portable mid-IR gas sensor.

Broad-band spatial light modulation with dual epsilon-near-zero modes

Epsilon-near-zero(ENZ)modes have attracted extensive interests due to its ultrasmall mode volume resulting in ex-tremely strong light-matter interaction(LMI)for active optoelectronic devices.The ENZ modes can be electrically toggled between on and off states with a classic metal-insulator-semiconductor(MIS)configuration and therefore allow access to electro-absorption(E-A)modulation.Relying on the quantum confinement of charge-carriers in the doped semiconductor,the fundamental limitation of achieving high modulation efficiency with MIS junction is that only a nanometer-thin ENZ confinement layer can contribute to the strength of E-A.Further,for the ENZ based spatial light modulation,the require-ment of resonant coupling inevitably leads to small absolute modulation depth and limited spectral bandwidth as restric-ted by the properties of the plasmonic or high-Q resonance systems.In this paper,we proposed and demonstrated a dual-ENZ mode scheme for spatial light modulation with a TCOs/dielectric/silicon nanotrench configuration for the first time.Such a SIS junction can build up two distinct ENZ layers arising from the induced charge-carriers of opposite polar-ities adjacent to both faces of the dielectric layer.The non-resonant and low-loss deep nanotrench framework allows the free space light to be modulated efficiently via interaction of dual ENZ modes in an elongated manner.Our theoretical and experimental studies reveal that the dual ENZ mode scheme in the SIS configuration leverages the large modulation depth,extended spectral bandwidth together with high speed switching,thus holding great promise for achieving electric-ally addressed spatial light modulation in near-to mid-infrared regions.

Phase-controlled van der Waals growth of wafer-scale 2D MoTe_(2) layers for integrated high-sensitivity broadband infrared photodetection

Being capable of sensing broadband infrared(IR)light is vitally important for wide-ranging applications from fundamental science to industrial purposes.Two-dimensional(2D)topological semimetals are being extensively explored for broadband IR detection due to their gapless electronic structure and the linear energy dispersion relation.However,the low charge separation efficiency,high noise level,and on-chip integration difficulty of these semimetals significantly hinder their further technological applications.Here,we demonstrate a facile thermal-assisted tellurization route for the van der Waals(vdW)growth of wafer-scale phase-controlled 2D MoTe_(2)layers.Importantly,the type-ⅡWeyl semimetal 1T'-MoTe_(2)features a unique orthorhombic lattice structure with a broken inversion symmetry,which ensures efficient carrier transportation and thus reduces the carrier recombination.This characteristic is a key merit for the well-designed 1T'-MoTe_(2)/Si vertical Schottky junction photodetector to achieve excellent performance with an ultrabroadband detection range of up to 10.6μm and a large room temperature specific detectivity of over 108 Jones in the mid-infrared(MIR)range.Moreover,the large-area synthesis of 2D MoTe_(2)layers enables the demonstration of high-resolution uncooled MIR imaging capability by using an integrated device array.This work provides a new approach to assembling uncooled IR photodetectors based on 2D materials.

RSPSSL:A novel high-fidelity Raman spectral preprocessing scheme to enhance biomedical applications and chemical resolution visualization

Raman spectroscopy has tremendous potential for material analysis with its molecular fingerprinting capability in many branches of science and technology.It is also an emerging omics technique for metabolic profiling to shape precision medicine.However,precisely attributing vibration peaks coupled with specific environmental,instrumental,and specimen noise is problematic.Intelligent Raman spectral preprocessing to remove statistical bias noise and sample-related errors should provide a powerful tool for valuable information extraction.Here,we propose a novel Raman spectral preprocessing scheme based on self-supervised learning(RSPSSL)with high capacity and spectral fidelity.It can preprocess arbitrary Raman spectra without further training at a speed of~1900 spectra per second without human interference.The experimental data preprocessing trial demonstrated its excellent capacity and signal fidelity with an 88%reduction in root mean square error and a 60%reduction in infinite norm(L__(∞))compared to established techniques.With this advantage,it remarkably enhanced various biomedical applications with a 400%accuracy elevation(ΔAUC)in cancer diagnosis,an average 38%(few-shot)and 242%accuracy improvement in paraquat concentration prediction,and unsealed the chemical resolution of biomedical hyperspectral images,especially in the spectral fingerprint region.It precisely preprocessed various Raman spectra from different spectroscopy devices,laboratories,and diverse applications.This scheme will enable biomedical mechanism screening with the label-free volumetric molecular imaging tool on organism and disease metabolomics profiling with a scenario of high throughput,cross-device,various analyte complexity,and diverse applications.

Manipulation and detection of single nanoparticles and biomolecules by a photonic nanojet

Optical methods to manipulate and detect nanoscale objects are highly desired in both nanomaterials and molecular biology fields.Optical tweezers have been used to manipulate objects that range in size from a few hundred nanometres to several micrometres.The emergence of near-field methods that overcome the diffraction limit has enabled the manipulation of objects below 100 nm.A highly free manipulation with signal-enhanced real-time detection,however,remains a challenge for single sub-100-nm nanoparticles or biomolecules.Here we show an approach that uses a photonic nanojet to perform the manipulation and detection of single sub-100-nm objects.With the photonic nanojet generated by a dielectric microlens bound to an optical fibre probe,three-dimensional manipulations were achieved for a single 85-nm fluorescent polystyrene nanoparticle as well as for a plasmid DNA molecule.Backscattering and fluorescent signals were detected with the enhancement factors up to~103 and~30,respectively.The demonstrated approach provides a potentially powerful tool for nanostructure assembly,biosensing and single-biomolecule studies.

Surface enhanced Raman scattering of gold nanoparticles aggregated by a gold-nanofilm-coated nanofiber

Aggregation of metal nanoparticles plays an important role in surface enhanced Raman scattering(SERS). Here, a strategy of dynamically aggregating/releasing gold nanoparticles is demonstrated using a gold-nanofilm-coated nanofiber, with the assistance of enhanced optical force and plasmonic photothermal effect. Strong SERS signals of rhodamine 6 G are achieved at the hotspots formed in the inter-particle and film-particle nanogaps. The proposed SERS substrate was demonstrated to have a sensitivity of 10-12 M, reliable reproducibility, and good stability.

Light-induced thermal convection for collection and removal of carbon nanotubes

Carbon nanotubes(CNTs)have exhibited immense potential for applications in biology and medicine,and once their intended purpose is fulfilled,the elimination of residual CNTs is essential to avoid negative effects.In this study,we demonstrated the effective collection and simple removal of CNTs dispersed in a suspension via thermal convection.First,a tapered fiber tip with a cone angle and end diameter of 10°and 3μm,respectively,was fabricated via a heating and pulling method.Further,a laser beam with a power and wavelength of 100 mW and 1.55^m,respectively,was launched into the tapered fiber tip,which was placed in a CNT suspension,resulting in the formation of a microbubble on the fiber tip.The temperature gradient on the microbubble and suspension surface induced thermal convection in the suspension,which resulted in the accumulation of CNTs on the fiber tip.The experimentally formed CNT cluster possessed a circular top surface with a diameter of 87 nm and an arched cross-section with a height of 19μm.Furthermore,this CNT cluster was firmly attached to the fiber tip.Therefore,the removal of CNT clusters can be realized by simply removing the fiber tip from the suspension.Moreover,we simulated the thermal convection that caused CNT aggregation.The obtained results indicate that convection near the fiber tip flows toward it,which pushes the CNTs toward the fiber tip and enables their attachment to it.Further,the flow velocity is symmetrically distributed as a Gaussian function,which results in the formation of a circular top surface and arched cross-sectional profile for the CNT cluster.Our method may be applied in biomedicine for the collection and removal of nano-drug residues.

The complex Maxwell stress tensor theorem:The imaginary stress tensor and the reactive strength of orbital momentum.A novel scenery underlying electromagnetic optical forces

We uncover the existence of a universal phenomenon concerning the electromagnetic optical force exerted by light or other electromagnetic waves on a distribution of charges and currents in general,and of particles in particular.This conveys the appearence of underlying reactive quantities that hinder radiation pressure and currently observed timeaveraged forces.This constitutes a novel paradigm of the mechanical effciency of light on matter,and completes the landscape of the optical,and generally electromagnetic,force in photonics and classical electrodynamics;widening our understanding in the design of both llumination and particles in optical manipulation without the need of increasing the illuminating power,and thus lowering dissipation and heating.We show that this may be accomplished through the minimization of what we establish as the reactive strength of orbital(or canonical)momentum,which plays against the optical force a role analogous to that of the reactive power versus the radiation effciency of an antenna.This long time overlooked quantity,important for current progress of optical manipulation,and that stems from the complex Maxwell theorem of conservation of complex momentum that we put forward,as well as its alternating flow associated to the imaginary part of the complex Maxwell stress tensor,conform the imaginary Lorentz force that we introduce in this work,and that like the reactive strength of orbital momentum,is antagonistic to the well-known time-averaged force;thus making this reactive Lorentz force indirectly observable near wavelengths at which the time-averaged force is lowered.The Minkowski and Abraham momenta are also addressed.

On-chip ultrasensitive and rapid hydrogen sensing based on plasmon-induced hot electron-molecule interaction

Hydrogen energy is a zero-carbon replacement for fossil fuels.However,hydrogen is highly flammable and explosive hence timely sensitive leak detection is crucial.Existing optical sensing techniques rely on complex instruments,while electrical sensing techniques usually operate at high temperatures and biasing condition.In this paper an on-chip plasmonic-catalytic hydrogen sensing concept with a concentration detection limit down to 1 ppm is presented that is based on a metal-insulator-semiconductor(MIS)nanojunction operating at room temperature and zero bias.The sensing signal of the device was enhanced by three orders of magnitude at a one-order of magnitude higher response speed compared to alternative non-plasmonic devices.The excellent performance is attributed to the hydrogen induced interfacial dipole charge layer and the associated plasmonic hot electron modulated photoelectric response.Excellent agreements were achieved between experiment and theoretical calculations based on a quantum tunneling model.Such an on-chip combination of plasmonic optics,photoelectric detection and photocatalysis offers promising strategies for next-generation optical gas sensors that require high sensitivity,low time delay,low cost,high portability and flexibility.

Polychromatic full-polarization control in mid-infrared light

Objects with different shapes,materials and temperatures can emit distinct polarizations and spectral information in mid-infrared band,which provides a unique signature in the transparent window for object identification.However,the crosstalk among various polarization and wavelength channels prevents from accurate mid-infrared detections at high signal-to-noise ratio.Here,we report full-polarization metasurfaces to break the inherent eigen-polarization constraint over the wavelengths in mid-infrared.This recipe enables to select arbitrary orthogonal polarization basis at individual wavelength independently,therefore alleviating the crosstalk and efficiency degradation.A six-channel all-silicon metasurface is specifically presented to project focused mid-infrared light to distinct positions at three wavelengths,each with a pair of arbitrarily chosen orthogonal polarizations.An isolation ratio of 117 between neighboring polarization channels is experimentally recorded,exhibiting detection sensitivity one order of magnitude higher than existing infrared detectors.Remarkably,the high aspect ratio~30 of our meta-structures manufactured by deep silicon etching technology at temperature−150℃ guarantees the large and precise phase dispersion control over a broadband from 3 to 4.5μm.We believe our results would benefit the noise-immune mid-infrared detections in remote sensing and space-to-ground communications.

Interface charge separation in Cu_(2)CoSnS_(4)/ZnIn_(2)S_(4) heterojunction for boosting photocatalytic hydrogen production

The practical application of hexagonal ZnIn_(2)S_(4)(ZIS)as a visible-light photocatalyst for hydrogen(H_(2))production is hindered by rapid internal charge recombination.In this study,we successfully synthesized Cu_(2)CoSnS_(4)(CCTS)nanocrystals and loaded them onto the surface of ZIS nanosheets to create a p-n heterojunction photocatalyst.The optimized Cu_(2)CoSnS_(4)/ZnIn_(2)S_(4)(CCTS/ZIS)heterojunction exhibited a significantly higher visible-light photo-catalytic H_(2)evolution rate of 4.90 mmol·g^(-1)·h^(-1)compared to ZIS and CCTS alone.The enhanced photocatalytic efficiency was attributed to improved electron transfer and charge separation at the heterojunction interface.The formation of p-n heterojunction facilitated the accumulation of valence band electrons in ZIS and conduction band holes in CCTS,effectively suppressing the recombination of photogenerated electrons and holes.Theoretical calculations,spectroscopic,and photoelectrochemical characterizations supported the findings.This work pre-sents a promising approach for designing efficient p-n heterojunction semiconductor photocatalysts for practical applications in visible-light-driven hydrogen evolution.

Single-cell biomagnifier for optical nanoscopes and nanotweezers

Optical microscopes and optical tweezers,which were invented to image and manipulate microscale objects,have revolutionized cellular and molecular biology.However,the optical resolution is hampered by the diffraction limit;thus,optical microscopes and optical tweezers cannot be directly used to image and manipulate nano-objects.The emerging plasmonic/photonic nanoscopes and nanotweezers can achieve nanometer resolution,but the high-index material structures will easily cause mechanical and photothermal damage to biospecimens.Here,we demonstrate subdiffraction-limit imaging and manipulation of nano-objects by a noninvasive device that was constructed by trapping a cell on a fiber tip.The trapped cell,acting as a biomagnifier,could magnify nanostructures with a resolution of 100 nm(λ/5.5)under white-light microscopy.The focus of the biomagnifier formed a nano-optical trap that allowed precise manipulation of an individual nanoparticle with a radius of 50 nm.This biomagnifier provides a high-precision tool for optical imaging,sensing,and assembly of bionanomaterials.

Subwavelength imaging and detection using adjustable and movable droplet microlenses

We developed adjustable and movable droplet microlenses consisting of a liquid with a high refractive index.The microlenses were prepared via ultrasonic shaking in deionized water,and the diameter of the microlenses ranged from 1 to 50μm.By stretching the microlenses,the focal length can be adjusted from 13 to 25μm.With the assistance of an optical tweezer,controllable assembly and movement of microlens arrays were also realized.The results showed that an imaging system combined with droplet microlenses could image 80 nm beads under white light illumination.Using the droplet microlenses,fluorescence emission at 550 nm from Cd Se@Zn S quantum dots was efficiently excited and collected.Moreover,Raman scattering signals from a silicon wafer were enhanced by^19 times.The presented droplet microlenses may offer new opportunities for flexible liquid devices in subwavelength imaging and detection.

Fiber-based optical trapping and manipulation

An optical fiber serves as a versatile tool for optical trapping and manipulation owing to its many advantages over conventional optical tweezers,including ease of fabrication,compact configurations,flexible manipulation capabilities,ease of integration,and wide applicability.Here,we review recent progress in fiberbased optical trapping and manipulation,which includes mainly photothermal-based and optical-force-based trapping and manipulation.We focus on five topics in our review of progress in this area: massive photothermal trapping and manipulation,evanescent-field-based trapping and manipulation,dual-fiber tweezers for singlenanoparticle trapping and manipulation,single-fiber tweezers for single-particle trapping and manipulation,and single-fiber tweezers for multiple-particle/cell trapping and assembly.

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance (LSPR) enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts. In the past decades, noble metal nanoparticles (Au and Ag) with LSPR feature have found wide applications in solar energy conversion. Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures. However, high cost and scarce reserve of noble metals largely limit their further practical use, which drives the focus gradually shift to low-cost and abundant nonmetallic nanostructures. Recently, various heavily doped semiconductors (such as WO_(3-x), MoO_(3-x), Cu_(2-x)S, TiN) have emerged as potential alternatives to costly noble metals for efficient photocatalysis due to their strong LSPR property in visible-near infrared region. This review starts with a brief introduction to LSPR property and LSPR-enhanced photocatalysis, the following highlights recent advances of plasmonic photocatalysts from noble metal to semiconductor-based plasmonic nanostructures. Their synthesis methods and promising applicability in plasmon-driven photocatalytic reactions such as water splitting, CO_(2) reduction and pollution decomposition are also summarized in details. This review is expected to give guidelines for exploring more efficient plasmonic systems and provide a perspective on development of plasmonic photocatalysis.

Integrating the optical tweezers and spanner onto an individual single-layer metasurface

Optical tweezers(OTs)and optical spanners(OSs)are powerful tools of optical manipulation,which are responsible for particle trapping and rotation,respectively.Conventionally,the OT and OS are built using bulky three-dimensional devices,such as microscope objectives and spatial light modulators.Recently,metasurfaces are proposed for setting up them on a microscale platform,which greatly miniaturizes the systems.However,the realization of both OT and OS with one identical metasurface is posing a challenge.Here,we offer a metasurface-based solution to integrate the OT and OS.Using the prevailing approach based on geometric and dynamic phases,we show that it is possible to construct an output field,which promises a high-numerical-aperture focal spot,accompanied with a coaxial vortex.Optical trapping and rotation are numerically demonstrated by estimating the mechanical effects on a particle probe.Moreover,we demonstrate an on-demand control of the OT-to-OS distance and the topological charge possessed by the OS.By revealing the OT–OS metasurfaces,our results may empower advanced applications in on-chip particle manipulation.

Biophotonic probes for bio-detection and imaging

The rapid development of biophotonics and biomedical sciences makes a high demand on photonic structures to be interfaced with biological systems that are capable of manipulating light at small scales for sensitive detection of biological signals and precise imaging of cellular structures.However,conventional photonic structures based on artificial materials(either inorganic or toxic organic)inevitably show incompatibility and invasiveness when interfacing with biological systems.The design of biophotonic probes from the abundant natural materials,particularly biological entities such as virus,cells and tissues,with the capability of multifunctional light manipulation at target sites greatly increases the biocompatibility and minimizes the invasiveness to biological microenvironment.In this review,advances in biophotonic probes for bio-detection and imaging are reviewed.We emphatically and systematically describe biological entities-based photonic probes that offer appropriate optical properties,biocompatibility,and biodegradability with different optical functions from light generation,to light transportation and light modulation.Three representative biophotonic probes,i.e.,biological lasers,cell-based biophotonic waveguides and biomicrolenses,are reviewed with applications for bio-detection and imaging.Finally,perspectives on future opportunities and potential improvements of biophotonic probes are also provided.

MicroRNA-activated hydrogel scaffold generated by 3D printing accelerates bone regeneration

Bone defects remain a major threat to human health and bone tissue regeneration has become a prominent clinical demand worldwide.The combination of microRNA(miRNA)therapy with 3D printed scaffolds has always posed a challenge.It can mimic physiological bone healing processes,in which a biodegradable scaffold is gradually replaced by neo-tissue,and the sustained release of miRNA plays a vital role in creating an optimal osteogenic microenvironment,thus achieving promising bone repair outcomes.However,the balance between two key factors-scaffold degradation behavior and miRNA release profile-on osteogenesis and bone formation is still poorly understood.Herein,we construct a series of miRNA-activated hydrogel scaffolds(MAHSs)generated by 3D printing with different crosslinking degree to screened the interplay between scaffold degradation and miRNA release in the osteoinduction activity both in vitro and in vivo.Although MAHSs with a lower crosslinking degree(MAHS-0 and MAHS-0.25)released a higher amount of miR-29b in a sustained release profile,they degraded too fast to provide prolonged support for cell and tissue ingrowth.On the contrary,although the slow degradation of MAHSs with a higher crosslinking degree(MAHS-1 and MAHS-2.5)led to insufficient release of miR-29b,their adaptable degradation rate endowed them with more efficient osteoinductive behavior over the long term.MAHS-1 gave the most well-matched degradation rate and miR-29b release characteristics and was identified as the preferred MAHSs for accelerated bone regeneration.This study suggests that the bio-adaptable balance between scaffold degradation behavior and bioactive factors release profile plays a critical role in bone regeneration.These findings will provide a valuable reference about designing miRNAs as well as other bioactive molecules activated scaffold for tissue regeneration.

Lipid droplets as endogenous intracellular microlenses

Using a single biological element as a photonic component with well-defined features has become a new intriguing paradigm in biophotonics.Here we show that endogenous lipid droplets in the mature adipose cells can behave as fully biocompatible microlenses to strengthen the ability of microscopic imaging as well as detecting intra-and extracellular signals.By the assistance of biolenses made of the lipid droplets,enhanced fluorescence imaging of cytoskeleton,lysosomes,and adenoviruses has been achieved.At the same time,we demonstrated that the required excitation power can be reduced by up to 73%.The lipidic microlenses are finely manipulated by optical tweezers in order to address targets and perform their real-time imaging inside the cells.An efficient detecting of fluorescence signal of cancer cells in extracellular fluid was accomplished due to the focusing effect of incident light by the lipid droplets.The lipid droplets acting as endogenous intracellular microlenses open the intriguing route for a multifunctional biocompatible optics tool for biosensing,endoscopic imaging,and single-cell diagnosis.