Self-confocal NIR-II fluorescence microscopy for multifunctional in vivo imaging

Fluorescence imaging in the second near-infrared window(NIR-II,900–1880 nm)with less scattering background in biological tissues has been combined with the confocal microscopic system for achieving deep in vivo imaging with high spatial resolution.However,the traditional NIR-IIfluorescence confocal microscope with separate excitation focus and detection pinhole makes it possess low confocal e±ciency,as well as di±cultly to adjust.Two types of upgraded NIR-IIfluorescence confocal microscopes,sharing the same pinhole by excitation and emission focus,leading to higher confocal e±ciency,are built in this work.One type is-ber-pinhole-based confocal microscope applicable to CW laser excitation.It is constructed forfluorescence intensity imaging with large depth,high stabilization and low cost,which could replace multiphotonfluorescence microscopy in some applications(e.g.,cerebrovascular and hepatocellular imaging).The other type is air-pinhole-based confocal microscope applicable to femtosecond(fs)laser excitation.It can be employed not only for NIR-IIfluorescence intensity imaging,but also for multi-channelfluorescence lifetime imaging to recognize different structures with similarfluorescence spectrum.Moreover,it can be facilely combined with multiphotonfluorescence microscopy.A single fs pulsed laser is utilized to achieve up-conversion(visible multiphotonfluorescence)and down-conversion(NIR-II one-photonfluorescence)excitation simultaneously,extending imaging spectral channels,and thus facilitates multi-structure and multi-functional observation.

Oscillation of Dzyaloshinskii–Moriya interaction driven by weak electric fields

Dzyaloshinskii–Moriya interaction(DMI) is under extensive investigation considering its crucial status in chiral magnetic orders, such as Néel-type domain wall(DW) and skyrmions. It has been reported that the interfacial DMI originating from Rashba spin–orbit coupling(SOC) can be linearly tuned with strong external electric fields. In this work, we experimentally demonstrate that the strength of DMI exhibits rapid fluctuations, ranging from 10% to 30% of its original value, as a function of applied electric fields in Pt/Co/MgO heterostructures within the small field regime(< 10-2V/nm). Brillouin light scattering(BLS) experiments have been performed to measure DMI, and first-principles calculations show agreement with this observation, which can be explained by the variation in orbital hybridization at the Co/MgO interface in response to the weak electric fields. Our results on voltage control of DMI(VCDMI) suggest that research related to the voltage control of magnetic anisotropy for spin–orbit torque or the motion control of skyrmions might also have to consider the role of the external electric field on DMI as small voltages are generally used for the magnetoresistance detection.

Oxidative exfoliation of spent cathode carbon:A two-in-one strategy for its decontamination and high-valued application

Spent cathode carbon(SCC)from aluminum electrolysis is a potential graphite resource.However,full use of the SCC remains a challenge,since it contains many hazardous substances(e.g.,fluoride salts,cyanides),encapsulated within the thick carbon layers and thus posing serious environmental concerns.This work presents a chemical oxidative exfoliation route to achieve the recycling of SCC and the decontaminated SCC with high-valued graphene oxide(GO)-like carbon structures(SCC-GO)is applied as an excellent adsorbent for organic pollutants.Specifically,after the oxidative exfoliation,the embedded hazardous constituents are fully exposed,facilitating their subsequent removal by aqueous leaching.Moreover,benefiting from the enhanced specific surface areas along with abundant O-containing functional groups,the as-produced SCC-GO,shows an adsorption capacity as high as 347 mg·g^(-1)when considering methylene blue as a pollutant model,which exceeds most of the recently reported carbon-based adsorbents.Our study provides a feasible solution for the efficient recycling of hazardous carbonaceous wastes.

Ultra-stable near-infrared Tm^(3+)-doped upconversion nanoparticles for in vivo wide-field two-photon angiography with a low excitation intensity

Two-photon luminescence with near-infrared(NIR)excitation of upconversion nanoparticles(NPs)is of great importance in biological imaging due to deep penetration in high-scattering tissues,low auto-luminescence and good sectioning ability.Unfortunately,common two-photon luminescence is in visible band with an extremely high exciation power density,which limits its application.Here,we synthesized NaYF_(4):Yb/Tm@NaYF_(4)upconversion NPs with strong twophoton NIR emission and a low excitation power density.Furthermore,NaYF_(4):Yb/Tm@NaYF_(4)@SiO_(2)@OTMS@F127 NPs with high chemical stability were obtained by a modified multilayer coating method which was applied to upconversion NPs for thefirst time.In addition,it is shown that the as-prepared hydrophillic upconversion NPs have great biocompatibility and kept stable for 6 hours during in vivo whole-body imaging.The vessels with two-photon luminescence were clear even under an excitation power density as low as 25mW/cm^(2).Vivid visualizations of capillaries and vessels in a mouse brain were also obtained with low background and high contrast.Because of cheaper instruments and safer power density,the NIR two-photon luminescence of NaYF_(4):Yb/Tm@NaYF_(4)upconversion NPs could promote wider application of two-photon technology.The modified multilayer coating method could be widely used for upconversion NPs to increase the stable time of the in vivo circulation.Our work possesses a great potential for deep imaging and imaging-guided treatment in the future.

Shedding light on the reversible deactivation of carbon-supported single-atom catalysts in hydrogenation reaction

Carbon-supported single-atom catalysts were found to suffer reversible deactivation in catalytic hydrogenation,but the mechanism is still unclear.Herein,nitro compounds hydrogenation catalyzed by N-doped carbon-supported Co single atom(Co1/NC)was taken as a model to uncover the mechanism of the reversible deactivation phenomenon.Co1/NC exhibited moderate adsorption towards the substrate molecules(i.e.,nitro compounds or related intermediates),which could be strengthened by the confinement effect from the porous structure.Consequently,substrate molecules tend to accumulate within the pore channel,especially micropores that host Co1,making it difficult for the reactants to access the active sites and finally leading to their deactivation.The situation could be even worse when the substrate molecules possess a large size.Nevertheless,the catalytic activity of Co1/NC could be restored via a simple thermal treatment,which could remove the adsorbates within the pore channel,hence releasing active sites that were originally inaccessible to reactants.

An integrated thermoelectric-assisted photoelectrochemical system to boost water splitting

Common solar-driven photoelectrochemical(PEC) cells for water splitting were designed by using semiconducting photoactive materials as working photoelectrodes to capture sunlight. Due to the thermodynamic requirement of 1.23 eV and kinetic energy loss of about 0.6 eV, a photo-voltage of 1.8 V produced by PEC cells is generally required for spontaneous water splitting. Therefore, the minimum bandgap of1.8 eV is demanded for photoactive materials in single-photoelectrode PEC cells, and the bandgap of about 1 eV for back photoactive materials is appropriate in tandem PEC cells. All these PEC cells cannot effectively utilize the infrared light from 1250 to 2500 nm. In order to realize the full spectrum utilization of solar light, here, we develop a solar-driven PEC water splitting system integrated with a thermoelectric device. The key feature of this system is that the thermoelectric device produces a voltage as an additional bias for the PEC system by using the temperature difference between the incident infrared-light heated aqueous electrolyte in the PEC cell as the hot source and unirradiated external water as the cold source. Compared to a reference PEC system without the thermoelectric device, this system has a significantly improved overall water splitting activity of 1.6 times and may provide a strategy for accelerating the application of full spectrum solar light-driven PEC cells for hydrogen production.

Quantum dots assisted in vivo two-photon microscopy with NIR-Ⅱemission

With the advantages of high resolution and deep penetration depth,two-photon excited NIR-Ⅱ(900–1880 nm)fluorescence(2PF)microscopic bioimaging is promising.However,due to the lack of imaging systems and suitable probes,few such works,to our best knowledge,were demonstrated utilizing NIR-II excitation and NIR-Ⅱfluorescence simultaneously.Herein,we used aqueously dispersible Pb S/Cd S quantum dots with bright NIR-II fluorescence as the contrast agents.Under the excitation of a 1550 nm femtosecond(fs)laser,they emitted bright 2 PF in the NIR-Ⅱregion.Moreover,a 2PF lifetime imaging microscopic(2PFLIM)system was implemented,and in vivo 2PFLIM images of mouse brain blood vessels were obtained for the first time to our best knowledge.To improve imaging speed,an in vivo two-photon fluorescence microscopy(2 PFM)system based on an In Ga As camera was implemented,and in vivo 2PFM images of QDs-stained mouse brain blood vessels were obtained.

Digital light processing 3D printing for microfluidic chips with enhanced resolution via dosing-and zoning-controlled vat photopolymerization

Conventional manufacturing techniques to fabricate microfluidic chips,such as soft lithography and hot embossing process,have limitations that include difficulty in preparing multiple-layered structures,cost-and labor-consuming fabrication process,and low productivity.Digital light processing(DLP)technology has recently emerged as a costefficient microfabrication approach for the 3D printing of microfluidic chips;however,the fabrication resolution for microchannels is still limited to sub-100 microns at best.Here,we developed an innovative DLP printing strategy for high resolution and scalable microchannel fabrication by dosing-and zoning-controlled vat photopolymerization(DZC-VPP).Specifically,we proposed a modified mathematical model to precisely predict the accumulated UV irradiance for resin photopolymerization,thereby providing guidance for the fabrication of microchannels with enhanced resolution.By fine-tuning the printing parameters,including optical irradiance,exposure time,projection region,and step distance,we can precisely tailor the penetration irradiance stemming from the photopolymerization of the neighboring resin layers,thereby preventing channel blockage due to UV overexposure or compromised bonding stability owing to insufficient resin curing.Remarkably,this strategy can allow the preparation of microchannels with cross-sectional dimensions of 20μm×20μm using a commercial printer with a pixel size of 10μm×10μm;this is significantly higher resolution than previous reports.In addition,this method can enable the scalable and biocompatible fabrication of microfluidic drop-maker units that can be used for cell encapsulation.In general,the current DZC-VPP method can enable major advances in precise and scalable microchannel fabrication and represents a significant step forward for widespread applications of microfluidics-based techniques in biomedical fields.

Constructing CdSe QDs modified porous g-C_(3)N_(4)heterostructures for visible light photocatalytic hydrogen production

Constructing heterostructures with narrow-band-gap semiconductors is a promising strategy to extend light absorption range of graphitic carbon nitride(g-C_(3)N_(4))and simultaneously promote charge separation for its photocatalytic activity improvement.However,its highly localized electronic states of g-C_(3)N_(4)hinder photo-carrier migration through bulk towards heterostructure interfaces,resulting in low charge carrier separation efficiency of solid bulk g-C_(3)N_(4)-based heterostructures.Herein,porous g-C_(3)N_(4)(PCN)material with greatly shortened migration distance of photo-carriers from bulk to surface was used as an effective substrate to host Cd Se quantum dots to construct type II heterostructure of Cd Se/PCN for photocatalytic hydrogen production.The homogeneous modification of the Cd Se quantum dots throughout the whole bulk of PCN together with proper band alignments between Cd Se and PCN enables the effective separation of photo-generated charge carriers in the heterostructure.Consequently,the Cd Se/PCN heterostructure photocatalyst gives the greatly enhanced photocatalytic hydrogen production activity of192.3μmol h^(-1),which is 4.4 and 8.1 times that of Cd Se and PCN,respectively.This work provides a feasible strategy to construct carbon nitride-based heterostructure photocatalysts for boosting visible light driven water splitting performance.