High-quality quasi-bound state in the continuum enabled single-nanoparticle virus detection.

Bound states in the continuum (BICs) have emerged as a powerful platform for boosting light-matter interactions because they provide an alternative way of realizing optical resonances with ultrahigh quality(Q-) factors, accompanied by extreme field confinement. In this work, we realized an optical biosensor by introducing a quasi-BIC (qBIC) supported by an elaborated all-dielectric dimer grating. Thanks to the excellent field confinement within the air gap of grating enabled by such a high-Q qBIC, the figure of merit (FOM) of a biosensor is up to 18,908.7 RIU-1. Furthermore, we demonstrated that such a high-Q grating can help push the limit of optical biosensing to the single-particle level. Our results may find exciting applications in extreme biochemical sensing like COVID-19 with ultralow concentration.

Efficient monodisperse upconversion composite prepared using high-density local field and its dual-mode temperature sensing.

Enhanced upconversion via plasmonics has considerable potential in biosensors and solar cells; however, conventional plasmonic configurations such as core-shell assemblies or nanoarray platforms still suffer from the compromise between the enhancement factor and monodispersity, which has failed to meet the requirement of the materials for the in vivo all-solution-prepared solar cells and biosensors. We herein report a monodisperse metal-dielectric-metal (MDM) type upconverted hybrid material with high efficiency. The lanthanide-doped upconversion nanoparticles (UCNPs) were sandwiched by two gold nanodisk mirrors, and the highly localized excitation field around the UCNPs together with the efficient coupling enhanced the upconversion. The upconversion intensity can then be effectively regulated and improved by three to four orders of magnitude. As per the measurement of the temperature-dependent fluorescence intensity and spectra shift, a dual-mode nanothermometer based on our proposed hybrid materials was demonstrated. This MDM-type upconverted hybrid material demonstrated the merits of high efficiency and monodispersity, which demonstrated promise in in vivo biosensors and solar cell fabrication techniques such as spin-coating and roll-to-roll.

Organophosphorus-Catalyzed Direct Dehydroxylative Thioetherification of Alcohols with Hypervalent Organosulfur Compounds.

A metal-free and thiol-free organophosphorus-catalyzed method for forming thioethers was disclosed, driven by PIII/PV═O redox cycling. In this work, one-step dehydroxylative thioetherification of alcohols was fulfilled with various hypervalent organosulfur compounds. This established strategy features an excellent functional group tolerance and broad substrate scope, especially inactivated alcohols. The scale-up reaction and further transformation of the product were also successful. Additionally, this method offers a protecting-group-free and step-efficient approach for synthesizing peroxisome proliferator-activated receptor agonists which exhibited promising potential for treating osteoporosis in mammals.

Ultrastrong Infrared Emission at 1460 nm from Lanthanide-Doped Nanoparticles with Interfacial Sensitization.

Fluorescent imaging in the second near-infrared window (NIR-II; 1000-1700 nm) has recently received tremendous attention due to its excellent tissue probing depths and high resolution. Under NIR pumping, lanthanide-doped nanoparticles can emit infrared light covering a wide range of 800-3000 nm which has good potential for NIR-II imaging and detection. However, the low efficiency hinders their application. Here, we report intense infrared emission at 1460 nm from lanthanide-doped core/shell nanoparticles with efficient interfacial sensitization. The emitter Tm3+ ion and the sensitizer Yb3+ and Nd3+ ions are spatially separated in core and shells so that the efficient interfacial energy transfer is established between Tm3+ and Yb3+/Nd3+ ions, while thermal vibration spread of high concentration of Yb3+ ions and cross-relaxation among Tm3+, Yb3+, and Nd3+ ions are suppressed. As a result, the ultrastrong NIR-II emission at 1460 nm is achieved, which is more than 100-times that in classic core/shell nanoparticles doped with Tm3+ (NaYF4:20%Yb,0.5%Tm@ NaYF4).

An optical strategy for detecting hypochlorite in vitro and cells with high selectivity and stability based on a lanthanide-doped upconversion probe.

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans. More importantly, owing to hypochlorite being a biomarker of immune responses in living organisms, its abnormal production can damage nucleic acids and protein molecules, eventually causing many diseases (even cancer). Exploring a reliable, rapid, and non-invasive method to monitor the hypochlorite level in vitro and in cells can be significant. Herein, we report a novel ratiometric fluorescence sensing strategy based on Astrazon Brilliant Red 4G dye-sensitized NaGdF4:Yb3+, Er3+@NaYF4 core-shell upconversion nanoparticles (UCNPs@ABR 4G). Based on the combination mechanism of the fluorescent resonant energy transfer effect (FRET) and redox, a linear model of fluorescence intensity ratio and hypochlorite concentration was constructed for a fast response and high selectivity monitoring of hypochlorite in vitro and in vivo. The detection limit was calculated to be 0.39 µM. In addition, this sensing strategy possessed good stability and circularity, making it valuable both for the quantitative detection of hypochlorite in water and for the visualization of intracellular hypochlorite. The proposed optical probe is promising for the efficient and stable non-invasive detection of hypochlorite.

Manipulating Energy Transfer in UCNPs@SiO2@Ag Nanoparticles for Efficient Infrared Photocatalysis.

Conventional photocatalysts must be activated by ultraviolet or visible light to meet the energy requirement of populating an initial excited state, while infrared light has a high penetration depth to reaction media but does not have enough photon energy to activate conventional photocatalysts. Here, we report the activation of Ag nanoparticles by upconversion nanoparticles (UCNPs) in UCNPs@SiO2@Ag with manipulated energy transfer for infrared photocatalysis. UCNPs can efficiently convert infrared light to visible and ultraviolet light and are very ideal candidates for bridging the advantage of infrared light and the activation energy requirement of conventional photocatalysts. In the UCNPs@SiO2@Ag nanosystem, we employ the UCNPs to activate conventional Ag nanoparticles under infrared light irradiation. The evanescent field of UCNPs is confined for enhancing the near-field energy-transfer efficiency using a designed core/shell heterostructure, while a SiO2 layer is used for blocking the phonon exchange of thermal vibration between photon upconverters and Ag nanoparticles. Based on the manipulated energy transfer, UCNPs@SiO2@Ag nanoparticles exhibit efficient photocatalytic activity under the irradiation of 980 nm infrared light, while single Ag nanoparticles have negligible catalytic activity under infrared irradiation.

Nanoscale Ultrasensitive Temperature Sensing Based on Upconversion Nanoparticles with Lattice Self-Adaptation.

Upconversion nanoparticles have recently received increasing attention due to their outstanding performance in temperature sensing at the nanoscale. Although much effort has been devoted to improve their thermal sensitivity, there is no efficient way for achieving significant enhancement. Here, we show that lattice self-adaptation can unlock a new route for remarkably enhancing the thermal sensitivity of upconversion nanoparticles. The thermally sensitive fluorescence intensity ratio (FIR) of the dopant Er3+ is used for indicating the temperature variation, while a heterojunction of NaGdF4/NaYF4 is prepared as host material to produce a lattice distortion at the interface which is also sensitive to temperature. With the increase of temperature, the FIR of the transitions 2H11/2/4S3/2 → 4I15/2 increases, accompanied by the self-adapted decrease of interface lattice distortion that leads to the additional increase in FIR. Using core/shell upconversion nanoparticles with lattice self-adaptation, we achieve an enhanced thermal sensitivity three times higher than core-only nanoparticles.

Nanoporous fluorescent sensor based on upconversion nanoparticles for the detection of dichloromethane with high sensitivity.

A sensor with high sensitivity and response rate is still lacking in the detection of poisonous and volatile chemicals. Here, we report a highly sensitive nanoporous fluorescence sensor based on core@shell upconversion nanoparticles (UCNPs) for the detection of dichloromethane. UCNPs were deposited on porous anodic alumina oxide (AAO) templates supported by glass slides to form a thin film-like gas sensor in which UCNPs with active shells exhibit intense background-free fluorescence and simultaneously high optical sensitivity, while an AAO template acts as a porous substrate for UCNPs to increase the absorption capacity for molecules to be tested. A detection limit of 2.91 ppm was obtained for dichloromethane based on this sensor at room temperature. The involved response mechanism was attributed to lowered surface fluorescence quenching and scattering of UCNPs by dichloromethane.

Mechanistic Analysis of Embedded Copper Oxide in Organic Thin-Film Transistors with Controllable Threshold Voltage.

The modulation of threshold voltage (V TH) of organic thin-film transistors (OTFTs) was investigated by embedding a thin CuO layer between the two semiconductor layers. The results showed that the V TH of OTFTs with a CuO layer can be effectively tuned by controlling the positive gate-to-source voltage (V GS0) under stress of gate-to-source voltages. The V TH shifts from -3.67 to -0.82 V when the positive V GS0 varies from 30 to 50 V. This can be explained by the mechanism of trapping electrons at the interface between the CuO charge-separation layer and the active layer. To confirm the role of the CuO layer acting as the charge-separation source, two organic thin-film diodes, indium-tin oxide(ITO)/tris (8-quinolinolato) aluminum(III) (Alq3)/pentacene/Al (inverted-stack diode) and ITO/Alq3/CuO/pentacene/Al (inverted-stack diode with a CuO layer), were fabricated and their diode current characteristics were measured. For the second device, a large current flow was observed at positive bias on the ITO electrodes, which is ascribed to the internal bipolar charge separation within the added CuO zone.

Preparation and in vitro release kinetics of nitrendipine-loaded PLLA-PEG-PLLA microparticles by supercritical solution impregnation process.

In this work, drug-loaded polymer microparticles were prepared by a supercritical solution impregnation (SSI) process with nitrendipine as the model drug and PLLA-PEG-PLLA as the drug carrier. The morphology, size, distribution and functional groups of the drug-loaded microparticles were characterized by scanning electron microscopy (SEM), laser particle size analyzer and fourier transform infrared analysis (FTIR). The effects of pressure, temperature and cosolvent concentration on the drug loading and release property of the microparticles prepared with and without cosolvent were investigated. The in vitro drug release kinetics of drug-loaded microparticles was studied with five models. The results indicated that the morphology of the drug-loaded polymer microparticles was not influenced by the SSI process. And the addition of ethanol cosolvent could significantly improve the drug loading of the microparticles. The most satisfied drug loading and the release properties of the microparticles were achieved under 55 °C, 13 MPa and cosolvent ethanol concentration of 3%. The drug could be released for more than 140 h. The analysis of the drug release kinetics showed that the experimental data fitted with Ritger-Peppas model were optimal. According to the release exponent value, the in vitro release process of the nitrendipine-loaded microparticles was controlled by Fickian diffusion, which can provides a theoretical basis for drug release of this type of experiment.

Upconversion core/shell nanoparticles with lowered surface quenching for fluorescence detection of Hg2+ ions.

In this study, we reported a fluorescent nanoprobe assembled with upconversion core/shell nanoparticles and a chromophore ruthenium complex (N719@UCNPs). Functional groups (NCS) of the ruthenium complex N719 could react with Hg2+, which made N719 lose the efficacy in quenching the fluorescence of upconversion nanoparticles (UCNPs) and resulted in the recovery of the fluorescence intensity of UCNPs eventually. This fluorescent nanoprobe could provide a rapid and efficient detection of Hg2+ ions in vivo based on the fluorescence resonance energy transfer (FRET) between UCNPs and N719, and a detection limit of 0.1 µg mL-1 can be achieved based on this nanoprobe. It's worth mentioning that, compared with bare core upconversion nanoparticles, the core/shell UCNPs could greatly reduce the surface quenching of the fluorescence induced by solvents instead of N719, thus leading to the enhancement of signal-to-noise ratios. Moreover, the excitation of core/shell UCNPs requires a much lower power (0.06 W cm-2) than that of bare cores, which is beneficial for reducing the decomposition of N719 to stabilize the FRET processes.

Core/shell upconversion nanoparticles with intense fluorescence for detecting doxorubicin in vivo.

Doxorubicin (Dox) is a chemotherapy medication used to treat cancer. Herein, we report a rapid and efficient method for detecting Dox in vivo based on a NaGdF4:Yb3+,Er3+@NaYF4 core/shell upconversion nanoparticles (UCNPs) probe. We found that the intensity ratio of green to red emission (IGVRE) bands of the core/shell NaGdF4:Yb3+,Er3+@NaYF4 nanoparticles was sensitive to Dox in blood samples, and drops as the concentration of Dox increases. In addition, the proposed UCNPs probe possessed the advantage that no nanoparticles leaked into the living body, thus overcoming the intrinsic defect (difficulty in removing UCNPs from blood vessels) of the fluorescence resonance energy transfer (FRET) approach. This proposed UCNP probe design and results may provide some guidance for the real-time and efficient detection of Dox, and can be helpful in biomedical applications.

Correction: Core/shell upconversion nanoparticles with intense fluorescence for detecting doxorubicin in vivo.

[This corrects the article DOI: 10.1039/C8RA02928H.].

Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels.

The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration.

Plasma optical modulation for lasers based on the plasma induced by femtosecond pulses.

We present a theoretical and experimental study of plasma optical modulation for probe lasers based on the plasma induced by pump pulses. This concept relies on two co-propagating laser pulses in carbon disulfide, where a drive laser pulse first excites plasma channels while a following carrier laser pulse is modulated by the plasma. The modulation on the probe beam can be conveniently adjusted through electron density, plasma width, propagation distance of plasma, the power of pump lasers, or the pump beam's profile. The experimental results and theoretical solutions are very consistent, which fully illustrates that this method for plasma optical modulation is reasonable. This pump-probe method is also a potential measurement technique for inferring the on-axis plasma density shape.

Magnetic tuning of upconversion luminescence in Au/NaGdF4:Yb3+/Er3+ nanocomposite.

Lanthanide-doped upconversion nanoparticles (UCNPs) NaGdF4:Yb3+/Er3+ have received increasing attention due to their unique optical-magnetic bifunctional properties. Here, we show that the luminescent intensity from NaGdF4:Yb3+/Er3+ nanoparticles decreases monotonously with increasing the applied magnetic field from 0 to 37.1 T, while plasmon-enhanced upconversion luminescence in Au/NaGdF4:Yb3+/Er3+ nanocomposite is independent of a magnetic field lower than 6 T. The surface plasmon resonances could compensate for the energetic mismatching between the excitation light and the energy-level gaps induced by magnetic field and enhance the radiative efficiency, which is the main factor for achieving this stable upconversion emission in this nanocomposite under a magnetic field not higher than 6 T. These findings provide a novel route for exploring the magnetic control of upconversion luminescence in lanthanide-doped bifunctional nanoparticles.

Theoretical analysis and applications in inverse T-shape structure.

An inverse T-shape structure, consisting of a bus waveguide coupled with two perpendicular rectangular cavities, has been investigated numerically and theoretically. The position of the transparency window can be manipulated by adjusting the lateral displacement between the two perpendicular cavities. The effects of changing different structural parameters on the transmission features are investigated in detail. The results indicate that the length of two cavities play important roles in optimizing optical response. Finally, two simple applications based on the inverse T-shape structure are briefly discussed. The findings demonstrate that the first- and second-order modes can be separated without interference, and the sensitivity of the inverse T-shape is as high as 1750 nm per refractive index unit (RIU); the corresponding figure of merit (FOM) reaches up to 77.1 RIU-1, which is higher than in previous reports. The plasmonic configuration possesses the advantages of easy fabrication, compactness, and higher sensitivity as well as higher FOM, which will greatly benefit the compact plasmonic filter and high-sensitivity nanosensor in highly integrated optical devices.

Tunable high quality factor in two multimode plasmonic stubs waveguide.

We numerically investigate the optical characteristics of a metal-dielectric-metal (MDM) waveguide side-coupled with two identical multimode stub resonators. Double plasmon-induced transparency (PIT) peaks with narrow full width at half maximum (FWHM) and high quality factor (Q-factor) can be observed in this structure. The Q-factors of PIT peaks in two stub resonators system are larger than those in single stub resonator system. A multimode coupled-radiation oscillator theory (MC-ROT), which is derived from ROT, is proposed to analyze the spectral response in the multimode system for the first time. The analytical results are confirmed by the finite-difference time-domain (FDTD) simulation results. We can also find that the Q-factors of the two PIT peaks have an opposite evolution tendency with the change of the stubs parameters and the maximum can reach to 427. These results may provide some applications for ultrasensitive sensors, switches and efficient filters.

Tunable nanoplasmonic sensor based on the asymmetric degree of Fano resonance in MDM waveguide.

We first report a simple nanoplasmonic sensor for both universal and slow-light sensing in a Fano resonance-based waveguide system. A theoretical model based on the coupling of resonant modes is provided for the inside physics mechanism, which is supported by the numerical FDTD results. The revealed evolution of the sensing property shows that the Fano asymmetric factor p plays an important role in adjusting the FOM of sensor, and a maximum of ~4800 is obtained when p = 1. Finally, the slow-light sensing in such nanoplasmonic sensor is also investigated. It is found that the contradiction between the sensing width with slow-light (SWS) and the relevant sensitivity can be resolved by tuning the Fano asymmetric factor p and the quality factor of the superradiant mode. The presented theoretical model and the pronounced features of this simple nanoplasmonic sensor, such as the tunable sensing and convenient integration, have significant applications in integrated plasmonic devices.

Tunable Multi-switching in Plasmonic Waveguide with Kerr Nonlinear Resonator.

We propose a nanoplasmonic waveguide side-coupled with bright-dark-dark resonators in our paper. A multi-oscillator theory derived from the typical two-oscillator model, is established to describe spectral features as well as slow-light effects in bright-dark-dark structures, and confirmed by the finite-difference time domain (FDTD). That a typical plasmon induced transparency (PIT) turns to double PIT spectra is observed in this waveguide structure. At the same time, multi-switching effects with obvious double slow-light bands based on double PIT are also discovered in our proposed structure. What's more, dynamically tuning the multi-switching is achieved by means of filling Fabry-Perot resonators with the Kerr nonlinear material Ag-BaO. These results may have applications in all-optical devices, moreover, the multi-oscillator theory may play a guiding role in designing plasmonic devices.