7-aminocephalosporanic acid, a novel HSP90ß inhibitor, attenuates HFD-induced hepatic steatosis.

Hepatic steatosis is one of the most important causes of liver disease worldwide. Heat shock protein 90 (HSP90) is essential for numerous client proteins. Recently, more attention was focused on increased HSP90 levels in hepatic steatosis, especially HSP90ß. Thus, great efforts have been made to develop HSP90ß inhibitors, and most natural inhibitors are derived from microorganisms. In this study, using microarray chips and surface pasmon resonance (SPR) technology, we screened 189 antibiotics in order to obtain an inhibitor directly binding to the non-N-terminal domain of HSP90ß. Finally, we discovered an antibiotic, 7-aminocephalosporanic acid (7ACA), with a KD value of 6.201 µM between 7ACA and non-N-terminal domain of HSP90ß. Besides, 7ACA was predicted to interact with the middle domain (MD) of HSP90ß. In HepG2 cells, we found that 7ACA reduced cellular total cholesterol (TC) and triglyceride (TG) by decreasing sterol regulatory element-binding proteins (SREBPs). In HFD fed mice, administration of 7ACA (5, 10, and 25 mg kg-1 d-1, ig, for 12 weeks) dose-dependently decreased serum TC and TG and played an important role in protecting liver and adipose tissue from lipid accumulation. In conclusion, our study demonstrated that antibiotic 7ACA, as an HSP90ß middle domain inhibitor, was promising for the development of lipid-lowering drugs.

A thiocarbonate-caged fluorescent probe for specific visualization of peroxynitrite in living cells and zebrafish.

Peroxynitrite (ONOO-), a highly reactive oxygen species (ROS), is implicated with many physiological and pathological processes including cancer, neurodegenerative diseases and inflammation. In this regard, developing effective tools for highly selective tracking of ONOO- is urgently needed. Herein, we constructed a concise and specific fluorescent probe NA-ONOO for sensing ONOO- by conjugating an ONOO--specific recognition group ((4-methoxyphenylthio)carbonyl, a thiocarbonate derivative) with a naphthalene fluorophore. The probe, NA-ONOO, was in a dark state because the high electrophilicity of (4-methoxyphenylthio)carbonyl disturbs the intramolecular charge transfer (ICT) in the fluorophore. Upon treatment with ONOO-, the fluorescent emission was sharply boosted (quantum yield Φ: 3% to 56.6%) owing to an ONOO- triggered release of (4-methoxyphenylthio)carbonyl from NA-ONOO. Optical analyses showed that NA-ONOO presented high selectivity and sensitivity toward ONOO-. With good cell permeability and biocompatibility, the NA-ONOO probe was successfully applied to imaging and tracing exogenous and endogenous ONOO- in living cells and zebrafish. The probe NA-ONOO presents a new recognition group and a promising method for further investigating ONOO- in living systems.

Simultaneous enantioselective determination of six pesticides in aqueous environmental samples by chiral liquid chromatography with tandem mass spectrometry.

A robust and sensitive method was developed for the enantiomeric analysis of six chiral pesticides (including metalaxyl, epoxiconazole, myclobutanil, hexaconazole, napropamide, and isocarbophos) in aquatic environmental samples. The optimized chromatographic conditions for the quantification of all the 12 enantiomers were performed with Chiralcel OD-RH column using mobile phase consisting of 0.1% aqueous formic acid and acetonitrile operated under reversed-phase conditions and then analyzed using liquid chromatography with tandem mass spectrometry. Twelve enantiomers were detected in multiple reaction monitoring mode. Solid-phase extraction and dispersive liquid-liquid microextraction were employed in this study. Response surface methodology was applied to assist in the dispersive liquid-liquid microextraction optimization. Under the optimum conditions, recoveries of pesticides enantiomers varied from 83.0 to 103.2% at two spiked levels with relative standard deviation less than 11.5%. The concentration factors were up to 1000 times. Method detection and quantification limits varied from 0.11 to 0.48 ng/L and from 0.46 to 1.49 ng/L, respectively. Finally, this method was used to determination of the enantiomers composition of the six pesticides in environmental aqueous matrices, which will help better understand the behavior of individual enantiomer and make accurate risk assessment to ecosystems.

Investigation on the thermal effects of NaYF4:Er under 1550 nm irradiation.

The thermal effects of NaYF4:Er microcrystals under 1550 nm laser diode irradiation were investigated using an infrared thermal imaging method. The results revealed that the temperature of the LD irradiation beam area was non-uniform. The NaYF4:Er sample exhibits a rapid temperature increase within 5-10 s, and the heating process reaches its steady state after 60 s of irradiation when exposed to 1550 nm LD. The response time, temperature increase, and emission intensity of the samples depend on the excitation power density and concentration of doped Er3+ ions. Low excitation power density is required to avoid the influence of thermal effects on the up-conversion emission spectra measurement. Rapid scanning in up-conversion emission spectra measurement is not effective in preventing the heating effect under high excitation power pumping. In addition, a relative deviation of temperature, existing in fluorescence intensity ratio technique, decreased with the increasing irradiation time.

Porous CuO Microspheres as Long-Lifespan Cathode Materials for Aqueous Zinc-Ion Batteries.

Cathode materials with conversion mechanisms for aqueous zinc-ion batteries (AZIBs) have shown a great potential as next-generation energy storage materials due to their high discharge capacity and high energy density. However, improving their cycling stability has been the biggest challenge plaguing researchers. In this study, CuO microspheres were prepared using a simple hydrothermal reaction, and the morphology and crystallinity of the samples were modulated by controlling the hydrothermal reaction time. The as-synthesized materials were used as cathode materials for AZIBs. The electrochemical experiments showed that the CuO-4h sample, undergoing a hydrothermal reaction for 4 h, had the longest lifecycle and the best rate of capability. A discharge capacity of 131.7 mAh g-1 was still available after 700 cycles at a current density of 500 mA g-1. At a high current density of 1.5 A g-1, the maintained capacity of the cell is 85.4 mA h g-1. The structural evolutions and valence changes in the CuO-4h cathode material were carefully explored by using ex situ XRD and ex situ XPS. CuO was reduced to Cu2O and Cu after the initial discharge, and Cu was oxidized to Cu2O instead of CuO during subsequent charging processes. We believe that these findings could introduce a novel approach to exploring high-performance cathode materials for AZIBs.

Daily impact of the simultaneous passage of binary typhoons on sea surface chlorophyll-a concentration dynamics in the Northwestern Pacific.

Typhoons are recognized as one of the most destructive meteorological phenomena, exerting significant influences on marine ecosystems. Sea surface chlorophyll-a concentration (CHL)an essential indicator of phytoplankton biomass, can be utilized to characterize the disturbances of typhoons on the marine ecosystem. However, it is challenging to investigate this impact at a daily scale due to the missing CHL remote sensing data caused by cloud cover. Given that concurrent passing typhoons may interact with CHL, this study analyzes the effect of the simultaneous passage of binary typhoons Tembin and Bolaven on CHL by using daily CHL reconstruction data, and investigates the role of ocean environmental factors in driving the dynamics of CHL, including sea surface temperature (SST), mixed layer depth (MLD), and sea surface height anomaly (SSHA). The results show that typhoons Tembin and Bolaven increase CHL with the maximum increment of ∼3.2 mg∙m-3 during 4-6 days after typhoons passage. The maximum change areas of CHL are distributed near the intersection of typhoon track of (32°N, 125.2°E), corresponding to the regions of greater variation in SST and MLD. During 15 days before and after typhoons (i.e., from 15 August to 15 September 2012), SST is negatively correlated with CHL (the correlation coefficient of -0.85) and MLD is positively correlated with CHL (the correlation coefficient of -0.80). SST immediately declines after typhoons with a maximum cooling of 7.8 deg. C, showing the decreased SST from ∼28 deg. C to ∼23 deg. C can promote phytoplankton growth. MLD deepens from 10 m to >25 m caused by typhoon-induced strong winds, allowing more nutrients to be transported from the subsurface layer to the euphotic layer for phytoplankton blooms. Furthermore, oceanic eddies captured by SSHA change from cyclonic to anticyclonic eddies accompanied by the beginning of CHL increases, and the largest CHL increases correspond to the distribution of pre-existing cyclonic eddies. It suggests that Tembin and Boravin promote phytoplankton growth to increase CHL by enhancing vertical mixing and upwelling to transport nutrients to the sea surface. These findings inspire us to rethink the daily effects of typhoons on CHL, with critical importance for predicting and managing the ecological consequences of typhoons in the ocean.

Rapid detection of microalgae cells based on upconversion nanoprobes.

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.

Color-reversible fluorescence tracking for the dynamic interaction of SO2 with Hg2+ in living cells.

Mercury ion (Hg2+) is one of the most threatening substances to human health, and the mercury poisoning can damage physiological homeostasis severely in human, even cause death. Intriguingly, Sulfur dioxide (SO2), a gas signal molecule in human, can specifically interact with Hg2+ for relieving mercury poisoning. However, the dynamic interaction of Hg2+ with SO2 at the tempospatial level and the correlation between Hg2+ and SO2 in the pathological process of mercury poisoning are still elusive. Herein, we rationally designed a reversible and dual color fluorescent probe (CCS) for dynamically visualizing Hg2+ and SO2 and deciphering their interrelationship in mercury poisoning. CCS held good sensitivity, selectivity and reversibility to Hg2+ and SO2, that enabled CCS to specifically detect SO2 and Hg2+ via cyan fluorescence channel (centered around 485 nm) and red fluorescence channel (centered around 679 nm), respectively. Notably, the separate fluorescence signal changes of CCS realized the dynamic tracing of Hg2+ and SO2 in living cells, and presented the potential for exploring the correlation between SO2 and Hg2+ in mercury poisoning.

Promising lanthanide-doped double molybdates KYb(MoO4)2 phosphors for highly efficient upconversion luminescence and temperature sensing.

Here we report the highly efficient upconversion luminescence (UCL) and optical temperature sensing based on the novel host of KYb(MoO4)2 doped with trivalent lanthanide (Ln3+) ions at 980 nm excitation. The high Yb3+ concentration and unique ordered layer structure in KYb(MoO4)2 host are beneficial for the enhancement of UCL efficiency by improving the absorption and the negative migration of excitation energy. Ho3+, Er3+, and Tm3+ ions were selected to singly dope the KYb(MoO4)2 host, achieving three primary colors of red, green, blue UCL, respectively. At the optimal doping concentration, the blue upconversion quantum yield (UCQY) of the KYb(MoO4)2: 1.0%Tm3+ phosphor reaches 0.13%, which is rare for the Tm3+-doped oxides. By leveraging the efficient blue light, we achieved high-brightness white UCL by co-doping Ho3+ in KYb(MoO4)2: Tm3+. Furthermore, the temperature sensing performance of the KYb(MoO4)2: Tm3+, Ho3+ phosphors operating within the first biological window (BW-I) was evaluated based on a thermo-responsive fluorescence intensity ratio (FIR) of far-red to near-infrared (NIR) emission from completely separated 3F2,3/3H4 → 3H6 transitions of Tm3+. At the excitation of 980 nm, the maximum absolute and relative sensitivities were determined as 0.25 × 10-3 K-1 at 673 K and 2.84% K-1 at 303 K, respectively. These results indicate that the double alkali-rare-earth molybdate KYb(MoO4)2 can be used as a promising host to achieve highly efficient UCL and temperature sensing, suggesting potential applications in the fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Paraventricular hypothalamic RUVBL2 neurons suppress appetite by enhancing excitatory synaptic transmission in distinct neurocircuits.

The paraventricular hypothalamus (PVH) is crucial for food intake control, yet the presynaptic mechanisms underlying PVH neurons remain unclear. Here, we show that RUVBL2 in the PVH is significantly reduced during energy deficit, and knockout (KO) of PVH RUVBL2 results in hyperphagic obesity in mice. RUVBL2-expressing neurons in the PVH (PVHRUVBL2) exert the anorexigenic effect by projecting to the arcuate hypothalamus, the dorsomedial hypothalamus, and the parabrachial complex. We further demonstrate that PVHRUVBL2 neurons form the synaptic connections with POMC and AgRP neurons in the ARC. PVH RUVBL2 KO impairs the excitatory synaptic transmission by reducing presynaptic boutons and synaptic vesicles near active zone. Finally, RUVBL2 overexpression in the PVH suppresses food intake and protects against diet induced obesity. Together, this study demonstrates an essential role for PVH RUVBL2 in food intake control, and suggests that modulation of synaptic plasticity could be an effective way to curb appetite and obesity.

Upconversion nanoparticles@single-walled carbon nanotubes composites as efficient self-monitored photo-thermal agents.

Conventional photothermal therapy (PTT) usually relies on a macroscopic heat source to raise the temperature of tissues to 41-45 °C, which not only kills the pathological cells but causes severe side effects on nearby normal tissues, thus reducing the accuracy of PTT. Here we successfully fabricated nanocomposites of NaYF4:Yb3+,Tm3+@NaYF4:Yb3+@SiO2-SWCNTs, in which the upconversion nanoparticles (UCNPs) serve as real-time temperature-feedback moiety and the single-walled carbon nanotubes (SWCNTs) serve as efficient nano-heaters. The sample displays an excellent photothermal conversion capacity, i.e., the temperature of the aqueous dispersion increases from 23.3 °C up to 60.1 °C under 980 nm excitation due to the intense absorption and highly efficient heat generation of SWCNTs. Meanwhile, the temperature of the nanocomposites is monitored in real time based on the fluorescent intensity ratio of UCNPs. The in-vitro experiments demonstrate that the temperature of the nanocomposites at tissue injection of 1 mm can reach PTT temperature of 42.2 °C with a facile surrounding temperature of 36.2 °C under moderate laser power (980 nm, 2.0 W cm-2). These results provide a novel design for multifunctional nanocomposites that enable safe and controlled PTT.

Investigating the AIE and water sensing properties of a concise naphthalimide fluorophore.

A simple naphthalimide fluorophore NAP-H2O was designed and synthesized. Basic photophysical properties were investigated, especially found that the probe showed robust green fluorescence in water compared with that in various organic solvents, and the specific mechanism was conformed to be the aggregation induced emission (AIE) through dynamic light scattering (DLS) analysis, solid-state luminescence and fluorescence imaging. Accordingly, the capability of NAP-H2O for water sensing was examined, and good linear relationships between fluorescence intensities at the green emission band and the water content were obtained, enabling quantitative detection of water in organic solvents. The detection limits were calculated to be 0.004 % (v/v) in ACN, 0.117 % (v/v) in 1,4-dioxane, 0.028 % (v/v) in THF, 0.022 % (v/v) in DMF and 0.146 % (v/v) in DMSO, respectively. In addition, the probe presented fast response time within 5 s to water and good photostability. Furthermore, the probe was successfully applied for fast and naked-eye detection of water in organic solvents via test papers. This work provides a rapid, sensitive and naked-eye method for trace amount detection of water in organic solvents and has potential for practical applications.

HSP90ß promotes osteoclastogenesis by dual-activation of cholesterol synthesis and NF-κB signaling.

Heat shock protein 90ß (Hsp90ß, encoded by Hsp90ab1 gene) is the most abundant proteins in the cells and contributes to variety of biological processes including metabolism, cell growth and neural functions. However, genetic evidences showing Hsp90ß in vivo functions using tissue specific knockout mice are still lacking. Here, we showed that Hsp90ß exerted paralogue-specific role in osteoclastogenesis. Using myeloid-specific Hsp90ab1 knockout mice, we provided the first genetic evidence showing the in vivo function of Hsp90ß. Hsp90ß binds to Ikkß and reduces its ubiquitylation and proteasomal degradation, thus leading to activated NF-κB signaling. Meanwhile, Hsp90ß increases cholesterol biosynthesis by activating Srebp2. Both pathways promote osteoclastogenic genes expression. Genetic deletion of Hsp90ab1 in osteoclast or pharmacological inhibition of Hsp90ß alleviates bone loss in ovariectomy-induced mice. Therefore, Hsp90ß is a promising druggable target for the treatment of osteoporosis.

[White light upconversion luminescence and its mechanism of Yb3+/Ho3+/Tm3+ co-doped tellurite glass].

Yb3+ /Ho3+, Yb3+ /Tm3+ and Yb3+ /Ho3+ /Tm3+ co-doped tellurite glasses were prepared by melt-quenching method. Under the excitation of 980 nm laser, Yb3+ /Ho3+/Tm3+ co-doped glass sample shows strong blue, green and red emissions, corresponding to the transitions 1G4 --> 3H6 of Tm3+, 5F4 (5S2) --> 5 I8 of Ho3+, as well as 5F5 -->5 I8 of Ho3+ and 1G4 --> 3F4 of Tm3+ ions, respectively. It was found that the integrated emission intensity ratio of the red to green in Yb3+/Ho3+ /Tm3+ co-doped sample (3.95) is greater than that in Yb3+/Ho3+ co-doped sample (1.69) due to the cross-relaxation between Ho3+ and Tm3+ ions : 3H4 (Tm3+) + 5 I6 (Ho3+) -->3F4 (Tm3+) + 5F5 (Ho3+), and 3F4 (Tm3+ ) + 5 I8 (Ho3+) --> 3H6 (Tm3+) +5 I7 (Ho3+). When the pump power density is 8.2 W x cm(-2), the calculated color coordinates of Yb3+ /Ho3+ /Tm3+ co-doped sample are x = 0.345, y = 0.338, which is very close to the equal energy white light (x = 0.333, y = 0.333).

Design and Implementation of Balance Ability Assessment Training System for Special Children Based on Education Cloud Integration.

Many children with special needs have body balance disorders, which will not only bring inconvenience to their daily lives but also have a certain impact on their spirits, making them insecure. It will lead to a decline in their social skills, which will also seriously affect their study and work as well as reduce their quality of life. The purpose of this paper is to design and discuss a system for evaluating and training the balance ability of children with special needs based on the integration of education cloud. The balance ability evaluation module of the system performs a series of calculations on the projection coordinates of the center of gravity of the human body in various postures, and the obtained parameter values are the basis of the evaluation. This paper analyzes the role of education cloud integration in the evaluation of balance ability of special children, evaluates and trains the balance ability of special children, and verifies the feasibility of the balance ability evaluation and training system for special children. This study found that in a feasibility trial evaluating the balance ability of children with special needs, the balance stability of the tested children was improved, and the overall balance ability improved by 60%. The balance ability evaluation training system developed in this paper can effectively improve the independent standing ability of young children. Children over the age of 4 do not have any difficulties in understanding and mastering movements, and training difficulties for children are also applicable. At the same time, the results of these exercises also showed that this kind of exercise can help children maintain their balance.

Vanadium Hexacyanoferrate as a High-Capacity and High-Voltage Cathode for Aqueous Rechargeable Zinc Ion Batteries.

Prussian blue analogs (PBAs) are widely used as electrode materials for secondary batteries because of their cheapness, ease of synthesis, and unique structural properties. Nevertheless, the unsatisfactory capacity and cyclic stability of PBAs are seriously preventing their practical applications. Here, vanadium hexacyanoferrate (VHCF) is successfully prepared and used as a cathode for aqueous zinc-ion batteries (AZIBs). When using 3 M Zn(CF3SO3)2 as the electrolyte, a high capacity of ~230 mA h g-1 and a high voltage of ~1.2 V can be achieved. The XRD result and XPS analysis indicate that the outstanding Zn2+ storage capability is due to the presence of dual electrochemical redox centers in VHCF (Fe2+ ⇋ Fe3+ and V5+ ⇋ V4+ ⇋ V3+). However, the battery shows a short cycle life (7.1% remaining capacity after 1000 cycles) due to the dissolution of VHCF. To elongate the cycle life of the battery, a high-concentration hybrid electrolyte is used to reduce the activity of water molecules. The improved battery exhibits an impressive capacity of 235.8 mA h g-1 and good capacity retention (92.9%) after 1000 cycles.

Data reconstruction of daily MODIS chlorophyll-a concentration and spatio-temporal variations in the Northwestern Pacific.

Sea surface chlorophyll-a concentration (Chl-a) is a key proxy for phytoplankton biomass. Spatio-temporal continuous Chl-a data are important to understand the mechanisms of chlorophyll occurrence and development and track phytoplankton changes. However, the greatest challenge in utilizing daily Chl-a data is massive missing pixels due to orbital position and cloud coverage. This study proposes the application of a spatial filling method using the machine learning-based Extreme Gradient Boosting (BST) to reconstruct missing pixels of daily MODIS Chl-a data from 2007 to 2018. The approach is applied to different trophic biogeographical subregions of the Northwestern Pacific where it has complex phytoplankton dynamics and frequent data missing. Various environmental variables are taken into consideration, including meteorological forcing, geographic and topographic features, and oceanic physical components. The BST-reconstructed Chl-a (BST Chl-a) is validated using in-situ Chl-a measurements, VIIRS and Himawari-8 Chl-a products. The results show that the BST model is highly adaptive in reconstructing Chl-a data, and it performs well in pelagic, offshore and coastal with the best performance in pelagic. BST Chl-a improves coverage without significant quality degradation compared to the original MODIS Chl-a. BST Chl-a agrees better with in-situ data than that of MODIS, with CC of 0.742, RMSE of 0.247, MAE of 0.202 and Bias of 0.089. Cross-satellite validation using VIIRS and Himawari-8 Chl-a also shows promising results with the CC of 0.861 and 0.765, respectively, suggesting the high accuracy of BST Chl-a. The inter-annual trend of BST Chl-a decreases in coastal and increases in offshore and pelagic. BST Chl-a images present similar spatial patterns to MODIS Chl-a under different missing rates, with gradual decreases from coastal to pelagic. It indicates that phytoplankton bloom patterns can be identified by daily BST Chl-a images.

Engineering Er3+-sensitized nanocrystals to enhance NIR II-responsive upconversion luminescence.

An Er3+-sensitized system with a high response to 1550 nm radiation in the second near-infrared window (NIR II) has been considered for a new class of potential candidates for applications in bio-imaging and advanced anti-counterfeiting, yet the achievement of highly efficient upconversion emission still remains a challenge. Here, we constructed a novel Er3+-sensitized core-shell-shell upconversion nanostructure with a Yb3+-enriched core as the emitting layer. This designed nanostructure allows the Yb3+ emitting layer to more efficiently trap and lock excitation energy by combining the interfacial energy transfer (IET) from the shell (Er3+) to the core (Yb3+), high activator Yb3+ content, and minimized energy back-transfer. As a result, the NIR II emission at 1000 nm is remarkably enhanced with a high quantum yield (QY) of 11.5%. Based on this trap and lock-in effect of the excitation energy in the Yb3+-enriched core, highly efficient 1550 nm-responsive visible and NIR upconversion emissions are also achieved by co-doping with other activator ions (e.g., Ho3+ and Tm3+). Our research provides a new functional design for improving NIR II-responsive upconversion luminescence, which is significant for developing practical applications.

Near-infrared-emitting upconverting BiVO4 nanoprobes for in vivo fluorescent imaging.

Near-infrared (NIR) emitting BiVO4:Yb3+,Tm3+ nanoparticles are synthesized by a new solvothermal strategy using solvents of oleic acid and methanol. The obtained BiVO4:Yb3+,Tm3+ samples show an average particle size of ≈164 nm and exhibit an asymmetry monoclinic crystal structure of BiVO4. At NIR excitation of 980 nm, the BiVO4:Yb3+,Tm3+ sample exhibits a nearly single NIR emission at ≈796 nm with extremely weak blue emissions from Tm3+ ions. These high-energy visible emissions are absorbed by the semiconducting host of BiVO4 that possesses a bandgap of ≈2.2 eV. Therefore, the NIR excitation to a single intense NIR emission fluorescent BiVO4 materials could be a potential ideal probe for deep-tissue high-resolution bioimaging. To validate the ability of BiVO4 materials for bio-applications, we conduct the cytotoxicity experiments. The results show that the cytotoxicity of HeLa cells is negligible at a concentration of 0.2 mg/ml of BiVO4:Yb3+,Tm3+ , and the cell viability approaches 90% at a high dosage of 0.5 mg/ml. The Daphnia magna and Zebrafish treated with nanoparticles (0.5 mg/ml) display bright NIR emission without any background, indicating the excellent in vivo fluorescent imaging capacity of BiVO4:Yb3+,Tm3+ nanoparticles. Our findings offer an environment-friendly strategy to synthesize BiVO4 UCL nanophosphors and provide a promising new class of fluorescent probes for biological applications.

Enhancing red luminescence by doping Yb3+ into Er3+ self-sensitized Gd2O2S upconverting nanoparticles under excitation at 1530 nm.

Red upconversion luminescence (UCL) nanoparticles are of significant importance for applications in the fields of deep tissue imaging, photothermal therapy and security ink. In this work, a highly efficient red emission was achieved by introducing Yb3+ ions as mediators in Er3+ self-sensitized Gd2O2S nanoparticles under excitation at 1530 nm. The results show that the Gd2O2S:Yb3+,Er3+ nanoparticles synthesized by a homogeneous precipitation method exhibit a uniform spherical shape and narrow size distribution with a mean particle diameter of ≈65 nm. Moreover, the integral emission intensity ratio of red to green of the Gd2O2S:Yb3+,Er3+ sample is significantly enhanced 3-fold compared with the Gd2O2S:Er3+ sample without Yb3+ doping. The enhancement mechanisms are discussed in detail on the basis of steady-state luminescence spectra and decay dynamics measurements under various excitations at 380, 808, 980 and 1530 nm, respectively. It has been demonstrated that the enhanced red luminescence is induced by cross-relaxation energy transfer from Er3+ to Yb3via4S3/2 (Er3+) + 2F7/2 (Yb3+) → 4I13/2 (Er3+) + 2F5/2 (Yb3+) and 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+), and further followed by back energy transfer from Yb3+ to Er3+ through 4I13/2 (Er3+) + 2F5/2 (Yb3+) → 4F9/2 (Er3+) + 2F7/2 (Yb3+). The former cross-relaxation procedure effectively populates the red emission level of 4F9/2 by depopulating the green emission level of 3S3/2. Our findings provide a feasible way to enhance the red UCL and new insights into red UCL mechanisms in the Er3+ self-sensitized system under ≈1500 nm excitation, by combining with the nontoxic oxysulfide host, indicating their potential application as safe fluorescent nanoprobes in the bio-field.