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Lipid droplets (LDs), which are ubiquitous organelles existing in almost all eukaryotic cells, have attracted a lot of attention in the field of cell biology over the last decade. For the biological study of LDs via fluorescence imaging, the superior LD fluorescent probes with environmental polarity-sensitive character are highly desired and powerful but are very scarce. Herein, we have newly developed such a kind of fluorescent probe named LDs-Red which enables us to visualize LDs and to further reveal their polarity information. This fluorescent probe displays the advantages of intense red/near-infrared emission, high LD staining specificity, and good photostability; thus, it would be very useful for LD fluorescence imaging application. As a result, the three-dimensional confocal imaging to visualize spatial distribution of LDs and the multicolor confocal imaging to simultaneously observe LDs and other cellular organelles have been realized using this new LD fluorescent probe. Furthermore, the polarity-sensitive emission character of this probe enables us to quantitatively determine the LD polarity via spectral scan imaging. Consequently, the cancer cells (HepG2, HeLa, and Panc02) displaying lower polarity of LDs than the normal cells (L929, U251, and HT22) have been systematically demonstrated. In addition, this polarity-sensitive probe displaying shorter fluorescence wavelengths in cancer cells than in normal cells has an important and potential ability to distinguish them.

Portable and sensitive mixed-potential type solid-state electrolyte (MPSE) gas sensors can detect exhaled biomarkers in a noninvasive and inexpensive way, which is significant for convenient disease diagnosis and saving medical resources. However, high working temperature is still one of the main bottlenecks for hindering MPSE gas sensors' applications in disease diagnosis. Here, we, for the first time, developed and fabricated new room-temperature MPSE gas sensors utilizing K2Fe4O7 electrolyte and Ni/Fe-MOF (Ni/Fe clusters are coordinated with 1,4-H2BDC) sensing electrodes (SEs) for the detection of ppb-level NO. Among different MOF SEs, the sensor attached with the Ni-MOF SE presents the highest NO sensitivities. This is attributed to a reducing oxygen reduction reaction activity and enhancing NO electrochemical catalytic reaction activity, verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. In addition, the presented sensor also shows a low detection limit (20 ppb), fast response/recovery characteristic (17 s/6 s to 50 ppb NO), excellent selectivity, acceptable repeatability, and long-term stability of 34 days to NO at 25 °C and 60%RH. Simultaneously, the mechanism of humidity effect on the sensing performance was investigated by EIS and CV tests. Our work provides new insight into the development of room-temperature solid-state electrolyte gas sensors based on the mixed-potential mechanism and enlarges the potential application domain.

Lipid droplets (LDs) are spherical organelles that participate in numerous biological processes. In order to visualize LDs on the nanoscale, nanoscopy fluorescence imaging is considered as the most attractive technique but is substantially limited by the characteristics of fluorescent probes. Thus, the development of a superior fluorescent probe that is capable of nanoscopy fluorescence imaging has attracted enormous attention. Herein, a benzodithiophene-tetraoxide-based molecule Lipi-BDTO has been developed that can easily undergo the stimulated emission depletion (STED) process and displays high photostability. These two characteristics of fluorescent probes finely satisfy the requirements of STED nanoscopy imaging. Indeed, applying the probe for STED imaging achieves a high resolution of 65 nm, belonging to one of the leading results of LDs fluorescence imaging. Furthermore, the high photostability of this fluorescent probe enables it to monitor the dynamics of LDs by time-lapse STED imaging as well as to visualize the three-dimensional (3D) spatial distribution of LDs by 3D STED imaging. Notably, the resolution of the 3D STED image represents one of the best LDs fluorescence imaging results so far. Besides STED nanoscopy imaging, the superior utility of this fluorescent probe has been also demonstrated in two-color 3D confocal imaging and four-color confocal imaging.

Yttrium-stabilized zirconia (YSZ)-based mixed potential-type NOx sensors have broad application prospects in automotive exhaust gas detection. Great efforts continue to be made in developing high-performance sensitive electrode materials for mixed potential-type NO2 gas sensors. However, only five kinds of new sensing electrode materials have been developed for this type of gas sensor in the last 3 years. In this work, four different tree-based machine learning models were trained to find potentially sensitive electrode materials for NO2 detection. More than 400 materials were selected from 8000 materials by the above machine learning models. To further verify the reliability of the model, 13 of these materials containing unexploited elements were selected as sensitive electrode materials for making sensors and testing their gas-sensing performances. The experimental results showed that all 13 materials exhibited good gas-sensing performance for NO2. More interestingly, an electrode material BPO4, which does not contain any metal elements, was also screened out and showed good sensing properties to NO2. In a short period of time, 13 new sensitive electrode materials for NO2 detection were targeted and screened, which was difficult to achieve by a trial-and-error procedure.

It remains a challenge to design and fabricate high-performance gas sensors using metal-organic framework (MOF)-derived metal oxide semiconductors (MOS) as sensing materials due to the structural damage during the annealing process. In this study, the mesoporous In2O3-NiO hollow spheres consisting of nanosheets were prepared via a solvothermal reaction and subsequent cation exchange. More importantly, the transformation of Ni-MOF into In/Ni-MOF through exchanging the Ni2+ ion with In3+ ion can prevent the destruction of the porous reticular skeleton and hierarchical structure of Ni-MOF during calcination. Thus, the mesoporous In2O3-NiO hollow composites possess high porosity and large specific surface area (55.5 m2 g-1), which can produce sufficient permeability pathways for volatile organic compound (VOCs) molecules, maximize the active sites, and enhance the capacity of VOC capture. The mesoporous In2O3-NiO-based sensors exhibit enhanced triethylamine (TEA) sensing performance (S = 33.9-100 ppm) with distinct selectivity, good long-term stability, and lower detection limit (500 ppb) at 200 °C. These results can be attributed to the mesoporous hollow hierarchical structure and p-n junction of In2O3-NiO. The preparation concept mentioned in this work may provide a versatile platform applicable to various mesoporous composite sensing material-based hollow structures.

Lipid droplets (LDs) are important cellular organelles associated with many physiological processes. To visualize and study LDs, particularly the nascent LDs (diameters of 30–60 nm), super-resoluti...

On-site quantitative analysis of pesticide is of significant importance for addressing serious public health issues in clinical, food, and environmental settings. Herein, we designed a novel smartphone-assisted sensing platform for on-site monitoring of 2,4-dichlorophenoxyacetic acid (2,4-D) based on carbon dots/cobalt oxyhydroxide nanosheet (CDs/CoOOH) composite. In this work, a red emissive CDs/CoOOH composite was proposed as a signal indicator for shielding background interference, enhancing anti-interference capability. 2,4-D as an inhibitor of alkaline phosphatase could specifically suppress the production of ascorbic acid, which restrained in situ etching of the CDs/CoOOH composite and further triggered the fluorescence response of the biosensor. By employing a lab-on-smartphone based device and self-designed application software, the fluorescence image was directly captured and analyzed with a sensitive detection limit of 100 μg L

Precise on-site profiling of organophosphate pesticides (OPs) is of significant importance for monitoring pollution and estimating poisoning. Herein, we designed a simple and convenient portable kit based on Ag+-responsive hydrogels for accurate detection of OPs. The newly developed hydrogels employed o-phenylenediamine (OPD) and silicon quantum dots (SiQDs) as indicator, which possessed ratiometric response. In this sensor, OPs as inhibitor of acetylcholinesterase prevented the generation of thiocholine, which blocked the formation of metal-polymer with Ag+, further triggered the oxidation of OPD to yield yellow 2,3-diaminophenazine (DAP) with fluorescence emission at 557 nm. The fluorescence intensity of SiQDs (444 nm) was quenched by DAP through inner filter effect (IFE) process, emerging a typical ratiometric response. Interestingly, the ratiometric signal of kit, which was recorded by smartphone's camera, can be transduced by ImageJ software into the hue parameter that was linearly proportional to the concentration of OPs. The simplicity of portable kit combined with smartphone operation, which possessed high sensitivity (detection limit

Organic light-emitting materials with thermally activated delayed fluorescence (TADF) are promising for promoting the efficiency of organic light-emitting diodes (OLEDs) without any precious metals...

Ti3C2T x MXene with an organ-like structure was synthesized from Ti3AlC2 (MAX phase) through the typical hydrofluoric (HF) acid etching method. Ti3C2T x MXene was further alkaline-treated with a sodium hydroxide solution to obtain alkalized Ti3C2T x. Room-temperature planar-type gas- and humidity-sensing devices were also fabricated by utilizing Ti3C2T x MXene and alkalized Ti3C2T x sensing material based on the dip coating method, respectively. The intercalation of the alkali metal ion (Na+) and the increase of the surface terminal oxygen-fluorine ratio ([O]/[F]) in Ti3C2T x can effectively improve humidity- and gas-sensing properties at room temperature. The developed alkalized Ti3C2T x sensor exhibited excellent humidity-sensing characteristics (approximately 60 times response signal change) in the relative humidity (RH) with a range of 11-95% and considerable NH3 sensing performance (28.87% response value to 100 ppm of NH3) at room temperature. The improvement of NH3 and humidity-sensing properties indicated that alkalized Ti3C2T x has great potential in chemical sensors, especially in NH3 and humidity sensors.

Rapid and precise profiling of acetylcholine (ACh) has become important for diagnosing diseases and safeguarding health care because of its pivotal role in the central nervous system. Herein, we developed a new colorimetric sensor based on protein-inorganic hybrid nanoflowers as artificial peroxidase, comprising a test kit and a smartphone reader, which sensitively quantifies ACh in human serum. In this sensor, ACh indirectly triggered the substrate reaction with the help of a multienzyme system including acetylcholinesterase, choline oxidase, and mimic peroxidase (nanoflowers), accompanying the enhancement of absorbance intensity at 652 nm. Therefore, the multienzyme platform can be used to detect ACh via monitoring the change of the absorbance in a range from 0.0005 to 6.0 mmol L-1. It is worth mentioning that the platform was used to prepare a portable agarose gel-based kit for rapid qualitative monitoring of ACh. Coupling with ImageJ program, the image information of test kits can be transduced into the hue parameter, which provides a directly quantitative tool to identify ACh. Based on the advantages of simple operation, good selectivity, and low cost, the availability of a portable kit for point-of-care testing will achieve the needs of frequent screening and diagnostic tracking.

Understanding the effect of substitutional doping on gas-sensing performances is essential for designing high-activity sensing nanomaterials. Herein, formaldehyde sensors based on gallium-doped In2O3 inverse opal (IO-(Ga xIn1- x)2O3) microspheres were purposefully prepared by a simple ultrasonic spray pyrolysis method combined with self-assembled sulfonated polystyrene sphere templates. The well-aligned inverse opal structure, with three different-sized pores, plays the dual role of accelerating the diffusion of gas molecules and providing more active sites. The Ga substitutional doping can alter the electronic energy level structure of (Ga xIn1- x)2O3, leading to the elevation of the Fermi level and the modulation of the band gap close to a suitable value (3.90 eV), hence, effectively optimizing the oxidative catalytic activity for preferential CH2O oxidation and increasing the amount of adsorbed oxygen. More importantly, the gas selectivity could be controlled by varying the energy level of adsorbed oxygen. Accordingly, the IO-(Ga0.2In0.8)2O3 microsphere sensor showed a high response toward formaldehyde with fast response and recovery speeds, and ultralow detection limit (50 ppb). Our findings finally offer implications for designing Fermi level-tailorable semiconductor nanomaterials for the control of selectivity and monitoring indoor air pollutants.

The development of ultra-fast response semiconductor gas sensors for high-accuracy detection of trace volatile organic compounds in human exhaled breath still remains a challenge. Herein, we propose a novel self-assembly synthesis concept for preparing intricate three-dimensional (3D) opal porous (OP) SnO2–ZnO hollow microspheres (HM), by employing sulfonated polystyrene (S-PS) spheres template-assisted ultrasonic spray pyrolysis. The high gas accessibility of the unique opal hollow structures resulted in the existence of 3D interconnection and bimodal (mesoscale and macroscale) pores, and the n–n heterojunction-induced change in oxygen adsorption. The 3D OP SnO2–ZnO HM sensor exhibited high response and ultra-fast dynamic process (response time ∼4 s and recovery time ∼17 s) to 1.8 ppm acetone under highly humid ambient condition (98% relative humidity), and it could rapidly identify the states of the exhaled breath of healthy people and simulated diabetics. In addition, the rational structure design of t...

This contribution describes a facile strategy for constructing octahedral-like CuO/In2O3 mesocages with double-shell architectures. The synthetic method included first preparation of unifrom Cu2O as an ideal self-sacrificial template and then decoration by a In2O3 outer layer through room-temperature Cu2O-engaged redox etching reaction combined with subsequent annealing process. Various characterization techniques manifested that In2O3 nanoparticles were uniformly grown on the surface of CuO mesocages, resulting in a well-defined double-shelled heterostructure. When evaluated as a novel sensing material for hydrogen sulfide (H2S) detection, the resultant octahedral-like CuO/In2O3 heterostructures exhibited obviously enhanced sensing response, lower operating temperature as well as faster response/recover speed during the dynamic measurement compared to the pristine CuO particles, which is likely related to the high-level of adsorbed oxygen concentration, resistance modulation effect, and unique microstructure of as-prepared CuO/In2O3 heterostructure.

Indium tungsten oxide ellipsoidal nanospheres were prepared with different In/W ratios by using a simple hydrothermal method without any surfactant for the first time. Sensors based on different In/W ratios samples were fabricated, and one of the samples exhibited better response to methanol compared with others. High content of defective oxygen (Ov) and proper output proportion of In to W might be the main reasons for the better gas sensing properties. The length of the nanosphere was about 150-200 nm, and the width was about 100 nm. Various techniques were applied to investigate the nanospheres. Sensing characteristics toward methanol were investigated. Significantly, the sensor exhibited ultrafast response to methanol. The response time to 400 ppm methanol was no more than 2 s and the recovery time was 9 s at 312 °C. Most importantly, the humidity almost had no effect on the response of the sensor fabricated here, which is hard to achieve in gas-sensing applications.

This paper presents a facile hydrolysis reaction and annealing for preparing a novel hierarchical nanoheterostructure via assembly of α-Fe2O3 nanorods onto multiwall carbon nanotubes (MWCNTs) backbones. The as-synthesized nanocomposites were characterized using XRD (X-ray diffraction), FESEM (Field emission scanning electron microscopy), TEM (Transmission electron microscopy), XPS (X-ray photoelectron spectroscopy) and BET (Surface Area and Porosity System). The observations showed uniform α-Fe2O3 nanorods approximately 100–200 nm in length and 50–100 nm in diameter that were hierarchically assembled onto the surface of the MWCNTs. The formation of the heterostructure was investigated by observing the evolution of the microstructure of the products at different reaction times. The X-ray photoelectron spectra (XPS) showed that the ability of the absorbing oxygen was enhanced by the formation of the heterostructure composites. Moreover, as a proof-of-concept presentation, the novel CNTs@α-Fe2O3 hierarchical...

A well-ordered porous three-phase boundary (TPB) was prepared with a polystyrene sphere as template and examined to improve the sensitivity of yttria-stabilized zirconia (YSZ)-based mixed-potential-type NO2 sensor due to the increase of the electrochemical reaction active sites. The shape of pore array on the YSZ substrate surface can be controlled through changing the concentration of the precursor solution (Zr(4+)/Y(3+) = 23 mol/L/4 mol/L) and treatment conditions. An ordered hemispherical array was obtained when CZr(4+) = 0.2 mol/L. The processed YSZ substrates were used to fabricate the sensors, and different sensitivities caused by different morphologies were tested. The sensor with well-ordered porous TPB exhibited the highest sensitivity to NO2 with a response value of 105 mV to 100 ppm of NO2, which is approximately twice as much as the smooth one. In addition, the sensor also showed good stability and speedy response kinetics. All these enhanced sensing properties might be due to the structure and morphology of the enlarged TPB.

The pure and Al-doped NiO nanorod-flowers with uniform sizes and well-defined morphologies were synthesized for the first time by a facile solvothermal reaction. As the gas sensing materials of MOS gas sensors, their sensing properties were investigated systematically. The results indicated that the 2.15 at% Al-doped NiO nanorod-flowers showed improved gas sensing properties compared to those of pure NiO nanorod-flowers. The incorporation of Al ions with NiO nanocrystals adjusts the carrier concentration, and induces the change of the oxygen deficiency and chemisorbed oxygen of NiO nanorod-flowers. Thus, the doping of Al3+ into NiO nanorod-flowers should be a promising method for designing and fabricating the high performance gas sensor.

We present the preparation of a hierarchical nanoheterostructure consisting of inner SnO2 hollow spheres (SHS) surrounded by an outer α-Fe2O3 nanosheet (FNS). Deposition of the FNS on the SHS outer surface was achieved by a facile microwave hydrothermal reaction to generate a double-shell SHS@FNS nanostructure. Such a composite with novel heterostructure acted as a sensing material for gas sensors. Significantly, the hierarchical composites exhibit excellent sensing performance toward ethanol, which is superior to the single component (SHS), mainly because of the synergistic effect and heterojunction.

In this study, double-shell composites consisting of inner ZnO hollow microspheres (ZHS) surrounded by outer ZnFe2O4 nanosheets were successfully synthesized. The growth of the ultrathin ZnFe2O4 nanosheets (∼10 nm) on the ZHS outer surface was carried out at room temperature via solution reactions in order to generate a double-shell configuration that could provide a large surface area. As a proof-of-concept demonstration of the design, a comparative sensing investigation between the sensors based on the as-obtained ZnO/ZnFe2O4 composites and its two individual components (ZnO hollow spheres and ZnFe2O4 nanosheets) was performed. As expected, the response of the ZnFe2O4-decorated ZnO composites to 100 ppm acetone was about 3 times higher than that of initial ZnO microspheres. Moreover, a dramatic reduction of response/recover time has been achieved at different operating temperature. Such favorable sensing performances endow these ZnO/ZnFe2O4 heterostructures with a potential application in gas sensing.

Semiconductor oxides with hierarchically hollow architecture can provide significant advantages as sensing materials for gas sensors by facilitating the diffusion of target gases. Herein, we develop a facile template-free solvothermal strategy combined with the subsequent thermal treatment process toward the successful synthesis of novel ZnFe2O4 hollow flower-like microspheres. The images of electron microscopy unambiguously indicated that the ZnFe2O4 nanosheets with thickness of around 20 nm assembled hierarchically to form the unique flower-like architecture. As a proof-of-concept demonstration of the function, the as-prepared product was utilized as sensing material for gas sensor. Significantly, in virtue of the porous shell structure, hollow interior, and large surface area, ZnFe2O4 hierarchical microspheres exhibited high response, excellent cyclability, and long-term stability to acetone at the operating temperature of 215 °C.

ZnO/α-Fe2O3 composites built from plenty of ZnO nanoparticles decorated on the surfaces of uniform round-edged α-Fe2O3 hexahedrons were successfully prepared via a facile solvothermal method. Various techniques were employed to obtain the crystalline and morphological characterization of the as-prepared samples. In addition, a comparative sensing performance investigation between the two kinds of sensing materials clearly demonstrated that the sensing properties of ZnO/α-Fe2O3 composites were substantially enhanced compared with those of the single α-Fe2O3 component, which manifest the superiority of the ZnO decoration as we expected. For instance, the response of ZnO/α-Fe2O3 composites to 100 ppm acetone is ∼30, which is ∼3.15-fold higher than that of primary α-Fe2O3 hexahedrons. The synergetic effect is believed to be the source of the improvement of gas-sensing properties.

The Au@ZnO yolk-shell nanospheres with a distinctive core@void@shell configuration have been successfully synthesized by deposition of ZnO on Au@carbon nanospheres. Various techniques were employed for the characterization of the structure and morphology of as-obtained hybrid nanostructures. The results indicated that the Au@ZnO yolk-shell nanospheres have an average diameter of about 280 nm and the average thickness of the ZnO shell is ca. 40 nm. To demonstrate how such a unique structure might bring about more excellent gas sensing property, we carried out a comparison of the sensing performances of ZnO nanospheres with different inner structures. It was found that Au@ZnO yolk-shell nanospheres exhibited an obvious improvement in response to acetone compared with the pure ZnO nanospheres with hollow and solid inner structures. For instance, the response of the Au@ZnO nanospheres to 100 ppm acetone was about 37, which was about 2 (3) times higher than that of ZnO hollow (solid) nanostructures. The enhanced sensing properties were attributed to their unique microstructures (porous shell and internal voids) and the catalytic effect of the encapsulated Au nanoparticles.

Urchinlike CuO modified by reduced graphene oxide (rGO) was synthesized by a one-pot microwave-assisted hydrothermal method. The as-prepared composites were characterized using various characterization methods. A humidity sensor based on the CuO/rGO composites was fabricated and tested. The results revealed that the sensor based on the composites showed much higher impedance than pure CuO. Compared with the sensors based on pristine rGO and CuO, the sensor fabricated with the composites exhibited relatively good humidity-sensing performance in terms of response time and response value. The humidity-sensing mechanism was also briefly introduced. The enlargement of the impedance and improvement of the humidity-sensing properties are briefly explained by the Schottky junction theory.

A trilaminar layer photoanode for dye-sensitized solar cells (DSSCs) was constructed using urchin-like TiO2 hierarchical microspheres and P25. The top layer made of hierarchical microspheres enhanced light scattering; the middle layer consisting of P25 and as-prepared microspheres is a multifunctional layer for DSSCs, high adsorption ability to the dye, light scattering ability, and slow recombination rates coexistence; the bottom layer used P25. The DSSCs based on the photoanode with tripartite-layers structure exhibited a much higher short-circuit photocurrent density of 18.97 mA cm–2 and energy conversion efficiency of 8.80%, which indicated a 36% increase in the conversion efficiency compared to those of the P25 electrode (14.51 mA cm–2, 6.50%). The great improvements of photocurrent density and energy conversion efficiency for hierarchical TiO2 microspheres were mainly attributed to a considerable surface area, a higher light scattering ability, and slower electron recombination rates for the former.

We have successfully fabricated hierarchical ZnSnO3 nanocages via a facile one-pot solution synthesis method. Field emission scanning electron microscopic and transmission electron microscopic results reveal that the cubic ZnSnO3 samples with hollow interior and porous shells are cage-like structure with the side length of 200−400 nm, where the subunits are irregular-shaped nanoparticles. The time-dependent morphology of the ZnSnO3 samples has been investigated, and a possible formation mechanism of these hierarchical structures is proposed. Moreover, gas sensor based on hierarchical ZnSnO3 nanocages exhibits better sensing properties compared with the solid ZnSnO3 nanocubes. The facile preparation method may provide an easy path to the extendable synthesis of other functional nanomaterials with hollow structure and further exploitation of the potential applications.