Molecular imprinting-based triple-emission ratiometric fluorescence sensor with aggregation-induced emission effect for visual detection of doxycycline.

The development of high-performance sensors for doxycycline (DOX) detection is necessary because its residue accumulation will cause serious harm to human health and the environment. Here, a novel tri-emission ratiometric fluorescence sensor was proposed by using "post-mixing" strategy of different emissions fluorescence molecularly imprinted polymers with salicylamide as dummy template (DMIPs). BSA was chosen as assistant functional monomer, and also acted as sensitizers for the aggregation-induced emission (AIE) effect of DOX. The blue-emitting carbon dots and the red-emitting CdTe quantum dots were separately introduced into DMIPs as the response signals. Upon DOX recognition within 2 min, blue and red fluorescence of the tri-emission DMIPs sensor were quenched while green fluorescence of DOX was enhanced, resulting in a wide range of color variations observed over bluish violet-rosered-light pink-orange-yellow-green with a detection limit of 0.061 µM. The sensor possessed highly selective recognition and was successfully applied to detect DOX in complicated real samples. Moreover, with the fluorescent color collection and data processing, the smartphone-assisted visual detection of the sensors showed satisfied sensitivity with low detection limit. This work provides great potential applications for rapid and visual detection of antibiotics in complex substrates.

Functional Groups Dominate Aboveground Net Primary Production under Long-Term Nutrient Additions in a Tibetan Alpine Meadow.

Anthropogenic nutrient additions are influencing the structure and function of alpine grassland ecosystems. However, the underlying mechanisms of the direct and indirect effects of nutrient additions on aboveground net primary productivity (ANPP) are not well understood. In this study, we conducted an eight-year field experiment to explore the ecological consequences of nitrogen (N) and/or phosphorous (P) additions on the northern Tibetan Plateau. ANPP, species diversity, functional diversity, and functional groups were used to assess species' responses to increasing nutrients. Our results showed that nutrient additions significantly increased ANPP due to the release in nutrient limitations. Although N addition had a significant effect on species richness and functional richness, and P and N + P additions altered functional diversity, it was functional groups rather than biodiversity that drove changes in ANPP in the indirect pathways. We identified the important roles of N and P additions in begetting the dominance of grasses and forbs, respectively. The study highlights that the shift of functional groups should be taken into consideration to better predict the structure, function, and biodiversity-ANPP relationship in grasslands, particularly under future multifaceted global change.

Nitrogen-doped metal-organic framework derived porous carbon/polymer membrane for the simultaneous extraction of four benzotriazole ultraviolet stabilizers in environmental water.

Benzotriazole ultraviolet stabilizers (BUVSs) that are added to pharmaceutical and personal care products (PPCPs) have raised global concerns because of their high toxicity. An efficient method to monitor its pollution level is urgently imperative. Here, a nitrogen-doped metal-organic framework (MOF) derived porous carbon (UiO-66-NH2/DC) was prepared and integrated into polyvinylidene fluoride mixed matrix membrane (PVDF MMM) as an adsorbent for the first time. The hydrophobic UiO-66-NH2/DC with a pore size of 162 Å exhibited outstanding extraction performance for BUVSs, which solves the problem of difficult enrichment of large-size and hydrophobic targets. Notably, the density functional theory simulation was employed to reveal the structure of the derived carbon material and explored the recognition and enrichment mechanism (synergy of π-π conjugation, hydrogen bond, coordination, hydrophobic interaction and mesoporous channel) of BUVSs by UiO-66-NH2/DC-PVDF MMM. And then, an influential method based on dispersive membrane extraction (DME) coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for the simultaneous analysis of four BUVSs in environmental water samples. The validated method benefited from the high sensitivity (the limits of detection within 0.25-1.40 ng/L), accuracy (recoveries of 71.9-102.8% for wastewater) and rapidity (50 min to enrich 9 samples). This study expands the application prospects of porous carbon derived from MOF for sample pretreatment of pollutants in water.

Microbial metabolic limitation and carbon use feedback in lead contaminated agricultural soils.

Potentially toxic elements (PTEs) pollution causes a great threat to microbial metabolism, which plays a vital role in studying soil nutrient cycling and predicting carbon (C) storage in agroecosystems. However, the responses of microbial metabolism characteristic to heavy metal contamination and the mechanisms through which microbial metabolism mediate nutrient cycling and C dynamics in contaminated soil remain elusive. Here, we performed an incubation experiment over 80 days to investigate the variations in microbial metabolic limitation under various Pb levels (0, 100, 500, 800, 1500, 2000, and 3000 mg Pb kg-1 dry soil) in cropland soil using extracellular enzymatic stoichiometry, and to reveal the impact of Pb stress on soil C storage by associating with microbial metabolic quotients (qCO2) and C use efficiency (CUE). The results showed microbial relative C limitation and phosphorus (P) limitation were observed in Pb-contaminated soils. Pb addition enhanced the microbial relative C limitation by approximately 7.3%, while decreasing the P limitation by approximately 12.3%. Furthermore, Pb addition led to higher qCO2 (from 8.75 to 108 µg C kg-1 MBC-1 d-1) duo to the increase of microbial relative C limitation, suggesting that the more CO2 was released of per unit of microbial biomass C. The increase of microbial relative C limitation reduced CUE (from 0.35 to 0.10) because of the change in microbial metabolism from growth to respiration maintenance under Pb stress. Consequently, the CUE and qCO2 together determined the loss of soil C. Our study reveals that microbial relative C limitation is the dominant driver of soil C loss and provides important knowledge of microbial metabolic limitation regulating soil C turnover in PTEs-contaminated agricultural soils.

Variation of plant CSR strategies across a precipitation gradient in the alpine grasslands on the northern Tibet Plateau.

Identifying ecological strategies based on functional traits can help us better understand plants' adaptations and changes in ecological processes, and thus predict the impact of climate change on ecosystems, especially in the vulnerable alpine grasslands. Herein, we investigated the plant CSR strategies of four grassland types (alpine meadows, AM; alpine meadow steppes, AMS; alpine steppes, AS; and alpine desert steppes, ADS) and its functional groups (grasses, sedges, legumes, and forbs) along the east-to-west gradient of decreasing precipitation on the northern Tibetan grasslands by using Grime's CSR (C: competitor, S: stress tolerator, and R: ruderal) analysis. Although alpine grasslands were dominated by S-strategy, our results also indicated that AM with higher water, nitrogen (N) and phosphorus (P) availability had significantly lower S-strategy values and relatively higher C- and R-strategy values (C: S: R = 6: 63: 31 %) than those in AMS (C: S: R = 3: 94: 3 %,), AS (C: S: R = 3: 87: 10 %), and ADS (C: S: R = 1: 94: 5 %). The CSR strategy values of forbs and legumes showed greater variability compared with grasses and sedges in the environmental gradient. Furthermore, water variability on the precipitation gradient eventually affected plant traits and CSR strategies through soil N and P availability and pH. Our findings highlighted that plant CSR strategies were regulated by the availability of soil resources, and plants adopted more flexible adaptation strategies in relatively resource-rich environments. This study sheds light on the mechanisms of plant adaptation to the changing environment in the alpine grasslands.

Functional identity of leaf dry matter content regulates community stability in the northern Tibetan grasslands.

Biodiversity-stability mechanisms have been the focus of many long-term community stability studies. Community functional composition (i.e., functional diversity and functional identity of community plant functional traits) is critical for community stability; however, this topic has received less attention in large-scale studies. Here, we combined a field survey of biodiversity and plant functional traits in 22 alpine grassland sites throughout the northern Tibetan Plateau with 20 years of satellite-sensed proxy data (enhanced vegetation index) of community productivity to identify the factors influencing community stability. Our results showed that functional composition influenced community stability the most, explaining 61.71% of the variation in community stability (of which functional diversity explained 18.56% and functional identity explained 43.15%), which was a higher contribution than that of biodiversity (Berger-Parker index and species evenness; 35.04%). Structural equation modeling suggested that functional identity strongly affected community stability, whereas biodiversity had a minor impact. Furthermore, functional identity of leaf dry matter content regulated community stability by enhancing species dominance (Berger-Parker index). Our findings demonstrate that functional composition, specifically functional identity, plays a key role in community stability, highlighting the importance of functional identity in understanding and revealing the stabilizing mechanisms in these fragile alpine ecosystems which are subjected to increasing environmental fluctuations.

[Applications of microfluidic paper-based chips in environmental analysis and detection].

Microfluidic paper-based chips have many advantages such as ease of integration, miniaturization, and automation; high throughput; low production cost; easy portability; easy storage and transportation, environmental friendliness, and feasibility of instantaneous detection. These chips are widely used in clinical diagnosis, food quality control, and immunoassays. With the continuous development of microfluidic paper microarrays in recent years, they have also received great attention for environmental contaminant analysis and detection, and research in this field has been intensive, showing excellent prospects for application. This review summarizes the latest research progress in environmental analysis from the perspective of the application of microfluidic paper-based chips, as well as future development trends and challenges. More than 150 papers from the Science Citation Index (SCI) and Chinese core journals are cited in this paper. This review includes the advantages of microfluidic paper-based chips for environmental analysis and detection; the introduction of paper chip fabrication methods, including wax printing, photolithography, dicing, plasma, laser, and inkjet etching; and the introduction of advanced analytical methods based on paper chips, such as electrochemical analysis, fluorescence analysis, colorimetric analysis, surface-enhanced Raman analysis, and integrated sensing methods. The future development trends and prospects of environmental analysis based on microfluidic paper-based chips are also reviewed. Through a rich and comprehensive review of recent related research, it is shown that although microfluidic paper-based chip technology has only been developed for little more than a decade since its introduction, this technology has seen rapid development in environmental analysis-related research and has yielded rich results. The hydrophilic and porous nature of cellulose in paper as a chip substrate allows the passive transport of liquids without an external power source. The diversity of available microfluidic paper-based chip fabrication and analysis methods allows flexible selection and matching according to different environmental conditions and detection requirements, so that the best detection results can be obtained. Moreover, microfluidic paper chips as detection platforms show good biocompatibility in the analysis and detection of environmental pollutants, enabling the analysis of more types of pollutants. The used paper is biodegradable and can be directly disposed of as ordinary garbage after appropriate degradation treatment; thus it is environmentally friendly and does not impact the health of the operators. In addition, the low production cost and simple operation of the paper chip design study make it possible to fabricate low-cost, portable, and practical analytical equipment, which is important for rapid testing of the conventional environment. However, there are some inherent disadvantages: the mechanical strength of the paper is not sufficiently high to resist deformation; degree of fluid control is difficult to achieve the desired effect, and the sample flow may be lost due to leakage; multiple contaminants may interfere with one another when analyzed in parallel; there are difficulties in commercial mass production. However, these problems also point to the direction for the research and development of microfluidic paper-based chips in the field of environmental testing. With continuous advances in manufacturing and analysis technologies, microfluidic paper-based chips are expected to play a more prominent role in future environmental analysis.

Exogenous application of signaling molecules to enhance the resistance of legume-rhizobium symbiosis in Pb/Cd-contaminated soils.

Being signaling molecules, nitric oxide (NO) and hydrogen sulfide (H2S) can mediate a wide range of physiological processes caused by plant metal toxicity. Moreover, legume-rhizobium symbiosis has gained increasing attention in mitigating heavy metal stress. However, systematic regulatory mechanisms used for the exogenous application of signaling molecules to alter the resistance of legume-rhizobium symbiosis under metal stress are currently unknown. In this study, we examined the exogenous effects of sodium nitroprusside (SNP) as an NO donor additive and sodium hydrosulfide (NaHS) as a H2S donor additive on the phytotoxicity and soil quality of alfalfa (Medicago sativa)-rhizobium symbiosis in lead/cadmium (Pb/Cd)-contaminated soils. Results showed that rhizobia inoculation markedly promoted alfalfa growth by increasing chlorophyll content, fresh weight, and plant height and biomass. Compared to the inoculated rhizobia treatment alone, the addition of NO and H2S significantly reduced the bioaccumulation of Pb and Cd in alfalfa-rhizobium symbiosis, respectively, thus avoiding the phytotoxicity caused by the excessive presence of metals. The addition of signaling molecules also alleviated metal-induced phytotoxicity by increasing antioxidant enzyme activity and inhibiting the level of lipid peroxidation and reactive oxygen species (ROS) in legume-rhizobium symbiosis. Also, signaling molecules improved soil nutrient cycling, increased soil enzyme activities, and promoted rhizosphere bacterial community diversity. Both partial least squares path modeling (PLS-PM) and variation partitioning analysis (VPA) identified that using signaling molecules can improve plant growth by regulating major controlling variables (i.e., soil enzymes, soil nutrients, and microbial diversity/plant oxidative damage) in legume-rhizobium symbiosis. This study offers integrated insight that confirms that the exogenous application of signaling molecules can enhance the resistance of legume-rhizobium symbiosis under metal toxicity by regulating the biochemical response of the plant-soil system, thereby minimizing potential health risks.

Fluorescent nanosensor designing via hybrid of carbon dots and post-imprinted polymers for the detection of ovalbumin.

We reported a facile strategy to assemble a ratiometric nanosensor for the ovalbumin (OVA) fluorescence determination and meanwhile it can be utilized for selective visual identification by naked eyes with fluorescent test papers under 365 nm UV lamp. The nanosensor was prepared through simply mixing blue color carbon dots (CDs) and green color core-shell imprinted polymers. Blue CDs were used directly as the internal reference without participating in the imprinting process and modified molecularly imprinted polymers (MIPs) were synthesized by post-imprinting, using fluorescein isothiocyanate (FITC) as fluorescence enhanced signal. Upon the addition of different concentrations of OVA, the fluorescence intensity of FITC was enhanced, while the fluorescence intensity of CDs was almost unchanged, leading to a detection limit as low as 15.4 nM. Accordingly, the fluorescence color was gradually changed from blue to dark olive green to green with naked eyes observation. Moreover, the ratiometric nanosensor was successfully applied to detect OVA in the human urine samples with satisfactory recoveries attaining of 92.0-104.0% with relative standard deviation (RSD) of 3.3-3.9% and 93.3-101.0% with RSDs of 2.7-3.8% for the spiked chicken egg white samples. This strategy reported here opens a novel pathway for biomacromolecule detection in real applications and can realize the visual observation on fluorescent test papers.

Functional ZnS:Mn(II) quantum dot modified with L-cysteine and 6-mercaptonicotinic acid as a fluorometric probe for copper(II).

Manganese-doped ZnS quantum dots (ZnS:Mn(II) QDs) were synthesized and modified with L-cysteine (L-Cys) and 6-mercaptonicotinic acid (MNA). This prevents the aggregation of the QDs and makes them available for the interaction with Cu(II) ions via Cu(II)-S interaction. As a result, the fluorescence of the QDs is quenched by Cu(II) due to an electron transfer mechanism. The QDs display two emission peaks under 325 nm excitation, one (being red) peaking at 593 nm, the other (blue) at 412 nm. The red fluorescence is strongly quenched, while the blue fluorescence is not affected. An easily distinguishable color change from orange red to purple can be observed in fluorescence as the concentration of Cu(II) is increased. The probe is selective over commonly encountered other ions. The ratio of fluorescence intensities at 593 and 412 nm increases linearly in the 5 to 500 nM Cu(II) concentration range, and the detection limit is 1.2 nM. Graphical abstract Schematic of the preparation of manganese-doped quantum dots functionalized with L-cysteine and 6-mercaptonicotinic acid for selective and sensitive visual detection of copper ions.

A molecular imprinting-based turn-on Ratiometric fluorescence sensor for highly selective and sensitive detection of 2,4-dichlorophenoxyacetic acid (2,4-D).

A novel molecular imprinting-based turn-on ratiometric fluorescence sensor was constructed via a facile sol-gel polymerization for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) on the basis of photoinduced electron transfer (PET) by using nitrobenzoxadiazole (NBD) as detection signal source and quantum dots (QDs) as reference signal source. With the presence and increase of 2,4-D, the amine groups on the surface of QDs@SiO2 could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited, while the QDs maintained constant intensities. Accordingly, the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D, along with continuous color changes from orange-red to green readily observed by the naked eye. The as-prepared fluorescence sensor obtained high sensitivity with a low detection limit of 0.14µM within 5min, and distinguished recognition selectivity for 2,4-D over its analogs. Moreover, the sensor was successfully applied to determine 2,4-D in real water samples, and high recoveries at three spiking levels of 2,4-D ranged from 95.0% to 110.1% with precisions below 4.5%. The simple, rapid and reliable visual sensing strategy would not only provide potential applications for high selective ultratrace analysis of complicated matrices, but also greatly enrich the research connotations of molecularly imprinted sensors.

Molecular imprinting ratiometric fluorescence sensor for highly selective and sensitive detection of phycocyanin.

A facile strategy was developed to prepare molecular imprinting ratiometric fluorescence sensor for highly selective and sensitive detection of phycocyanin (PC) based on fluorescence resonance energy transfer (FRET), via a sol-gel polymerization process using nitrobenzoxadiazole (NBD) as fluorescent signal source. The ratio of two fluorescence peak emission intensities of NBD and PC was utilized to determine the concentration of PC, which could effectively reduce the background interference and fluctuation of diverse conditions. As a result, this sensor obtained high sensitivity with a low detection limit of 0.14 nM within 6 min, and excellent recognition specificity for PC over its analogues with a high imprinting factor of 9.1. Furthermore, the sensor attained high recoveries in the range of 93.8-110.2% at three spiking levels of PC, with precisions below 4.7% in seawater and lake water samples. The developed sensor strategy demonstrated simplicity, reliability, rapidity, high selectivity and high sensitivity, proving to be a feasible way to develop high efficient fluorescence sensors and thus potentially applicable for ultratrace analysis of complicated matrices.