Excluding interference and detecting Microcystin-LR in the natural lakes and cells based a unique fluorescence method

Unraveling the mechanisms underlying the fluorescent probe detection of microcystin-LR and its binding with CT-DNA

Cyanobacteria blooms are concerning due to algal toxins like microcystin-leucine arginine (MC-LR). Despite progress in detecting MC-LR and understanding its toxic effects, including calf thymus DNA (CT-DNA) damage, the mechanisms for fluorescent probe detection of MC-LR and its binding to CT-DNA are poorly understood. In this study, we designed three fluorescent probes for MC-LR detection. Probe 1, with an acidic recognition site, is effective but influenced by solution pH. Probe 2, featuring a benzene ring structure, shows stable detection regardless of pH. Probe 3 offers the best performance, combining a long-chain and benzene ring structure. This suggests that combining these structures is beneficial for MC-LR probe design. Using Probe 3, we observed a strong interaction between MC-LR and CT-DNA. UV absorption spectroscopy, circular dichroism (CD) spectra, and molecular docking techniques provided the first evidence of MC-LR binding to CT-DNA through intercalation, with a binding saturation value of 8.33, significantly impacting CT-DNA structure. This study introduces a novel strategy for designing fluorescent probes for MC-LR detection, along with new insights into the interactions between MC-LR and CT-DNA.

Visualization of MC-LR in lakes using near-infrared technology

Microcystin-LR (MC-LR), a secondary metabolite produced by cyanobacteria, poses significant ecological and health risks, particularly in lakes, where fluctuations in its concentration directly affect water quality and the living environment of nearby residents. However, the complexity of lake environments and the absence of suitable rapid monitoring tools have made long-term and extensive MC-LR monitoring challenging. This study proposed an effective monitoring tool based on near-infrared (NIR) fluorescence technology for the rapid assessment of MC-LR in lakes. The results demonstrated that the NIR fluorescent probe specifically binds to MC-LR, inducing changes in the fluorescence signal. Fluorescence analysis revealed a significant positive correlation between the probe's signal and MC-LR concentrations in lakes with varying pollution levels. Stepwise multiple linear regression and random forest analyses confirmed that fluorescence signal changes were primarily influenced by MC-LR. Additionally, the probe's long emission wavelength (699-783 nm) reduced background fluorescence interference, while its large Stokes shift (> 100 nm) minimized excitation light interference, significantly enhancing the signal-to-noise ratio of the measurements. The NIR fluorescent probe offers a promising solution for detecting MC-LR in natural lakes, advancing water quality monitoring by providing a rapid and reliable assessment tool.

A water quality assessment model involving novel fluorescence technology

The reasonable utilization of water resources and real-time monitoring of water pollution are the core tasks of current world hydrological and water conservancy work. Novel technologies and methods for monitoring water pollution are important means to ensure water health. However, the absence of intuitive and simple analysis methods for the assessment of regional pollution in large-scale water bodies has prevented scientists from quickly grasping the overall situation of water pollution. In this study, we propose a strategy based on the unique combination of fluorescence technology and simple kriging (SK) interpolation (FL-SK) for the first time. This strategy could present the relative magnitude and distribution of the physicochemical indicators of a whole natural lake intuitively and accurately. The unique FL-SK model firstly offers a simple and effective water quality method that provides the pollution index of different sampling points in lakes. The macroscopic evaluation of large-scale water bodies by the FL-SK model primarily relies on the fluorescence response of the RDM-TPE to the comprehensive indicators of the water body, as experimental results have revealed a good correlation between fluorescent responses and six normalized physicochemical indicators. Multiple linear regression and fluorescence response experiments on RDM-TPE indicate that to some extent, the fluorescence signals of the FL-SK model may originate from a certain type of sulfide in the water body. Pattern discovery could enable the analysis of pollution levels in other ecosystems and promote early pollution assessment in the future.

Molecular engineering of a new method for effective removal of cadmium from water

Cadmium (Cd) is a widespread and highly toxic environmental pollutant, seriously threatening animal and plant growth. Therefore, monitoring and employing robust tools to enrich and remove Cd from the environment is a major challenge. In this work, by conjugating a fluorescent indicator (CCP) with a functionalized glass slide, a special composite material (CCPB) was constructed to enrich, remove, and monitor Cd2+ in water rapidly. Then Cd2+ could be effectively eluted by immersing the Cd-enriched CCPB in an ethylenediaminetetraacetic acid (EDTA) solution. With this, the CCPB was continuously reused. Its recovery of Cd2+was above and below 100 % after multiple uses by flame atomic absorption spectrometry (FAAS), which was excellent for practical use in enriching and removing Cd2+ in real aqueous samples. Therefore, CCPB is an ideal material for monitoring, enriching, and removing Cd2+ in wastewater, providing a robust tool for future practical applications of Cd enrichment and removal in the environment.

Introducing fluorescent probe technology for detecting microcystin-LR in the water and cells

BACKGROUND

For a long time, the environment hazards caused by cyanobacteria bloom and associated microcystins have attracted attention worldwide. Microcystin-LR (MC-LR) is the most widely distributed and most toxic toxin. At present, numerous MC-LR detection methods exist many drawbacks. Therefore, a quick and accurate method for identifying and detecting MC-LR is crucial and necessary. In this work, we strived to introduce a novel fluorescence assay to detect MC-LR in the water and cells.

RESULTS

According to the special spatial configuration and physicochemical properties of MC-LR, we designed and constructed six fluorescent probes. The design concepts of the probes were exhaustively elaborated. MC-YdTPA, MC-YdTPE, MC-RdTPA, and MC-RdTPE could show significant fluorescence enhancement in MC-LR solution. Significantly, MC-YdTPA, MC-YdTPE, and MC-RdTPA could also response well in the cells treated with MC-LR, demonstrating these fluorescent probes' values. The recognition mechanism between probes and MC-LR were also deeply explored: (1) The polyphenylene ring structure of probes may have nested or hydrogen bond weak interaction with the ring structure of MC-LR. (2) The probes can generate a reaction to the hydrogen ions ionized by MC-LR.

SIGNIFICANCE

We proposed the novel ideas for designing MC-LR probes. This research can provide valuable experiences and important assistance in synthesizing MC-LR fluorescent probes. We expect that this work may bring new ideas to develop fluorescent probes for researching MC-LR in vivo and in vitro.

Visualization of microcystin-LR and sulfides in plateau lakes

In eutrophic water bodies, sulfides are closely related to the growth of cyanobacteria and the production of microcystin-LR (MC-LR). To date, the underlying interaction mechanism between a sulfides and MC-LR remains controversial. Thus, visually presenting the distribution characteristics of sulfides and MC-LR in contaminated water is crucial. Here, we propose a novel and expeditious practical approach, utilizing fluorescence probe technology, to assess the distribution characteristics of MC-LR and sulfur in natural lakes. We have developed novel probes, pib2, to detect HSO3- and HS-, and pib18, to simultaneously identify MC-LR and sulfides. Through correlation analysis of fluorescence data and physicochemical indicators at sampling points, it is found that fluorescence data has good correlation with sulfides and MC-LR, and speculated that pib2 and pib18 may be able to detect sulfides and MC-LR in lakes. Using this method, we rapidly obtained the distribution of MC-LR and sulfur in Qilu and Erhai Lakes. Notably, for the first time, we rapidly displayed the distributions of sulfides and MC-LR across lakes by the fluorescent probe technology.

Feedback of lake trophic status via MC-LR fluorescence technique

Eutrophication remains one of the most challenging environmental problems, and microcystin-leucine-arginine (MC-LR) produced in eutrophic waters would cause serious ecological risks. However, the traditional assessment methods of trophic status, such as water quality index (WQI) and trophic status index (TSI), could not directly reflect the existence or concentration of MC-LR in water. Moreover, traditional MC-LR detection methods are costly and time-consuming. Therefore, it remains a challenge to develop a method that can simply and quickly reflect the level of MC-LR. Herein, a novel probe with specific response to MC-LR was proposed to assess the distribution characteristics of MC-LR in water bodies. By combining the response signal of the probe with the filtered water sample and the water quality parameters, a more accurate assessment tool for MC-LR was obtained. This probe can specifically respond to MC-LR in aqueous solution, and its fluorescence signal is enhanced with the increase of MC-LR concentration. More importantly, the fluorescent signal of the probe showed a significant positive correlation with MC-LR concentration in water samples. This visualization tool has practical application potential for the preliminary assessment of MC-LR in eutrophic waters.

Immobilization of Microcystin by the Hydrogel-Biochar Composite to Enhance Biodegradation during Drinking Water Treatment

Microcystin-LR (MC-LR), the most common algal toxin in freshwater, poses an escalating threat to safe drinking water. This study aims to develop an engineered biofiltration system for water treatment, employing a composite of poly(diallyldimethylammonium chloride)-biochar (PDDA-BC) as a filtration medium. The objective is to capture MC-LR selectively and quickly from water, enabling subsequent biodegradation of toxin by bacteria embedded on the composite. The results showed that PDDA-BC exhibited a high selectivity in adsorbing MC-LR, even in the presence of competing natural organic matter and anions. The adsorption kinetics of MC-LR was faster, and capacity was greater compared to traditional adsorbents, achieving a capture rate of 98% for MC-LR (200 μg/L) within minutes to tens of minutes. Notably, the efficient adsorption of MC-LR was also observed in natural lake waters, underscoring the substantial potential of PDDA-BC for immobilizing MC-LR during biofiltration. Density functional theory calculations revealed that the synergetic effects of electrostatic interaction and π-π stacking predominantly contribute to the adsorption selectivity of MC-LR. Furthermore, experimental results validated that the combination of PDDA-BC with MC-degrading bacteria offered a promising and effective approach to achieve a sustainable removal of MC-LR through an "adsorption-biodegradation" process.

Assessing the pollution level of a subtropical lake by using a novel hydrogen sulfide fluorescence technology

Hydrogen sulfide (H₂S) is an important environmental toxin with bi-directional biological effects on organisms. In natural waters, H₂S complexes with heavy metal ions in an anaerobic environment influence heavy metals' bioavailability and induce phosphorus release and eutrophication in water columns. Traditional detection techniques, such as colorimetric, electrochemical, and chromatographic, cannot simultaneously detect H₂S and pollution assessment of subtropical lakes. To address these technical defects, we developed small-molecule fluorescent probes to evaluate the pollution level in natural water bodies. This method relies on the combination of the probes' response signals to raw water and the water quality index, thereby enhancing the accuracy and reliability of water quality assessments. Furthermore, this novel material has a large Stokes shift. It can detect complex levels of H₂S concentrations in natural water bodies by correlating the degree of contamination and fluorescence signals. The development of this visual research tool for detecting environmental H₂S levels in natural water bodies is expected to have meaningful, practical applications.

Visible light-driven photocatalytic degradation of Microcystin-LR by Bi2WO6/Reduced graphene oxide heterojunctions: Mechanistic insight, DFT calculation and degradation pathways

Developing heterostructure photocatalysts for removing Microcystin-LR (MC-LR) under visible light was of positive significance to control the risk of Microcystins and ensure the safety of water quality. Herein, the Bi₂WO₆/Reduced graphene oxide (RGO) nanocomposites were prepared via a simple one-spot hydrothermal method for the first time to degrade MC-LR. The optimized Bi₂WO₆/RGO (Bi₂WO₆/RGO_3%) achieved a removal efficiency of 82.3% toward MC-LR, with 1.9-fold higher efficiencies than Bi₂WO₆, and it showed superior reusability and high stability after 5 cycles. The degradation efficiency of MC-LR demonstrated a negative trend with the initial concentration of MC-LR, fulvic acid, and initial algal density increased, while MC-LR removal rate for the presence of anions was in the order of Cl^- > CO₃^-2 > NO₃^- > H₂PO₄^-. The degradation efficiency of MC-LR could reach up to 82.3% within 180 min in the neutral condition. The active species detection experiments and EPR measurements demonstrated that the holes (h⁺), hydroxide radicals (∙OH), and superoxide radicals (∙O₂^-) participated in the degradation of MC-LR. The DFT calculations showed that 0.56 of electron transferred from Bi₂WO₆ to RGO, indicating RGO introduction could prevent the recombination of photoelectrons and holes and was beneficial for MC-LR degradation. Finally, the possible intermediate products and degradation pathways were also proposed by the LC-MS/MS analysis.

Bioinspired polydopamine-mediated metal-organic framework click-grafting aptamers functionalized fabric for highly-specific recognition of microcystin-leucine arginine

Fabricating functional electrospun nanofiber coating for highly selective extraction of microcystin-LR (MC-LR) was of significant importance for water-safety monitoring. Herein, a novel MOF@aptamer functionalized nanofabric was presented via a facile and reliable strategy integrating polydopamine (PDA) mediation and thiol-ene chemistry and applied for specific recognition of the MC-LR model analyte. Using polydopamine (PDA) as the mediating layer, vinyl-UiO-66 MOF was grown in situ, followed by post-synthetic modification (PSM) of Zr⁴⁺ with vinyl phosphate and rapid UV-initiated click reaction of aptamers. Uniform deposition of Zr-based MOF (vinyl-UiO-66) on the nanofibers was directly produced, and the tedious co-electrospinning process was abandoned to prevent the aggregation and encapsulation of MOF. Via an efficient "thiol-ene" chemistry, massive thiol-terminated aptamers were grafted on MOF within one step under friendly conditions, rather than the time-consuming nanoparticle adsorption or unfriendly covalent chemical reactions. As a result, the robust MOF@aptamer-coated nano-fabrics were obtained, and a highly selective performance towards MC-LR was illustrated with a limit of detection (LOD) at 0.002 ng/mL, good precision (CV<8.3%), good repeatability (2.2∼6.0%) when coupled with LC-MS. Almost 1∼2 orders of magnitude higher detection sensitivity was exhibited than that of the common non-specific SPE/SPME fiber reported so far. Applied to water samples, the good matrix-resistance ability, and acceptable recovery yields were achieved with high specificity. This strategy might provide a rapid and friendly protocol to efficiently fabricate MOF@aptamer functionalized nano-fabrics through electrospinning and interfacial "thiol-ene" chemistry for highly-selective microextraction.