Branch-Migration Based Fluorescent Probe for Highly Sensitive Detection of Mercury

A novel red-to-near-infrared AIE fluorescent probe for detection of Hg2+ with large Stokes shift in plant and living cells

Due to the highly toxic nature of mercury ions to living organisms, accurately detecting Hg2+ in water samples and biological systems is of great significance. In this study, we designed and synthesized a novel red-to-near-infrared Aggregation-Induced Emission (AIE) fluorescent probe (named as DS) based Fluorene derivatives on specifically for Hg2+ detection. Probe DS can visually identify Hg2+ through an red-to-near-infrared fluorescence enhancement change, characterized by a large Stokes shift (130 nm) and AIE feature. This probe offers a fast response, high selectivity and sensitivity. The Hg2+-induced deprotection reaction of the thioketal mechanism was thoroughly investigated using nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS) and density functional theory (DFT) calculation. Additionly, dynamic light scattering (DLS) results indicated that the aggregation states changes of the molecular play a crucial role in the AIE fluorescence response of probe DS toward Hg2+. The red-to-near-infrared response with AIE feature not only avoids the interference of auto-fluorescence signals in complex environments, but also reduces the fluorescence quenching caused by probe molecular aggregation. This makes probe DS highly suitable for high-quality imaging detection of Hg2+ in aqueous environments. Furthermore, probe DS demonstrates the capability for visual fluorescence detection of Hg2+ concentrations in water sample, plant roots and living cells.

Detection and application of hypochlorous acid in both aqueous environments and living organisms

The scarcity of water resources has raised concerns regarding drinking water safety. Excessive addition of hypochlorous acid (OCl-) as a disinfectant in drinking water can result in severe consequences. Moreover, abnormal levels of OCl- within the human body can lead to various diseases. Employing fluorescence analysis, the design and synthesis of specific fluorescent probes for simultaneous detection of OCl- in water environments and living organisms holds strategic significance in ensuring the safety of drinking water and mitigating potential risks caused by its abnormal concentrations. This article utilizes naphthalimide as a precursor to develop a novel probe enabling highly sensitive detection of OCl- in water environments and at the organelle level within living organisms. This endeavor serves to provide assurance for drinking water safety and offers health alerts.

Fluorescent ovalbumin-functionalized gold nanocluster as a highly sensitive and selective sensor for relay detection of salicylaldehyde, Hg(II) and folic acid

A sensitive and selective relay-based scheme for the detection of salicylaldehyde, Hg2+, and folic acid (FA) has been demonstrated using fluorescent ovalbumin functionalized gold nanoclusters (OVA-AuNCs, λem = 655 nm) in this article. The OVA-AuNCs were conjugated to salicylaldehyde via an imine linkage to form Salic_OVA-AuNCs conjugate. The molecular docking study reveals that multiple functional groups and amino acid residues are involved in the interaction between salicylaldehyde and the OVA-AuNCs. The coupling of salicylaldehyde with OVA-AuNCs results in fluorescence quenching at 655 nm and concomitant formation of an emission band at 500 nm, which have leveraged to detect salicylaldehyde down to 2.02 µM. Following that, the Salic_OVA-AuNCs has been used for the detection of Hg2+ and FA. Several processes, such as internal charge transfer (ICT), photoinduced electron transfer (PET) and metallophilic interactions, are involved between the Salic_OVA-AuNCs nanoprobe and the analytes, which allowed to detect Hg2+ and FA down to 0.13 nM and 0.11 nM, respectively. The Salic_OVA-AuNCs nanoprobe has an additional naked-eye utility when applied to paper-strip sensing strategy for Hg2+ and FA detection.

Parthenium hysterophorus derived nanostructures as an efficient carbocatalyst for the electrochemical sensing of mercury(II) ions

The sustainable utilization of resources motivate us to create eco-friendly processes for synthesizing novel carbon nanomaterials from waste biomass by minimizing chemical usage and reducing energy demands. By keeping sustainability as a prime focus in the present work, we have made the effective management of Parthenium weeds by converting them into carbon-based nanomaterial through hydrothermal treatment followed by heating in a tube furnace under the nitrogen atmosphere. The XPS studies confirm the natural presence of nitrogen and oxygen-containing functional groups in the biomass-derived carbon. The nanostructure has adopted a layered two-dimensional structure, clearly indicated through HRTEM images. Further, the nanomaterials are analyzed for their ability towards the electrochemical detection of mercury, with a detection limit of 6.17 μM, while the limit of quantification and sensitivity was found to be 18.7 μM and 0.4723 μM μA-1 cm-2, respectively. The obtained two-dimensional architecture has increased the surface area, while the nitrogen and oxygen functional groups act as an active site for sensing the mercury ions. This study will open a new door for developing metal-free catalysts through a green and sustainable approach by recycling and utilization of waste biomass.

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.

Identification of DNA variants at ultra-low variant allele frequencies via Taq polymerase cleavage of wild-specific blockers

Detecting mutations related to tumors holds immense clinical significance for cancer diagnosis and treatment. However, the presence of highly redundant wild DNA poses a challenge for the advancement of low-copy mutant ctDNA genotyping in cancer cases. To address this, a Taqman qPCR strategy to identify rare mutations at low variant allele fractions (VAFs) has been developed. This strategy combines mutant-specific primers with wild-specific blockers. Diverging from other blocker-mediated PCRs, which rely on primer-induced strand displacement or the use of modified oligos resistant to Taq polymerase, our innovation is built upon the cleavage of specific blockers by Taq polymerase. Given its unique design, which does not hinge on strand displacement or base modification, we refer to this novel method as unmodified-blocker cleavage PCR (UBC-PCR). Multiple experiments consistently confirmed that variant distinction was improved significantly by introduction of 5' unmatched blockers into the reaction. Moreover, UBC-PCR successfully detected mutant DNA at VAFs as low as 0.01% across six different variant contexts. Multiplex UBC-PCR was also performed to identify a reference target and three mutations with a sensitivity of 0.01% VAFs in one single tube. In profiling the gene status from 12 lung cancer ctDNA samples and 22 thyroid cancer FNA DNA samples, UBC-PCR exhibited a 100% concordance rate with ddPCR and a commercial ARMS kit, respectively. Our work demonstrates that UBC-PCR can identify low-abundance variants with high sensitivity in multiplex reactions, independent of strand displacement and base modification. This strategy holds the potential to significantly impact clinical practice and precision medicine.

Development and analysis of a universal label-free micro/nano component for three-channel detection of silver ions, mercury ions, and tetracycline

In this paper, an enzyme-free and label-free fluorescent nanomodule is proposed for rapid, simple and sensitive detection of Ag+, Hg2+ and tetracycline (TC). The strategy is cleverly designed to enable multiple-purpose detection with as little as 31 nt of ssDNA. Both the embedded dye SYBR Green I and the nanomaterial graphene oxide (GO) are able to distinguish single-stranded DNA from double-stranded DNA; thus, the combination of the two instead of using traditional molecular beacon (MB)-labeled fluorophores and quencher groups can effectively reduce the cost of experiments while efficiently reducing the background noise. Performance testing experiments confirmed the stability and selectivity of the platform; the limits of detection (LODs) of Ag+ and Hg2+ were 1.41 nM and 1.79 nM, respectively, and the detection range were within the WHO standards. In addition, only some base sequences in the flexible functional domain of the nanoloop needed to be programmed to build a universal platform, which was feasible using TC as a target. Therefore, the designed nanomodule has the potential to detect various types of targets, such as antibiotics, proteins, and target genes, and has broad application prospects in environmental monitoring, food testing, and disease diagnosis.

Logic-Gates of Gas Pressure for Portable, Intelligent and Multiple Analysis of Metal Ions

DNA logic gates have shown outstanding magic in intelligent biology applications, but it remains challenging to construct a portable, affordable and convenient DNA logic gate. Herein, logic gates of gas pressure were innovatively developed for multiplex analysis of metal ions. Hg²⁺ and Ag⁺ were input to interact specifically with the respective mismatched base pairs, which activated DNA extension reaction by polymerase and led to the enrichment of platinum nanoparticles for catalyzing the decomposition of peroxide hydrogen. Thus, the gas pressure obtained from a sealed well was used as output for detecting or identifying metal ions. Hg²⁺ and Ag⁺ were sensitively and selectively detected, and the assay of the real samples was also satisfactory. Based on this, DNA logic gates, including YES, NOT, AND, OR, NAND, NOR, INHIBIT, and XOR were successfully established using a portable and hand-held gas pressure meter as detector. So, the interactions between DNA and metal ions were intelligently transferred into the output of gas pressure, which made metal ions to be detected portably and identified intelligently. Given the remarkable merits of simplicity, logic operation, and portable output, the metal ion-driven DNA logic gate of gas pressure provides a promising way for intelligent and portable biosensing.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

Design and Synthesis of Dipeptidomimetic Isocyanonaphthalene as Enhanced-Fluorescent Chemodosimeter for Sensing Mercury Ion and Living Cells

A novel valine-based isocyanonaphthalene (NpI) was designed and synthesized by using an easy method and enabled the selective fluorescence detection of Hg2+. The chemodosimeter can display an immediate turn-on fluorescence response (500-fold) towards target metal ions upon the Hg2+-mediated conversion of isocyano to amino within NpI. Based on this specific reaction, the fluorescence-enhancement probe revealed a high sensitivity toward Hg2+ over other common metal ions and exhibited excellent aqueous solubility, good antijamming capability, high sensitivity (detection limit: 14.2 nM), and real-time detection. The response mechanism of NpI was supported by NMR spectroscopy, MS analysis and DFT theoretical calculation using various techniques. Moreover, a dipeptidomimetic NpI probe was successfully applied to visualize intracellular Hg2+ in living cells and monitor Hg2+ in real water samples with good recoveries and small relative standard deviations.

Versatile Integration of Liquid-Phase Microextraction and Fluorescent Aptamer Beacons: A Synergistic Effect for Bioanalysis

Fluorescent aptamer beacons (FABs) are a major category of biosensors widely used in environmental analysis. However, due to their low compatibility, it is difficult to use the common FABs for biological samples. To overcome this challenge, construction of FABs with complex structures to adapt the nature of biological samples is currently in progress in this field. Unlike previous works, we moved our range of vision from the FAB itself to the biological sample. Inspired by this idea, in this work, flat membrane-based liquid-phase microextraction (FM-LPME) with sufficient sample cleanup and preconcentration capacities was integrated with FABs. With the merits of both FM-LPME and FABs, the integrated LPME-FAB system displayed a clear synergistic enhancement for target analysis. Specifically, LPME in the LPME-FAB system provided purified and enriched Hg²⁺ for the FAB recognition, while the FAB recognition event promoted the extraction efficiency of LPME. Due to superior performances, the LPME-FAB system achieved highly sensitive analysis of Hg²⁺ in urine samples with a detection limit of 27 nM and accuracies in the range of 98-113%. To the best of our knowledge, this is the first time that an integrated LPME-FAB system was constructed for target analysis in biological samples. We believe that this study will provide a new insight into the next generation of biosensors, where the integration of sample preparation with detection probes is as important as the design of complex probes in the field of bioanalysis.

Ultrasensitive colorimetric strategy for Hg2+ detection based on T-Hg2+-T configuration and target recycling amplification

A novelty aptasensor for ultrasensitive detection of Hg²⁺ is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg²⁺, a DNA duplex can be formed due to the strong coordination of Hg²⁺ and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3' to 5' direction, resulting in the releasing of Hg²⁺. Then, the released Hg²⁺ binds with another ssDNA probe through T-Hg²⁺-T coordination. After Exo III-assisted Hg²⁺ cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg²⁺ with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg²⁺ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg²⁺ in sea water samples with good recovery.

Highly selective fluorescence probe with peptide backbone for imaging mercury ions in living cells based on aggregation-induced emission effect

Mercury is an anthropogenic toxic heavy metal found in the environment. It is highly desirable to develop a fluorescence probe that can selectively and sensitively detect mercury ions using a turn-on response. This paper reports the successful development of a peptide fluorescence probe, TP-2 (TPE-Trp-Pro-Gln-His-Glu-NH₂), which uses aggregation-induced emission effects and high selectivity to detect Hg²⁺. After fluorescence was activated, Hg²⁺ was efficiently detected using the change in fluorescence intensity. The detection limit for Hg²⁺ in the buffer solution was 41 nM (R² = 0.9952). Owing to its high sensitivity, high cell permeability, and low biotoxicity, the probe could perform live cell imaging under biological conditions. This study demonstrated that TP-2 can detect Hg²⁺ in complex biological environments.

Biosensors for wastewater-based epidemiology for monitoring public health

Public health is attracting increasing attention due to the current global pandemic, and wastewater-based epidemiology (WBE) has emerged as a powerful tool for monitoring of public health by analysis of a variety of biomarkers (e.g., chemicals and pathogens) in wastewater. Rapid development of WBE requires rapid and on-site analytical tools for monitoring of sewage biomarkers to provide immediate decision and intervention. Biosensors have been demonstrated to be highly sensitive and selective tools for the analysis of sewage biomarkers due to their fast response, ease-to-use, low cost and the potential for field-testing. This paper presents biosensors as effective tools for wastewater analysis of potential biomarkers and monitoring of public health via WBE. In particular, we discuss the use of sewage sensors for rapid detection of a range of targets, including rapid monitoring of community-wide illicit drug consumption and pathogens for early warning of infectious diseases outbreaks. Finally, we provide a perspective on the future use of the biosensor technology for WBE to enable rapid on-site monitoring of sewage, which will provide nearly real-time data for public health assessment and effective intervention.

Development of highly efficient chemosensors for Cu2+ and N2H4 detection based on 2D polyaniline derivatives by template-free chemical polymerization method

Chemosensors play an important role in environmental protection, medical diagnosis and energy conservation. Although polyaniline and its derivatives and two-dimensional (2D) materials have been applied as chemosensors in many reports, the concept of two-dimensional (2D) polyaniline derivatives has not been achieved in chemosensors. Here, two kinds of two-dimensional (2D) polyaniline derivatives are designed and synthesized by template-free chemical polymerization. It can be found that these two two-dimensional (2D) chemosensors exhibit high selectivity and sensitivity to Cu²⁺ and N₂H₄. Moreover, it is noteworthy that one of the two-dimensional materials can achieve the limit of detection (LOD) of 45 nM and 8 nM for Cu²⁺ and N₂H₄, respectively. Especially, these results imply that this two-dimensional polyaniline derivative is promising as the chemosensor in sensing field.

Th4+ tuned aggregation-induced emission: A novel strategy for sequential ultrasensitive detection and separation of Th4+ and Hg2

A novel strategy, Th⁴⁺ tuned aggregation-induced emission, for sequential ultrasensitive detection and separation of Th⁴⁺ and Hg²⁺ was developed successfully. For demonstration this strategy, we designed and synthesized two tripodal gelators TH (tri-(isoniazid-4-yl)-functionalized trimesic acylhydrazine) and TA (tri-(pyridine-4-yl)-functionalized trimesic amide). The TH and TA could assemble into a stable supramolecular polymer hydrogel THTA-G in DMSO/H₂O (3.3:6.7, v/v) binary-solution. The THTA-G does not show aggregation-induced emission (AIE) effect. However, after addition of Th⁴⁺ into the THTA-G, the obtained metallogel THTA-GTh shows strong green AIE effect, which indicated that Th⁴⁺ could tune the gel generation of AIE effect. Interestingly, the THTA-G could ultrasensitive fluorescently detect Th⁴⁺, and the corresponding metallogel THTA-GTh could ultrasensitively detect Hg²⁺. The detection limits of THTA-G and THTA-GTh for Th⁴⁺ and Hg²⁺ are 8.61 × 10^-11 mol/L and 1.08 × 10^-11 mol/L, respectively. Additionally, the xerogels of THTA-G and THTA-GTh could separate Th⁴⁺ and Hg²⁺ from aqueous solution with excellent ingestion capacity, and the THTA-G could be used as a writable smart light-emitting material.

Sensors Applied for the Detection of Pesticides and Heavy Metals in Freshwaters

Water is essential for every life living on the planet. However, we are facing a more serious situation such as water pollution since the industrial revolution. Fortunately, many efforts have been done to alleviate/restore water quality in freshwaters. Numerous sensors have been developed to monitor the dynamic change of water quality for ecological, early warning, and protection reasons. In the present review, we briefly introduced the pollution status of two major pollutants, i.e., pesticides and heavy metals, in freshwaters worldwide. Then, we collected data on the sensors applied to detect the two categories of pollutants in freshwaters. Special focuses were given on the sensitivity of sensors indicated by the limit of detection (LOD), sensor types, and applied waterbodies. Our results showed that most of the sensors can be applied for stream and river water. The average LOD was72.53±12.69 ng/ml (n=180) for all pesticides, which is significantly higher than that for heavy metals (65.36±47.51 ng/ml,n=117). However, the LODs of a considerable part of pesticides and heavy metal sensors were higher than the criterion maximum concentration for aquatic life or the maximum contaminant limit concentration for drinking water. For pesticide sensors, the average LODs did not differ among insecticides (63.83±17.42 ng/ml,n=87), herbicides (98.06±23.39 ng/ml,n=71), and fungicides (24.60±14.41 ng/ml,n=22). The LODs that differed among sensor types with biosensors had the highest sensitivity, while electrochemical optical and biooptical sensors showed the lowest sensitivity. The sensitivity of heavy metal sensors varied among heavy metals and sensor types. Most of the sensors were targeted on lead, cadmium, mercury, and copper using electrochemical methods. These results imply that future development of pesticides and heavy metal sensors should (1) enhance the sensitivity to meet the requirements for the protection of aquatic ecosystems and human health and (2) cover more diverse pesticides and heavy metals especially those toxic pollutants that are widely used and frequently been detected in freshwaters (e.g., glyphosate, fungicides, zinc, chromium, and arsenic).

DNA bioassays based on the fluorescence 'turn off' of silver nanocluster beacon

Recognition and quantification of oligonucleotide sequences play important roles in medical diagnosis. In this study, a new fluorescent oligonucleotide-stabilized silver nanocluster beacon (NCB) probe was designed for sensitive detection of oligonucleotide sequence targets. This probe contained two tailored DNA strands. One strand was a signal probe strand containing a cytosine-rich strand template for fluorescent silver nanocluster (Ag NC) synthesis and a detection sections at each end. The other strand was a fluorescence enhancing strand containing a guanine-rich section for signal enhancement at one end and a linker section complementary to one end of the signal probe strand. After synthesis of the Ag NCs and hybridization of the two strands, the fluorescence intensity of the as-prepared silver NCB was enhanced 200-fold compared with the Ag NCs. Two NCBs were designed to detect two disease-related oligonucleotide sequences, and results indicated that the two target oligonucleotide sequences in the range 50.0-600.0 and 50.0-200.0 nM could be linearly detected with detection limits of 20 and 25 nM, respectively. The developed fluorescence method using NCBs for oligonucleotide sequence detection was sensitive, facile and had potential for use in bioanalysis and diagnosis.