Integration detection of mercury(ii) and GSH with a fluorescent “on-off-on” switch sensor based on nitrogen,sulfur co-doped carbon dots

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg²⁺ and glutathione (GSH). This was attributed to Hg²⁺ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg²⁺ and the sulfhydryl of GSH. Based on the “on-off-on” tactic, the detection limits of Hg²⁺ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg²⁺ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

NS-CDs are employed as a sensitive sensor for the integration detection of Hg²⁺ and GSH. Hg²⁺ effectively quenching the fluorescence by static quenching. GSH is able to recover the fluorescence owing to the stronger binding between Hg²⁺ and GSH.     

On-site,rapid and visual method for nanomolar Hg2+ detection based on the thymine–Hg2+–thymine triggered “double” aggregation of Au nanoparticles enhancing the Tyndall effect

This work describes a new nanosensor for the simple, rapid, portable, colorimetric analysis of mercury(ii) (Hg²⁺) ions by combining the sensitive Tyndall effect (TE) of colloidal Au nanoparticles (AuNPs) with specific thymine–Hg²⁺–thymine (T–Hg²⁺–T) coordination chemistry for the first time. For the TE-inspired assay (TEA), in the presence of Hg²⁺ in a sample, the analyte can selectively mediate the hybridization of three types of flexible single-stranded DNAs (ssDNAs) to form stable rigid double-stranded DNAs (dsDNAs) via the T–Hg²⁺–T ligand interaction. Subsequent self-assembly of the dsDNAs with terminal thiol groups on the AuNPs'' surfaces led to their “double” aggregation in addition to the lack of sufficient ssDNAs as the stabilizing molecules in a high-salt solution, resulting in a remarkably enhanced TE signal that positively relied on the Hg²⁺ level. The results demonstrated that such a TEA method enabled rapid naked-eye qualitative analysis of 625 nM Hg²⁺ within 10 min with an inexpensive laser pointer pen as an inexpensive handheld light source to generate the TE response. Making use of a smartphone for portable TE readout could further quantitatively detect the Hg²⁺ ions in a linear concentration range from 156 to 2500 nM with a limit of detection as low as 25 nM. Moreover, the developed equipment-free nanosensor was also used to analyze the Hg²⁺ ions in real samples including tap water, drinking water, and pond water, the obtained recoveries were within the range of 93.68 to 108.71%. To the best of our knowledge, this is the first report of using the AuNPs and functional nucleic acids to design a TE-based biosensor for the analysis of highly toxic heavy metal ions.

A new equipment-free colorimetric nanosensor was initially developed for quantitative point-of-need detection of nanomolar Hg²⁺ ions based on the enhancement in Tyndall effect of Au nanoparticles via their target-triggered “double” aggregation.     

Porous BMTTPA–CS–GO nanocomposite for the efficient removal of heavy metal ions from aqueous solutions

In this study, a stable, cost-effective and environmentally friendly porous 2,5-bis(methylthio)terephthalaldehyde–chitosan–grafted graphene oxide (BMTTPA–CS–GO) nanocomposite was synthesized by covalently grafting BMTTPA–CS onto the surfaces of graphene oxide and used for removing heavy metal ions from polluted water. According to well-established Hg²⁺–thioether coordination chemistry, the newly designed covalently linked stable porous BMTTPA–CS–GO nanocomposite with thioether units on the pore walls greatly increases the adsorption capacity of Hg²⁺ and does not cause secondary pollution to the environment. The results of sorption experiments and inductively coupled plasma mass spectrometry measurements demonstrate that the maximum adsorption capacity of Hg²⁺ on BMTTPA–CS–GO at pH 7 is 306.8 mg g⁻¹, indicating that BMTTPA–CS–GO has excellent adsorption performance for Hg²⁺. The experimental results show that this stable, environmentally friendly, cost-effective and excellent adsorption performance of BMTTPA–CS–GO makes it a potential nanocomposite for removing Hg²⁺ and other heavy metal ions from polluted water, and even drinking water. This study suggests that covalently linked crucial groups on the surface of carbon-based materials are essential for improving the adsorption capacity of adsorbents for heavy metal ions.

Novel porous BMTTPA–CS–GO nanocomposites are prepared by covalently grafting BMTTPA–CS onto GO surfaces, and used for efficient removal of heavy metal ions from polluted water.     

Ultrasmall aqueous starch-capped CuS quantum dots with tunable localized surface plasmon resonance and composition for the selective and sensitive detection of mercury(ii) ions

Ultrasmall starch-capped CuS quantum dots (QDs) with controllable size were chemically fabricated in an aqueous medium. The phase of the CuS QDs was confirmed via X-ray diffraction (XRD), whereas the characteristic localized surface plasmon resonance (LSPR) peak in the near-infrared (NIR) region was measured using UV-Vis spectroscopy. Transmission electron microscopy and high bandgap analysis confirmed the formation of ultrasmall CuS QDs in the size range of 4–8 nm. CuS QDs have been used for the selective and sensitive detection of Hg²⁺ ions through colorimetric and spectroscopic techniques. The selective sensing of Hg²⁺ ions from various metal ions was detected via a remarkable change in color, damping in LSPR intensity, significant change in the Fourier-transform infrared spectra and X-ray photoelectron spectroscopic measurements. The mechanism of interaction between the CuS QDs and Hg²⁺ ions has been deeply explored in terms of the role played by the starch and the reorganization of sulfide and disulfide bonds to facilitate the access of Hg²⁺ ions into the CuS lattice. Finally, an intermediate Cu_2−xHg_xS nanostructure resulted in the leaching of Cu⁺ ions into the solution, which were further recovered and reused for the formation of fluorescent Cu₂S nanoparticles. Thus, the entire process of synthesis, sensing and reuse paves the way for sustainable nanotechnology.

Colorimetric response of CuS QDs with mercury ions.     

A new class of fluorogenic thiazolo[2,3-b]quinazolinone receptor: selective detection towards mercury and hydrogen bisulfate ions in aqueous medium

A series of fluorophoric and structurally diverse thiazoloquinazoline derivatives were synthesized in a one-pot multicomponent cascade reaction using a microwave irradiation technique. The unique structural arrangement of the synthesized compounds encouraged us to design a new type of bioactive molecular receptor. This receptor interacts with HSO₄⁻ in 1 : 1 and Hg²⁺ in 1 : 2 binding stoichiometric ratios resulting in a change in fluorescence as well as absorption spectra in aqueous medium. The ion bonded receptor complex possibly enhances the fluorescence signal of the receptor via H-bonded complex formation with HSO₄⁻ ions and co-ordinate complex formation with Hg²⁺ ions.

Fluorophoric thiazoloquinazoline derivatives were synthesized under microwave assisted one-pot three-component cascade reaction. Owing to their unique structural arrangement, a new bioactive molecular receptor was developed for HSO⁴⁻ and Hg²⁺ ions.     

Rational design of fluorescent probe for Hg2+ by changing the chemical bond type

Two kinds of fluorescent probes DFBT and DFABT, and their corresponding water-soluble compounds WDFBT and WDFABT, based on the trimers containing a benzo[2,1,3]thiadiazole moiety and two fluorene moieties are synthesized. Their luminescent behavior towards Hg²⁺ ions and other various metal ions in organic and water solutions are studied in detail via absorption and emission spectroscopy. All these probes show a selective “on–off-type” fluorescent response to Hg²⁺ ions in solution over other metal ions with a maximum detection limit of 10⁻⁷ M. Importantly, the probe type can be changed from irreversible to reversible by altering the bridge mode between the functional units from C C triple bond to C–C single bond. Their detection mechanisms towards Hg²⁺ are studied in detail via mass spectrometry and Job plots, which are attributed to irreversible chemical reaction for DFABT and WDFABT and a reversible coordination reaction for DFBT and WDFBT respectively. Our research results about this kind of organic fluorescent probe provide valuable information to the future design of practical Hg²⁺ fluorescent probes.

Two kinds of fluorescent probes for Hg²⁺ with different detection mechanism have been realized by simply changing the chemical bond.     

Sulfhydryl functionalized carbon quantum dots as a turn-off fluorescent probe for sensitive detection of Hg2+

Mercury ion (Hg²⁺) is one of the most toxic heavy metal ions and lowering the detection limit of Hg²⁺ is always a challenge in analytical chemistry and environmental analysis. In this work, sulfhydryl functionalized carbon quantum dots (HS-CQDs) were synthesized through a one-pot hydrothermal method. The obtained HS-CQDs were able to detect mercury ions Hg²⁺ rapidly and sensitively through fluorescence quenching, which may be ascribed to the formation of nonfluorescent ground-state complexes and electron transfer reaction between HS-CQDs and Hg²⁺. A modification of the HS-CQD surface by –SH was confirmed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The HS-CQDs sensing system obtained a good linear relationship over a Hg²⁺ concentration ranging from 0.45 μM to 2.1 μM with a detection limit of 12 nM. Delightfully, the sensor has been successfully used to detect Hg²⁺ in real samples with satisfactory results. This means that the sensor has the potential to be used for testing actual samples.

Schematic presentation of the synthesis of HS-CQDs and the application as a “turn-off” fluorescent probe for Hg²⁺ detection.     

A highly selective colorimetric fluorescent probe for detection of Hg2+ and its application on test strips

An efficient fluorescent probe Pyr-Rhy based on pyrazole was developed, which can detect Hg²⁺ in water. Its fluorescence properties were studied by UV-vis and fluorescence spectroscopy, and the study results indicated that this probe can selectively detect Hg²⁺via complexation reaction, and then cause a remarkable color change from colorless to pink and a strong fluorescence enhancement can be observed. Furthermore, this probe showed high sensitivity with the detection limit down to 2.07 × 10⁻⁸ M, and its stoichiometric ratio toward Hg²⁺ ions was 1 : 1. The sensing mechanism was investigated by Job''s plot ¹H NMR titrations, and FT-IR spectra analysis, which demonstrated a chelation-enhanced fluorescence (CHEF) mechanism. More importantly, obvious color changes of sensor Pyr-Rhy can be observed when it was impregnated on filter paper testing strips and immersed in Hg²⁺ solution (water as solution), indicating its potential application for trace Hg²⁺ detection in environmental samples.

An efficient fluorescent probe Pyr-Rhy based on pyrazole was developed, which can detect Hg²⁺ in water.     

Bis-BODIPY linked-triazole based on catechol core for selective dual detection of Ag+ and Hg2+

Herein, we introduced a new chemosensor, bis-BODIPY linked-triazole based on catechol (BODIPY-OO) prepared by bridging two units of BODIPY fluorophore/triazole binding group with a catechol unit. A solution of this compound displayed 4- and 2-fold enhancements in fluorescence intensity after adding a mole equivalent amount of Ag⁺ and Hg²⁺ ions in methanol media, respectively. ¹H NMR titrations of BODIPY-OO with Ag⁺ and Hg²⁺ suggested that the triazole was involved in the recognition process. BODIPY-OO showed high sensitivity toward Ag⁺ and Hg²⁺ over other metal ions with detection limits of 0.45 μM and 1 μM, respectively. It can also distinguish Hg²⁺ from Ag⁺ by addition of an EDTA. This compound can therefore be employed as practical fluorescent probe for monitoring the presence of Ag⁺ and Hg²⁺ ions.

BODIPY–triazole–catechol combination serves as a “turn-on” fluorescent probe for dual detection and differentiation of Hg²⁺ and Ag⁺ ions.     

Rapid electrochemical quantification of trace Hg2+ using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg²⁺) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn–Ag–In–S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg²⁺ detection. Based on the “turn-off” reaction of a hairpin DNA probe binding with a mismatched target and Hg²⁺ through the formation of T–Hg²⁺–T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg²⁺ with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg²⁺. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg²⁺ was studied in vitro, with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg²⁺ ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg²⁺ in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.

A ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quantum dot on screen-printed gold electrodes, was developed for Hg²⁺ detection.     

Environmentally friendly synthesis of photoluminescent biochar dots from waste soy residues for rapid monitoring of potentially toxic elements

Single-step environmentally friendly synthesis of biochar dots (BCDs) was developed using hydrothermal treatment of waste biomass. Using soy residue as the carbon precursor, the resultant BCDs had strong and stable photoluminescence. Characterization by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy indicates that the BCDs prepared were water soluble, spherical, oxygenous and nitrogen-doped carbon nanoparticles with 10–20 nm in diameter. The fluorescence quantum yield of the BCDs was 3.7%. The use of the BCDs as a very effective fluorescent probe for label-free, rapid, and selective detection of Hg²⁺ and Fe³⁺ ions was further demonstrated with good linear relationships at 0–50 μM and 10–50 μM, respectively. The minimum detection limits of Hg²⁺ and Fe³⁺ were 100 nM and 30 nM. Furthermore, the feasibility of using the BCDs for monitoring of Hg²⁺ and Fe³⁺ in open waters was also established.

Waste biomass was used as a carbon precursor to prepare photoluminescent biochar dots for economical and eco-friendly monitoring of Hg²⁺ and Fe³⁺ ions.     

Development of a fused imidazo[1,2-a]pyridine based fluorescent probe for Fe3+ and Hg2+ in aqueous media and HeLa cells

A new fluorescent sensor 5 based on a fused imidazopyridine scaffold has been designed and synthesized via cascade cyclization. The reaction features the formation of three different C–N bonds in sequence. Imidazopyridine based fluorescent probe 5 exhibits highly sensitive and selective fluorescent sensing for Fe³⁺(‘turn-on’) and Hg²⁺(‘turn-off’). The excellent selectivity of imidazopyridine for Fe³⁺/Hg²⁺ was not hampered in the presence of any of the competing cations. The limit of detection (LOD) of 5 toward Fe³⁺ and Hg²⁺ has been estimated to be 4.0 ppb and 1.0 ppb, respectively, with a good linear relationship (R² = 0.99). Notably, 5 selectively detects Fe³⁺/Hg²⁺ through fluorescence enhancement signalling both in vitro and in HeLa cells.

A new fluorescent sensor 5 having fused imidazopyridine scaffold has been synthesized via cascade cyclization. It exhibits highly sensitive and selective detection of Fe³⁺ (‘turn-on’) and Hg²⁺ (‘turn-off’) in vitro and in HeLa cells.     

A pH-stable Ag(i) multifunctional luminescent sensor for the efficient detection of organic solvents,organochlorine pesticides and heavy metal ions

Developing novel luminescent materials for sensitive and rapid detection of heavy metal ions, organic solvents and organochlorine pesticides is vital for environmental monitoring. Herein, a new Ag(i) luminescent coordination polymer [Ag(3-dpyb)(H₃odpa)]·H₂O (LCP 1) (3-dpyb = N,N′-bis(3-pyridinecarboxamide)-1,4-butane, H₄odpa = 4,4′-oxydiphthalic acid) was obtained by a hydrothermal reaction and characterized by single crystal, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and luminescence spectroscopy. LCP 1 is a three-dimensional (3D) supramolecular framework formed from 1D [Ag-3-dpyb-H₃odpa]_n chains and H-bond interactions. The luminescence sensing study of LCP 1 for recognizing organic solvents, organochlorine pesticides and heavy metal ions was performed, which demonstrated it to be a potential luminescent sensor for Hacac, NB, 2,6-DCN, Fe²⁺, Hg²⁺, and Fe³⁺. Fe²⁺, Hg²⁺, and Fe³⁺ in river water were determined using LCP 1 with satisfying recovery.

3D supramolecular LCP 1 can detect Hacac, NB, 2,6-DCN, Fe²⁺, Hg²⁺, and Fe³⁺ with a low detection limit and pH stability.     

Synthesis of MoS2 nanosheets for mercury speciation analysis by HPLC-UV-HG-AFS

Mercury species have aroused wide concern in the past several decades due to their high toxicity. However, it is still difficult to detect ultra-trace mercury species due to their biochemical transformation in complex samples. To establish a simpler and more sensitive method for pre-concentration and determination of trace mercury species, molybdenum disulfide (MoS₂) nanosheets with sulfur-rich characteristics and enlarged interlayer spacing were prepared by a hydrothermal method coupled with a sonication-assisted liquid exfoliation method and acted as solid-phase extraction adsorbent. The nano-MoS₂ had high adsorption capacity, fast adsorption rate and excellent selectivity towards mercury ions (Hg²⁺), methyl mercury (MeHg⁺) and ethyl mercury (EtHg⁺) in a wide pH range and complex matrices. And it could be easily regenerated by 4 mol L⁻¹ HCl and reused several times. After optimizing HPLC-UV-HG-AFS conditions, a great linearity (1.0–10.0 μg L⁻¹, R² = 0.999 for Hg²⁺, MeHg⁺ and EtHg⁺), lower detection limits (0.017, 0.037 and 0.021 ng mL⁻¹ for Hg²⁺, MeHg⁺ and EtHg⁺, respectively), relative standard deviations (<5%) and addition recoveries of the samples within 82.75–113.38% were observed. In summary, trace inorganic and organic mercury species in environmental and biological samples could be selectively enriched by the prepared nano-MoS₂ and efficiently seperated and detected by HPLC-UV-HG-AFS. The present study will help provide a better strategy for environmental monitoring and health assessment of mercury pollutants.

As-synthesized few-layered molybdenum disulfide nanosheets were used as solid-phase extraction absorbent for ultra-trace mercury speciation analysis by HPLC-UV-HG-AFS.     

Synthesis,characterisation and ion-binding properties of oxathiacrown ethers appended to [Ru(bpy)2]2+. Selectivity towards Hg2+, Cd2+ and Pb2+

A series of complexes with oxathiacrown ethers appended to a [Ru(bpy)₂]²⁺ moiety have been synthesized and characterised using ¹H NMR, ¹³C NMR, IR, electronic absorption and emission spectroscopies, mass spectrometry and elemental analyses. The complexes exhibit strong MLCT luminescence bands in the range 608–611 nm and one reversible metal centred oxidation potential in the range 1.00–1.02 V. Their selectivity and sensitivity towards Hg²⁺, Cd²⁺ and Pb²⁺ metal ions have been investigated using electronic absorption, luminescence, cyclic and differential pulse voltammetry titrations. Their responses towards selected cations and anions have also been investigated using electronic absorption and luminescence. While the complexes are selective towards Hg²⁺ and Cd²⁺ ions, none of them is selective towards Pb²⁺ ions. In particular, complex 2 gives a selective change in the UV/Vis absorbance with Hg²⁺ making it possible to detect mercury down to a detection limit of 68 ppm. The binding constants and limits of detection of the complexes have been calculated, with values ranging from 4.37 to 5.38 and 1.4 × 10⁻³ to 6.8 × 10⁻⁵ for log K_s and LOD respectively.

Oxathiacrown ether modified ruthenium complex 2 facilitates a selective naked-eye detection of Hg²⁺ with an instrumental detection limit of 68 ppm.     

Sensitive electrochemical sensor based on poly(l-glutamic acid)/graphene oxide composite material for simultaneous detection of heavy metal ions

Heavy metal pollution can be toxic to humans and wildlife, thus it is of great significance to develop rapid and sensitive methods to detect heavy metal ions. Here, a novel type of electrochemical sensor for the simultaneous detection of heavy metal ions has been prepared by using poly(l-glutamic acid) (PGA) and graphene oxide (GO) composite materials to modify the glassy carbon electrode (GCE). Due to the good binding properties of poly(l-glutamic acid) (PGA) for the heavy metal ions (such as Cu²⁺, Cd²⁺, and Hg²⁺) as well as good electron conductivity of graphene oxide (GO), the heavy metal ions, Cu²⁺, Cd²⁺, and Hg²⁺ in aqueous solution can be accurately detected by using differential pulse anodic stripping voltammetry method (DPASV). Under the optimized experiment conditions, the modified GCE shows excellent electrochemical performance toward Cu²⁺, Cd²⁺, and Hg²⁺, and the linear range of PG/GCE for Cu²⁺, Cd²⁺, and Hg²⁺ is 0.25–5.5 μM, and the limits of detection (LODs, S/N ≥ 3) Cu²⁺, Cd²⁺, and Hg²⁺ are estimated to be 0.024 μM, 0.015 μM and 0.032 μM, respectively. Moreover, the modified GCE is successfully applied to the determination of Cu²⁺, Cd²⁺, and Hg²⁺ in real samples. All obtained results show that the modified electrode not only has the advantages of simple preparation, high sensitivity, and good stability, but also can be applied in the field of heavy metal ion detection.

A novel electrochemical sensor with high stability and good reproducibility for the simultaneous detection of heavy metal ions was prepared by using PGA/GO to modify the GCE, showing high sensitivity of superior to most of the reported values.     

A colorimetric and fluorescent chemosensor for Hg2+ based on a photochromic diarylethene with a quinoline unit

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized. The chemosensor 1O demonstrated selective and sensitive detection of Hg²⁺ ions in the presence of other competitive metal ions in acetonitrile. The stoichiometric ratio of the sensor 1O for Hg²⁺ was determined to be 1 : 1, and the limit of detection of the probe 1O was calculated to be 56.3 nM for Hg²⁺. In addition, a molecular logic circuit with four inputs and one output was successfully constructed with UV/vis light and metal-responsive behavior. ESI-MS spectroscopy, Job''s plot analysis, and ¹H NMR titration experiments confirm the binding behavior between 1O and Hg²⁺.

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized.     

Highly selective and sensitive fluorescent probe for the rapid detection of mercury ions

Mercury (Hg) is one of the major toxic heavy metals, harmful to the environment and human health. Thus, it is significantly important to find an easy and quick method to detect Hg²⁺. In this study, we designed and synthesized a simple fluorescent probe with excellent properties, such as high sensitivity and selectivity, rapid response, and outstanding water solubility. When Hg²⁺ (5 μM) was added to the probe solution, it exhibited a very large fluorescent enhancement (about 350-fold stronger than the free probe) with the help of hydrogen peroxide (H₂O₂). Probe HCDC could quantitatively detect Hg²⁺ in the range of 0–10 μM using the fluorescence spectroscopy method and the detection limit was measured to be about 0.3 nM (based on a 3σ/slope). Analytical application was also studied, and the probe HCDC exhibited excellent response to Hg²⁺ with the addition of H₂O₂ in real water samples. So, our proposed probe HCDC provided a practical and promising method for determining Hg²⁺ in the environment.

A novel water-soluble, highly selective and sensitive rapid-response fluorescent probe was developed to monitor mercury ions in real water samples.     

Sensitive distance-based paper-based quantification of mercury ions using carbon nanodots and heating-based preconcentration

This article reports the first fluorescent distance-based paper device coupled with an evaporating preconcentration system for determining trace mercury ions (Hg²⁺) in water. The fluorescent nitrogen-doped carbon dots (NCDs) were synthesized by a one-step microwave method using citric acid and ethylenediamine. The fluorescence turn-off of the NCDs in the presence of Hg²⁺ was visualized with a common black light, and the distance of the quenched fluorescence correlated to Hg²⁺ concentration. The optimal conditions for pH, NCD concentration, sample volume, and reaction time were investigated. Heating preconcentration was used to improve the detection limits of the fluorescent distance-based paper device by a factor of 100. Under the optimal conditions, the naked eye limit of detection (LOD) was 5 μg L⁻¹ Hg²⁺. This LOD is sufficient for monitoring drinking water where the maximum allowable mercury level is 6 μg L⁻¹ as established by the World Health Organization (WHO). The fluorescent distance-based paper device was successfully applied for Hg²⁺ quantification in water samples without interference from other cations. The proposed method provides several advantages over atomic absorption spectroscopy including ease of use, inexpensive material and fabrication, and portability. In addition, the devices are simple to fabricate and have a long shelf-life (>5 months).

This article reports the first fluorescent distance-based paper device coupled with an evaporating preconcentration system for determining trace mercury ions (Hg²⁺) in water.     

A ratiometric and colorimetric probe for detecting Hg2+ based on naphthalimide–rhodamine and its staining function in cell imaging

In this work, a rhodamine derivative was developed as a colorimetric and ratiometric fluorescent probe for Hg²⁺. It exhibited a highly sensitive fluorescence response toward Hg²⁺. Importantly, studies revealed that the probe could be used for ratiometric detection of Hg²⁺, with a low detection limit of 0.679 μM. The mechanism of Hg²⁺ detection using compound 1 was confirmed by ESI-MS, ¹H NMR, and HPLC. Upon the addition of Hg²⁺, the rhodamine receptor was induced to be in the ring-opening form via an Hg²⁺-promoted hydrolysis of rhodamine hydrazide to rhodamine acid. In addition to Hg²⁺ detection, the naphthalimide–rhodamine compound was proven to be effective in cell imaging.

A new probe based on naphthalimide–rhodamine was applied in recognition of Hg²⁺ by a FRET mechanism.