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.     

A rapid and ultrasensitive colorimetric biosensor based on aptamer functionalized Au nanoparticles for detection of saxitoxin

Saxitoxin (STX) is one of the most important marine toxins which affects the safety of domestic water. Rapid, sensitive and selective recognition of STX is crucial in environment monitoring. Here, we demonstrate a facile and ultrasensitive colorimetric sensor based on gold nanoparticles (Au NPs) and aptamer (Au NPs-aptamer biosensor) for specific and quantitative detection of STX. The aptamer reacts specifically with STX, resulting in the aggregation of Au NPs and the color change of the Au NP solution. The lowest detection concentration of the colorimetric sensor is 10 fM (3 fg mL⁻¹), and a good linear relationship (R² = 0.9852) between the absorbance ratio and STX concentrations (10 fM to 0.1 μM) indicates that our Au NPs-aptamer biosensor can be used for quantitative sensing of STX. The detection time of STX is 30 minutes, and the sensor is successfully applied in the specific detection of STX in seawater. The Au NP-aptamer biosensor shows great potential in practical applications to monitor environmental pollution, marine aquaculture pollution, and seafood safety.

We demonstrate a facile and ultrasensitive colorimetric sensor based on gold nanoparticles (Au NPs) and aptamer (Au NPs-aptamer biosensor) for specific and quantitative detection of STX.      

A novel coumarin-based colorimetric and fluorescent probe for detecting increasing concentrations of Hg2+in vitro and in vivo

Mercury has complex biological toxicity and can cause a variety of physiological diseases and even death, so it is of great importance to develop novel strategies for detecting trace mercury in environmental and biological samples. In this work, we designed a new coumarin-based colorimetric and fluorescent probe CNS, which could be obtained from inexpensive starting materials with high overall yield in three steps. Probe CNS could selectively respond to Hg²⁺ with obvious color and fluorescence changes, and the presence of other metal ions had no effect on the fluorescence changes. Probe CNS also exhibited high sensitivity against Hg²⁺, with a detection limit as low as 2.78 × 10⁻⁸ M. More importantly, the behavioral tracks of zebrafish had no obvious changes upon treatment with 10 μM probe CNS, thus indicating its low toxicity. The probe showed potential application value and was successfully used for detecting Hg²⁺ in a test strip, HeLa cells and living zebrafish larvae.

Mercury has complex biological toxicity and can cause a variety of physiological diseases and even death, so it is of great importance to develop novel strategies for detecting trace mercury in environmental and biological samples.     

Two novel colorimetric fluorescent probes: Hg2+ and Al3+ in the visual colorimetric recognition environment

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively. The two probes were characterized by FTIR, ¹H NMR, ¹³C NMR and HRMS, and their optical properties were detected by UV and FL. Test results showed the probes'' detection of Hg²⁺ and Al³⁺ compared to other metal ions (Ag⁺, Co²⁺, Cd²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Ba²⁺, Pb²⁺, Cr³⁺, Al³⁺, Zn²⁺, Hg²⁺, K⁺, Ga²⁺ and Fe³⁺), respectively. Besides, the detection limits were determined to be 1.61 × 10⁻⁸ M and 1.15 × 10⁻⁸ M through the standard curve plot, respectively. The photoelectron transfer (PET) mechanism was guessed by the Job''s plot and the infrared titration. Corresponding orbital electron distribution and molecular geometry configurations of the compounds were predicted by density functional theory (DFT). In addition, the prepared test paper changed from white to pink when the target ion was detected. The color changed from colorless to pink in a solution having a concentration of 10⁻⁵ M.

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively.     

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.     

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.     

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.     

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.     

Removal of As3+, As5+, Sb3+, and Hg2+ ions from aqueous solutions by pure and co-precipitated akaganeite nanoparticles: adsorption kinetics studies

Adsorption kinetics models have been used to evaluate the adsorption behaviour of pollutants on different materials but there are no reports for the adsorption of As⁵⁺, As³⁺, Sb³⁺ and Hg²⁺ on co-precipitated akaganeite nanoparticles which were previously formed in the presence of these ions. In this research, the performance of pure and co-precipitated akaganeite nanoparticles as adsorbents of As³⁺, As⁵⁺, Sb³⁺ and Hg²⁺ in aqueous solutions was evaluated using the nonlinear kinetics models of Langmuir, Lagergren, Ho–McKay, Bangham, Elovich and simplified Elovich. In addition, transmission ⁵⁷Fe Mössbauer spectrometry was used for the first time to compare the physico-chemical properties of akaganeite before and after the adsorption processes. The results showed that co-precipitated akaganeites had much better adsorption capacities than pure akaganeites. On the other hand, the Sb³⁺ and Hg²⁺ were the fastest and slowest pollutants respectively adsorbed on all akaganeites. The kinetics models that best described the experimental data for As³⁺, As⁵⁺ and Sb³⁺ were those of Elovich and simplified Elovich. For Hg²⁺, the kinetic model that best described the experimental data was that of Bangham. The 300 K and 77 K Mössbauer spectrometry showed only slight variations in some of the hyperfine parameters for the akaganeites after adsorption.

Morphologically-modified akaganeite nanoparticles adsorbed As³⁺, As⁵⁺, Sb³⁺ and Hg²⁺. Sb³⁺ was the better adsorbed pollutant, whereas Hg²⁺ was the least.     

An aggregation-induced emission-based fluorescence turn-on probe for Hg2+ and its application to detect Hg2+ in food samples

In this work, we presented a new tetraphenylethene-derived fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution. Probe TPE-M is molecularly dissolved in CH₃OH/PBS (20 mM, pH = 7.4) (3 : 7, v/v) mixed solution and is almost non-emissive. Reaction of TPE-M with Hg²⁺ leads to release of an AIE-active precursor 4, and results in a significant fluorescence enhancement. The Hg²⁺ recognition process has some distinct advantages including rapid response, high selectivity and sensitivity, strong anti-interference ability, and a low detection limit (4.16 × 10⁻⁶ M). Moreover, the probe is applicable to detect Hg²⁺ in real food samples such as shrimp, crab and teas, suggesting the practical applicability of TPE-M.

A new AIE-based fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution has been developed.     

A gold nanoparticle based colorimetric and fluorescent dual-channel probe for acetylcholinesterase detection and inhibitor screening

Based on the competitive host–guest interaction between p-sulfonatocalix[6]arene (p-SC₆A) capped AuNPs and Rhodamine B (RhB)/acetylthiocholine, a fluorescent and colorimetric dual channel probe was developed for rapid detection of AChE with high sensitivity and selectivity. The detection limit was estimated to be 0.16 mU mL⁻¹. Crucially, due to the specific host–guest interaction, the high selectivity of the bioassay permitted the discrimination of AChE from other cations and proteins including biothiols and enzymes. Furthermore, the present method was also successfully applied to determinate AChE levels and screen AChE inhibitors in real cerebrospinal fluid (CSF) samples, which suggested that our proposed method has great potential to be applied in monitoring the disease progression and drug treatment effects of Alzheimer''s disease (AD).

A novel colorimetric and fluorescent dual-channel probe was developed for acetylcholinesterase detection and inhibitor screening with high sensitivity and selectivity.     

Highly sensitive and selective colorimetric detection of dual metal ions (Hg2+ and Sn2+) in water: an eco-friendly approach

Application of an alliin-based precursor for the synthesis of silver nanoparticles (Ag NPs) which is an emerging, reliable and rapid sensor of heavy metal ion contaminants in water is reported here. The Ag NPs were characterized by using UV-visible spectroscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy analysis techniques. The Ag NPs simultaneously and selectively detect Hg²⁺ and Sn²⁺ ions from aqueous solution. The sensitivity and selectivity of the prepared Ag NPs towards other representative transition-metal ions, alkali metal ions and alkaline earth metal ions were also studied. For more precise evidence, a density functional theory study was carried out to understand the possible mechanism and interaction in the detection of Hg²⁺ and Sn²⁺ by Ag NPs. The limits of detection for Hg²⁺ and Sn²⁺ ions were found as 15.7 nM and 11.25 nM, respectively. This assay indicates the possible use of garlic extract-synthesized Ag NPs for sensing Hg²⁺ and Sn²⁺ in aqueous solution very significantly. So, the simple, green, eco-friendly and easy method to detect the dual metal ions may further lead to a potential sensor of heavy metal ion contaminants in water of industrial importance.

Synthesis of Ag nanoparticles using Allin based garlic extract for highly sensitive and selective detection of metal ions Hg²⁺ and Sn²⁺ in water. The limit of detection (LoD) for Hg²⁺ and Sn²⁺ ions were found as 15.7 nM and 11.25 nM respectively.     

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit

A novel solvent-dependent chemosensor 1o based on a diarylethene containing a rhodamine B unit has been designed. It could be used as a dual-functional chemosensor for selective detection of Hg²⁺ and Cu²⁺ by monitoring the changes in the fluorescence and UV-vis spectral in different solvents. A striking fluorescence enhancement at 617 nm was observed in DMSO upon the addition of Hg²⁺. However, 1o showed a remarkable absorption band appeared with maximum absorption at 555 nm after the addition of Cu²⁺ in THF. The results of ESI-MS spectra and Job''s plot confirmed a 1 : 1 binding stoichiometry between 1o and the two ions. The limits of detection of Hg²⁺ and Cu²⁺ were determined to be 0.14 μM and 0.51 μM, respectively. A 1 : 2 demultiplexer circuit was constructed by using UV light as data input, Cu²⁺ as the address input, and the absorbance at 555 nm and the absorbance ratio of (A₆₀₃/A₂₇₄) as the dual data outputs.

A novel solvent-dependent chemosensor based on a diarylethene derivative for fluorescent “turn-on” recognition of Hg²⁺ and colorimetric detection of Cu²⁺ was synthesized, its multi-controllable photoswitchable behaviors with light and chemical stimuli were investigated.     

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.     

Removal of Au3+ and Ag+ from aqueous media with magnetic nanoparticles functionalized with squaramide derivatives

New magnetic hybrid nanoparticles of Fe₃O₄ coated with organosulfur-squaramide compounds are prepared. The modified-nanoparticles show a good coordination for Ag⁺ and Hg²⁺ cations in water, and present a high affinity for Au³⁺ ions. The behaviour of the squaramide-coated nanoparticles differs significantly from that previously reported for nanoparticles used as Au³⁺ scavengers. In the presence of organosulfur-squaramide, the Au³⁺ salt is reduced to gold nanoparticles that are deposited upon Fe₃O₄ nanoparticles. For the first time, the coordination capacity of the carbonyl squaramide groups with the gold cation, based on purely electrostatic cation–dipole interactions, is proved.

An efficient methodology, based on squaramide-coated magnetite nanoparticles, for the removal of Au³⁺ and Ag⁺ by magneto filtration from water.     

Novel single excitation dual-emission carbon dots for colorimetric and ratiometric fluorescent dual mode detection of Cu2+ and Al3+ ions

In this study, dual-emission carbon dots (D-CDs) are synthesized via a simple one-step solvothermal treatment of red tea. The obtained D-CDs are characterized by XPS, IR, TEM, XRD, fluorescence and UV-vis spectroscopy techniques. It is found that D-CDs present a strong red fluorescence emission peak at 671 nm and weak blue fluorescence emission peak at 478 nm under the excitation wavelength of 410 nm. The unique dual-emission properties of D-CDs provide great opportunities in ratiometric fluorescence sensing applications. The results show that Cu²⁺ ions can quench the fluorescence of the red emission band of D-CDs effectively, resulting in the disappearance of red fluorescence ultimately. Upon the addition of Al³⁺ ions, the fluorescence of blue emission band at 478 nm grows apparently, and the fluorescence color transforms gradually from red to orange, then to yellow-green. Based on these findings, a novel ratiometric fluorescence and colorimetric dual mode nanosensor is developed for simultaneous detection of Cu²⁺ and Al³⁺ ions. Regarding Cu²⁺ ions, the fluorescent detection linear range is 0.1–50 μM with detection limit of 0.1 μM, and the colorimetric detection limit is estimated as 25 μM. With regard to Al³⁺ ions, the fluorescent detection linear range is 0–20 μM and 25–100 μM with detection limit of 0.5 μM, and the colorimetric detection limit is 20 μM. Furthermore, the fluorescence response mechanisms of Cu²⁺ and Al³⁺ ions were discussed detailed. To the best of our current knowledge, this will be the first research work on the simultaneous determination of Cu²⁺ and Al³⁺ using D-CDs as fluorescent probes.

D-CDs with strong red emission and weak blue emission as an effective colorimetric and ratiometric fluorescence sensing probe are employed to realize the simultaneous detection of Cu²⁺ and Al³⁺ ions without any interference effect.     

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.     

Functionalization of silver nanoparticles with mPEGylated luteolin for selective visual detection of Hg2+ in water sample

A novel colorimetric sensor based on mPEGylated luteolin-functionalized silver nanoparticles (mPEGylated luteolin-AgNPs) in an aqueous solution was prepared. The mPEGylated luteolin-AgNP solution was utilized to detect Hg²⁺ with high sensitivity and selectivity in the presence of other metal cations including Na⁺, K⁺, Mg²⁺, Zn²⁺, Ni²⁺, Mn²⁺, Ba²⁺, Pb²⁺, Sr²⁺, Ca²⁺, Cd²⁺, Al³⁺ and Cu²⁺. The solution could be induced to aggregate, and a color change from yellow-brown to colorless was observed in the presence of Hg²⁺. Meanwhile, the sensor was successfully used to detect Hg²⁺ in tap water with satisfactory recovery ranges using the standard addition method.

A novel colorimetric sensor for selective detection of Hg²⁺ based on mPEGylated luteolin functionalized silver nanoparticles was prepared.     

1,3,4-Thiadiazol derivative functionalized-Fe3O4@SiO2 nanocomposites as a fluorescent probe for detection of Hg2+ in water samples

5-Amino-1,3,4-thiadiazole-2-thiol was used to synthesize a novel fluorescent functionalizing group on a Fe₃O₄@SiO₂ magnetic nanocomposite surface for detection of heavy metal ions in water samples. The prepared probe was characterized by using X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and a vibrating sample magnetometer. Among various tested ions, the new nanocomposite responded to Hg²⁺ ions with an intense fluorescence “turn-off”. The limit of detection of the probe shows that it is sensitive to the minimum Hg²⁺ concentration of 48.7 nM. Theoretical calculations were done for estimating binding energies of the three possible bonding modes and the visualized molecular orbitals were presented.

VBYT-Fe₃O₄@SiO₂ fluorescent probe was designed for sensitive detection of mercury in water samples.