The use of S2O82− and H2O2 as novel specific masking agents for highly selective “turn-on” fluorescent switching recognition of CN− and I− based on Hg2+–graphene quantum dots

In this study, we report that both CN⁻ and I⁻ can enhance the fluorescent intensity of Hg²⁺–graphene quantum dots (Hg²⁺–GQDs). However, the selectivity of the sensor was poor. Accordingly, simple specific masking agents can be directly used to solve this problem. Here, for the first time, we report the use of persulfate ion (S₂O₈²⁻) as a turn-on fluorescent probe of Hg²⁺–GQDs for selective CN⁻ detection, while hydrogen peroxide (H₂O₂) was selected for its sensing ability towards I⁻ ion detection. Interestingly, the signal was immediately measured after addition of the masking agent to Hg²⁺–GQDs and the sample because its interaction was very fast and efficient. The method had a linear response in the concentration ranges of 0.5–8 μM (R² = 0.9994) and 1–12 μM (R² = 0.9998) with detection limits of 0.17 and 0.20 μM for CN⁻ and I⁻, respectively. The sensor was successfully used for the dual detection of both CN⁻ and I⁻ in real water samples with satisfactory results. In conclusion, the specific masking agents in a Hg²⁺–GQDs system appeared to be good candidates for fluorometric “turn-on” sensors for CN⁻ and I⁻ with excellent selectivity over other ions.

In this study, we report that both CN⁻ and I⁻ can enhance the fluorescent intensity of Hg²⁺–graphene quantum dots (Hg²⁺–GQDs).     

A rapid “on–off–on” mitochondria-targeted phosphorescent probe for selective and consecutive detection of Cu2+ and cysteine in live cells and zebrafish

The detection of mitochondrial Cu²⁺ and cysteine is very important for investigating cellular functions or dysfunctions. In this study, we designed a novel cyclometalated iridium(iii) luminescence chemosensor Ir bearing a bidentate chelating pyrazolyl-pyridine ligand as a copper-specific receptor. The biocompatible and photostable Ir complex exhibited not only mitochondria-targeting properties but also an “on–off–on” type phosphorescence change for the reversible dual detection of Cu²⁺ and cysteine. Ir had a highly sensitive (detection limit = 20 nM) and selective sensor performance for Cu²⁺ in aqueous solution due to the formation of a non-phosphorescent Ir–Cu(ii) ensemble through 1 : 1 binding. According to the displacement approach, Ir was released from the Ir–Cu(ii) ensemble accompanied with “turn-on” phosphorescence in the presence of 0–10 μM cysteine, with a low detection limit of 54 nM. This “on–off–on” process could be accomplished within 30 s and repeated at least five times without significant loss of signal strength. Moreover, benefiting from its good permeability, low cytotoxicity, high efficiency, and anti-interference properties, Ir was found to be suitable for imaging and detecting mitochondrial Cu²⁺ and cysteine in living cells and zebrafish.

An iridium(iii) complex-based mitochondria targeting phosphorescent probe for selectively detecting Cu²⁺ and Cys in aqueous solution, living cells and zebrafish has been developed.     

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.     

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.     

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.     

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.     

Plasmonic nanoprobes based on the shape transition of Au/Ag core–shell nanorods to dumbbells for sensitive Hg-ion detection

We report a sensitive and selective localized surface plasmon resonance (LSPR) nanoprobe for the detection of mercuric ions (Hg²⁺) using gold/silver core–shell nanorods as an optical nanosubstrate. Sulfide can quickly react with silver atoms to generate Ag₂S at room temperature in the presence of oxygen. The transformation from Ag shell to Ag₂S on the nanorod surface results in its LSPR absorption band shifting to a longer wavelength, which is attributed to their different refractive indices. Interestingly, the morphology also changed from a rod-like to dumbbell shape. However, in the presence of Hg²⁺, this morphology transformation is inhibited because the sulfide reacts with free Hg²⁺ prior to the Ag atoms. The amount of Ag₂S reduced with the increasing concentration of Hg²⁺, and the absorption band shift was also decreased. According to this “rod-like to dumbbell or not” shape change, a sensitive and selective LSPR nanoprobe was established, assisted by UV-Vis absorption spectroscopy. The detection limit of this probe for Hg²⁺ was as low as 13 nM. The efficiency of this probe in complex samples was evaluated by the detection of Hg²⁺ in spiked water samples.

Sensitive plasmonic nanoprobes for the sensitive detection of mercury ions based on a “rod-like to dumbbell or not” morphology transition of the Au/Ag core–shell hybrid nanorods.     

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.     

Synthesis of BINOL–xylose-conjugates as “Turn-off” fluorescent receptors for Fe3+ and secondary recognition of cysteine by their complexes

A novel chiral fluorescence “turn-off” sensor was synthesised using the click reaction. The sensor was a BINOL–xylose derivative, modified at the 2-position and linked by 1,2,3-triazole. It was structurally characterized by ¹HNMR, ¹³CNMR, ESI-MS and IR analysis. The selectivity of R-β-d-2 in methanol solution has been studied. Among the 19 transition metal ions, alkaline metal ions and alkaline earth metal ions studied, R-β-d-2 had a selective fluorescence quenching reaction for Fe³⁺. The detection limit of R-β-d-2 for Fe³⁺ was 0.91 μmol L⁻¹. Complexation between R-β-d-2 and Fe³⁺ was investigated by ESI-MS and ¹HNMR. The stoichiometric ratio of R-β-d-2 was 1 : 1. In addition, the R-β-d-2–Fe³⁺ complex was titrated with 20 naturally occurring amino acids and Hcy with GSH. It was found that the complex R-β-d-2–Fe³⁺ had a secondary recognition effect on Cys by switching to fluorescence.

A fluorescence sensor of BINOL–xylose derivative was synthesized, which could only detect Fe³⁺ by 1 + 1 complex with high selectivity and sensitivity. The complex of the derivative with Fe³⁺ was found to perform secondary recognition of cysteine.     

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.     

A novel strategy for sensitive and rapid detection of ascorbic acid via the Tyndall effect of cobalt hydroxide nanoflakes

Cobalt oxyhydroxide (CoOOH) nanoflakes, as nanoenzymes and fluorescence quenchers, have been widely used in colorimetric and fluorescent analysis. However, their promising light scattering property—the Tyndall effect (TE)—has never been applied in biosensors and biological analysis to date. Herein, we report for the first time a novel strategy for point-of-care detection of ascorbic acid (AA) with the TE of CoOOH nanoflakes providing colorimetric signaling. In this detection system, CoOOH nanoflakes exhibit a strong red TE signal under the illumination of a hand-held 635 nm laser pointer pen. However, the introduction of AA could induce a significant decrease of the TE because it could reduce CoOOH into Co²⁺ and results in the degradation of the CoOOH nanoflakes. The changes in the TE intensity could be read-out using a smartphone for the portable quantitative analysis of AA. The results showed that this CoOOH nanoflake-based TE-inspired assay (TEA) exhibited a good linear range from 0.25 μM to 40 μM for AA, with a detection limit of 12 nM. It also showed high selectivity toward AA over common potential interfering species. Importantly, this method possessed the advantages of simple operation, low consumption of time and equipment-free analysis and was successfully applied to the detection of AA in vitamin C tablets.

A novel colorimetric nanosensor was initially developed for the equipment-free sensitive detection of ascorbic acid based on the Tyndall effect of cobalt hydroxide nanoflakes.     

A highly selective “turn-on” water-soluble fluorescent sensor for gallium ion detection

In this work, a novel sensor, (E)-N′-(3-(tert-butyl)-2-hydroxybenzylidene)thiophene-2-carbohydrazide (1), based on salicylaldehyde and thiophene hydrazide moieties was designed and synthesized. The single-crystal structure of 1 was achieved and studied for understanding its functional properties. The interaction and recognition abilities of 1 with different metal ions were investigated. Sensor 1 showed excellent “turn-on” fluorescence with highly selective and specific recognition ability in the presence of gallium ions (Ga³⁺) in an aqueous solution. The sensing behavior of 1 with Ga³⁺ was also studied by photophysical experiments, ESI-MS analysis, and ¹H NMR titration. The limit of detection (LOD) and limit of quantification (LOQ) of 1 for the detection of Ga³⁺ in an aqueous solution were calculated as 58 nM, and 192 nM, respectively. DFT calculations were carried out to optimize the configuration of 1 and 1–Ga³⁺ complexes and rationalize the photophysical experimental data. Highly selective test strips based on sensor 1 were developed for Ga³⁺ detection. Sensor 1 was also used to detect Ga³⁺ in actual water samples, and a considerable recovery rate was obtained.

In this work, a highly selective water-soluble “turn-on” fluorescent sensor for gallium ion recognition was reported.     

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.     

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.     

An innovative study on the “on–off–on” detection of sulfur ions based on a TSPP–riboflavin fluorescent probe

In this paper, 5,10,15,20-(4-sulphonatophenyl) porphyrin (TSPP) was synthesized by a facile route and used as a fluorescent probe to construct a sensor system based on the high water solubility and high quantum yield. It was found that when riboflavin (RF) was introduced into the TSPP solution, the fluorescence intensity of TSPP decreased for the peaks at 645 nm and 700 nm based on the principle of the electrostatic attractions and hydrophobic interactions between TSPP and riboflavin. When the fluorescence emission peak of riboflavin appeared at 550 nm, the fluorescence sensor system changed from the “on” state to the “off” state. When sulfur ions (S²⁻) were further introduced into the TSPP–riboflavin system, the fluorescence intensity of riboflavin was further decreased based on the specific reaction between S²⁻ and riboflavin. However, the fluorescence signal of TSPP was restored and the fluorescence sensing system changed from the “off” state to the “on” state. Therefore, TSPP was used as a fluorescent probe to construct an “on–off–on” fluorescent sensing system, the linear range of S²⁻ detected by this system is 5.0 × 10⁻⁹ to 3.6 × 10⁻⁵ M, and the detection limit (LOD) is 1.1 × 10⁻⁹ M. The sensing system has higher accuracy and sensitivity, and it can be successfully used in the sensing of S²⁻ in real samples.

In this paper, 5,10,15,20-(4-sulphonatophenyl) porphyrin (TSPP) was synthesized by a facile route and used as a fluorescent probe to construct a sensor system based on the high water solubility and high quantum yield.     

Poly(adenine)-mediated DNA-functionalized gold nanoparticles for sensitive detection of mercury ions in aqueous media

In this work, a facile and sensitive colorimetric sensor for Hg²⁺ ions based on poly (adenine)-mediated DNA-functionalized gold nanoparticles (Au NPs) is reported. One DNA sequence consisting of poly-A and T-rich DNA was designed rationally. Poly-A was used as an anchoring block to bind tightly to Au NPs, and T-rich DNA was utilized for specific recognition of Hg²⁺ ions. With the assistance of poly-A, T-rich DNA was easily introduced onto the surface of Au NPs and kept an upright orientation. In the presence of Hg²⁺ ions, T base binding with Hg²⁺ ions results in the formation of “T–Hg²⁺–T” among the Au NPs, which caused aggregation of the Au NPs and a subsequent change in the color of the solution, from wine red to grayish blue. On this occasion, the limit of detection (LOD) was 3.75 nM Hg²⁺ ions with a linear range from 5 nM to 200 nM, as measured by UV-Vis spectroscopy. Moreover, successful application of this method for the detection of Hg²⁺ ions in real samples was demonstrated.

In this work, a facile and sensitive colorimetric sensor for Hg²⁺ ions based on poly (adenine)-mediated DNA-functionalized gold nanoparticles (Au NPs) is reported.     

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.     

A dual colorimetric probe for rapid environmental monitoring of Hg2+ and As3+ using gold nanoparticles functionalized with d-penicillamine

A highly sensitive and selective colorimetric assay for the dual detection of Hg²⁺ and As³⁺ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed. When Hg²⁺ and As³⁺ ions coordinate with AuNP-bound DPLs, the interparticle distance decreases, inducing aggregation; this results in a significant color change from wine red to dark midnight blue. The Hg4f and As3d signals in the X-ray photoelectron spectra of Hg²⁺ (As³⁺)-DPL-AuNPs presented binding energies indicative of Hg²⁺–N(O) and As³⁺–N(O) bonds, and the molecular fragment observed in time-of-flight secondary ion mass spectra confirmed that Hg²⁺ and As³⁺ coordinated with two oxygen and two nitrogen atoms in DPL. The detection of Hg²⁺ and As³⁺ can be accomplished by observing the color change with the naked eye or by photometric methods, and this was optimized to provide optimal probe sensitivity. The assay method can be applied for environmental monitoring by first selectively quantifying Hg²⁺ in water samples at pH 6, then estimating the As³⁺ concentration at pH 4.5. The efficiency of the DPL-AuNP probe was evaluated for the sequential quantification of Hg²⁺ and As³⁺ in tap, pond, waste, and river water samples, and absorbance ratios (A₇₃₀/A₅₂₅) were correlated with Hg²⁺ and As³⁺ concentrations in the linear range of 0–1.4 μM. The limits of detection in water samples were found to be 0.5 and 0.7 nM for Hg²⁺ and As³⁺, respectively. This novel probe can be utilized for the dual determination of Hg²⁺ and As³⁺, even in the presence of interfering substances in environmental samples.

A highly sensitive and selective colorimetric assay for the dual detection of Hg²⁺ and As³⁺ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed.     

An ‘‘off–on–off’’ sensor for sequential detection of Cu2+ and hydrogen sulfide based on a naphthalimide–rhodamine B derivative and its application in dual-channel cell imaging

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu²⁺ and hydrogen sulfide (H₂S) was synthesized from naphthalimide–rhodamine B through the PET and FRET mechanism. The sensor showed a selective “off–on” fluorescence response with a 120-fold increase toward Cu²⁺, and its limits of detection were 0.26 μM and 0.17 μM for UV-vis and fluorescence measurements, respectively. In addition, 1–Cu²⁺ was an efficient “on–off” sensor to detect H₂S with detection limits of 0.40 μM (UV-vis measurement) and 0.23 μM (fluorescence measurement), respectively. Furthermore, the sensor can also be used for biological imaging of intracellular staining in living cells. Therefore, the sensor should be highly promising for the detection of low level Cu²⁺ and H₂S with great potential in many practical applications.

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu²⁺ and hydrogen sulfide (H₂S) was synthesized from naphthalimide–rhodamine B through the PET and FRET mechanism.     

A near-infrared fluorescent probe with an improved Stokes shift achieved by tuning the donor–acceptor–donor character of the rhodamine skeleton and its applications

In this paper, we report a novel near-infrared (NIR) mitochondrion-targeted fluorescent probe, RQS, with an improved Stokes shift (96 nm) for the specific detection of mitochondrial mercury ion (Hg²⁺) because mitochondrion is one of the main targeted organelles of Hg²⁺. For the preparation of the probe, a novel asymmetrical fluorescent xanthene dye RQ was first synthesized by tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton, and then the probe RQS was constructed by the mechanism of mercury-promoted ring-opening reaction. As expected, RQS could be used for the specific detection of Hg²⁺ with high selectivity, high sensitivity, and a detection limit down to the nanomolar range (2 nM). Importantly, RQS is capable of specifically distributing in mitochondria, and thus detect Hg²⁺ in real-time and provided a potential tool for studying the cytotoxic mechanisms of Hg²⁺.

A novel mitochondrion-targeting Hg²⁺ probe, RQS, with NIR emission (680 nm) and a large Stokes shift (96 nm) was developed by tuning the D–A–D character of the rhodamine skeleton.