Luminescent Pyrene-based Schiff base Receptor for Hazardous Mercury(II) Detection Demonstrated by Cell Imaging and Test Strip

Qualitative and quantitative analysis of mercury at concentration levels as low as parts per billion (ppb) is a basic and practical concern. The vast majority of research in this field has centered on the development of potent chemosensor to monitor mercuric (Hg²⁺) ions. Mercury exists in three oxidation states, + 2, + 1 and 0, all of which are highly poisonous. In this study, (N¹E,N²E)-N¹,N²-bis(pyrene-1-ylmethylene)benzene-1,2-diamine (PAPM), a novel photoluminescent sensor based on pyrene platform was synthesized. Over the tested metal ions (Cd²⁺, Co²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ni²⁺, K⁺, Na⁺, Zn²⁺, Sr²⁺, Pb²⁺, Al³⁺, Cr³⁺ and Fe³⁺) the sensor responds only to Hg²⁺ by showing high selectivity and sensitivity. After treatment with mercuric ions at room temperature, the luminescence intensity of probe was quenched at 456 nm. The quenching of fluorescence intensity of probe upon addition of mercury is due to the effect of "turn-off" chelation enhanced quenching (CHEQ) by the formation of 1:1 complex. The ESI-MS spectrum and the Job's experimental results confirm the formation of 1:1 complex between PAPM and Hg²⁺. The detection limit and association constant of sensor for mercury is computed using fluorescence titration data and were found to be 9.0 × 10^-8 M and 1.29 × 10⁵ M^-1 respectively. The practical application of sensor towards recognition of mercury(II) ions was explored through economically viable test strips and also using cell imaging studies.

Ultrasensitive mercury ion and biothiol detection based on Dansyl-His-Pro-Gly-Asp-NH2 fluorescent sensor

Mercury is an environmental contaminant, which is highly toxic even at extremely low concentrations. Long-term accumulation of mercury in human body will damage the central nervous system or digestive tract system. Here, a new fluorescent chemical sensor Dansyl-His-Pro-Gly-Asp-NH₂ (D-P4) was synthesized for the determination of Hg²⁺. The D-P4 sensor exhibits excellent selectivity and sensitivity to Hg²⁺ in aqueous solution with a 'turn-off' fluorescence response. Furthermore, D-P4-Hg system displays a good 'turn-on' fluorescence response to biothiols. The calculated binding constant for the 1:1 complex of D-P4 with Hg^{2 +} is 1.07 × 10⁵ M^-1, which also confirms the high affinity of D-P4 for Hg²⁺. Results indicate that the detection limit of D-P4 for Hg²⁺ is 61.0 nM, and that of D-P4-Hg system for Cys is as low as 80.0 nM.

A New Highly Selective Colorimetric and Fluorometric Coumarin-based Chemosensor for Hg2

A novel colorimetric and fluorometric method based on coumarin as signalling unit was developed for Hg²⁺ recognition and quantification. Initially, the alkyne functionality was incorporated into a coumarin system and the resulting molecule showed higher specificity and sensitivity for Hg²⁺ over other cations in both absorption and emission sensing assays. The Hg²⁺ recognition was detected as visible colour change from colourless to yellow and as fluorescence quenching. The colour change was assigned to the increased intramolecular charge transfer (ICT) in the signalling unit upon Hg²⁺ binding whereas a decline in the fluorescence intensity was ascribed to the heavy atom effect from Hg²⁺. In order to generate a material with high sensing performance level, alkyne-functionalized molecule was hosted into a polymeric material. The resulting functionalized polymer showed higher sensitivity and selectivity for Hg²⁺ over its corresponding coumarin molecule. The investigation of the possible binding modes for Hg²⁺ suggested both alkyne and triazole functionalities as potential binding sites for Hg²⁺. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were evaluated and values less than a recommended maximum level of Hg²⁺contaminant in drinking water (2.00 μg/L) were obtained (LOD = 0.44 μg/L and LOQ = 1.33μg/L). The real-life application of the method was investigated using natural water samples containing Hg²⁺ levels equivalent to the maximum tolerable concentration of Hg²⁺ in drinking water. The outcomes suggested that the method could be used in the sensing and determination of Hg²⁺ level of contaminant in the environment.

Multianalyte azo dye as an on-site assay kit for colorimetric detection of Hg2+ions and electrochemical sensing of Zn2+ ions

A new tailor-made colorimetric chemosensor, (E)-1-(benzo[d]thiazol-2-yl)-3-(pyridin-3-yldiazenyl)naphthalen-2-ol (1), containing benzothiazole and pyridine moieties connected through an azo (-N=N-) linkage has been designed and synthesized. The synthesized chemosensor displayed an eye-catching color change upon binding to acetate [AcO^-;colorless to russet] and mercury (II) [Hg²⁺;colorless to greenish blue] ions in 9:1 (v/v) aqueous CH₃CN (pH 7.0 HEPES buffer).The mechanism of interaction between the chemosensor and the Hg²⁺/AcO^- ions has been confirmed by ¹H NMR titration experiments. Moreover, the colorimetric chemosensor 1 displayed potential in-field applications as on-site assay kit and detection of Hg²⁺ ions in real water samples. Importantly chemosensor 1 gave selective electrochemical response towards Zn²⁺ ions, enabling simple azo-dye 1 as multichannel chemosensor for colorimetric detection of Hg²⁺ ions and electrochemical detection of Zn²⁺ ions.

A novel rhodamine-based optical probe for mercury(II) ion in aqueous medium: A nanomolar detection, wide pH range and real water sample application

In present work, we designed and synthesized new chemosensor RPy, containing the rhodamine and 2,6-pyridinedicarboxaldehyde functionality, for the selective detection of mercury (II) (Hg²⁺) ion in aqueous DMSO solvents. The RPy acts as "turn ON" probe for Hg²⁺ ion with high selectivity and sensitivity over the series of other competing metal ions based on colorimetric and fluorimetric techniques. Due to the incorporation of two rhodamine moieties enhance the chelation sites for mercury binding, which reflects in the lowering of the detection limit up to 26 nM. The Job plot method confirms the 1:2 stoichiometric interactions between the RPy and Hg²⁺ ion. The formation of the chelation complex between RPy and Hg²⁺ ion with spirolactam ring opening was thoroughly investigated by absorption, emission, ¹H NMR, and mass analysis. The detection of Hg²⁺ ion by RPy is retained at broad pH range 4-9. Further, the probe RPy is successfully explored to measure the contamination of Hg²⁺ ion in the real water samples using spike and recovery method.

Dimethylaniline functionalised pyrene fluorophores; dual colour pH switching in solution and self-assembled monolayers

A pyrene charge transfer fluorophore with three ionizable N,N-dimethylaniline moieities was explored as an interfacial pH switch. The parent carboxylate compound and the thiolated derivative were shown by spectroscopy combined with DFT calculation to be successively and reversibly protonated. Protonation leads to progressive decrease of intensity of the 550 nm centered N,N-dimethylaniline to pyrene charge transfer emission which on protonation of the third site, leads to extinction of this transition and evolution of an intense blue (450 nm) pyrene-centered emission. Concomitant loss of the charge transfer absorbance was observed and the changes are reversed on neutralization of pH. A self-assembled monolayer of the thiolated derivative was prepared on gold and found from voltammetry of ferricyanide/ferrocyanide probe to form close packed monolayers. The probe voltammetry, label-free electrochemical impedance spectroscopy of the film was monitored as a function of pH and progressive, but reversible protonation steps were reflected in decreasing film resistance. The Stokes shift of the probe prevents self-quenching so a broad, charge transfer fluorescence centered around 540 nm was recorded for the self-assembled monolayer where as per solution, progressive and reversible reduction in intensity was observed. The facile assembly, impedance and optical switching make these materials potentially interesting as on-off or two colour on-off-on fluorescence switches with potential applications in logic gates or in responsive surface applications.

Multifunctional peptide-based fluorescent chemosensor for detection of Hg2+ , Cu2+ and S2- ions

A novel multifunctional fluorescent peptide sensor based on pentapeptide dansyl-Gly-His-Gly-Gly-Trp-COOH (D-P5) was designed and synthesized efficiently using Fmoc solid-phase peptide synthesis (SPPS). This fluorescent peptide sensor shows selective and sensitive responses to Hg²⁺ and Cu²⁺ among 17 metal ions and six anions studied in N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid (HEPES) buffer solution. The peptide probe differentiates Hg²⁺ and Cu²⁺ ions by a 'turn-on' response to Hg²⁺ and a 'turn-off' response to Cu²⁺ . Upon addition of Hg²⁺ or Cu²⁺ ions, the sensor displayed an apparent color change that was visible under an ultraviolet lamp to the naked eye. The limits of detection (LOD) of DP-5 were 25.0 nM for Hg²⁺ and 85.0 nM for Cu²⁺ ; the detection limits for Cu²⁺ were much lower than the drinking water maximum contaminant levels set out by the United States Environmental Protection Agency (USEPA). It is noteworthy that both D-P5-Hg and D-P5-Cu systems were also used to detect S^2- successfully based on the formation of ternary complexes. The LODs of D-P5-Hg and D-P5-Cu systems for S^2- were 217.0 nM and 380.0 nM, respectively. Furthermore, the binding stoichiometry, binding affinity and pH sensitivity of the probe for Hg²⁺ and Cu²⁺ were investigated. This study gives new possibilities for using a short fluorescent peptide sensor for multifunctional detection, especially for anions.

Dual-response detection of Ni2+ and Cu2+ ions by a pyrazolopyrimidine-based fluorescent sensor and the application of this sensor in bioimaging

Herein, a dual-response fluorescent sensor, L, based on pyrazolopyrimidine was designed and developed for the simultaneous detection of Ni²⁺ and Cu²⁺ ions in the presence of other metal ions; the structural characterization of L was carried out by FTIR spectroscopy, NMR spectroscopy, HRMS and X-ray diffraction analysis. The sensor L effectively displayed fluorescence quenching towards the Ni²⁺ and Cu²⁺ ions with high sensitivity without interference from other metal ions. The results reveal that L binds to Ni²⁺ and Cu²⁺ in a 2 : 1 pattern, which matches well with the result of the Job's plot. The association constants of L with Ni²⁺ and Cu²⁺ were 3.2 × 10⁴ M⁻¹ and 7.57 × 10⁴ M⁻¹, respectively. The detection limits (DLs) are down to 8.9 nM for Ni²⁺ and 8.7 nM for Cu²⁺. The fluorescence imaging of L in T-24 cells was investigated because of the low cytotoxicity of L, indicating that L could be used to detect Ni²⁺ and Cu²⁺ in living cells.

A pyrazolopyrimidine-based fluorescent sensor L was developed and applied for detection of Cu²⁺ and Ni²⁺ in ethanol solution by photoluminescence quenching. It shows low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells.

A thiourea-appended rhodamine chemodosimeter for mercury(II) and its bioimaging application

A rhodamine-thiourea conjugate RTP with an o-phenylenediamine linker was developed as a fluorogenic chemodosimeter for Hg²⁺ detection. In the presence of Hg²⁺, a colorless solution of RTP turned pink with a maximum absorption band at 555nm and with a 62-fold fluorescence enhancement at 578nm (Φ=0.34). RTP is highly selective to Hg²⁺ among other metal ions with a detection limit of 1.6nM (0.3ppb). A similar rhodamine analog with a flexible ethylenediamine spacer was less selective and less sensitive than RTP. Hg²⁺ induced cyclic guanylation to yield a benzimidazole moiety and a subsequent ring-opening of the spirolactam unit resulted in chromogenic and fluorogenic changes. The membrane-permeable RTP probe was successfully demonstrated in monitoring of Hg²⁺ in cultured HeLa cells.

Fluorescent sensor based models for the detection of environmentally-related toxic heavy metals

The quest for industrial and biotechnological revolution has been contributed in increasing environmental contamination issues, worldwide. The controlled or uncontrolled release of hazardous pollutants from various industrial sectors is one of the key problems facing humanity. Among them, adverse influences of lead, cadmium, and mercury on human health are well known to cause many disorders like reproductive, neurological, endocrine system, and cardiovascular, etc. Besides their presence at lower concentrations, most of these toxic heavy metals are posing noteworthy toxicological concerns. In this context, notable efforts from various regulatory authorities, the increase in the concentration of these toxic heavy metals in the environment is of serious concern, so real-time monitoring is urgently required. This necessitates the exploration for novel and efficient probes for recognition of these toxic agents. Among various methodologies adopted for tailoring such probes, generally the methodologies, in which changes associated with spectral properties, are preferred for the deceptive ease in the recognition process. Accordingly, a promising modality has emerged in the form of radiometric and colorimetric monitoring of these toxic agents. Herein, we review fluorescent sensor based models and their potentialities to address the detection fate of hazardous pollutants for a cleaner environment. Second, recent advances regarding small molecule and rhodamine-based fluorescent sensors, radiometric and colorimetric probes are discussed. The information is also given on the photoinduced electron transfer (PET) mechanism, chelation enhancement fluorescence (CHEF) effect and spirocyclic ring opening mechanism.

Fluorogenic mercury ion sensor based on pyrene-amino mercapto thiadiazole unit

A highly selective and sensitive determination of Hg²⁺ in water samples with bioimaging applications in living cells using a fluorogenic pyrene-amino mercapto thiadiazole (PYAMT) probe is described. The probe PYAMT exhibited three absorption peaks at 333, 348 and 394nm and emission maxima at 378, 388 and 397nm (λ_ex=348nm). It showed significant fluorescent quenching (96%) with I/I₀=0.051 upon the addition of 2.5μM Hg²⁺ ion in CH₃CN(ACN):H₂O (1:1, v/v; pH 7.2), whereas its fluorescence remained unaltered in the presence of other metal ions. The quenching phenomenon is attributed to the heavy atom effect of Hg²⁺ ion followed by electron transfer. The fluorescence intensity decreased linearly against a wide range from 100nM to 2.5μM Hg²⁺ (R²=0.9937) with a limit of detection as low as 0.35nM (S/N=3). The binding stoichiometry ratio of PYAMT-Hg²⁺ is proved to be 1:1 by fluorescence and DFT measurements. The sensor possesses high association constant with Hg²⁺ ion in the order of 9.08×10⁵M^-1 and it is also capable of reversibly detecting cysteine with OFF-ON mechanism. Finally, the proposed method is successfully applied to selectively detect Hg²⁺ ion in real water samples and bioimaging studies in live cells.

Rhodamine–benzothiazole conjugate as an efficient multimodal sensor for Hg2+ ions and its application to imaging in living cells

A rhodamine B dye bearing a benzothiazole conjugate is designed and synthesized, it shows a highly selective and sensitive naked-eye color change and turn-on fluorescence response to Hg²⁺ ions.

Three-in-one type fluorescent sensor based on a pyrene pyridoxal cascade for the selective detection of Zn(ii), hydrogen phosphate and cysteine

A novel fluorescent receptor L was developed for the selective detection of important bioactive analytes.

A highly sensitive turn-on fluorescent chemosensor for recognition of Zn2+ and Hg2+ and applications

A fluorescence probe has been designed and synthesized, and applied with a combined theoretical and experimental study. Research suggests that the probe can be used to sense Zn²⁺ and Hg²⁺ through selective turn-on fluorescence responses in the aqueous HEPES buffer (0.05M, pH=7.4). The limit of detection (LOD) were determined as 1.46×10^-7M (Zn²⁺) and 2.50×10^-7M (Hg²⁺). Moreover, based on DFT, the geometry optimizations of probe 1, [1-Hg²⁺] complex and [1-Zn²⁺] complex were carried out using the Gaussian 09 program, in which the B3LYP function was used. The electronic properties of free probe 1 and the metal complexes were studied based on the Natural Bond Orbital (NBO) analyses. The probe 1 has also been successfully applied to detection of Zn²⁺ and Hg²⁺ in living cells.

A novel 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al(iii) sensor in a purely aqueous medium with intracellular application: experimental and computational studies

A new 8-hydroxyquinoline-pyrazole based probe senses Al³⁺ and hence Al³⁺–8Q-NH-Pyz complex mediated F⁻ in a purely aqueous medium.

An efficient non-reaction based colorimetric and fluorescent probe for the highly selective discrimination of Pd0 and Pd2+ in aqueous media

A novel anthraquinone-imidazole based colorimetric and fluorogenic probe 1 discriminates the oxidation states of Pd⁰ and Pd²⁺ by naked eye with high selectivity in aqueous media due to the difference in coordination in the pocket of probe molecule.

A facile Al(iii)-specific fluorescence probe and its application in biological systems

A facile fluorescent probe for Al(iii) was developed and applied in biological systems.

A novel fluorescence “on–off–on” chemosensor for Hg2+via a water-assistant blocking heavy atom effect

The heavy atom effect and blocking thereof were demonstrated within the same system by the use of a C₃-symmetric homooxacalix[3]arene scaffold.

A dansyl based fluorescence chemosensor for Hg(2+) and its application in the complicated environment samples

We have developed a novel fluorescent chemosensor (DAM) based on dansyl and morpholine units for the detection of mercury ion with excellent selectivity and sensitivity. In the presence of Hg(2+) in a mixture solution of HEPES buffer (pH 7.5, 20 mM) and MeCN (2/8, v/v) at room temperature, the fluorescence of DAM was almost completely quenched from green to colorless with fast response time. Moreover, DAM also showed its excellent anti-interference capability even in the presence of large amount of interfering ions. It is worth noting that DAM could be used to detect Hg(2+) specifically in the Yellow River samples, which significantly implied the potential applications of DAM in the complicated environment samples.

Thiophene aldehyde-diamino uracil Schiff base: A novel fluorescent probe for detection and quantification of cupric, silver and ferric ions

A new Schiff base from the condensation of 5,6-diamino-1,3-dimethyluracil with 5-methylthiophene-2-carboxaldehyde was synthesized. The compound was characterized by spectral data (UV-Vis, IR, (1)H NMR, fluorescence, MS). Ethanolic solutions of the Schiff base exhibit a strong fluorescence emission at 385 nm (λex=341 nm), and have been employed as a "turn-off" fluorescent probe for selective detection of Ag(+), Cu(2+) and Fe(3+) ions in presence of other cations such as Na(+), K(+), Ca(2+) and Mg(2+) ions abundant in natural water. The interaction between the tested compound and copper, silver or iron ions is associated with a significant fluorescence decrease, showing detection limits of 2.1-14.2 ppb. Under optimal conditions, the developed sensor was successfully employed to determine Ag(+), Cu(2+) and Fe(3+) ions in real samples and proved to be selective and sensitive.

Masking agent-free and channel-switch-mode simultaneous sensing of Fe(3+) and Hg(2+) using dual-excitation graphene quantum dots

A novel channel-switch-mode strategy for simultaneous sensing of Fe(3+) and Hg(2+) is developed with dual-excitation single-emission graphene quantum dots (GQDs). By utilizing the dual-channel fluorescence response performance of GQDs, this strategy achieved a facile, low-cost, masking agent-free, quantitative and selective dual-ion assay even in mixed ion samples and practical water samples.

Novel pyrazoline-based fluorescent probe for detecting thiols and its application in cells

A new compound, N-(4-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)phenyl)-acrylamide (probe L), was designed and synthesized as a highly sensitive and selective fluorescent probe for recognizing and detecting thiol from other amino acids. On being mixed with thiol in buffered DMSO:HEPES=1:1 solution at pH 7.4, the probe exhibited the blue emission at 474 nm. This probe is very sensitive and displayed a linear fluorescence off-on response to thiol. The fluorescence emission of the probe is pH independent in the physiological pH range. Living cell imaging of HeLa cells confirmed its cell permeability and its ability to selectively detect thiol in cells. The structure of the probe was characterized by IR, NMR and HRMS spectroscopy analysis.

Synthesis and characterization on novel fluorescent sensors for Pd2+/Pd0 with high selectivity

Novel chemosensors based on triaryl 1H-imidazo[4,5-b]pyrazine with high selectivity for palladium (Pd⁰/Pd²⁺) detection have been synthesized simply.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

A pyrene based Schiff base probe for selective fluorescence turn-on detection of Hg2+ ions with live cell application

A novel pyrene based free thiol containing a Schiff base derivative PT1 was synthesized and reported as a fluorescence turn-on sensor for Hg²⁺ ions, via CHEF and excimer (PT1-PT1*) formation with live cell imaging.

Rational design of the first furoquinolinol based molecular systems for easy detection of Cu2+with potential applications in the area of membrane sensing

Two highly selective furoquinolinol based molecular systems for Cu²⁺have been designed with potential application in areas of membrane sensing.

Multifunctional fibrous silica composite with high optical sensing performance and effective removal ability toward Hg2+ions

A multifunctional organic–inorganic hybrid sensing material (RB-KCC-1) decorated with rhodamine-based receptor has been successfully synthesized, aiming to detect and remove Hg²⁺from aqueous media.

An anion induced multisignaling probe for Hg2+ and its application for fish kidney and liver tissue imaging studies

A highly efficient binder for the selective recognition and determination of Hg(NO₃)₂ concentration in kidney and liver tissues of fish using a fluorescence method is described.

Phenothiazine based sensor for naked-eye detection and bioimaging of Hg(ii) and F− ions

The design and development of new phenothiazine-based fluorescent probes, which displays selective fluorescence response to Hg²⁺ and F⁻ ions in a reversible manner. The probe is the first example that facilitates the detection of Hg²⁺ at nanomolar concentration.

A highly selective fluorescent ‘turn-on’ chemosensor for Hg2+ based on a phthalazin-hydrazone derivative and its application in human cervical cancer cell imaging

Sensor 1 showed a high selectivity and sensitivity towards Hg²⁺ by giving significant fluorescence enhancement.

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg(2+), Pb(2+), light metal Al(3+) ion, alkali, alkaline earth, and transition metal ions by UV-visible and fluorescent techniques in ACN/H2O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb(2+)/Al(3+) metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb(2+) and Al(3+) ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb(2+) and Al(3+) ions.