“Off-On” based fluorescent chemosensor for Cu2+ in aqueous media and living cells

An Isoniazid Based Schiff Base Sensor for Selective Detection of Pd2+ Ions

Here, we developed a novel isoniazid based fluorescent probe (E)-N'-(thiophen-2-ylmethylene)isonicotinohydrazide (TINH) through simple condensation reaction and employed for selective detection of Pd2+ ions with a low detection limit of 4.102 × 10-11 M. Among the many existing cations, TINH bound Pd2+ ions with an association affinity of 9.794 × 105 M-1. Adding Pd2+ ions to ligand solution increased the absorption intensity in UV-Visible and quenched the emission intensity in fluorescence spectroscopic experiments. More importantly, this TINH complexed to Pd2+ ions in 1:1 stoichiometric ratio. To evaluate the stability of complexed system, pH experiments has been performed. The binding insights among the ligand and Pd2+ ions has been confirmed by IR spectroscopic and MASS spectrometric methods. Additionally, TINH also applied to real water samples for the identification and measurement of Pd2+ ions. Hence, this system could be highly applicable for detection of Pd2+ ions in environmental and industrial samples with in low detection range.

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

Fluorescence Variation in Selective Sensing of Hg2+and Cu2+ Ions By Coumarin-xanthene Fused Optical Probe

The fluorescent moieties coumarin and xanthene (R6GCP) combined in a single molecule was designed and synthesized. The colorimetric and fluorescent variation of the probe towards the copper and mercury ions sensing is examined. With the added copper/mercury ions to the solution of R6GCP in DMF:H2O (2:8, v/v), the probe showed deep red color from yellow color. The probe showed turn-off and turn-on fluorescence for copper and mercury ion respectively. In the presence of other competing metal ions, the probe showed better sensitivity towards copper and mercury ions. The probe's detection limit found to be 5.29 × 10^-6 M and 1.24 × 10^-5 M for Cu²⁺ and Hg²⁺ ion respectively by the UV-visible spectral measurement. Fluorescence measurement, the detection limit for the Cu²⁺ and Hg²⁺ ions detection by this probe is 1.91 × 10^-7 M, and 1.32 × 10^-8 M respectively. 1:1 binding stoichiometry was confirmed between the probe and Cu²⁺/Hg²⁺ ions from jobs plot by UV-visible spectral technique. Moreover, R6GCP combined filter paper were prepared. These test paper containing probe could detect Cu²⁺/Hg²⁺ ions in real-time with a spontaneous color change.

A Ratiometric Selective Fluorescent Probe Derived from Pyrene for Cu2+ Detection

A novel ratiometric Cu2+-selective probe was rationally constructed based on pyrene derivative. Compared to other tested metal ions, the probe presented the selective recognition for Cu2+ which could be detected by a significant turn-on fluorescent response at 393 nm and 415 nm. Under the optimized conditions, a detection limit of 0.16 μM Cu2+ in aqueous media was found. Besides this, a 1:1 metal–ligand complex was confirmed by MS spectra and Job’s plot experiment, and the binding mode was also studied by 1H NMR experiment. Meanwhile, the fluorescence imaging in living cells was performed to detect Cu2+ with satisfactory results.

A novel water-soluble naphthalimide-based turn-on fluorescent probe for mercury ion detection in living cells and zebrafish

Mercury (Hg), as the only heavy metal that can complete the cycle in the biosphere, can further accumulate in the human body through the food chain, causing irreversible damage to...

High-contrast colourimetric probes for fluoride and trace water based on tautomerization of naphthalimide and application in fingerprint imaging

Three probes for fluoride ion and trace water based on naphthalimide were designed and synthesized. A new sensing mechanism based on naphthalimide tautomerization induced by fluoride ion and water was explored in the aprotic organic solvent. In the fluoride ion sensing process, the probes exhibited a remarkable absorption peak centred at 560 nm in the visible range of 400-700 nm. When trace water presented, the newly formed absorption peak centred at 560 nm gradually disappeared. The sensitive colour variation of the probe also was used in fingerprint imaging. Accordingly, the significant changes in chemical shift of dept135 and ¹HNMR spectrum confirmed the structural transformation of the probes with high contrast. Furthermore, this work also presented an optimization strategy for the sensitivity of the probe based on regulatory tautomerization.

Lipase sensing by naphthalene diimide based fluorescent organic nanoparticles: a solvent induced manifestation of self-assembly

The precise control of supramolecular self-assembly is gaining utmost interest for the demanding applications of manifested nano-architecture across the scientific domain. This study delineates the morphological transformation of naphthalene diimide (NDI) derived amphiphiles with varying water content in dimethyl sulfoxide (DMSO) and the selective sensing of lipase using its aggregation-induced emission (AIE) properties. To this end, NDI-based, benzyl alcohol protected alkyl chain (C1, C5, and C10) linked amphiphilic molecules (NDI-1,2,3) were synthesized. Among the synthesized amphiphiles, benzyl ester linked C5 tailored naphthalene diimide (NDI-2) exhibited AIE with an emission maximum at 490 nm in a DMSO-water binary solvent system from fw = 30% and above water content. The fibrous morphology of NDI-2 at fw = 30% got gradually transformed to spherical aggregated particles along with steady increment in the emission intensity upon increasing the amount of water in DMSO. At fw = 99% water in DMSO, complete transformation to fluorescent organic nanoparticles (FONPs) was observed. Microscopic and spectroscopic techniques demonstrated the solvent driven morphological transformation and the AIE property of NDI-2. Moreover, this AIE of NDI-2 FONPs was employed in the selective turn-off sensing of lipase against many other enzymes including esterase, through hydrolysis of a benzyl ester linkage with a limit of detection 10.0 ± 0.8 μg L-1. The NDI-2 FONP also exhibited its lipase sensing efficiency in vitro using a human serum sample.

Mesoporous nanosensors for sensitive monitoring and removal of copper ions in wastewater samples

FHNS nanosensors allow for the ultra-sensitive monitoring and capture of Cu²⁺ ions with a low detection limit and high adsorption capacity.

A Coumarin-Based Fluorescent Probe for Ratiometric Detection of Cu2+ and Its Application in Bioimaging

The fluorescent probe L, based on naphthalimide-modified coumarin, was designed, synthesized, and characterized, which could recognize Cu2+ from other cations selectively and sensitively in HEPES buffer (10 mM, Ph = 7. 4)/CH3CN (1:4, V/V). When the probe L interacted with Cu2+, the color and the fluorescent intensity changed obviously and it provided the naked-eye detection for Cu2+. The recognition mode between them was achieved by Job's plot, IR, MS, SEM, and 1HNMR. In addition, test strips made from L could still interact with Cu2+ in tap water effectively. The limit of detection (LOD) of L was 3.5 × 10-6 M. Additionally, the density functional theory (DFT) calculation method was used to analyze the action mechanism of L toward Cu2+. Importantly, the fluorescent probe L could demonstrate favorable selectivity toward Cu2+ in Caenorhabditis elegans. Thus, L was considered to have some potential for application in bioimaging.

MPA-CdTe quantum dots as "on-off-on" sensitive fluorescence probe to detect ascorbic acid via redox reaction

Mercaptopropionic acid (MPA) capped CdTe quantum dots (MPA-CdTe QDs) were synthesized in aqueous medium by hydrothermal method, which modified by Fe³⁺ could be used as a fluorescent probe to detect ascorbic acid (AA). MPA-CdTe QDs fluorescence probe could be used as successive sensor for metal ions and AA with "on-off-on" process. The fluorescence of QDs was quenched after adding Fe³⁺ to MPA-CdTe QDs. Then, the fluorescence of the Fe³⁺@MPA-CdTe QDs can be sensitively turned on by AA to give an "on-off-on" fluorescence response according to the oxidation-reduction between Fe³⁺ and AA. There was a linear relationship between fluorescence intensity quenching value and the concentration of Fe³⁺ in the range of 2-10 μM since Fe³⁺ sensitively reacted with CdTe QDs. The linear detection range for AA was 0.1-1 μM with a limit of detection of 6.6 nM. The principle is proved by fluorescence emission spectroscopy, nuclear magnetic resonance spectroscopy. The proposed method is successfully used to detect the AA in human plasma sample.

Retinal-based polyene fluorescent probe for selectively detection of Cu2+ in physiological saline and serum

Retinal is a flexible natural chromophore and widely present in organisms. The slender conjugated polyene structure retinal is conducive to entering protein structure. In this work, a novel turn-on fluorescent probe for Cu²⁺ based on retinal and phenylenediamine was designed and synthesized. The probe achieved recognition of copper ions in human serum complex protein environment. Furthermore, the high sensitivity, selectivity for Cu²⁺ and the sensing mechanism was also investigated.

Rhodamine probes for Fe3+: theoretical calculation for specific recognition and instant fluorescent bioimaging

Aim: To overcome the existing difficulty in distinguishing Fe(III) from Fe(II), rhodamine-containing Fe3+ probes, giving off different fluorescence responses to ferric and ferrous ions, were synthesized. Materials & methods: Color change in Fe3+ recognition, accompanying spirolactam opening–closing, could be used for ‘naked-eye’ detection. Theoretical calculations revealed the possible Fe3+-probe combination mechanism. Results: Apart from the probes’ specific response toward Fe3+, the Fe3+-probe demonstrated highly quantitative relationships in fluorescence titration, instant labeling and dynamic tracking of intracellular Fe3+ in bioimaging. Conclusion: Cytotoxity and bioimaging in living L929 suggested the probes’ future applications as real-time detection methods for Fe3+ in clinical diagnosis. Instant and time-lapse imagings, based on fluorescence-time stability of Fe3+-probe, enables the dynamic labeling and tracking of Fe3+ in living systems.

Multifunctional supramolecular self-assembly system for colorimetric detection of Hg2+, Fe3+, Cu2+ and continuous sensing of volatile acids and organic amine gases

A novel multifunctional gelator (1) based on an azobenzene derivative was designed and characterized. This compound could gelate some solvents including hexane, petroleum ether, DMSO, acetonitrile and ethanol through a heating-cooling procedure. The self-assembly process in different solvents was studied by means of UV-vis absorption and Fourier transform infrared (FTIR) spectra, field emission scanning electron microscopy (FESEM), rheological measurements, X-ray powder diffraction and water contact angle experiments. Interestingly, compound 1 had a high-contrast colorimetric detection ability towards Hg2+, Cu2+, Fe3+ and volatile acids and further organic amine gases in solution through its color change. At the same time, organogel 1 in acetonitrile also exhibited detection performance through a color or gel state change. In the response process, the self-assembly structures were changed from a nanofiber into a microsphere under induction by analytes. More significantly, film 1 could continuously detect volatile acids and organic amine gases. The number of cycles of film 1 for the detection of volatile acids and organic amine gases was at least seven times. The limit of detection (LOD) of film 1 towards TFA was calculated to be 0.0848 ppb. The sensing mechanisms were studied using 1HNMR, FESEM, UV-vis absorption spectra and HRMS. The intramolecular cyclization occurred on molecule 1 and a H2S molecule was lost during the detection process of Hg2+. It was proposed that the -N[double bond, length as m-dash]N- bonding could be coordinated by Fe3+ and Cu2+ and this further induced the absorption spectra and color change. For a volatile acid, it was possible that the volatile acid was combined with the N,N-dimethyl amine group of molecule 1. This research opens up a novel pathway to the fabrication of supramolecular self-assembly gels to detect polymetallic ions and trace volatile acids in the environment.

A Highly Selective Turn-on and Reversible Fluorescent Chemosensor for Al3+ Detection Based on Novel Salicylidene Schiff Base-Terminated PEG in Pure Aqueous Solution

The development of highly selective and sensitive chemosensors for Al³⁺ detection in pure aqueous solution is still a significant challenge. In this work, a novel water-soluble polymer PEGBAB based on salicylidene Schiff base has been designed and synthesized as a turn-on fluorescent chemosensor for the detection of Al³⁺ in 100% aqueous solution. PEGBAB exhibited high sensitivity and selectivity to Al³⁺ over other competitive metal ions with the detection limit as low as 4.05 × 10⁻⁹ M. PEGBAB displayed high selectivity to Al³⁺ in the pH range of 5–10. The fluorescence response of PEGBAB to Al³⁺ was reversible in the presence of ethylenediaminetetraacetic acid (EDTA). Based on the fluorescence response, an INHIBIT logic gate was constructed with Al³⁺ and EDTA as two inputs. Moreover, test strips based on PEGBAB were fabricated facilely for convenient on-site detection of Al³⁺.

Novel fluorescent probe with a bridged Si–O–Si bond for the reversible detection of hypochlorous acid and biothiol amino acids in live cells and zebrafish

Herein, we report the design of a novel fluorescent probe consisting of a naphthalimide fluorophore and a silicone small molecule for the reversible detection of hypochlorous acid and biothiol amino acids.

Detection of Zn2+, Cd2+, Hg2+, and Pb2+ ions through label-free poly-L-glutamic acid

Detection of heavy metal ions in water is important for environmental sustainability and food safety. Current fluorescent sensors interact with metal ions directly through chelation or chemical reactions. Those sensors are expensive to produce and often can detect only one ion at a time. Here we report a fluorescent turn-on sensor that can detect three group IIB metal ions and Pb²⁺ ions through label-free polypeptides in water. In our sensor-polypeptide mixture, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ ions induce helix formation and inter-chain aggregation in poly-L-α-glutamic acid (PGA). The acridinium-based sensor molecules incorporate into the polypeptides and emit strongly with characteristic color for each group IIB ion under UV lamp. By adjusting the size of polypeptides or the length of the side chain carboxyl groups, we can selectively turn off or turn on the sensor emission for Hg²⁺ ions.

A highly selective fluorescence "turn-on" sensor for Ca2+ based on diarylethene with a triazozoyl hydrazine unit

A new photochromic diarylethene derivative with a triazozoyl hydrazine unit has been designed and synthesized. Its photochromism and photoswitchable fluorescence behaviors were studied systematically by the stimuli of lights and chemical substances in acetonitrile solution. With the addition of Ca2+, the emission intensity enhanced 6.7 fold, accompanied by an obvious fluorescent color change from dark to light blue. The complexation between the derivative and Ca2+ is reversible with the 1 : 1 stoichiometry, which was verified by Job's plot and MS. The limit of detection (LOD) for Ca2+ was determined to be 2.49 × 10-8 mol L-1. Based on this unimolecular platform, a logic circuit was designed with fluorescence intensity at 482 nm as the output and the combined stimuli of UV/vis and Ca2+/EDTA as four inputs.

All Organic Label-like Copper(II) Ions Fluorescent Film Sensors with High Sensitivity and Stretchability

Deep learning and analysis of heavy metal concentration are very crucial to our life, for it plays an essential role in both environmental and human health. In this paper, we developed a new Cu (II) ions sensor made by all organic material with bending and stretching properties. The new sensor consists of chlorophyll-a extracted from fresh leaves of Common Garcinia, plant fiber and with the use of PDMS as a substrate. Fluorescence spectra study shows that chlorophyll-a is significantly much more sensitive to Cu (II) ions than any other heavy metal ions and the device sensitivity outperforms all the Cu (II) ions sensors ever reported. The result fully shows the selectivity of chlorophyll-a toward Cu (II) ions. Bending and stretching tests show that the sensor has an outstanding durability, which can be used to develop accompanying applications, such as real-time sampling and the analysis of Cu (II) concentration specified in athlete's sweat or patients with brain death and Parkinson's disease.

A highly selective naphthalimide-based ratiometric fluorescent probe for the recognition of tyrosinase and cellular imaging

Upon the addition of tyrosinase to the probe solution, the monophenolic unit is oxidized to o-dihydroxy and consequently releases the 4-aminonaphthalimide unit.

A novel, highly sensitive, selective, reversible and turn-on chemi-sensor based on Schiff base for rapid detection of Cu(II)

In this work, a novel optical fluoro-chemisensor was designed and synthesized for copper (II) ions detection. The sensor film is created by embedded N,N-Bis(2-hydroxo-5-bromobenzyl)ethylenediamine in poly vinyl chloride (PVC) film in presence of dioctyl phthalate (DOP) as plasticizer. The receptor Schiff base reveals "off-on" mode with high selectivity, significant sensitivity to Cu(II) ions. The selectivity of optical sensor for Cu(II) ions is the result of chelation enhanced fluorescence (CHEF). The optimal conditions of pH and response time at which higher efficiency of sensor film is performed was found to be 6.8 and 2.48min. The possible interference of other metal ions in solution was examined in presence of different types of metal ions. This film shows high selectivity and ultra-sensitivity with low detection limit LOD (1.1×10^-8M). Thus, these considerable properties make it viable to monitor copper metal ions within very low concentration range (0-15×10^-6M Cu(II)) and highly selective even in the presence of different types of metal ions. The sensor reversibility was achieved by utilizing EDTA solution with concentration of 0.1M solution.

New highly selective turn-on fluorescence receptor for the detection of copper (II)

Three new receptors (1a-c) bearing a p-dimethylaminobenzamide fluorophore have been synthesized and evaluated in terms of their fluoroionophoric properties towards various metal ions. Notably, receptors 1a and 1c exhibited dramatic fluorescent enhancement towards Cu²⁺ in acetonitrile. Subsequent investigations revealed that the highly selective behavior of these receptors towards Cu²⁺ could be attributed to the Cu²⁺-mediated oxidative cyclization of these compounds to the corresponding 1,3,4-oxadiazoles. Solvent effects and quantum calculations indicated that 1a and 1c both possessed an intramolecular charge transfer channel, which could be obstructed by the oxidative cyclization of these receptors. Receptor 1a was successfully applied to the determination of the Cu²⁺ in drug sample with a low detection limit of 2.2×10^-8molL^-1.

Label-free, Water-soluble Fluorescent Peptide Probe for a Sensitive and Selective Determination of Copper Ions

This study aimed to develop a label-free, sensitive, selective, and environment-friendly fluorescent peptide probe His-His-Trp-His (HHWH) for determining the concentration of copper ion (Cu²⁺) in aqueous solutions. The results demonstrated that the designed HHWH has a high selectivity and sensitivity for monitoring the concentration of free Cu²⁺ via quenching of the probe fluorescence upon a binding of Cu²⁺. The fluorescence intensity of the HHWH had a linear relationship with the concentration of Cu²⁺ between 10 nM and 10 μM, and the detection limit was 8 nM. Furthermore, HHWH could be regenerated with sulfide ions at least five times. The concentrations of Cu²⁺ in three different real water samples were detected using this probe, and the results were consistent with the one detected using an atomic absorption spectrometer. Thus, HHWH can be used as an accurate and feasible fluorescent peptide probe for detecting Cu²⁺ in aqueous solutions.

Fluorescent organic nanoparticles (FONs) for selective recognition of Al3+: application to bio-imaging for bacterial sample

(a) Changes in fluorescence upon successive addition of Al³⁺ ions to salpn-ONPs; (b) titration profile of fluorescence; (c) recognition of Al³⁺ through bio-fluorescence Staphylococcus aureus bacterial cells.

Single fluorescent probe for reversibly detecting copper ions and cysteine in a pure water system

In this work, we have engineered a novel fluorescent probe PI, which remarkably can reversible detect copper ion and cysteine in pure water system for the first time.

Highly sensitive and selective “naked eye” sensing of Cu(ii) by a novel amido–imine based receptor: a spectrophotometric and DFT study with practical application

Synthesis of (E)-bis-N'-((1H-pyrrol-2-yl)-methylene)-pyridine-2,6-carbohydrazide and its sensing ability towards copper(ii) ion in aqueous medium by color change, the sensing limit being 4.0 × 10⁻⁹ M.

A novel Schiff-base as a Cu(II) ion fluorescent sensor in aqueous solution

A new fluorescent Cu(II) sensor (L) obtained from the Schiff base of 5,5'-methylene-bis-salicylaldehyde with amidol (2,4-diaminophenol) was synthesized and characterized by FT-IR, MS, (1)H NMR, (13)C NMR techniques. In the presence of pH 6.5 (KHPO4-Na2HPO4) buffer solutions, copper reacted with L to form a stable 2:1 complex. Fluorescence spectroscopic study showed that Schiff base is highly sensitive towards Cu(II) over other metal ions (K(+), Na(+), Al(3+), Ni(2+), Co(2+), Fe(3+), Zn(2+), Pb(2+)) in DMSO/H2O (30%, v/v). The sensor L was successfully applied to the determination of copper in standard reference material. The structural properties and molecular orbitals of the complex formed between L and Cu(2+) ions were also investigated using quantum chemical computations.

Highly sensitive and selective turn-on fluorescent probes for Cu2+ based on rhodamine B

A new rhodamine B-based fluorescent probe RL for Cu²⁺ has been designed, synthesized, and characterized.

A pyridine-containing Cu²⁺-selective probe based on naphthalimide derivative

A new fluorescent probe P derived from naphthalimide bearing a pyridine group has been synthesized and characterized. The proposed probe P shows high selectivity and sensitivity to Cu2+ in aqueous media. Under optimized conditions, the linear response of P (2 μM) toward Cu2+ was 0.05-0.9 μM in ethanol-water solution (3:2, v:v, 50 mM HEPES, pH 7.4), and the detection limit was 0.03 μM.

A selectively fluorescein-based colorimetric probe for detecting copper(II) ion

A novel fluorescein derivative 3-bromo-5-methylsalicylaldehyde fluorescein hydrazone (BMSFH) has been synthesized by reacting fluorescein hydrazide with 3-bromo-5-methylsalicylaldehyde and was developed as a new colorimetric probe for detection of Cu(2+). In the presence of Cu(2+) the BMSFH exhibits a rapid color change from colorless to yellow together with an obvious new band appeared at 502nm in the UV-vis absorption spectra. However, other common alkali-, alkaline earth-, transition- and rare earth metal ions induced no or minimal spectral changes. This change is attributed to BMSFH via coordination with Cu(2+) in a 1:1 stoichiometry and this binding to Cu(2+) is reversible, as indicated by the bleaching of the color when the Cu(2+) is extracted with EDTA. Experimental results indicate that the BMSFH can provide a rapid, selective and sensitive response to Cu(2+) with a linear dynamic range 3.0-330μmol/L and can be used as a potential Cu(2+) colorimetric probe in aqueous solution.

A selectively rhodamine-based colorimetric probe for detecting copper(II) ion

A novel rhodamine derivative 3-bromo-5-methylsalicylaldehyde rhodamine B hydrazone (BMSRH) has been synthesized by reacting rhodamine B hydrazide with 3-bromo-5-methylsalicylaldehyde and developed as a new colorimetric probe for the selective and sensitive detection of Cu2+. Addition of Cu2+ to the solution of BMSRH results in a rapid color change from colorless to red together with an obvious new band appeared at 552 nm in the UV-vis absorption spectra. This change is attributed to the spirocycle form of BMSRH opened via coordination with Cu2+ in a 1:1 stoichiometry and their association constant is determined as 3.2×10(4) L mol(-1). Experimental results indicate that the BMSRH can provide a rapid, selective and sensitive response to Cu2+ with a linear dynamic range 0.667-240 μmol/L. Common interferent ions do not show any interference on the Cu2+ determination. It is anticipated that BMSRH can be a good candidate probe and has potential application for Cu2+ determination. The proposed probe exhibits the following advantages: a quick, simple and facile synthesis.