Unusual red shift of the sensor while detecting the presence of Cd2+ in aqueous environment

Synthesis of Bis-tetraphenylethene as a Novel Turn-On Selective Zinc Sensor

The main purpose of this study is the synthesis of novel fluorescent Bis-TPE and the investigation of its wide range of photochemical behaviors. For this purpose, initially, Bis-TPE was synthesized. Following this, the interactions of Bis-TPE with a wide range of ions were studied in EtOH using ultraviolet-visible (UV-vis) and fluorescence spectroscopy. As a result of all UV-vis and fluorescence studies, it was determined that Bis-TPE showed turn-on sensor features against Zn²⁺ ions. Moreover, the limit of detection (LOD) and K_a values of Bis-TPE/Zn²⁺ were calculated as 0.97 μM (970 nM) and 3.76 × 10⁵ M^-1, respectively. Moreover, all reversal studies resulted in switchable on/off variation of the alternative addition of ZnCl₂ and [Bu₄N]OH to Bis-TPE. This result also implies that the probe Bis-TPE also exhibits specific OH^- sensor properties in the presence of zinc.

Aminoquinoline-anchored polynorbornene for sequential fluorescent sensing of Zn2+ and ATP

A novel aminoquinoline functionalized norbornene (1) and its ring-opening metathesis polymerization (ROMP) copolymer P1 have been designed and synthesized. The polymer probe P1 can self-assemble nano aggregation in aqueous solution. The fluorescent experiments revealed that both 1 and P1 show a ratiometric fluorescence response toward Zn²⁺ over other mental ions in Tris-HCl buffer solution, with the polymer probe P1 shows a better photostability and higher binding affinity than that of the small molecular probe 1. Furthermore, the in situ formed P1-Zn²⁺ ensemble was successfully used as the secondary sensor for ATP. P1 is also successfully used for monitoring intracellular Zn²⁺ and ATP in living cells.

Highly sensitive biosensor based on aptamer and hybridization chain reaction for detection of cadmium ions

In this work, a highly sensitive biosensor for detecting cadmium ions (Cd²⁺ ) was developed based on Cd²⁺ -specific DNA aptamer and hybridization chain reaction (HCR). The Cd²⁺ -aptamer (named S0) was used to recognize Cd²⁺ and trigger HCR reaction. Without Cd²⁺ , S0 initiated the HCR to form long nicked dsDNA structures to quench the fluorescence. Then, Cd²⁺ can bind with S0 to block HCR to recover fluorescence. This biosensor had high sensitivity with the detection limit of 0.36 nM and a linear range from 0 to 10 nM. Moreover, it showed a satisfactory selectivity and recovery rates.

The fluorescence turn-off mechanism of a norbornene-derived homopolymer – an Al3+ colorimetric and fluorescent chemosensor

A norbornene-derived hydrazone polymer was developed for high selectivity, and to be used as an effective colorimetric and fluorescent chemosensor of Al³⁺ in aqueous solutions.

8-Hydroxyquinoline Fluorophore for Sensing of Metal Ions and Anions

Among various known hydroxyquinolines, 8-hydroxyquinoline (8-HQ) is the most prevalent moiety due to excellent property for the formation of the complex with different metal ions and anions, and utilized in a wide variety of applications in pharmacological and medicinal fields. 8-Hydroxyquinoline moiety and its analogues acts as fluorophoric ligands on complex formation with alkali and alkaline as well as transition metal ions and anions, thus, considered as an ideal building block in metallo-supramolecular chemistry for recognition, separation, and quantitative investigation of cations. 8-Hydroxyquinoline moiety is also used in various applications for the advancement of novel fluorescent chemosensors in a wide variety of areas viz., material chemistry, bioorganic chemistry, molecular imaging, analytical chemistry, molecular recognition, medical and biological science communities. The present review emphasises on the progress of sensing properties of 8-HQ centred small-molecule fluorescent chemosensors towards several metal ions viz., Fe³⁺ , Al³⁺ , Ag⁺ , Hg²⁺ , Cu²⁺ , Pd²⁺ , Zn²⁺ , Cr³⁺ , Cd²⁺ , Mn²⁺ , Ca²⁺ , and K⁺ and anions such as F^- , CN^- and PPi, from 2008 to 2020, because of their sensitivity and selectivity in terms of diverse colour changes for different species. This critical and comprehensive review might facilitate the improvement of more prevailing chemosensors for future exciting and broad applications.

Unusual red-orange emission from rhodamine-derived polynorbornene for selective binding to Fe3+ ions in an aqueous environment

Norbornene-based rhodamine derivative (NR) was observed as an "off-on" probe for Fe3+ ions both colorimetrically and fluorimetrically in an aqueous environment. NR and its homopolymer (PNR) were capable of detecting Fe3+ ions with high selectivity and sensitivity in an aqueous environment. For NR and PNR the limit of detection (LOD) towards Fe3+ ions was found to be 49 nM and 19 nM, respectively, making these materials highly efficient. Most interestingly, PNR has more efficacy towards the detection of Fe3+ ions than NR, which is expected due to the favorable side-chain interaction in the presence of multiple sensing motifs between the polymer chains. The sensing behavior was thoroughly studied via spectroscopic techniques. We hypothesized that the Fe3+ ion was expected to induce the spirolactam ring-opening of the rhodamine unit due to its Lewis acid nature and preferable interactions with the N and O atoms present in NR as well as PNR.

Effect of charge transfer and structural rigidity on divergent luminescence response of a metal organic framework towards different metal ions: luminescence lifetime decay experiments and DFT calculations

We have thoroughly studied the luminescence behaviour of a cadmium based MOF, [Cd(C12N2H8)(C7N1O4H3)] {C12N2H8 = 1,10-phenanthroline, C7N1O4H3 = 2,5-pyridine dicarboxylate}, 1. Both steady-state and time-resolved luminescence spectroscopic experiments were performed to understand the dissimilar responses of compound 1 towards different metal ions in aqueous medium. Upon excitation at 280 nm, compound 1 showed a luminescence spectrum centered at 365 nm, which exhibited a three-fold turn-on in the presence of a trace amount of Zn2+ in aqueous solution, whereas in the presence of Co2+, Hg2+, Ni2+, Fe2+ and Cu2+ the luminescence of compound 1 got largely quenched. Compound 1 did not show any response in the presence of other common metal ions such as K+, Mg2+, Na+, Mn2+, and Cr3+. By analysing all the experimental results, we successfully explained the versatile luminescence behaviour of compound 1. The turn-on of luminescence in the presence of Zn2+ ions was due to coordination bond formation and enhancement of the rigidity of compound 1 which resulted in the reduction of non-radiative decay processes to a large extent. The quenching of luminescence in the presence of transition metal ions was found to be static in nature, and was due to the possibility of ligand to metal charge transfer using the vacant d-orbital of the metal ions. In the case of Hg2+ which is a closed cell heavy metal ion, the quenching of luminescence was also static in nature and was due to a two-way charge transfer mechanism. We have also performed density functional theory calculations and obtained supportive results for the proposed mechanisms of luminescence turn-on and quenching. Moreover, compound 1 could be established as a selective and efficient sensor of Zn2+ in aqueous solution even in the presence of Cd2+ and other metal ions.

A selective fluorescent chemosensor for Cd2+ based on 8-hydroxylquinoline-benzothiazole conjugate and imaging application

A 8-hydroxylquinoline-benzothiazole conjugate (HQ-BT) was facilely synthesized by two steps with >60% total reaction yield. The HQ-BT showed a weak fluorescence that could be strongly enhanced by coordination with various metal ions such as Al³⁺, Cd²⁺, Zn²⁺ in methanol containing 1% water. Interestingly, the selectivity toward Cd²⁺ was achieved by increasing water fraction to 30% aqueous methanol solution. Thus, the HQ-BT was developed as a new and selective fluorescent chemosensor for Cd²⁺ in aqueous solution with a broad pH region 4-12. A good linear relationship between the fluorescence intensity and the Cd²⁺ concentration was found in the range of 0-5 μM with a detection limit of 0.1 μM (S/N = 3). It was also succesfully used for fluorescence imaging of Cd²⁺ in living cells.

A novel pyrene-based selective colorimetric and ratiometric turn-on sensing for copper

Detection of copper attracts important in most environmental and biological systems. In this study, a simple probe BisPyTSC containing bis-pyrene core was synthesized, and cation binding and sensing properties were studied using colorimetric and fluorometric detection. The research indicated that the specific ligand affinity for Cu²⁺ ions results in drastic color and spectral changes. According to the data obtained, while the peak intensity increases at 376 nm, the peak intensity decreased at 280 nm in the absorption spectrum of BisPyTSC and an increase in fluorescence intensity of BisPyTSC was observed in the presence of Cu²⁺ ions. The binding ratio of BisPyTSC to Cu²⁺ was found to be 1:1 according to Job's plot experiments. The binding constant was calculated using the Benesi-Hildebrand equation and found to be 3.26 × 10⁴ M^-1. Based on these concentration dependent fluorescence changes, the limit of detection (LOD) value was calculated to be 14.5 μM for Cu²⁺, which is the range of copper that should be in the blood (11.8-23.6 μM). As a result of all these studies, we can understand that BisPyTSC is a good selective candidate turn-on sensor that can be used for Cu²⁺ detection.

8-Hydroxyquinoline Functionalized Graphene Oxide: an Efficient Fluorescent Nanosensor for Zn2+ in Aqueous Media

A nanosensor, based on 8-hydroxyquinoline functionalized graphene oxide, was developed for the fluorescence detection of Zn²⁺. It showed high selectivity and sensitivity for Zn²⁺ion in aqueous solution over other metal ions such as Li⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Cd²⁺, Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Fe²⁺, Fe³⁺and Cr³⁺. Due to the linearity of the emission intensity toward Zn²⁺ concentration, fluorescent technique could be used for the detection of Zn²⁺ ion even at very low concentrations.

Efficient Removal of Cadmium Using Edible Fungus and Its Quantitative Fluorimetric Estimation Using (Z)-2-(4H-1,2,4-Triazol-4-yl)iminomethylphenol

Microbes accumulate heavy metals after adsorption or absorption. This study exhibited that Trametes versicolor can tolerate up to 5 mg/g concentration of cadmium. Change in fungus morphology due to cadmium along with its absorption were analyzed using SEM, XRD, and EDAX. Cadmium absorption usually increased with time, and it was determined quantitatively by a fluorimetry technique using a synthesized imine fluorophore as a specific probe and compared with results obtained from atomic absorption spectroscopy (AAS). The intensity of the cadmium-specific XRD peak gradually increased up to the seventh day, and the absorption by the organisms reduced the concentration of cadmium even from the effluent of the plating industry. After the seventh day, Trametes versicolor absorbed almost 0.300 mg/g concentration of cadmium as visualized under high content screening from the fluorescence appearance of hyphae. Hence it can be concluded that Trametes versicolor may play a key role in reducing cadmium from a contaminated environment.

Colorimetric and fluorimetric detection of Hg2+ and Cr3+ by boronic acid conjugated rhodamine derivatives: Mechanistic aspects and their bio-imaging application in bacterial cells

Colorimetric and fluorimetric detection of toxic metal ions such as Hg²⁺ and Cr³⁺ has gained tremendous popularity over the conventional methods due to their operational simplicity, high selectivity, and speediness. Although numerous colorimetric and fluorescent receptors for Hg²⁺ or Cr³⁺ were reported in the literature, boronic acid-based receptors for these metal ions are rather scarce in the literature. Hence, in the present study dual function boronic acid conjugated rhodamine derivatives were developed, and their toxic metal ion detection abilities were studied by absorption, emission and visual detection methods. Absorption and emission spectral studies revealed that these derivatives displayed selectivity towards Hg²⁺, Cr³⁺ and Fe³⁺ among the other metal ions studied by forming new absorption band. Both the derivatives exhibited colorimetric response towards Hg²⁺ and Cr³⁺ by the change in color of the solution to pink and reddish pink with Fe³⁺. The detailed mechanism involved in the detection of Hg²⁺ was deduced by ¹H NMR and ESI-MS studies. Further, these derivatives were used for fluorescence imaging of Hg²⁺ and Cr³⁺ in S. aureus bacterial cells. Thus the present manuscript demonstrated the use of boronic acid conjugated rhodamine derivatives as a dual function (colorimetric and fluorescent) probes and as imaging agents for Hg²⁺ and Cr³⁺, which are known for their toxic influence on bacterial cells.

A novel fluorescent peptidyl probe for highly sensitive and selective ratiometric detection of Cd(ii) in aqueous and bio-samplesviametal ion-mediated self-assembly

A fluorescent peptidyl probe based on a Cd(ii)-triggered self-assembling process was proposed for ratiometric detection for Cd(ii) in urine and live cells.

BODIPY-derived multi-channel polymeric chemosensor with pH-tunable sensitivity: selective colorimetric and fluorimetric detection of Hg2+ and HSO4− in aqueous media

A water-soluble BODIPY-containing polymeric chemosensor was synthesized for the selective colorimetric and turn-on fluorimetric detection of Hg²⁺ and HSO₄⁻ ions, respectively, in 100% aqueous media at physiological pH.

A Unique Sensitive and Highly Selective Fluorescent Naphthodiaza-Crown Macrocyclic Ligand Chemosensor for Hg2+ in Water

The noticeable enhancement in fluorescence emission of O₂N₂-donor naphthodiaza-crown macrocyclic ligand (L) in the presence of Hg²⁺ was observed in which the fluorescence quantum yield of free ligand L as well as L/Hg²⁺ complex were found to be as 0.29 and 0.49, respectively. The observed ultra-low limit of detection (LOD) for Hg²⁺ by L was determined as low as 1.0 × 10^-11 M in water. A 1:1 stoichiometry was also established for L/Hg²⁺ together with a binding constant K _BH = 66,543 by employing fluorescence spectrophotometry. The competition experiments on L/Hg²⁺ demonstrated highly selective detection of Hg²⁺ in the presence of the library cations. A two path mechanism for detection of metal ion in terms of coordination of metal ion to L and/or the formation of counter ion was proposed by using of ¹H NMR and fluorescence spectroscopy. Graphical Abstract pH dependence mechanism of interaction between Hg²⁺ and macrocyclic ligand L.

Nanomolar colorimetric quantitative detection of Fe³⁺ and PPi with high selectivity

A novel rhodamine and 8-hydroxyquinoline-based derivative was synthesized, which is shown to act as a colorimetric chemosensor for Fe(3+) in aqueous solution with high selectivity over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). Fe(3+) can be detected quantitatively in the concentration range from 6.7 to 16 μM and the detection limit (LOD) on UV-vis response of the sensor can be as low as 15 nM. The 'in situ' prepared Fe(3+) complex (1⋅Fe) showed high selectivity toward PPi against many common anions, and sensitivity (the LOD can be as low as 71 nM). In addition, both the chemosensor and the 'in situ' prepared Fe(3+) complex are reusable for the detection of Fe(3+) and PPi respectively.

A turn-on fluorescence chemosensor based on a tripodal amine [tris(pyrrolyl-α-methyl)amine]-rhodamine conjugate for the selective detection of zinc ions

A tris(pyrrolyl-α-methyl)amine (H3tpa) and rhodamine-based conjugate (PR) served as a sensor for the selective detection of Zn²⁺and their application of imaging living cells were studied.

Novel anti-diabetic and luminescent coordination compounds based on vanadium

Novel vanadium coordination compounds have been synthesized. Both compounds exhibit intense photoluminescence emission and showin vivoantidiabetic activity.

Selection of a DNA aptamer for cadmium detection based on cationic polymer mediated aggregation of gold nanoparticles

The demand for selection of aptamers against various small chemical molecules has substantially increased in recent years. To incubate and separate target-specific aptamers, the conventional SELEX procedures generally need to immobilize target molecules on a matrix, which may be impotent to screen aptamers toward small molecules without enough sites for immobilization. Herein we chose Cd(II) as a model of a small molecule with less sites, and proposed a novel SELEX strategy of immobilizing ssDNA libraries rather than target molecules on a matrix, for selection of aptamers with high affinity to Cd(II). After eleven rounds of positive and negative selection, twelve T and G-rich of nonrepeating ssDNA sequences were identified, of which the Cd-4 aptamer displayed the highest binding affinity to Cd(II). The secondary structures of these sequences revealed that a stem-loop structure folded by the domain of their 30-random sequence is critical for aptamers to bind targets. Then the interaction between the selected Cd-4 aptamer and Cd(II) was confirmed by CD analysis, and the binding specificity toward other competitive metal ions was also investigated. The dissociation constant (Kd) of Cd-4 aptamer was determined as 34.5 nM for Cd(II). Moreover, the Cd-4 aptamer was considered a recognition element for the colorimetric detection of Cd(II) based on the aggregation of AuNPs by cationic polymer. Through spectroscopic quantitative analysis, Cd(II) in aqueous solution can be detected as low as 4.6 nM. The selected Cd-4 aptamer will offer a new substitute for the detection of Cd(II) or other applications like recovery of cadmium from polluted samples.

A simple highly sensitive and selective TURN-ON fluorescent chemosensor for the detection of cadmium ions in physiological conditions

A very simple fluorophore was synthesized and applied as a chemosensor for Cd²⁺ion detection.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Benzodithieno-imidazole based π-conjugated fluorescent polymer probe for selective sensing of Cu2+

A benzodithieno-imidazole based π-conjugated fluorescent polymer probe shows excellent selectivity towards Cu²⁺ions through fluorescence quenching.

A novel polynorbornene-based chemosensor for the fluorescence sensing of Zn2+ and Cd2+ and subsequent detection of pyrophosphate in aqueous solutions

A novel 8-hydroxyquinoline anchored polynorbornene for the fluorescence sensing of Zn²⁺/Cd²⁺ and subsequent detection of pyrophosphate in aqueous solutions and its biological application is introduced.

2D-cadmium MOF and gismondine-like zinc coordination network based on the N-(2-tetrazolethyl)-4′-glycine linker

We have designed and synthesized two new metal-organic-frameworks (MOFs) using the novel N-(2-tetrazolethyl)-4′-glycine spacer (TeGly)²⁻. These materials exhibit intense photoluminescence.

Polynorbornene derived 8-hydroxyquinoline paper strips for ultrasensitive chemical nerve agent surrogate sensing

The detection of nerve agent simulants is achieved by the photoinduced electron transfer (PET) mechanism.