Easily synthesizable molecular probe for the nanomolar level detection of Cd2+ in near aqueous media: Theoretical investigations and live cell imaging

The present investigation highlights a quinoline-based small molecule probe (DEQ) for the detection of Cd2+ among other metal ions in near-aqueous media. The probe DEQ and its Cd2+ complex (DEQ-Cd) have been synthesized and characterized by all possible spectroscopic methods. The weakly emissive DEQ showed its strong emission in the presence of Cd2+, which is attributed to the photoinduced electron transfer (PET) along with the chelation-enhanced fluorescence (CHEF) mechanism. The 1:1 binding mode between ligand and Cd2+ is confirmed by single crystal XRD analysis, which is further supported by Job's plot and HRMS. The detection limit of the probe to recognize Cd2+ was found to be as low as 89 nM. Furthermore, DEQ can act as a reversible fluorescence probe with the off-on-off mechanism by the alternative addition of Cd2+ and EDTA. DFT and TD-DFT studies exposed the proposed mechanism after Cd2+ insertion and the obtained results for electronic spectra are in line with the experimental results. The response towards pH was quite interesting and allowed us to study its application in live cell imaging. With all the positive results, the proposed ligand DEQ can be used as a potential probe for the detection of Cd2+ in real-life applications.

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.

Highly selective and sensitive colorimetric chemosensor based on tricarboyanine for detection of Ag+ in industrial wastewater

Abstract

An efficient fluorescent probe 1 based on tricarbocyanine derivative was designed and synthesized, which can detect Ag+ in real industrial wastewater. UV-Vis absorption and fluorescent emission spectra of probe 1 were carried out and indicated this probe can bind Ag+ via complexation reaction, then leading to a remarkable color change from blue to light red. Furthermore, probe 1 showed high sensitive performance and excellent selectivity toward Ag+ over other common metal ions in neutral pH. The sensing mechanism was proposed and further confirmed by 1H NMR, which demonstrate analyte-induced destruction of the π-electron system could be shorten by the disruption of the pull-push π-conjugation system in probe 1. Moreover, a test strip was prepared by filter paper immersing in probe 1 solution, which further provide its potential application for trace Ag+ detection in real industrial wastewater.

Graphical abstract

An "OR-AND" logic gate based multifunctional colorimetric sensor for the discrimination of Pb2+ and Cd2

Pb²⁺ and Cd²⁺ are the most ubiquitous heavy metal ion pollutants, and they have aroused much attention due to their irreversible and significant damage to human organ. In this work, a new fluorescein-based "OR-AND" logic gate colorimetric probe 3',6'-bis((tert-butyldiphenylsilyl)oxy)-2-(2-((2-hydroxyphenyl)imino)ethylidene)aminspiro[isoindoline-1,9'-xanthen]-3-one (FP) was designed and synthesized via attaching 2-(2-((2-hydroxyphenyl)imino)ethylidene)amino and tert-butyldiphenylsilyl to fluorescein as the specific identification groups. This sensor can rapidly and sensitively discriminate Pb²⁺ and Cd²⁺ by utilizing F^- as an auxiliary reagent. When Pb²⁺ or Cd²⁺ was added into the FP solution, the absorption band at 533 nm increased and the peak at 374 nm decreased, the color changed from colorless to pale-purple, resulting in a ratiometric spectral change. However, adding fluoride ion to the FP solution containing Pb²⁺ or Cd²⁺ resulted in a distinct phenomenon in which the pale purple color fades out to colorless for a Pb²⁺-containing solution and deepen to dark purple for a Cd²⁺-containing solution, which is attributable to the different coordination mechanisms. In aqueous solution, the detection limits of FP can reach 0.42 μM for Pb²⁺ and 0.53 μM for Cd²⁺. The probe exhibited rapid responses for these analytes. Moreover, FP was successfully used to rapidly detect trace amounts of hazardous Pb²⁺ and Cd²⁺ in tap water with good relative recovery and the relative standard deviations (RSD) were 1.8% for Pb²⁺ and 0.3% for Cd²⁺, providing a novel approach for detecting Pb²⁺ and Cd²⁺ in practical application.

An efficient ICT-based ratio/colorimetric tripodal azobenzene probe for the recognition/discrimination of F-, AcO- and H2PO4- anions

The tripodal probe L was readily prepared via introducing rhodamine and azobenzene groups in a two-step procedure. Studies of the recognition properties indicated that probe L exhibited high sensitivity and selectivity towards F^-, AcO^- and H₂PO₄^- through a ratiometric colorimetric response with low detection limits of the order of 10^-7 M. The complexation behaviour was fully investigated by spectral titration, ¹H NMR spectroscopic titration and mass spectrometry. Probe L not only recognizes F^-, AcO^- and H₂PO₄^-, but can also distinguish between these three anions via the different ratiometric behaviour in their UV-vis spectra (387/505 nm for L-H₂PO₄^-, 387/530 nm for L-AcO^- and 387/575 nm for L-F^- complex) or via different colour changes (light coral for L-H₂PO₄^-, light pink for L-AcO^- and violet for the L-F^- complex). Additionally, given the presence of NH and OH groups in probe L, which can be protonated and deprotonated, probe L further exhibited an excellent pH response over a wide pH range (pH 3 to pH 12).

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.

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.

A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(ii) from zinc(ii) based on amide tautomerization

A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized.

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.

A highly sensitive naphthaoxazole-based cell-permeable ratiometric chemodosimeter for hydrazine

The present communication reports a ratiometric chemodosimeter (P1) for the efficient detection of hydrazine down to a lowest level of 1.79 × 10⁻⁹ M.

A highly sensitive and selective turn-on fluorescent probe for Pb(ii) ions based on a coumarin–quinoline platform

A new fluorescent probeT1, which contained a coumarin fluorophore with a triazole substituted 8-hydroxyquinoline (8-HQ) receptor and a Schiff base spacer, was rationally designed and synthesized.

Phenanthroimidazole derivatives as emitters for non-doped deep-blue organic light emitting devices

We synthesized eight phenanthroimidazole derivatives as blue emitters for OLED application and investigated the relationship between the molecule structure and optoelectronic properties.

A new visible-light-excitable ICT-CHEF-mediated fluorescence 'turn-on' probe for the selective detection of Cd(2+) in a mixed aqueous system with live-cell imaging

A new quinoline based sensor was developed and applied for the selective detection of Cd(2+) both in vitro and in vivo. The designed probe displays a straightforward approach for the selective detection of Cd(2+) with a prominent fluorescence enhancement along with a large red shift (∼38 nm), which may be because of the CHEF (chelation-enhanced fluorescence) and ICT (internal charge transfer) processes after interaction with Cd(2+). The interference from other biologically important competing metal ions, particularly Zn(2+), has not been observed. The visible-light excitability of the probe merits in the viewpoint of its biological application. The probe enables the detection of intracellular Cd(2+) with non-cytotoxic effects, which was demonstrated with the live RAW cells. The experimentally observed change in the structure and electronic properties of the sensor after the addition of Cd(2+) were modelled by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) computational calculations, respectively. Moreover, the test strip experiment with this sensor exhibits both absorption and fluorescence color changes when exposed to Cd(2+) in a mixed aqueous solution, which also makes the probe more useful. The minimum limit of detection of Cd(2+) by the probe was in the range of 9.9 × 10(-8) M level.

Cd(2+) Triggered the FRET "ON": A New Molecular Switch for the Ratiometric Detection of Cd(2+) with Live-Cell Imaging and Bound X-ray Structure

On the basis of the Förster resonance energy transfer mechanism between rhodamine and quinoline-benzothiazole conjugated dyad, a new colorimetric as well as fluorescence ratiometric probe was synthesized for the selective detection of Cd(2+). The complex formation of the probe with Cd(2+) was confirmed through Cd(2+)-bound single-crystal structure. Capability of the probe as imaging agent to detect the cellular uptake of Cd(2+) was demonstrated here using living RAW cells.

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.