Fluorescein-N-Methylimidazole Conjugate as Cu(2+) Sensor in Mixed Aqueous Media Through Electron Transfer

PbS/graphene hybrid nanostructures coated glassy carbon electrode for the electrochemical sensing of copper ions in aqueous solution

In this research, we have studied the electrochemical sensing of Cu(II) ions in aqueous solution using PbS/Graphene composite nanostructure coated glassy carbon electrode (GCE). The SEM-EDAX analysis revealed that the lead sulphide nanocrystals are homogeneously embedded on the graphene nanosheets with an uniform particle size of 100 nm, and the elements presents 92.32% and Lead content of 5.45% and Sulfur content of 0.91%. Raman spectra exhibits G with respect to the E2g sp² hybridized C-C and D band with respect to the A1g mode in the disordered edge region of the GNS. The composite nanostructure coated GCE (PbS/Graphene/GCE) was prepared and its performance in the existence of metal ions such us Cd(II),Pb(II), Mg(II), Cu(II) and Ni(II) was studied using the current voltage curves in double distilled water within the scan rates of 25 to 300mVs-¹. The PbS/Graphene coated carbon electrode exhibited the higher anodic and cathodic peak current for copper solution than the other metal ions studied, which various linearly proportional to concentration. The electrochemical sensing characteristics PbS/GNS/GCE was found to be significant towards detecting Cu²⁺ ion within the concentration range of 1 × 10^-4 to 1 × 10^-8 M, with a lowest sensing detection limit of 1 × 10^-8 M.

Fluorescein Based Fluorescence Sensors for the Selective Sensing of Various Analytes

Fluorescein molecules are extensively used to develop fluorescent probes for various analytes due to their excellent photophysical properties and the spirocyclic structure. The main structural modification of fluorescein occurs at the carboxyl group where different groups can be easily introduced to produce the spirolactam structure which is non-fluorescent. The spirolactam ring opening accounts for the fluorescence and the dual sensing of analytes using fluorescent sensors is still a topic of high interest. There is an increase in the number of dual sensors developed in the past five years and quite a good number of fluorescein derivatives were also reported based on reversible mechanisms. This review analyses environmentally and biologically important cations such as Cu²⁺, Hg²⁺, Fe³⁺, Pd²⁺, Zn²⁺, Cd²⁺, and Mg²⁺; anions (F^-, OCl^-) and small molecules (thiols, CO and H₂S). Structural modifications, binding mechanisms, different strategies and a comparative study for selected cations, anions and molecules are outlined in the article.

Sequential Detection of Palladium and Chromium Oxyanion by a Fluorescein Based Chemosensor in Mixed Aqueous Media

A new highly selective chemosensor, based on fluorescein-allyloxy benzene conjugate 1, was developed for the sequential detection of palladium and chromium oxyanions in a mixed aqueous media, and was studied by UV-visible and fluorescence spectroscopy. The sensing of palladium ions produces a chemodosimetric and ratiometric change in the emission band of 1 from 450 to 525 nm, followed by the sensing of chromate ions by 2 that quenches the emission band at 525 nm in a buffered H2O: DMF solution (9:1, pH = 7.4). The rate constants of palladium and chromate ions were found to be 8.6 × 105 M−1, 2.1 × 105 M−1, and 5.4 × 104 M−1 respectively. The chemosensor 1 has a palladium detection limit of 49 ppb while the sequential detection limit of chromate ions (CrO42− and Cr2O72−) were 127 and 259 ppb. The ratiometric change in the emission is produced due to the deallylation of 1 by palladium to produce 2 that restores the ESIPT (excited state intramolecular proton transfer) of the phenolic ring and enhances the electron transfer (ET) phenomenon from the phenolic group to fluorescein. The sequential binding of chromate ions to 2 inhibits the ESIPT and causes chelation enhanced quenching (CHEQ) of the fluorescence.

Ultrasensitive Optical Chemosensor for Cu(II) Detection

Herein, the main objective of this research is to design and synthesize a novel optical chemosensor, 2,6-Bis(4-dimethylaminophenyl)-4-(dicyanomethylene)-cyclohexane-1,1-dicarbo-nitrile (BDC), for detection of one of the most significant metal ions Cu(II). This novel fluorescent chemosensor exhibits unique optical properties with large Stokes shift (about 170 nm) approximately. The fluorescence and UV–vis absorption performance among the BDC probe and Cu(II) ions were examined in 1:9 (v/v) methanol–HEPES buffer (pH = 7.2) solution. Also, BDC displays high selectivity for Cu(II) concerning other cations. Moreover, this probe provides high selectivity and sensitivity based on their fluorescence properties and recognition abilities within a detection limit of the Cu(II) contents (LOD 2.3 x 10⁻⁷ M). The suggested mechanism of BDC sensor is attributed to the chelation process with Cu(II), to establish a 1:1 metal-ligand ratio complex with a binding constant (K_bind = 7.16 x 10⁴ M⁻¹). The detection process is accompanied by quenching the main emission peak of the BDC at 571 nm. All the experimental data were collected to investigate the effects of several important parameters such as reversibility and the concentration limits. Besides, we study the interference of various metal ions on selectivity and detection capacity of this significant Cu (II) ion. This novel chemosensor shows ultrasensitive, fast tracing of Cu(II) in the physiological pH range (pH 7.2) and therefore may propose a novel promising method for the investigation of the biological functions of Cu(II) in living cells.

A reusable multichannel anthraimidazoledione-based receptor for Hg2+and Cu2+ions: ultrasensitive, economical and facile detection of Hg2+in real water sources through fluorescence readout

A multichannel, ultrasensitive and selective receptor (1) has been developed for practical detection of Hg²⁺in various drinking waters.