Colorimetric and voltammetric sensing of mercury ions using 2,2′-(ethane-1,2-diylbis((2-(azulen-2-ylamino)-2-oxoethyl)azanediyl))diacetic acid

Electrochemical System for Field Control of Hg2+ Concentration in Wastewater Samples

The paper presents the validation of an electrochemical procedure for on-site Hg²⁺ ions determination in wastewater samples using a modified carbon screen-printed electrode (SPE) with a complexing polymeric film based on poly(2,2'-(ethane-1,2-diylbis((2-(azulen-2-ylamino)-2-oxoethyl)azanediyl))diacetic acid) (polyL). Using metal ions accumulation in an open circuit followed by anodic stripping voltammetry, the SPE-polyL electrode presents a linear range in the range of 20 µg/L to 150 µg/L, with a limit of detection (LOD) = 6 µg/L, limit of quantification (LOQ) = 20 µg/L, and an average measurement uncertainty of 26% of mercury ions. The results obtained in situ and in the laboratory using the SPE-polyL modified electrode were compared with those obtained by the atomic absorption spectrometry coupled with the cold vapor generation standardized method, with the average values indicating excellent recovery yields.

New sensing platform of poly(ester-urethane)urea doped with gold nanoparticles for rapid detection of mercury ions in fish tissue

A new electrochemical sensor has been fabricated based on the in situ synthesis of poly(ester-urethane) urea (PUU) doped with gold nanoparticles (AuNPs), and the obtained composite materials (PUU/AuNPs) were used as a new sensing platform for highly sensitive and selective detection of mercury(II) ions in fish tissue. PUU was synthesized and fully characterized by XRD, TGA, DSC, and FTIR to analyze the chemical structure, thermal stability, and morphological properties. As a polymeric structure, the PUU consists of urethane and urea groups that possess pronounced binding abilities to Hg²⁺ ions. SEM-EDX was carried out to confirm this kind of interaction. Using ferricyanide as the redox probe, PUU alone exhibited weak electrochemical signals due to its low electrical conductivity. Therefore, a new series of nanocomposites of PUU with different nanostructured materials were applied, and their electrochemical performances were evaluated. Among these materials, the PUU/AuNP-modified electrode showed high voltammetric signals towards Hg²⁺. Consequently, the parameters affecting the performance of the assay, such as electrode composition, scan rate, and sensing time, as well as the effect of electrolyte and pH were studied and optimized. The sensor showed a linear range of 5 ng mL^-1 to 155 ng mL^-1 with the regression coefficient R ² = 0.986, while the calculated values of the limit of detection (LOD) and limit of quantification (LOQ) were 0.235 ng mL^-1 and 0.710 ng mL^-1, respectively. In terms of cross reactivity testing, the sensor exhibited a high selectivity against heavy metals which are commonly determined in seafood (Cd²⁺, Pb²⁺, As³⁺, Cr³⁺, Mg²⁺, and Cu²⁺). For real applications, total Hg²⁺ ions in fish tissue were determined with very high recovery and no prior complicated treatments.

Recent advances of environmental pollutants detection via paper-based sensing strategy

Paper has become one of the most promising substrates for building low-cost and powerful sensing platforms due to its self-pumping ability and compatibility with multiple patterning methods. Paper-based sensors have been greatly developed in the field of environmental monitoring. In this review, we introduced the research and application of paper-based sensors in environmental monitoring, focusing on the deposition and patterning methods of building paper-based sensors, and summarized the applications of detecting environmental pollutants, including metal ions, anions, explosives, neurotoxins, volatile organic compounds, and small molecules. In addition, the development prospects and challenges of promoting paper-based sensors are also discussed. The current review will provide references for the construction of portable paper-based sensors, and has implications for the field of on-site real-time detection of the environment.

Electrochemical Comparison on New (Z)-5-(Azulen-1-Ylmethylene)-2-Thioxo-Thiazolidin-4-Ones

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These compounds, after their immobilization on glassy carbon electrodes during oxidative electropolymerization, were examined as complexing ligands for heavy metal ions from aqueous solutions through adsorptive stripping voltammetry.

Azulene-A Bright Core for Sensing and Imaging

Azulene is a hydrocarbon isomer of naphthalene known for its unusual colour and fluorescence properties. Through the harnessing of these properties, the literature has been enriched with a series of chemical sensors and dosimeters with distinct colorimetric and fluorescence responses. This review focuses specifically on the latter of these phenomena. The review is subdivided into two sections. Section one discusses turn-on fluorescent sensors employing azulene, for which the literature is dominated by examples of the unusual phenomenon of azulene protonation-dependent fluorescence. Section two focuses on fluorescent azulenes that have been used in the context of biological sensing and imaging. To aid the reader, the azulene skeleton is highlighted in blue in each compound.

Improving the Voltammetric Determination of Hg(II): A Comparison Between Ligand-Modified Glassy Carbon and Electrochemically Reduced Graphene Oxide Electrodes

A new thiosemicarbazone ligand was immobilized through a Cu(I)-catalyzed click reaction on the surface of glassy carbon (GC) and electrochemically reduced graphene oxide (GC-ERGO) electrodes grafted with phenylethynyl groups. Using the accumulation at open circuit followed by anodic stripping voltammetry, the modified electrodes showed a significant selectivity and sensibility for Hg(II) ions. A detection limit of 7 nM was achieved with the GC modified electrodes. Remarkably, GC-ERGO modified electrodes showed a significantly improved detection limit (0.8 nM), sensitivity, and linear range, which we attribute to an increased number of surface binding sites and better electron transfer properties. Both GC and GC-ERGO modified electrodes proved their applicability for the analysis of real water samples.

Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

A Colorimetric Chemosensor Based on a Nozoe Azulene That Detects Fluoride in Aqueous/Alcoholic Media

Colorimetry is an advantageous method for detecting fluoride in drinking water in a resource-limited context, e. g., in parts of the developing world where excess fluoride intake leads to harmful health effects. Here we report a selective colorimetric chemosensor for fluoride that employs an azulene as the reporter motif and a pinacolborane as the receptor motif. The chemosensor, NAz-6-Bpin, is prepared using the Nozoe azulene synthesis, which allows for its rapid and low-cost synthesis. The chemosensor gives a visually observable response to fluoride both in pure organic solvent and also in water/alcohol binary solvent mixtures.