Design and Characterization of Electrochemical Sensor for the Determination of Mercury(II) Ion in Real Samples Based upon a New Schiff Base Derivative as an Ionophore

2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

A Formyl Chromone Based Schiff Base Derivative: An Efficient Colorimetric and Fluorescence Chemosensor for the Selective Detection of Hg2+ Ions

A novel chromone-based Schiff base L was designed and synthesized by condensing an equimolar amount of 3-formyl chromone and 2,4-dinitro phenyl hydrazine. Schiff base L was developed as a potent colorimetric and fluorescent molecular probe to recognize Hg2+ ions over other competitive metal ions. In the presence of Hg2+, Schiff base L displays a naked-eye detectable color change under day and UV365 nm light. Various UV-Vis and fluorescence studies of L were performed in the absence and presence of Hg2+ to determine the sensitivity and the sensing mechanism. With high selectivity and specificity, the detection limit and association constant of L for Hg2+ were estimated at 1.87 µM and 1.234 × 107 M-1, respectively. The developed sensor L was applied to real soil samples for the detection of Hg2+.

Green-emitting functionalized silicon nanoparticles as an "off-on" fluorescence bio-probe for the sensitive and selective detection of mercury (II) and 3-mercaptopropionic acid

Herein, we developed a class of functionalized silicon nanoparticles (F-SiNPs) bio-probes named thiol-conjugated F-SiNPs. They combine excellent biocompatibility with small dimensions (<10 nm) and biological usefulness with sustained and robust fluorescence (3.32% photoluminescent quantum yield). Identifying 3-Mercaptopropionic acid (3-MPA), which lowers the quantity of gamma-aminobutyric acid in the brain, and mercury (Hg²⁺) was a crucially important step since their excessive levels are a sign of several disorders. Using F-SiNPs as a fluorescent bio-probe, we provided an "off-on" technique for sensitively and selectively determining Hg²⁺ and 3-MPA in this study. The 3-(2-aminoethylamino) propyl (dimethoxymethylsilane) and basic fuchsin as precursors were hydrothermally treated to produce the F-SiNPs exhibiting green fluorescence. Our results suggest that Hg²⁺ reduced the fluorescence of F-SiNPs because of strong ionic interactions and metal-ligand binding among many thiols and carboxyl groupings at the surface of Hg²⁺ and F-SiNPs. Additionally, the resultants demonstrated that after being quenched by Hg²⁺, the produced F-SiNPs led to the distinctive "off-on" response to 3-MPA. Moreover, the method could detect Hg²⁺ and 3-MPA with limits of detection of 0.065 μM and 0.017 μM, respectively. The technique employed is quick, easy, affordable, and environmentally friendly. The sensing platform has successfully determined Hg²⁺ and 3-MPA in urine, water, and human serum samples.

Construction of fluorescent logic gates for the detection of mercury(II) and ciprofloxacin based on phycocyanin

Chemical pollutants such as heavy metals and antibiotics in the environment pose a huge threat to humans and animals. Our studies have demonstrated that the fluorescence of phycocyanin showed quenching responses towards both mercury (Hg2+) and ciprofloxacin (CIP), which acted in accordance with the "OR" molecular logic gate. In order to discriminate Hg2+ and CIP in application scenarios, cysteine (Cys) was utilized to design another "INHIBIT" logic gate, in which Hg2+ and Cys were the two inputs. Thus, an intelligent biosensor with dual-target identification capacity was successfully developed by using a fluorescent natural protein in an ingenious logic gate system.

Rapid electrochemical sensor for uranium(vi) assessment in aqueous media

The significance of reliable monitoring of uranium levels in water recourses calls for the development of time-saving, robust, and accurate methods for its estimation. In this view, the current study describes the design and analytical parameters of a potentiometric membrane sensor for uranium(vi) ions. The sensor is based on a new Schiff base derivative, as an ionophore, that was synthesized and structurally characterized by elemental, FTIR, and ¹HNMR analyses. The impact of the membrane constituents was studied and the membrane composition of PVC (32.50) : o-NPOE (65.00) : ionophore (2.00) :  KTpClPB (0.50) (%, w/w) achieved the optimal performance. A Nernestian response was observed for uranium(vi) ions within the concentration range 1.00 × 10⁻⁶ to 1.00 × 10⁻¹ mol L⁻¹. The sensor revealed a low detection limit of 3.90 × 10⁻⁷ mol L⁻¹ with satisfactory reproducibility. Stable and reproducible potentials were obtained within a short time (9 s) over the pH range 2.10–4.21. The impact of possible competing ions was investigated and the selectivity coefficients revealed appropriate selectivity for uranium(vi) ions over various cations without significant interference. The sensor's performance was examined by determining the amount of uranium(vi) in water samples and the results showed no significant differences from those obtained by the ICP-OES method.

A new Schiff base was synthesized and applied as ionophore to construct potentiometric sensor for uranium(vi) determination.

Materials Approaches for Improving Electrochemical Sensor Performance

Electrochemical sensors have emerged as important diagnostic tools in recent years, due to their simplicity and ease of use. Compared to instrumental analysis methods that use complicated experimental and data analysis techniques─such as mass spectrometry, nuclear magnetic resonance (NMR), spectrophotometric methods, and chromatography─electrochemical sensors show promise for use in a wide range of real-time and in situ applications such as pharmaceutical testing, environmental monitoring, and medical diagnostics. In order to identify analytes in complex and/or biological samples, materials used for both the electrode materials and the chemically selective layer have been evolving throughout the years for optimizing the analytical performance of electrochemical sensors to increase sensitivity, selectivity and linear range. In this Perspective, attention will be focused on different types of materials that have been used for electrochemical sensing, including new combinations of well-studied materials as well as novel strategies to enhance the performance of sensing devices. The Perspective will also discuss existing challenges in the field and future strategies for addressing those challenges.

Dual-Emission Fluorescence Probe Based on CdTe Quantum Dots and Rhodamine B for Visual Detection of Mercury and Its Logic Gate Behavior

It is urgent that a convenient and sensitive technique of detecting Hg2+ be developed because of its toxicity. Conventional fluorescence analysis works with a single fluorescence probe, and it often suffers from signal fluctuations which are influenced by external factors. In this research, a novel dual-emission probe assembled through utilizing CdTe quantum dots (QDs) and rhodamine B was designed to detect Hg2+ visually. Only the emission of CdTe QDs was quenched after adding Hg2+ in the dual-emission probe, which caused an intensity ratio change of the two different emission wavelengths and hence facilitated the visual detection of Hg2+. Compared to single emission QDs-based probe, a better linear relationship was shown between the variation of fluorescence intensity and the concentration of Hg2+, and the limit of detection (LOD) was found to be11.4 nM in the range of 0-2.6 μM. Interestingly, the intensity of the probe containing Hg2+ could be recovered in presence of glutathione (GSH) due to the stronger binding affinity of Hg2+ towards GSH than that towards CdTe QDs. Based on this phenomenon, an IMPLICATION logic gate using Hg2+/GSH as inputs and the fluorescence signal of QDs as an output was constructed.