Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

Incorporation of perovskite nanocrystals into lanthanide metal-organic frameworks with enhanced stability for ratiometric and visual sensing of mercury in aqueous solution

In-situ growth of CsPbBr₃ nanocrystal into Eu-BTC was realized for synthesis of dual-emission CsPbBr₃@Eu-BTC by a facile solvothermal method, and a novel ratiometric fluorescence sensor based on the CsPbBr₃@Eu-BTC was prepared for rapid, sensitive and visual detection of Hg²⁺ in aqueous solution. The transmission electron microscopy (TEM), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis were used to verify the successful incorporation of CsPbBr₃ into the Eu-BTC. Meanwhile, the CsPbBr₃@Eu-BTC nanocomposite maintained high fluorescence performance and stability in aqueous solution. After adding Hg²⁺, the green fluorescence of CsPbBr₃ was quenched and the red fluorescence of Eu³⁺ remained unchanged, while the color changed from green to red obviously. The occurrence of dynamic quenching and electron transfer were verified by fluorescence lifetime, Stern-Volmer quenching constant and XPS analysis. The ratiometric fluorescence sensor shows high analytical performance for Hg²⁺ detection with a wide linear range of 0-1 μM and a low detection limit of 0.116 nM. In addition, it also shows high selectivity for the detection of Hg²⁺ and can be successfully applied to detect Hg²⁺ in environmental water samples. More importantly, a novel paper-based sensor based on the CsPbBr₃@Eu-BTC ratiometric probe was successfully manufactured for the visual detection of Hg²⁺ by naked eyes. This new type of ratiometric fluorescent sensor shows great potential for applications in point-of-care diagnostics.

Rhodamine 6G-based efficient chemosensor for trivalent metal ions (Al3+, Cr3+ and Fe3+) upon single excitation with applications in combinational logic circuits and memory devices

A new rhodamine 6G-based chemosensor (L3) was synthesized and characterized by ¹H, ¹³C, IR and mass spectroscopy studies. It exhibited an excellent selective and sensitive CHEF-based recognition of trivalent metal ions M³⁺ (M = Fe, Al and Cr) over mono and di-valent and other trivalent metal ions with prominent enhancement in the absorption and fluorescence intensity for Fe³⁺ (669-fold), Al³⁺ (653-fold) and Cr³⁺ (667-fold) upon the addition of 2.6 equivalent of these metal ions in the probe in H₂O/CH₃CN (7 : 3, v/v, pH 7.2). The corresponding K_d values were evaluated to be 1.94 × 10^-5 (Fe³⁺), 3.15 × 10^-5 (Al³⁺) and 2.26 × 10^-5 M (Cr³⁺). The quantum yields of L3, [L3-Fe³⁺], [L3-Al³⁺] and [L3-Cr³⁺] complexes in H₂O/CH₃CN (7 : 3, v/v, pH 7.2) were found to be 0.0005, 0.335, 0.327 and 0.333, respectively, using rhodamine-6G as the standard. The LODs for Fe³⁺, Al³⁺ and Cr³⁺ were determined by 3σ methods and found to be 2.57, 0.78 and 0.47 μM, respectively. The cyanide ion snatched Fe³⁺ from the [Fe³⁺-L3] complex and quenched its fluorescence via its ring-closed spirolactam form. Advanced level molecular logic devices using different inputs (2 and 4 input) and a memory device were constructed.

An oxacalix[4]arene-derived dual-sensing fluorescent probe for the relay recognition of Hg2+ and S2− ions

A rhodamine B-functionalized oxacalix[4]arene architecture has been designed as a dual-responsive probe for the sequential recognition of Hg2+ and S2− ions.

Comparison of two rhodamine-based polystyrene solid-phase fluorescent sensors for mercury(II) determination

Two novel rhodamine-based polystyrene solid-phase fluorescent sensors PS-AC-I and PS-AC-II with different coordination atoms (O or S) are synthesized and shown to be able to detect Hg(II) ions. They are characterized by Fourier-transform infrared spectroscopy and by scanning electron microscopy analysis. Their fluorescent properties, including response time, pH effects, fluorescence titrations, metal ion competition and recycling, are investigated and compared. Sensor PS-AC-II displayed higher selectivity and sensitivity to Hg(II), with a lower detection limit of 0.032 µM, which was 15 times better than PS-AC-I. A detection mechanism involving the Hg(II) chelation-induced ring-opening of the rhodamine spirolactam is proposed with the aid of theoretical calculations.

Rhodol-conjugated polymersome sensor for visual and highly-sensitive detection of hydrazine in aqueous media

Hydrazine is a hazardous environmental pollutant, which contaminates land, air and water posturing a severe risk to human health. For the first-hand estimation, a qualitative approach (colorimetric) for recognition of hydrazine could suffice. However, for accurate measurement, under the threshold limit value (TLV), a quantitative technique is desired. We report the polymersome-based sensor for visual detection and quantification of hydrazine in water. The rhodol-functionalized amphiphilic hyperbranched multiarm copolymer (HSP-RDL) was self-assembled into vesicles. The HSP-RDL vesicle probe exhibited high sensitivity and selectivity for hydrazine recognition in presence of various competitive species such as cations, anions, and neutral species. The fast responsive pink color change from colorless could be visualized with naked eye due to spirolactone ring opening by hydrazinolysis triggered strong fluorescence emission. The vesicle probe could detect hydrazine in water with a limit of detection (LOD) value of 2 nM (0.0652 ppb), which is lower than TLV (10 ppb) given by USEPA (United States Environmental Protection Agency). Furthermore, the vesicle probe could quantify hydrazine (recovery ≥ 99 %) in a wastewater sample collected from Huangpu river. The membrane-permeable characteristics of HSP-RDL led hydrazine detection in live cells through confocal fluorescence microscopy.

Fluorescence Sensing Platforms for Epinephrine Detection Based on Low Temperature Cofired Ceramics

A novel fluorescence-sensing pathway for epinephrine (EP) detection was investigated. The ceramic-based miniature biosensor was developed through the immobilization of an enzyme (laccase, tyrosinase) on a polymer—poly-(2,6-di([2,2′-bithiophen]-5-yl)-4-(5-hexylthiophen-2-yl)pyridine), based on low temperature cofired ceramics technology (LTCC). The detection procedure was based on the oxidation of the substrate, i.e., in the presence of the enzyme. An alternative enzyme-free system utilized the formation of a colorful complex between Fe²⁺ ions and epinephrine molecules. With the optimized conditions, the analytical performance illustrated high sensitivity and selectivity in a broad linear range with a detection limit of 0.14–2.10 nM. Moreover, the strategy was successfully used for an EP injection test with labeled pharmacological samples.

Fast and selective detection of mercury ions in environmental water by paper-based fluorescent sensor using boronic acid functionalized MoS2 quantum dots

In this study, the B-MoS₂ QDs, boronic acid functionalized MoS₂ quantum dots, are synthesized by a simple aminoacylation reaction between MoS₂ QDs and 3-aminobenzeneboronic acid (APBA). It not only exhibits excellent thermo-stability, photo-stability and good salt tolerance, but shows excellent fluorescence stability even under industrial wastewater with high concentration. These good characters can be used to construct a new fluorescence sensor for sensitive and selective detection of mercury ions (Hg²⁺). The fluorescence intensity of B-MoS₂ QDs linearly decreases with the increase of Hg²⁺ concentration ranging from 0.005 to 41 μmol L^-1, and the limit of detection as low as 1.8 nmol L^-1. Due to the mercury ion-promoted transmetalation reaction of aryl boronic acid, this proposed method exhibits fast response, ultra-sensitivity and high selectivity for analysis of Hg²⁺ in different environmental water, and which also uses to online monitoring of Hg²⁺. The B-MoS₂ QDs-based test paper can be used to detect the trace amounts of Hg²⁺ under UV lamp by naked eyes, suggesting that the proposed method has potential application in on-site monitoring of environmental Hg²⁺.

Metal Cation Detection in Drinking Water

Maintaining a clean water supply is of utmost importance for human civilization. Human activities are putting an increasing strain on Earth’s freshwater reserves and on the quality of available water on Earth. To ensure cleanliness and potability of water, sensors are required to monitor various water quality parameters in surface, ground, drinking, process, and waste water. One set of parameters with high importance is the presence of cations. Some cations can play a beneficial role in human biology, and others have detrimental effects. In this review, various lab-based and field-based methods of cation detection are discussed, and the uses of these methods for the monitoring of water are investigated for their selectivity and sensitivity. The cations chosen were barium, cadmium, chromium, copper, hardness (calcium, magnesium), lead, mercury, nickel, silver, uranium, and zinc. The methods investigated range from optical (absorbance/fluorescence) to electrical (potentiometry, voltammetry, chemiresistivity), mechanical (quartz crystal microbalance), and spectrometric (mass spectrometry). Emphasis is placed on recent developments in mobile sensing technologies, including for integration into microfluidics.

TiO2/SiO2 decorated carbon nanostructured materials as a multifunctional platform for emerging pollutants removal

Aquatic ecosystem contaminated with hazardous pollutants has become a high priority global concern leading to serious economic and environmental damage. Among various treatment approaches, carbon nanostructured materials have received particular interest as a novel platform for emerging pollutants removal owing to their unique chemical and electrical properties, biocompatibility, high scalability, and infinite functionalization possibility with an array of inorganic nanomaterials and bio-molecules. Within this framework, carbon nanotubes (CNTs) are widely used due to their hollow and layered structure and availability of large specific surface area for the incoming contaminants. Carbon nanotubes can be used either as single-walled, multi-walled, or functionalized nanoconstructs. TiO₂/SiO₂-functionalized CNTs are among the most promising heterogeneous photocatalytic candidates for the degradation of a range of organic compounds, heavy metals reduction, and selective oxidative reactions. Herein, we reviewed recent development in the application of TiO₂ and SiO₂ functionalized nanostructured carbon materials as potential environmental candidates. After a brief overview of synthesis and properties of CNTs, we explicitly discussed the potential applications of TiO₂/SiO₂ functionalized CNTs for the remediation of a variety of environmentally-related pollutants of high concern, including synthetic dyes or dye-based hazardous waste effluents, as polycyclic aromatic hydrocarbons (PAHs), pharmaceutically active compounds, pesticides, toxic heavy elements, remediation of metal-contaminated soil, and miscellaneous organic contaminants. The work is wrapped up by giving information on current challenges and recommended guidelines about future research in the field bearing in mind the conclusions of the current review.

A novel near-infrared fluorescent probe with a “donor–π–acceptor” type structure and its application in the selective detection of cysteine in living cells

A novel “donor–π–acceptor” type fluorescent probe has been prepared for the detection of Cys. This probe shows great fluorescent performance and obvious response to Cys, and has been successfully applied in visualizing Cys in living cells.

Development of rhodamine-based fluorescent probes for sensitive detection of Fe3+ in water: spectroscopic and computational investigations

Four novel rhodamine-based fluorescent probes (RE1–RE4) were designed and synthesized for sensitive detection of Fe³⁺ in water.

Antibacterial and aqueous dual-responsive sensing activities of monomeric complexes with uncoordinated imidazole sites

The butterfly-shaped monomeric complex is stable and slight soluble in water, which shows antibacterial and aqueous dual-responsive sensing activities.