Recent Trends in Macro-, Micro-, and Nanomaterial-Based Tools and Strategies for Heavy-Metal Detection

Phenothiazine-chitosan based eco-adsorbents: A special design for mercury removal and fast naked eye detection

The aim of the paper was to investigate the ability of an eco-friendly luminescent xerogel prepared by chitosan crosslinking with a phenothiazine luminogen to detect and remove heavy metals. Its ability to give a divergent morphological and optical response towards fifteen environmental relevant metals was investigated by naked eye and UV lamp, fluorescence spectroscopy and scanning electron microscopy. A distinct response was noted for mercury, consisting in the transformation of the xerogel into a rubber-like material accompanied by the red shifting of the color of emitted light from yellow-green to greenish-yellow domain. The particularities of the metals anchoring into the xerogel were analyzed by FTIR spectroscopy and X-ray diffraction. The morphological changes and the metal uptake were analyzed by SEM-EDAX, swelling and gravimetric methods. It was concluded that mercury has a superior affinity towards this heteroatoms rich system, leading to a secondary crosslinking. This directed a great absorption capacity of 1673 mg/g and a specific morphological response for mercury ion concentrations up to 0.001 ppm.

Microwave-Assisted Neat Synthesis of a Ferrocene Appended Phenolphthalein Diyne: A Designed Synthetic Scaffold for Hg2+ Ion

A C₂-symmetric internally conjugated 1,3-dialkyne system 5, containing phenolphthalein as a fluorophore and ferrocene as a redox moiety, has been synthesized via a microwave-assisted synthetic procedure. Compound 5 was synthesized by Cu-catalyzed Glaser-Hay coupling using a microwave reactor in neat condition for the first time. Compound 5 was found to be highly selective toward Fe³⁺, Cu²⁺, and Hg²⁺ ions via multichannels. Interestingly, Fe³⁺ and Cu²⁺ ions simply promote the oxidation of ferrocene unit to ferrocenium ion without binding to the receptor, whereas Hg²⁺ binds with the receptor 5 (ΔE_1/2 = 71 mV). The oxidation and binding phenomena were investigated by optical and electrochemical analyses. Furthermore, the binding site of Hg²⁺ ion with our designed probe was confirmed by ¹H, ¹³C NMR and IR titrations, which indicated that conjugated dialkyne unit interacts with Hg²⁺ ion by a favorable soft-soft interaction. Both receptor 5 and its metal complex, [5·2Hg²⁺], are stable in the physiological pH range (pH = 6-7) and thermally stable up to 78 °C. The experimental results of metal binding have been further supported by quantum chemical calculations (DFT), which explore the favorable geometry of the free ligand as well as its Hg²⁺ complex.

Real-Time Water Quality Monitoring with Chemical Sensors

Water quality is one of the most critical indicators of environmental pollution and it affects all of us. Water contamination can be accidental or intentional and the consequences are drastic unless the appropriate measures are adopted on the spot. This review provides a critical assessment of the applicability of various technologies for real-time water quality monitoring, focusing on those that have been reportedly tested in real-life scenarios. Specifically, the performance of sensors based on molecularly imprinted polymers is evaluated in detail, also giving insights into their principle of operation, stability in real on-site applications and mass production options. Such characteristics as sensing range and limit of detection are given for the most promising systems, that were verified outside of laboratory conditions. Then, novel trends of using microwave spectroscopy and chemical materials integration for achieving a higher sensitivity to and selectivity of pollutants in water are described.

A SERS-based capillary sensor for the detection of mercury ions in environmental water

Mercury ion (Hg²⁺) is one of the most toxic heavy metal ions which will cause permanent damage to the brain and kidneys. So, it is important to develop a sensitive, simple and reliable approach to detect Hg²⁺. In this work, we report a surface-enhanced Raman scatting (SERS) sensor by decorating the inner wall of capillary with 4,4'-dipyridyl (Dpy) functionalized silver nanoparticles (AgNPs). The main advantage of this sensor is that it can collect samples directly by capillary force and carry out on-site analysis by combining portable Raman spectrometer. In the presence of Hg²⁺, the Dpy molecules would be separated from the surface of AgNPs and coordinated with Hg²⁺, resulting in a decrease in the SERS signal. A linear correlation of Raman intensity with Hg²⁺ concentrations from 1 to 100 part-per-billion (ppb) was obtained for quantitative analysis and the limit of detection (LOD) was determined to be 0.1 ppb. The good reproducibility and selectivity of the sensor were also demonstrated. In addition, the sensors were successfully applied to detect Hg²⁺ in real environmental water samples, and the sampling process provided operation convenience compared to conventional methods. These results indicated that these capillary sensors had great potential for Hg²⁺ detection in practical use.

Sodium Alginate Cross-Linkable Planar 1D Photonic Crystals as a Promising Tool for Pb2+ Detection in Water

Due to its high toxicity, Pb2+ pollution is a serious threat for human health and environments. However, in situ real-time detection of Pb2+ pollution is difficult and laboratory instruments are usually required. Then, the possibility to monitor water quality without laboratory instruments could lead to the extensive assessment of polluted water sources, especially in rural environments and developing countries where large lead concentrations are often found in surface water. Consequently, new simple colorimetric sensors are highly interesting in the field. In this work we report for the first time disposable polymer planar 1D photonic crystals made of poly (N-vinylcarbazole) as high refractive index medium and sodium alginate as low refractive index and active medium for the detection of Pb2+ in water. The detection relies on the ionic exchange occurring into the alginate matrix. This process effectively induces a physical cross-linking phenomenon, which inhibits water solubilization of the polymer. In turn, this affects the spectral response of the planar 1D photonic crystals modifying its color.

Developments and applications of nanomaterial-based carbon paste electrodes

This review summarizes the progress that has been made in the past ten years in the field of electrochemical sensing using nanomaterial-based carbon paste electrodes. Following an introduction into the field, a first large section covers sensors for biological species and pharmaceutical compounds (with subsections on sensors for antioxidants, catecholamines and amino acids). The next section covers sensors for environmental pollutants (with subsections on sensors for pesticides and heavy metal ions). Several tables are presented that give an overview on the wealth of methods (differential pulse voltammetry, square wave voltammetry, amperometry, etc.) and different nanomaterials available. A concluding section summarizes the status, addresses future challenges, and gives an outlook on potential trends.

Metal-organic frameworks-based sensitive electrochemiluminescence biosensing

Metal-organic frameworks (MOFs) as porous materials have attracted much attention in various fields such as gas storage, catalysis, separation, and nanomedical engineering. However, their applications in electrochemiluminescence (ECL) biosensing are limited due to the poor conductivity, lack of modification sites, low stability and specificity, and weak biocompatibility. Integrating the functional materials into MOF structures endows MOF composites with improved conductivity and stability and facilitates the design of ECL sensors with multifunctional MOFs, which are potentially advantageous over their individual components. This review summarizes the strategies for designing ECL-active MOF composites including using luminophore as a ligand, in situ encapsulation of luminophore within the framework, and post-synthetic modification. As-prepared MOF composites can serve as innovative emitters, luminophore carriers, electrode modification materials and co-reaction accelerators in ECL biosensors. The sensing applications of ECl-active MOF composites in the past five years are highlighted including immunoassays, genosensors, and small molecule detection. Finally, the prospects and challenges associated with MOF composites and their related materials for ECL biosensing are tentatively proposed.

Microelement composition of serum in Dolgans, indigenous inhabitants of the Russian Arctic, in the conditions of industrial development of territories

The geochemical conditions of landscapes are the content in the environment of certain chemical elements and their compounds, the lack or excess of which causes deviations in the state of human health. This problem has arisen in connection with the extraction of alluvial diamonds and the forthcoming development of the Tomtor deposit of rare-earth metals in the territories where the indigenous peoples of the North live. The study included 107 indigenous people of the North, belonging to the ethnic group of Dolgans living in the village of Yuryung-Khaya, Anabar district, Yakutia of Russia. The method of mass spectrometry was used to study the content of 13 trace elements in blood serum (P, Sc, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Cs, Pb). The study revealed an increase in the content of the macroelement phosphorus (148 mg/L) and trace elements of chromium (277 μg/L), manganese (133 μg/L), iron (5219 μg/L), nickel (57 μg/L) in serum of Dolgans, which may affect the development of diseases of the cardiovascular system and other diseases among indigenous inhabitants of the Arctic under conditions of industrial development of territories.

Surface potential microscopy of surfactant-controlled single gold nanoparticle

The surface potential of nanoparticles plays a key role in numerous applications, such as drug delivery and cellular uptake. The estimation of the surface potential of nanoparticles as drug carriers or contrast agents is important for the design of nanoparticle-based biomedical platforms. Herein, we report the direct measurement of the surface potential of individual gold nanorods (GNRs) via Kelvin probe force microscopy (KPFM) at the nanoscale. GNRs were capped by a surfactant, cetyltrimethylammonium bromide (CTAB), which was removed by centrifugation. CTAB removal is essential for GNR-based biomedical applications because of the cytotoxicity of CTAB. Applying KPFM analysis, we found that the mean surface potential of the GNRs became more negative as the CTAB was removed from the GNR. The results indicate that the negative charge of GNRs is covered by the electrostatic charge of the CTAB molecules. Similar trends were observed in experiments with gold nanospheres (GNS) capped by citrates. Overall, KPFM-based techniques characterize the surfactant of individual nanoparticles (i.e. GNR or GNS) with high resolution by mapping the surface potential of a single nanoparticle, which aids in designing engineered nanoparticles for biomedical applications.

Magnetic-Separation-Assisted Magnetic Relaxation Switching Assay for Mercury Ion Based on the Concentration Change of Oligonucleotide-Functionalized Magnetic Nanoparticle

Magnetic-separation-assisted magnetic relaxation switching (MRS) assay based on the concentration change of magnetic nanoparticles switches has been designed for bacteria, biological macromolecules, and small molecules detection because of its better analysis performance. As one of the most hazardous pollutants and highly dangerous elements, mercury ion (Hg²⁺) was employed as a model to further investigate the applicability of nanoparticle switches concentration change-based MRS assay mode for detecting metal ions in this study. The principle is based on the specific and strong interaction between mercury ion with the thymine-thymine(T-T) mismatch in double-stranded DNA duplexes by employing oligonucleotide functionalized magnetic nanoparticle as magnetic capture probe and MRS signal probe, respectively. The result shows that magnetic nanoparticles concentration-dependent MRS sensing mode could be facile applied to detect metal ion of Hg²⁺ in tap water, lake water and serum with wider detection range and higher accuracy. The as-presented magnetic-separation-assisted MRS assay of Hg²⁺ in complicated samples shows potential application values for Hg²⁺ assay in clinical and environmental monitoring, which broadens its application.

High-Throughput Metal Trap: Sulfhydryl-Functionalized Wood Membrane Stacks for Rapid and Highly Efficient Heavy Metal Ion Removal

Heavy metal pollution is a severe problem worldwide. Great efforts have been devoted in developing effective and eco-friendly ways to remove heavy metal ions from contaminated water. However, challenges remain in terms of the high cost, the complex preparation processes required, low efficiency, and difficulties in scaling-up. Here, we report a sulfhydryl-functionalized wood (SH-wood) membrane featuring three-dimensional mesoporous and low-tortuosity lumens, which serve as multisite metal traps to achieve highly efficient heavy metal ion removal from wastewater. Benefiting from the unique microstructure of wood, the resulting membrane exhibits a high saturation uptake capacity of 169.5, 384.1, 593.9, and 710.0 mg·g^-1 for Cu²⁺, Pb²⁺, Cd²⁺, and Hg²⁺ ions, respectively. Meanwhile, the SH-wood membrane can be easily regenerated at least eight times without apparent performance loss. Furthermore, stacking multilayers of the SH-wood filter is designed. Because of its high yet universal heavy metal ion absorbance capability, the multilayer SH-wood filter can effectively remove diverse heavy metal ions from real contaminated water, meeting the WHO standards while also displaying a high flux rate of 1.3 × 10³ L·m^-2·h^-1. Our work presents a promising strategy for the scalable and highly efficient removal of heavy metal ions from sewage for environmental remediation.

Enhanced and Selective Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) Ions by a Dumbbell- and Flower-Shaped Potato Starch Phosphate Polymer: A Combined Experimental and DFT Calculation Study

Microwave-ultrasound-assisted facile synthesis of a dumbbell- and flower-shaped potato starch phosphate (PSP) polymer, hereafter PSP, was carried out by cross-linking the hydroxyl groups of native potato starch (NPS) using phosphoryl chloride as a cross-linking agent. Structural and morphological analysis manifested the successful formation of the dumbbell- and flower-shaped PSP biosorbent with enhanced specific surface area and thermal stability. Viscoelastic behavior of NPS and PSP suggested increased rigidity in PSP, which helped the material to store more deformation energy in an elastic manner. The synthesized PSP biosorbent material was successfully tested for efficient and quick uptake of Zn(II), Pb(II), Cd(II), and Hg(II) ions from aqueous medium under competitive and noncompetitive batch conditions with q m values of 130.54, 106.25, 91.84, and 51.38 mg g-1, respectively. The adsorption selectivity was in consonance with Pearson's hard and soft acids and bases (HSAB) theory in addition to their order of hydrated radius. Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) followed a second-order kinetics and the adsorption data fitted well with the Langmuir isotherm model. Quantum computations using density functional theory (DFT) further supported the experimental adsorption selectivity, Zn(II) > Pb(II) > Cd(II) > Hg(II), in terms of metal-oxygen binding energy measurements. What was more intriguing about PSP was its reusability over multiple adsorption cycles by treating the metal(II)-complexed PSP with 0.1 M HCl without any appreciable loss of its adsorption capacity.

Investigation on the Adsorption-Interaction Mechanism of Pb(II) at Surface of Silk Fibroin Protein-Derived Hybrid Nanoflower Adsorbent

For further the understanding of the adsorption mechanism of heavy metal ions on the surface of protein-inorganic hybrid nanoflowers, a novel protein-derived hybrid nanoflower was prepared to investigate the adsorption behavior and reveal the function of organic and inorganic parts on the surface of nanoflowers in the adsorption process in this study. Silk fibroin (SF)-derived and copper-based protein-inorganic hybrid nanoflowers of SF@Cu-NFs were prepared through self-assembly. The product was characterized and applied to adsorption of heavy metal ion of Pb(II). With Chinese peony flower-like morphology, the prepared SF@Cu-NFs showed ordered three-dimensional structure and exhibited excellent efficiency for Pb(II) removal. On one hand, the adsorption performance of SF@Cu-HNFs for Pb(II) removal was evaluated through systematical thermodynamic and adsorption kinetics investigation. The good fittings of Langmuir and pseudo-second-order models indicated the monolayer adsorption and high capacity of about 2000 mg g-1 of Pb(II) on SF@Cu-NFs. Meanwhile, the negative values of Δ r G m ( T ) θ and Δ r H m θ proved the spontaneous and exothermic process of Pb(II) adsorption. On the other hand, the adsorption mechanism of SF@Cu-HNFs for Pb(II) removal was revealed with respect to its individual organic and inorganic component. Organic SF protein was designated as responsible 'stamen' adsorption site for fast adsorption of Pb(II), which was originated from multiple coordinative interaction by numerous amide groups; inorganic Cu3(PO4)2 crystal was designated as responsible 'petal' adsorption site for slow adsorption of Pb(II), which was restricted from weak coordinative interaction by strong ion bond of Cu(II). With only about 10% weight content, SF protein was proven to play a key factor for SF@Cu-HNFs formation and have a significant effect on Pb(II) treatment. By fabricating SF@Cu-HNFs hybrid nanoflowers derived from SF protein, this work not only successfully provides insights on its adsorption performance and interaction mechanism for Pb(II) removal, but also provides a new idea for the preparation of adsorption materials for heavy metal ions in environmental sewage in the future.

Ultrasensitive determination of mercury ions using a glassy carbon electrode modified with nanocomposites consisting of conductive polymer and amino-functionalized graphene quantum dots

A one-pot method based on cyclic voltammetric scan was used to fabricate a glassy carbon electrode modified with nanocomposites consisting of poly(thionine) and amino-functionalized graphene quantum dots (afGQDs). Under near-neutral conditions, the dye polymer was effectively oxidized by hydroxyl radicals (·OH) that were derived from the copper-catalyzed Fenton-like reaction, and the cathodic peak current on the modified electrode greatly increased. The reaction of Cu²⁺ with thiourea (TU) and the generation of a complex, CuTU₂⁺, led to the decrease of Cu²⁺/Cu⁺ species, which inhibited the Fenton-like reaction and reduced the electrochemical response change. Due to a displacement reaction, the addition of Hg²⁺ into the H₂O₂-Cu²⁺-TU system resulted in the release of cuprous ions that benefited the Fenton-like reaction. Under the following optimal conditions: 6 mg mL^-1 afGQDs and the 25-cycle potential cycling for the fabrication of the modified electrode, pH 6.5, and the [Formula: see text] ratio of 1.0, the increasing extent of the cathodic peak current exhibited a good linear response to the logarithm of the Hg²⁺ concentration in the range of 1 pM-1 μM with a detection limit of 0.6 pM. Mercury ions in a water sample were determined with good recovery, ranging from 97 to 103%. The investigation on the uptake of Hg²⁺ into human vascular endothelial cells, HUVEC, shows that the cells incubated in the high-concentration glucose medium absorbed more mercury ions than HUVEC incubated in the normal medium. As a result, Hg²⁺ could lead to the greater damage to the former. Graphical abstract.

A cystine-based dual chemosensor for fluorescent-colorimetric detection of CN- and fluorescent detection of Fe3+ in aqueous media: Synthesis, spectroscopic, and DFT studies

A new dual-responsive chiral cystine based chemosensor, Cys(cou)₂, has been designed and characterized by ¹H NMR, ¹³C NMR, FT-IR, UV-vis as well as elemental analysis. This sensor exhibited an excellent response towards Fe³⁺ and CN^- with high selectivity and sensitivity by fluorescence turn-off mechanism. The binding mode of Cys(cou)₂ with Fe³⁺, and CN^- was confirmed by ESI-MS, ¹H NMR, and fluorescence titration and also quantum chemical calculation. These results showed that the stoichiometric ratio of Cys(cou)₂-Fe³⁺ and Cys(cou)₂-CN is 1:1 and 1:3 in DMSO/Tris aqueous buffer (1:1, v/v), respectively. The linear relationship of the Stern-Volmer plot illustrates the static quenching mechanism at different concentrations. The detection limit (LOD) and binding constant (K_a) for Fe³⁺ and CN^- are 0.029 μM, 1.28 × 10⁴ and 0.51 μM, 9.94 × 10⁶, respectively. Moreover, Cys(cou)₂ can act as a colorimetric sensor for CN^- in DMSO with the color change from colorless to yellow.

Solid-Phase Extraction, Preservation, Storage, Transport, and Analysis of Trace Contaminants for Water Quality Monitoring of Heavy Metals

Accurate quantification of trace contaminants currently requires collection, preservation, and transportation of large volumes (250-1000 mL) of water to centralized laboratories, which impedes monitoring of trace-level pollutants in many resource-limited environments. To overcome this logistical challenge, we propose a new paradigm for trace contaminant monitoring based on dry preservation: solid-phase extraction, preservation, storage, transport, and analysis of trace contaminants (SEPSTAT). We show that a few grams of low-cost, commercially available cation exchange resin can be repurposed to extract heavy metal cations from water samples even in the presence of background ions, dryly preserve these cations for at least 24 months, and release them by acid elution for accurate quantification. A compact, human-powered device incorporating the sorbent removes spiked contaminants from real water samples in a few minutes. The device can be stored and transported easily and produces a sample suitable for measurement by standard methods, predicting the original sample heavy metal concentration generally within an error of 15%. These results suggest that, by facilitating the collection, storage, handling, and transportation of water samples and by enabling cost-effective use of high-throughput capital-intensive instruments, SEPSTAT has the potential to increase the ease and reach of water quality monitoring of trace contaminants.

Arginine-derived carbon nanoparticles for determination of Cr(VI) in water samples

Hexavalent chromium, Cr(VI), is a toxic and carcinogenic ion that poses significant risks toward human health and the environment. Due to its extensive industrial use and high water solubility, Cr(VI) can easily contaminate drinking water sources. Therefore, it is essential to develop methods to detect Cr(VI) in water samples. Recently, carbon quantum dots - being biocompatible, easy to synthesize, and cost-effective fluorophores - have been successfully applied for the determination of different heavy metal ions. In this study, arginine-derived carbon nanoparticles were synthesized using a solvent-free one-pot thermal method. These carbon nanoparticles were characterized using transmission electron microscopy, dynamic light scattering analysis, infrared spectroscopy, ultraviolet-visible (UV-vis) light spectroscopy, fluorescence spectroscopy, and CHNO elemental analysis before being used to design a sensor for Cr(VI). The sensor's signal was optimized and the arginine-derived carbon nanoparticle-based Cr(VI) determination method was shown to have a limit of detection of 18 nM, a limit of quantification of 60 nM, and a linear response range of 0.06-100 μM. The sensor's selectivity toward Cr(VI) was studied and a potential interfering ion was identified and dealt with. Finally, the sensor was successfully applied for the determination of Cr(VI) in tap water and mineral water samples.

Sensitive Ratiometric Fluorescent Metal-Organic Framework Sensor for Calcium Signaling in Human Blood Ionic Concentration Media

A two-dimensional fluorescent metal-organic framework (MOF) sensor, TMU-5S, was synthesized by introducing rhodamine B into the framework of TMU-5. This dye-sensitized MOF was explored as a ratiometric fluorescent sensor for Ca²⁺ signaling in the presence of interfering cations in ionic concentrations similar to that of blood plasma that exhibits exceptional sensitivity and selectivity to Ca²⁺ and faster response and recovery times than any other reported fluorescent sensor. This can be attributed to strong electrostatic interactions between basic azine groups in the narrow pore walls of TMU-5S and Ca²⁺ as hard-hard acid-base interactions. The results show that the two-dimensional signal transduction can reduce interfering responses from the environment and thus create exceptional sensitivity.

A new 3-hydroxyphthalimide-based turn-on fluorescent probe for Hg2+ detection in aqueous solution

A new 3-hydroxyphthalimide-based turn-on fluorescent probe is designed and synthesized. This probe can be used to determine the presence of Hg2+ ions by fluorescence spectroscope with high selectivity over other metal ions in aqueous solution. The analytical detection limit for Hg2+ is as low as 6.5 × 10−7 M. The recognition mechanism is attributed to Hg2+-promoted carbonothioate group cleavage and a subsequent excited-state intramolecular proton transfer mechanisms.

A dual fluorescence probe for Zn2+ and Al3+ through differentially response and bioimaging in living cells

A novel Schiff base fluorescent probe 7-Hydroxy-8-(((2-(hydroxymethyl)quinolin-8-yl)imino)methyl)-coumarin (XL) consist of formylcoumarin and aminoquinoline moieties was synthesized for dual detection of Zn²⁺ and Al³⁺ ions. Probe XL exhibited high selective and sensitive response towards Zn²⁺ and Al³⁺ ions through different color changes and significant fluorescence turn-on response (270 fold higher for Zn²⁺ and 230 fold higher for Al³⁺) in MeOH-H₂O (4/1, v/v) over other cations, with detection limits (LOD) as low as 3.75 × 10^-8 and 1.14 × 10^-8 M, respectively. Moreover, probe XL exhibited preferential selectivity for Al³⁺ through displacing Zn²⁺ from the XL-Zn²⁺ complex by ligand-to-ligand transfer process. The binding mechanism of intramolecular charge transfer (ICT) were proposed from fluorescence and UV-vis titrations, Job's plot, ¹H NMR titration, HRMS and DFT calculations. The probe was proven to be suitable for actual samples detection of Zn²⁺ and Al³⁺ ions. The complex XL-Zn²⁺ and XL-Al³⁺ exhibited dramatic fluorescent "turn-off" properties for PPi and PPi/F^- respectively through snatching metal ions and released free XL. Moreover, probe XL showed low biotoxicity and sequentially "off-on-off" fluorescent bio-imaging of Zn²⁺/Al³⁺ and PPi/F^- in PC12 cells.

Revealing the Hydrolysis Mechanism of a Hg2+-Reactive Fluorescein Probe: Novel Insights on Thionocarbonated Dyes

As one of the most toxic metal pollutants, mercury is the subject of extensive research to improve current detection strategies, notably to develop sensitive, selective, fast, and affordable Hg²⁺-responsive fluorescent probes. Comprehending the sensing mechanism of these molecules is a crucial step in their design and optimization of their performance. Herein, a new fluorescein-based thionocarbonate-appended Hg²⁺-sensitive probe was synthesized to study the hydrolysis reactions involved in the sensing process. Autohydrolysis was revealed as a significant component of the signal generation mechanism, occurring concurrently with Hg²⁺-catalyzed hydrolysis. This knowledge was used to investigate the effects of key experimental conditions (pH, temperature, chloride ions) on sensing efficiency. Overall, the chemical and physical properties of this new thionocarbonated dye and the insights into its sensing mechanism will be instrumental in designing reliable and effective portable sensing strategies for mercury and other heavy metals.

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⁺.

Effect of tryptophan residues on gold mineralization by a gold reducing peptide

AuBP1, obtained by phage display selection, was previously shown to produce gold nanoparticles without reducing agents. The tryptophan (Trp) residue located at the N-terminus of this peptide contributes to the reduction of Au³⁺ to Au⁰ and is involved in the nucleation and crystal growth of gold nanoparticles. However, clear guidelines for relationships between the number of Trp residues in the peptide and its gold reducing ability have not been established. We focused on gold mineralization and attempted to elucidate aspects of the underlying mechanism. We performed a detailed evaluation of the effects of modifying the N-terminus of the core sequence on gold mineralization without reducing agents. Besides, advantages of utilizing peptides in manufacturing gold nanoparticles are shown. UV-Vis measurements, TEM observations, and kinetic analyses were used to show that increasing the number of Trp residues in the peptide increases the reducing ability, causing predominance of the nucleation reaction and the production of small gold nanoparticles. In addition, these peptides also had the ability as a dispersant to protect the surface of gold nanoparticles. Furthermore, the catalytic activity of mineralized gold nanoparticles with peptides was higher than that of a commercial gold nanoparticle. This study should help to elucidate the relationship between peptide sequence and mineralization ability for use in materials chemistry.

Increasing the number of tryptophan (Trp) in peptides led to higher gold reducing ability and the peptides could disperse the generated gold-nanoparticles.

A Novel Thiophene-Based Fluorescent Chemosensor for the Detection of Zn2+ and CN-: Imaging Applications in Live Cells and Zebrafish

A novel fluorescent turn-on chemosensor DHADC ((E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide) has been developed and used to detect Zn2+ and CN-. Compound DHADC displayed a notable fluorescence increase with Zn2+. The limit of detection (2.55 ± 0.05 μM) for zinc ion was far below the standard (76 μM) of the WHO (World Health Organization). In particular, compound DHADC could be applied to determine Zn2+ in real samples, and to image Zn2+ in both HeLa cells and zebrafish. Additionally, DHADC could detect CN- through a fluorescence enhancement with little inhibition with the existence of other types of anions. The detection processes of compound DHADC for Zn2+ and CN- were demonstrated with various analytical methods like Job plots, 1H NMR titrations, and ESI-Mass analyses.

Dual-Functionalized Fluorescent Cationic Organic Network: Highly Efficient Detection and Removal of Dichromate from Water

Dichromate is a widespread contaminant in wastewater, threatening the health of humans and other organisms. Therefore, effective detection and removal of dichromate from water is of great significance. Herein, a tetraphenylethylene functionalized cationic organic network (CON-LDU2) was constructed via a facile quaternization reaction. CON-LDU2 was successfully integrated with both detection and removal functionalities toward dichromate. On the one hand, benefiting from the strong fluorescence, CON-LDU2 was employed as a chemosensor, it could efficiently and selectively probe Cr₂O₇^2- in water with "turn-off" fluorescent response. On the other hand, the cationic skeleton and free anions inside framework make CON-LDU2 an excellent adsorbent for Cr₂O₇^2-, it could capture Cr₂O₇^2- from water with rapid kinetics and high capacity. The kinetic constant for adsorption of Cr₂O₇^2- can reach up to 1.784 g mg^-1 min^-1, while the capacity is determined as 325 mg g^-1. Furthermore, CON-LDU2 displayed good recyclability and can be reused for at least 5 cycles. Therefore, CON-LDU2 can serve as an ideal candidate not only in detection but also in removal of Cr₂O₇^2- in water medium.

A smart chemosensor: Discriminative multidetection and various logic operations in aqueous solution at biological pH

A novel rhodamine-pyrazole based molecular probe was designed and easily synthesized. The probe could to detect several analytes in aqueous solution at biological pH (HEPES, pH = 7.2). Several heavy metal cations, including Cu²⁺, Fe³⁺, Al³⁺, Hg²⁺ and Ni²⁺ were detected discriminately by the probe. Also, the novel compound exhibited a good sensory selectivity towards S₂O₅^2- by both absorption and emission spectra. Moreover, probe/Cu²⁺ complex could to detect several anions, including F^-, CN^-, S^2-, CH₃COO^-, CO₃^2- and NO₂^-. Furthermore, the probe exhibited a high potential to work as a molecular system able to perform a number of logical operations such as AND, NAND, NOR and INHIBIT logic gates.

Poly(methacrylate citric acid) with good biosafety as nanoadsorbents of heavy metal ions

Heavy metal ion in aqueous solutions has been a challenge to human health. Discovering efficient adsorbents to remove heavy metal ion from water can help address this problem. In this study, poly(methacrylate citric acid) (PCA) with a well-defined structure based on a hydrophilic citric acid monomer was synthesized and then applied as a nanoadsorbent to remove several heavy metal ion. PCA presented excellent solubility in aqueous solution, and after freeze-drying, a loose porous structure was observed. PCA exhibited higher adsorption capacity for all the heavy metal ions (Cu²⁺, Pb²⁺, and Cd²⁺) than citric acid, and had a selectivity for Pb²⁺ ions with a removal efficiency of >90%. PCA also showed a good selectivity for adsorption of Pb²⁺ in a Chinese medicine decoction, with a removal rate >50%, while the concentration of active ingredient was maintained. Cell cytotoxicity in a cell model and system toxicity in mice indicated good biosafety of PCA. These results suggested that PCA with a good biosafety could be utilized as nanoadsorbent to remove Pb²⁺ ion from aqueous solution and decoction.

A dual-responsive colorimetric probe for the detection of Cu2+ and Ni2+ species in real water samples and human serum

The monitoring of heavy transition metals has increasingly attracted great attention because they pollute the environment and have unique physiological functions. Chemosensors are useful tools for monitoring heavy transition metals due to their simple visualization, excellent sensitivity and high selectivity. Herein, we have developed a novel chemosensor for the detection of water-soluble Cu2+ and Ni2+ species with different mechanisms, and low detection limits of 2.1 nM for Cu2+ and 1.2 nM for Ni2+ were obtained. The colorimetric probe CPH has been applied to qualitative and quantitative detection of Cu2+ and Ni2+ species in real samples.

Insight into the Adsorption-Interaction Mechanism of Cr(VI) at the Silica Adsorbent Surface by Evanescent Wave Measurement

The investigation of adsorption performance at the adsorbent surface can help to reveal the treatment mechanism and improve the treatment efficiency of adsorption technology for heavy metal ions (HMIs). This work developed a methodology to investigate the adsorption behavior of HMI Cr(VI) at the silica surface by confined near-field evanescent wave (CNFEW) measurement. A silica optical fiber (SOF) was used as the adsorption substrate and light waveguide element to integrate both Cr(VI) adsorption and CNFEW production on its surface. According to the sensitive CNFEW response, the adsorption behavior of Cr(VI) was in situ monitored and real-time evaluated. The thermodynamic information of adsorption equilibrium constant (K_ads) and adsorption free energy (ΔG) and dynamic information of the apparent adsorption rate (v_ads) and adsorption time (t_ads) were obtained through Langmuir isotherm and kinetic fitting, respectively. Different reaction performances between Cr(VI) and adsorption sites were successfully differentiated, evaluated, and characterized. A site-decided-mechanism was therefore presented to describe the surface interaction process for Cr(VI), which including fast adsorption on type I Si-O^- site through electrostatic attraction with [Formula: see text] and slow adsorption on type II Si-OH site through coordinative interaction with ΔG_SiOH-Cr(VI)^II = -26.18 kJ mol^-1. The adsorption mechanism of Cr(VI) at the SOF silica surface was furthermore verified by zeta potential analysis, Fourier transform infrared investigation, and fluorescence imaging. Unlike conventional ex situ or in bulk detection, the present CNFEW-based approach targets the "localized" adsorption of Cr(VI) adsorbed to the solid adsorbent surface. Consequently, our work favorably constructs a surface platform and provides new insights on understanding the adsorption mechanism for HMIs.