A highly sensitive and selective turn-on fluorogenic and colorimetric sensor based on pyrene-functionalized magnetic nanoparticles for Hg2+ detection and cell imaging

Development of a novel sensory material for rapid detection of mercury ions in various water sources: Solution and solid-state analysis

A xanthene propane nitrile-based sensor material was successfully prepared, and an attempt towards the preparation of polymer bead form was made for the sensitive or selective detection of mercury ions (Hg2+) in water. The sensor material in solution as well as in polymeric form showed amazing selectivity over other added metal ions with a naked eye color change, UV visible spectral and fluorescence spectral change, and a rapid and excellent color change from colorless to purple. The 1H NMR study exposed the probable binding site of the probe with the added mercury ion. In this study, the imine nitrogen and the C = O interact with the mercury ion, resulting in the ring opening of lactam with a vivid color change. The EDTA test was done to verify the reversible behavior of the probe and confirmed its reversibility by UV-visible and fluorescence spectral studies. The polymer bead made using this probe can be used as a tool for monitoring mercury ions in real time in different sources of water samples. The sensor molecule itself senses the mercury ion in its solid state by simple grinding and changes its color from pale yellow to deep purple. The sensor color change response is very rapid towards mercury detection, which is confirmed by the prepared test strip.

The fabrication of a hybrid fluorescent nanosensing system and its practical applications via film kits for the selective determination of mercury ions

Heavy metal ions especially mercury exposure have severe toxic effects on living organisms and human health. Therefore, easy, accessible, and accurate determination strategies for the selective specification of mercury ions are essential for numerous disciplines. In the presented paper, new hybrid fluorescent iron oxide nanoparticles labeled with carbazole and triazole units (CT-IONP) were prepared via surface modification for the spectrofluorimetric determination of Hg2+ in environmental samples. The structure of the new sensing system is characterized via various spectroscopic, thermal, and microscopic techniques. Under optimized conditions, the hybrid system is not only used in fully water media but also highly fluorescent which led to the "turn-off" response towards Hg2+ ion in the presence of various competitive species. The presented sensing system was successfully used for the determination of Hg2+ ions in the wide linear working range (0.02-10.00 µmol.L-1) at nanomolar levels, where the limit of detection and quantification were calculated as 7.38 and 22.14 nmol.L-1. Importantly, the practical application of hybrid material was applied by CT-IONP embedded polycaprolactone (PCL) polymer film kits. The bluish color of fabricated film kits was instantly and dramatically turned colorless-dark patterns after the addition of Hg2+ ions, which resulted in convenient and rapid film test kits for selective detection.

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

Synthesis and applications of surface-modified magnetic nanoparticles: progress and future prospects

The growing use of magnetic nanoparticles (MNPs) demands cost-effective methods for their synthesis that allow proper control of particle size and size distribution. The unique properties of MNPs include high specific surface area, ease of functionalization, chemical stability and superparamagnetic behavior, with applications in catalysis, data and energy storage, environmental remediation and biomedicine. This review highlights breakthroughs in the use of MNPs since their initial introduction in biomedicine to the latest challenging applications; special attention is paid to the importance of proper coating and functionalization of the particle surface, which dictates the specific properties for each application. Starting from the first report following LaMer’s theory in 1950, this review discusses and analyzes methods of synthesizing MNPs, with an emphasis on functionality and applications. However, several hurdles, such as the design of reactors with suitable geometries, appropriate control of operating conditions and, in particular, reproducibility and scalability, continue to prevent many applications from reaching the market. The most recent strategy, the use of microfluidics to achieve continuous and controlled synthesis of MNPs, is therefore thoroughly analyzed. This review is the first to survey continuous microfluidic coating or functionalization of particles, including challenging properties and applications.

A hybrid nanosensor based on novel fluorescent iron oxide nanoparticles for highly selective determination of Hg2+ ions in environmental samples

Novel fluorescent iron oxide nanoparticles were prepared for the determination of Hg²⁺ in real samples. The fluorescence behaviors of the sensor were examined using absorption and fluorescence (steady-state, time-resolved, 3-D, EEM) spectroscopies.

Aggregation induced emission active fluorescent sensor for the sensitive detection of Hg2+ based on organic-inorganic hybrid mesoporous material

We report the preparation of an organic-inorganic hybrid mesoporous material, PHC-SBA-15, derived from the coupling of a pyrene-based derivative PHC and mesoporous SBA-15 silica. Compared with the stable aggregation-induced emission (AIE) properties of PHC, those of PHC-SBA-15 were more promoted and active due to the fixation of PHC and the space limitation in mesoporous SBA-15. The aggregation and disaggregation activities can be tuned by controlling the concentrations in aqueous media and changing the fluorescence color from yellow to blue. In addition to the controllable AIE properties, PHC-SBA-15 was applied for the highly selective and sensitive detection of Hg²⁺ through the fluorescence quenching of monomeric pyrene in aqueous media. The fluorescence intensity at 395 nm was linearly proportional to that of Hg²⁺ in the concentration ranges of 0-1.0 × 10^-5 and 1.0 × 10^-5-10 × 10^-5 M, showing a low detection limit of 1.02 × 10^-7 M. This work provides an effective strategy for modulating the AIE properties from non-active to active by introducing AIE stable molecule into mesoporous silica material. This method also favors the development of fluorescent sensors for detecting targets with high sensitivity and selectivity in aqueous media with less synthetic difficulties.

Synthesis and characterization of a flexible fluorescent magnetic Fe3O4@SiO2/CdTe-NH2 nanoprobe

In this study, we designed and synthesized two novel fluorescent magnetic nanoparticles. Fe₃O₄@SiO₂-NH-GSH-CdTe (FSGC) (GSH = glutathione) nanoparticles were synthesized using amino-functionalized Fe₃O₄@SiO₂ nanoparticles and GSH-stabilized CdTe quantum dots (CdTe QDs), while flexible Fe₃O₄@SiO₂-NH-GSH-CdTe-NH-NH₂ (FSGCN) nanoparticles were synthesized using the FSGC precursor and 1,6-hexamethylenediamine. These two kinds of nanoprobes exhibited excellent magnetic and fluorescent properties. By comparing the fluorescence quenching effect of folic acid (FA) on FSGC and FSGCN, we found that the quenching effect of FA on FSGC was acute and the process was too fast to determine the FA content. However, the quenching effect of FA on flexible FSGCN was mild and hence it could be used as a nanoprobe to determine FA concentration. At physiological pH, the fluorescence quenching effect of FA on the FSGCN nanoprobes was fitted according to the Stern-Volmer equation with a linear response in the concentration range of 0.14 to 4.20 μg mL^-1 with a detection limit of 15.1 × 10^-9 g mL^-1 (S/N = 3) under optimized experimental conditions. The proposed flexible nanoprobe was successfully used to determine the content of FA in folic acid tablets. Recovery was found to be in the range of 92.7%-105.6% with a relative standard deviation of 1.12%-3.84%. Owing to their good stability, environment-friendly characteristics, high selectivity, and good optical properties and biocompatibility, these nanoprobes have potential for usage in practical applications.

Real-time probing of mercury using an efficient “turn-on” strategy with potential as in-field mapping kit and in live cell imaging

Based on a rhodamine scaffold as a fluorophore and 2-aminothiazole as a receptor, we present a highly selective and sensitive sensor (TS).

A Unique Sensitive and Highly Selective Fluorescent Naphthodiaza-Crown Macrocyclic Ligand Chemosensor for Hg2+ in Water

The noticeable enhancement in fluorescence emission of O₂N₂-donor naphthodiaza-crown macrocyclic ligand (L) in the presence of Hg²⁺ was observed in which the fluorescence quantum yield of free ligand L as well as L/Hg²⁺ complex were found to be as 0.29 and 0.49, respectively. The observed ultra-low limit of detection (LOD) for Hg²⁺ by L was determined as low as 1.0 × 10^-11 M in water. A 1:1 stoichiometry was also established for L/Hg²⁺ together with a binding constant K _BH = 66,543 by employing fluorescence spectrophotometry. The competition experiments on L/Hg²⁺ demonstrated highly selective detection of Hg²⁺ in the presence of the library cations. A two path mechanism for detection of metal ion in terms of coordination of metal ion to L and/or the formation of counter ion was proposed by using of ¹H NMR and fluorescence spectroscopy. Graphical Abstract pH dependence mechanism of interaction between Hg²⁺ and macrocyclic ligand L.

Magnetic, Fluorescence and Transition Metal Ion Response Properties of 2,6-Diaminopyridine Modified Silica-Coated Fe₃O₄ Nanoparticles

Multi-functional nanoparticles possessing magnetic, fluorescence and transition metal ion response properties were prepared and characterized. The particles have a core/shell structure that consists of silica-coated magnetic Fe₃O₄ and 2,6-diaminopyridine anchored on the silica surface via organic linker molecules. The resultant nanoparticles were found by transmission electron microscopy to be well-dispersed spherical particles with an average diameter of 10–12 nm. X-ray diffraction analysis suggested the existence of Fe₃O₄ and silica in/on the particle. Fourier transform infrared spectra revealed that 2,6-diaminopyridine molecules were successfully covalently bonded to the surface of magnetic composite nanoparticles. The prepared particles possessed an emission peak at 364 nm with an excitation wavelength of 307 nm and have a strong reversible response property for some transition metal ions such as Cu²⁺ and Zn²⁺. This new material holds considerable promise in selective magneto separation and optical determination applications.

Efficient Detection of Trace Hg²⁺ in Water Based on the Fluorescence Quenching of Environment-friendly Thiol-functionalized Poly(vinyl alcohol) Capped CdS Quantum Dots Nanocomposite

Using environment-friendly materials for sensing toxic metal ions has drawn significant attention in recent research. Herein, we present an aqueous synthesis of stable CdS quantum dots (QDs) using thiol-functionalized poly(vinyl alcohol) (PVA) as the unique capping ligand for the detection of trace Hg(2+) in environmental water samples. The CdS QDs with an average size of 3.3 nm had good water-solubility and favorable fluorescence with a quantum yield of 32.8% and a longer luminescence lifetime of 31.9 ns. The fluorescence intensity of QDs aqueous solution in the 520 nm wavelength was quenched upon the addition of Hg(2+). Under the optimal conditions, the ratio of the blank fluorescence intensity to the quenched fluorescence intensity was linearly proportional to the Hg(2+) concentration from 2 to 4000 nM with a detection limit of 1 nM. Also, many co-existing metal ions were not interfered with the detection of Hg(2+). This nanomaterial was successfully applied to the measurement of Hg(2+) in water samples.

Highly Hg2+-sensitive and selective fluorescent sensors in aqueous solution and sensors-encapsulated polymeric membrane

The sensors in solutions and sensors encapsulated polymeric membranes exhibited high sensitivity and selectivity for Hg²⁺ detection, with detection limits of 0.2–49 ppb.

A type of novel fluorescent magnetic carbon quantum dots for cells imaging and detection

A new type of multifunctional fluorescent magnetic carbon quantum dots SPIO@CQDs(n) ([superparamagnetic iron oxide nanoparticles (SPIO), carbon quantum dots, (CQDs)]) with magnetic and fluorescence properties was designed and prepared through layer-by-layer self-assembly method. The as-synthesized SPIO@CQDs(n) exhibited different emission colors including blue, green, and red when they were excited at different excitation wavelengths, and its fluorescent intensity increased as the increase of CQD layer (n). SPIO@CQDs(n) with quite low toxicity could mark cytoplasm with fluorescence by means of nonimmune markers. The mixture sample of liver cells L02 and hepatoma carcinoma cells HepG2 was taken as an example, and HepG2 cells were successfully separated and detected effectively by SPIO@CQDs(n), with a separation rate of 90.31%. Importantly, the designed and prepared SPIO@CQDs( n ) are certified to be wonderful biological imaging and magnetic separation regents.

Spectroscopic study of the recognition of 2-quinolinone derivative on mercury ion

A new compound based on 2-quinolinone derivative with very little side effects on organisms, 3-(1H-benzo[d]imidazol-2-yl)-6,7-difluoroquinolin-2(1H)-one, has been designed, synthesized and characterized. And its recognition ability was firstly studied by spectroscopy. The result indicated that the compound shows high selectivity for Hg2+ over other metal ions with detectable fluorescent signals in aqueous-methanol media. The proposed mechanism is that the fluorescence of the probe was quenched due to the effect from spin-orbit coupling of Hg2+ after the probe coordinated with Hg2+, and was proved by ESI-MS and 1H NMR analysis.

Fluorescent graphene quantum dot nanoprobes for the sensitive and selective detection of mercury ions

Graphene quantum dots were prepared by ultrasonic route and served as a highly selective water-soluble probe for sensing of Hg(2+). The fluorescence emission spectrum of graphene quantum dots was at about 430nm. In the presence of Hg(2+), the fluorescence of the quantum dots significantly quenched. And the fluorescence intensity gradually decreased with the increasing concentration of Hg(2+). The change of fluorescence intensity is directly proportional to the concentration of Hg(2+). Under optimum conditions, the linear range for the detection of Hg(2+) was 8.0×10(-7) to 9×10(-6)M with a detection limit of 1.0×10(-7)M. In addition, the preliminary mechanism of fluorescence quenching was discussed in the paper. The constructed sensor with high sensitivity and selectivity, simple, rapid properties makes it valuable for further application.