Multifunctional Binding Strategy on Nonconjugated Polymer Nanoparticles for Ratiometric Detection and Effective Removal of Mercury Ions

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.

Concurrent manipulation of competitive mechanisms to construct glutathione-stabilized gold nanocluster-based dual-channel molecular classifier for metal ions detection and information steganography

Understanding charge transport in metal ion-mediated glutathione-stabilized gold nanoclusters (GSH-Au NCs) has proved difficult due to the presence of various competitive mechanisms, such as electron transfer (ET) and aggregation induction effect (AIE). In this paper, we present a dual-channel fluorescence (FL) and second-order Rayleigh scattering (SRS) sensing method for high-throughput classification of metal ions, relying on the competition between ET and AIE using GSH-Au NCs. The SRS signals show significant enhancement when Pb2+, Ag+, Al3+, Cu2+, Fe3+, and Hg2+ are present, as a result of the aggregation of GSH-Au NCs. Notably, the fluorescence signal exhibits the opposite trend. The FL intensities of GSH-Au NCs are enhanced by Pb2+, Ag+, and Al3+ through the AIE mechanism, while they are quenched by Cu2+, Fe3+, and Hg2+, which is dominated by the ET mechanism. By employing principal component analysis and hierarchical cluster analysis, these signals are transformed into unique fingerprints and Euclidean distances, respectively, enabling successful distinction of six metal ions and their mixtures with a low detection limit of 30 nM. This new strategy has successfully addressed interference from impurities in the testing of real water samples, demonstrating its strong ability to detect multiple metal ions. Impressively, we have achieved molecular cryptosteganography, which involves encoding, storing, and concealing information by transforming the selective response of GSH-Au NCs to binary strings. This research is anticipated to advance utilization of nanomaterials in logic sensing and information safety, bridging the gap between molecular sensors and information systems.

Heterometallic Eu/Zn-MOF-based ratiometric sensing platform: Highly sensitive fluorescence / second-order scattering identification of tetracycline analogs and its molecular informatization applications

The traditional preparation method of ratiometric probes faces challenges such as cumbersome preparation and low sensitivity. Thus, there is an urgent need to provide a simple method of preparing a highly sensitive ratiometric probe. Here, Eu3+-doped zinc-based organic framework (Eu/Zn-MOF) was prepared through hydrothermal method for the detection of tetracycline analogs (TCs). Under the same excitation conditions, the probe can simultaneously display valuable fluorescence and second-order scattering signals. The developed probe enabled specific identification and fast detection (1 min) of TCs, including tetracycline, oxytetracycline, doxycycline, and chlortetracycline. The linear detection ranges of tetracycline, oxytetracycline, doxycycline and chlortetracycline were respectively 100 nM - 200 μM, 100 nM - 200 μM, 98 nM - 195 μM, and 97 nM - 291 μM, and the corresponding detection limits were respectively 15.79 nM, 20.83 nM, 15.31 nM, and 28.30 nM. The developed sensor was successfully applied to detect TCs in real samples, and the recovery rate was from 92.54 % to 109.69 % and the relative standard deviation was from 0.04 % to 2.97 %. Moreover, the heterometallic Eu/Zn-MOF was designed as a ratiometric neuron for Boolean logic computing and information encryption based on the specific identification of TCs. As a proof of concept, molecular steganography was successfully employed to encode, store, and conceal information by transforming the specific identification patterns of Eu/Zn-MOF into binary strings. This study is anticipated to advance the application of metal-organic frameworks in logic detection and information security, and bridging the gap between molecular sensors and the realm of information.

Constructing an eco-friendly and ratiometric fluorescent sensor for highly efficient detection of mercury ion in environmental samples

Mercury ion (Hg2+) is a highly toxic and ubiquitous pollutant, whose effective detection has aroused widespread concern. A novel ratiometric fluorescent sensor has been designed to rapidly and efficiently detect Hg2+ based on blue/red carbon dots (CDs) with environmental friendliness. This sensor was well characterized via TEM, FTIR, XPS, UV-vis, and zeta potential analysis and displayed excellent fluorescence properties and stability. The fluorescence of blue CDs at 447 nm was significantly quenched with the addition of Hg2+ resulted from the static quenching, whereas that of red CDs at 650 nm remained invariable. A sensitive method for Hg2+ determination was constructed in the range of 0.05-7.0 nmol mL-1 with optimal conditions, and the detection limit was down to 0.028 nmol mL-1. Meanwhile, compared to other 17 metal ions, the ratiometric fluorescent sensor exhibited high selectivity for Hg2+. Furthermore, satisfied recoveries had also been obtained for measuring trace Hg2+ in practical environmental samples. This developed ratiometric fluorescent sensor provided a reliable, environmental-friendly, rapid, and efficient platform for the detection of Hg2+ in environmental applications.

Rationally designed calcium carbonate multifunctional trap for contaminants adsorption

Adsorption technology has been widely developed to control environmental pollution, which plays an important role in the sustainable development of modern society. Calcium carbonate (CaCO3) is characterized by its flexible pore design and functional group modification, which meet the high capacity and targeting requirements of adsorption. Therefore, its charm of "small materials for great use" makes it a suitable candidate for adsorption. Firstly, we comprehensively review the research progress of controlled synthesis and surface modification of CaCO3, and its application for adsorbing contaminants from water and air. Then, we systematically examine the structure-effect relationship between CaCO3 adsorbents and contaminants, while also intrinsic mechanism of remarkable capacity and targeted adsorption. Finally, from the perspective of material design and engineering application, we offer insightful discussion on the prospects and challenges of calcium carbonate adsorbents, providing a valuable reference for the further research in this field.

A wide-range ratiometric sensor mediating fluorescence and scattering based on carbon dots/metal-organic framework composites for the detection of bisulfite/sulfite in sugar

Bisulfite (HSO₃^-) and sulfite (SO₃^2-) are commonly employed in food preservatives and are also significant environmental pollutants. Thus, developing an effective method for detecting HSO₃^-/SO₃^2- is crucial for food safety and environment monitoring. In this work, based on carbon dots (CDs) and zeolitic imidazolate framework-90 (ZIF-90), a composite probe (named CDs@ZIF-90) is constructed. The fluorescence signal and the second-order scattering signal of CDs@ZIF-90 are employed to ratiometricly detect HSO₃^-/SO₃^2-. This proposed strategy exhibits a broad linear range for HSO₃^-/SO₃^2- determination (10 µM to 8.5 mM) with a limit of detection of 2.74 μM. This strategy is successfully applied for evaluating HSO₃^-/SO₃^2- in sugar with satisfactory recoveries. Therefore, this work has uniquely combined the fluorescence and second-order scattering signals to establish a novel sensing system with a wide linear range, which is applicable for ratiometric sensing of HSO₃^-/SO₃^2- in actual samples.

Colorimetric method transforms into highly sensitive homogeneous voltammetric sensing strategy for mercury ion based on mercury-stimulated Ti3C2Tx MXene nanoribbons@gold nanozyme activity

Nanozymes were emerged as the next generation of enzyme-mimics which exhibit great applications in various fields, but there is rarely report in the electrochemical detection of heavy metal ions. In this work, Ti₃C₂T_x MXene nanoribbons@gold (Ti₃C₂T_x MNR@Au) nanohybrid was prepared firstly via a simple self-reduction process and its nanozyme activity was studied. The results showed the peroxidase-like activity of bare Ti₃C₂T_x MNR@Au is extremely weak, while in the presence of Hg²⁺, the related nanozyme activity is stimulated and improved remarkably, which can easily catalyze oxidation of several colorless substrates (e.g., o-phenylenediamine) to form colored products. Interestingly, the product of o-phenylenediamine exhibits a strong reduction current which is considerably sensitive to the Hg²⁺ concentration. Based on this phenomenon, an innovative and highly sensitive homogeneous voltammetric (HVC) sensing strategy was then proposed to detect Hg²⁺ via transforming the colorimetric method into electrochemistry since it can exhibit several unique advantages (e.g., rapid responsiveness, high sensitivity and quantificational). Compared to the conventional electrochemical sensing methods for Hg²⁺, the designed HVC strategy can avoid the modification processes of electrode coupled with enhanced sensing performances. Therefore, we expect the as-proposed nanozyme-based HVC sensing strategy provides a new development direction for detecting Hg²⁺ and other heavy metals.

Reversible detection of Hg(II) in pure water based on thymine modified nitrogen, sulfur co-doped carbon dots combined with antidote

Conventional Hg²⁺ visual sensors are unsustainable, hindering their practical application for improved water quality and health. In order to address this challenge, herein, N, S co-doped carbon nanodots (NS-CDs) were prepared and well characterized, presented the fluorescent monitoring for Hg²⁺ over other metal ions with the limit of detection (LOD) of 0.47 µM. Next, the CDs were successfully modified by thymine without any fluorescence labelling (referred to as T-NS-CDs). The sensitivity to Hg²⁺ cloud be noticeable enhanced due to the formation of T-Hg²⁺-T specific base pairs. Accordingly, the LOD was calculated with values as low as 1.56 nM. Furthermore, Hg²⁺ could be released and complexed with antidote (meso-2,3-dimercaptosuccinic acid) (DMSA-Hg²⁺), being the responsible for the reversible interconversion between T-Hg²⁺-T and DMSA-Hg²⁺. Interestingly, the proposed sensing system also applies to the fluorescent sensing for Hg²⁺ in tap water with satisfactory recoveries (96.97 %-101.38 %, RSD < 2 %). Thus, by simply combination of elemental doping and surface functionalization, the surface state and functionalities of CDs could be tailorable, endowing the fluorometric sensing towards Hg²⁺ in environmental system.

Stable and reusable acrylic ion-exchangers. From HMIs highly polluted tailing pond to safe and clean water

The application of several ion-exchange resins (IExR) with amino and amphoteric functionalities in batch retention of heavy metal ions (HMIs) (Cu(II), Fe(II), Mn(II), Zn(II)) from mono- and multicomponent simulated waters and from real polluted water collected from tailings pond of Tarnita (Suceava, Romania) sterile dump is deeply herein explored. The tested resins exhibited high sorption capacities, as evaluated by atomic absorption spectrometry, results supported by infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The effect of pH on the IExR sorption capacity in competitive condition evidenced the optimum pH where IExR sorption efficiency is maximum. Reutilization of IExR in six consecutive sorption/desorption/regeneration cycles showed their renewable sorption properties. Wheat germination tests demonstrated that the Tarnita collected water had a high toxic effect whereas the resulted supernatant after batch sorption was nontoxic. The study shows that HMIs content after IExR sorption is under the admitted maximum level for surface water, and represents an important step on the efforts to solve the environmental problem in Tarnita area, by removing the main contaminants found in the local river water.

A novel fluorescent "OFF-ON" sensing strategy for Hg (II) in water based on functionalized gold nanoparticles

Mercury ion (Hg²⁺) is a heavy metal pollutant that can affect the safety of water environment and endanger human health. A novel detection strategy (GNPs-_L-Cys-Rh6G2) for Hg²⁺ based on a fluorescence "OFF-ON" was proposed. Gold nanoparticles (GNPs) were assembled with _l-cysteine (_L-Cys), which was used as a "bridge" to link with rhodamine 6G derivatives (Rh6G2). The fluorescence state transition of GNPs-_L-Cys-Rh6G2 switching from "OFF"-"ON" was observed because Hg²⁺ opened the spirolactam ring through a catalytic hydrolysis mechanism. The fluorescence signal of the GNPs-_L-Cys-Rh6G2 system mixed with Hg²⁺ in the concentration range of 10-100 μM was analyzed and determined with a limit of detection (LOD) of 2 μM (S/N = 3). Moreover, the spiked Hg²⁺ concentration in real water samples were successfully quantified by GNPs-_L-Cys-Rh6G2, which was in line with the ideal average recovery rate and relative standard deviation. The proposed strategy exhibited high specificity, sensitivity and stability, providing a novel sensing platform for heavy metal ions detection in water environment.

Thioether-functionalized porphyrin-based polymers for Hg2+ efficient removal in aqueous solution

In this paper, thioether-functionalized porphyrin-based polymers (TPPs) were constructed according to two different "bottom-up" and "top-down" strategies and they were applied for Hg²⁺ capture in aqueous solution. TPP1, which was constructed by one-step polycondensation of 2,5-bis(methylthio) terephthalaldehyde (BMTA) with pyrrole according to the "bottom-up" strategy, owned high Brunauer-Emmett-Teller (BET) surface area (S_BET, 554 m²/g), pore volume (V_total, 0.32 cm³/g), and S content (16.8%), resulting in high Hg²⁺ capture (913 mg/g) with high removal efficiency (> 99%). The adsorption mechanism clarified that the strong coordination between the S species and Hg²⁺ was the main driving force. In comparison, TPP2 and TPP3 were fabricated by the thioether functionalization of the porphyrin-based polymers according to the "top-down" strategy. They showed much lower S_BET, V_total, and S content for the reason that the post-functionalization process greatly blocked the pores and the functional sites were hardly fully post-functionalized, resulting in much lower Hg²⁺ capture (555 mg/g and 609 mg/g, respectively). This work reveals the advantage of the "bottom-up" strategy for the construction of the thioether-functionalized polymers and it offers the guidance for the construction of some other thioether-functionalized polymers.

Removal and Recovery of Gaseous Elemental Mercury Using a Cl-Doped Protonated Polypyrrole@MWCNTs Composite Membrane

Due to the restrictions on mercury mining, recovering the mercury from mercury-containing waste is attracting increasing attention. This study successfully achieved the removal and recovery of gaseous elemental mercury (Hg⁰) by using membrane technology. A novel composite membrane of Cl-doped protonated polypyrrole-coated multiwall carbon nanotubes (Cl-PPy@MWCNTs) was fabricated in which MWCNTs acted as the framework to support the active component Cl-PPy. The morphology, structure, and composition of the prepared membranes were determined by field emission scanning electron microcopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, etc. The composite membrane exhibited an excellent performance in Hg⁰ removal (97.3%) at a high space velocity of 200,000 h^-1. The dynamical adsorption capacity of Hg⁰ was 3.87 mg/g when the Hg⁰ breakthrough reached 10%. The adsorbed Hg⁰ could be recovered/enriched via a leaching process using acidic NaCl solution; meanwhile, the membrane was regenerated. The recovered mercury was identified in the form of Hg²⁺, with a recovery efficiency of over 99%. Density functional theory calculations and mechanism analysis clarified that the electrons of Hg⁰ transported to the delocalized electron orbits of protonated PPy and then combined with Cl^- to form Hg₂Cl₂/HgCl₂. Finally, we first demonstrated that the analogous protonated conductive polymers (e.g., polyaniline) also possessed good Hg⁰ removal ability, implying that such species may offer more outstanding answers and attract attention in future.

Plasmonic Gold Nanoparticles Stain Hydrogels for the Portable and High-Throughput Monitoring of Mercury Ions

The hybrid of l-cysteine and agarose can reduce HAuCl₄ and support the rapid growth of plasmonic gold nanoparticles (Au NPs) in the hydrogel phase. The l-cysteine-doped agarose hydrogel (C-AGH) not only offers the substrate the capacity to reduce Au(III) ions but also stabilizes and precisely modulates the in situ grown Au NPs with high repeatability, easy operation, and anti-interference performance. Herein, before the incubation of HAuCl₄, the improved hydrogel is preincubated in the aqueous solution containing mercury ions, and the cysteine can specifically conjugate with mercury via the thiol groups. Subsequently, the responsive allochroic bands from dark blue to red can be identified in the solid hydrogel after the incubation of HAuCl₄, which is attributed to the formation of regulated Au-Hg nanoamalgams. As a proof-of-concept, toxic Hg²⁺ ions are exploited as targets for constructing novel sensing assays based on the improved C-AGH protocol. Based on naked-eye recognition, Hg²⁺ could be rapidly and simply measured. Additionally, the high-throughput and trace analysis with a low limit of detection (3.7 nM) is performed using a microplate reader. On the basis of the filtering technique and remodeling of hydrogels, C-AGH working as the filtering membrane can even achieve the integration of enrichment and measurement with enhanced sensitivity. Significantly, the strategy of using an allochroic hydrogel with the staining of Au NPs can promote the rapid and primary assessment of water quality in environmental analysis.

An optical sensing system with ratiometric and turn-off dual-mode of CDs@MnO2 nanosheets for the determination of H2O2 and glucose based on a combination of first-order scattering, fluorescence, and second-order scattering

The optical sensor with ratiometric and turn-off dual modes is constructed to detect H₂O₂ and glucose based on blue fluorescent carbon dots (CDs) and MnO₂ nanosheets with great ability of fluorescence quenching and scattering. Employing CDs@MnO₂ nanosheets nanocomposite as the probe, H₂O₂ is detected by simultaneously collecting first-order scattering (FOS, 353.5 nm), fluorescence (440 nm), and second-order scattering (SOS, 710 nm) under the excitation of 350 nm. H₂O₂ with strong oxidation property can etch the lamellar structure of MnO₂ nanosheets into nano-fragments, which made the fluorescence of CDs in the system recover and the scattering intensity (FOS and SOS) of the system decrease significantly. Therefore, the optical sensor combined FOS and fluorescence signals in ratiometric mode, and SOS signal in turn-off mode to realize sensitive determination of H₂O₂. The linear ranges of ratiometric mode and turn-off mode for H₂O₂ detection were 0.2-40 and 0.2-15 μM, respectively. And the limits of detection (LODs) of two modes were 73 and 104 nM, respectively. Furthermore, the sensor was also successfully applied to the detection of glucose which can react to produce H₂O₂. Satisfactorily, the LODs of this sensor for glucose detection were 95 and 113 nM for ratiometric mode and turn-off mode, respectively. This work not only provides a new method for the accurate detection of H₂O₂ and glucose, but also extends a new idea for the study of the combination of scattering and fluorescence.

The highly sensitive “turn-on” detection of morin using fluorescent nitrogen-doped carbon dots

Graphic diagram of the synthesis of the N-CDs and the N-CDs based fluorescent sensor for the determination of morin.

Innovative ratiometric optical strategy: Nonconjugated polymer dots based fluorescence-scattering dual signal output for sensing mercury ions

A new ratiometric platform was developed for sensing Hg²⁺, which combined fluorescence and scattering simultaneously. This ratiometric strategy reflected superiorities over conventional methods, since the two independent signals at irrelevant categories meet the requirements of sufficient wavelength separation, stimulation under one excitation, and collection on single instrument. Herein, nonconjugated polymer dots (N-PDs) were served as the recognition unit for Hg²⁺ with turn-off fluorescence and turn-on scattering. Additionally, two signal collection tactics were proposed to achieve fluorescence and scattering in a window: one was to record down-conversion fluorescence and second-order scattering spectra (FL@SOS), and the other was to gather the fluorescence excited by second-order diffraction light and first-order scattering (SODL-FL@FOS). This ratiometric sensor exhibited outstanding performance toward Hg²⁺ in the range of 0.1-50 μM with the detection limit of 27 nM. By contrast, the present proposal provided a more ingenious and scalable way to construct ratiometric sensor than traditional approach.

Ratiometric fluorescence assay based on carbon dots and Cu2+-catalyzed oxidation of O-phenylenediamine for the effective detection of deferasirox

The monitoring of deferasirox (DEF) has important clinical roles in patients who need iron excretion. However, analytical methods with practicability and simplicity are limited. Moreover, ratiometric fluorescence strategies based on Förster resonance energy transfer (FRET) from carbon dots (CDs) as a donor are rarely reported as a drug monitor. In this work, CDs with an appropriate emitting wavelength at 480 nm and excitation around 370 nm were prepared by hydrothermal approach and HCl post-treatment. O-Phenylenediamine (OPD) can be oxidized by Cu2+ to produce yellow fluorescent 2,3-diaminophenazine (oxOPD) in the system of Cu2+ and OPD (Cu-OPD). Correspondingly, a remarkable FRET from CDs to oxOPD in the system of CDs, Cu2+ and OPD (CDs-Cu-OPD) was fabricated with the quenching illustration of CDs, but emitting property of oxOPD. Attributed to the chelation ability of DEF on Cu2+, the inhibitory effects of DEF on the Cu2+-triggered oxidative capability reduced the FRET system by the decreased oxOPD. Thus, the recovered CDs at F 480 and decreased oxOPD at F 560 were found through a ratiometric mode by the addition of DEF in CDs-Cu-OPD for the DEF assay. The FRET behavior of CDs and oxOPD in CDs-Cu-OPD was proved clearly through the calculation of the association constant, binding constant, number of binding sites, and the distance between the donor and acceptor. Furthermore, this ratiometric method exhibited promising analytical performance for DEF with the application in real samples. The implementation of this work expands the application field of CDs and OPD oxidation in drug monitoring, and even other biological analyses through ratiometric strategy.

Adsorption-improved MoSe2 nanosheet by heteroatom doping and its application for simultaneous detection and removal of mercury (II)

Water pollution arising from heavy metal ions continues to be a major environmental problem, which represents a serious threat to human beings and animals worldwide. New materials that can simultaneously detect and remove these toxic ions are urgently required. Herein, nitrogen and sulfur co-doped molybdenum selenide nanosheets (N, S-MoSe₂) were prepared and found to be fluorescently responsive to mercury (II) with an improved adsorption capacity (208.33 mg g^-1), thereby providing the possibility for the simultaneous detection and removal of mercury (II) in water samples. The great affinity was the result of the complexation of mercury (II) with Se and S atoms in N, S-MoSe₂ as well as the electrostatic adsorption of cation mercury (II) on negatively charged N, S-MoSe₂. Besides good sensitivity and selectivity toward mercury (II), N, S-MoSe₂ displayed a relatively consistent performance under a wide pH range from 3 to 10. The removal efficiency reached 87.5% with fast adsorption kinetics, and N, S-MoSe₂ could be reused after simple treatment. Thus, this work is expected to provide new material for the detection and removal of mercury (II) in an aqueous solution and offer an insight into the interaction between heavy metal ions and inorganic nanomaterials.