A method to detect Hg2+ in vegetable via a “Turn–ON” Hg2+–Fluorescent sensor with a nanomolar sensitivity

Propargylic-linked [5]helicene derivative for selective Au3+ detection in near-perfect aqueous media with applications in diverse real samples, paper test strips, and human cells

Gold is classified as a heavy metal, and its ion (Au3+) can manifest adverse impacts on ecological and human health. Thus, an effective method for Au3+ detection is highly required. In this work, a new [5]helicene-based fluorescence sensor (M202P) was synthesized and applied for Au3+ monitoring in near-perfect aqueous media. M202Prapidly detected Au3+ through a fluorescence quenching response and furnished a large Stokes shift of 157 nm. The Au3+ sensing ability of M202P allowed it to withstand interference from other metal ions, with a detection limit for Au3+ of 8.0 ppb. The mechanism underlying its Au3+ detection was the coordination of Au3+ with the alkyne and carbonyl oxygen, leading to the later hydration of alkynyl moiety, as thoroughly proven by FTIR, 1H NMR, 13C NMR, and HRMS, with the stoichiometric ratio of 1:1 according to Job's plot. In addition, M202P can be used for the quantitative analysis and qualitative fluorescence assay of Au3+ levels in environmental waters and fertilizer solutions. This sensor also demonstrated high potential as a fluorescence tracking agent in human cells and was utilized in fabricating a paper test strip.

Recent advances in colorimetric and photoluminescent fibrillar devices, photonic crystals and carbon dot-based sensors for mercury (II) ion detection

The escalating environmental contamination with mercury has become a pressing issue, significantly impacting human beings and nature. For instance, small-scale gold mining has led to severe contamination in the Brazilian Yanomami village, highlighting the urgent need for action. The development of fibrillar-based sensors for mercury (II) ions represents an important issue to be considered in the point-of-care and simple detection of contaminants in water. Herein, this review discussed different colorimetric/photoluminescent-based prototypes for Hg2+ ions sensors and corresponding strategies to improve selectivity and sensitivity associated with the regeneration and reuse of the devices. Given these aspects, the electrospinning technique is promising for developing advanced mercury (II) ion sensors.

Theoretical study on optimizing dipeptidomimetic isocyanonaphthalene chemosensor and the fluorescence mechanism for detecting Hg2

The excited (S1) state charge distribution characteristics and fluorescence mechanism of fluorescence probes benzyl (6-cyano-2-naphthoyl)-L-valinate (NPI) and benzyl (6-amino-2-naphthoyl)-L-valinate (NPA) have been discussed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Further analysis by constructing a torsional potential energy curve (PEC) shows that a well-defined minimum energy conformation is observed when the C-C single bond between the valine benzyl ester and naphthalene ring in NPI rotates. For NPA, the most stable conformation is the naphthalene ring conformation with dihedral angle N2C1C2C3 of -30.60°, whose total energy is 0.17 kcal/mol lower than that of the second most stable conformer. The frontier molecular orbitals (FMOs) demonstrate that NPI exhibits a low degree of charge coupling, and the oscillator intensity is close to zero, indicating that it is not conducive to luminescence. However, in the S1 state, the oscillator strength of NPA is 1.2044, which is a bright state, resulting in the strong emitting. Additionally, fluorescence imaging is favored as a visual observation technique, and Stokes shift is an important physical parameter to measure fluorescence. According to the idea that changing the number and position of functional groups can affect the photophysical properties of fluorescent dyes, o-NPDI, p-NPDI and m-NPDI dyes were newly designed and o-NPDA, p-NPDA, m-NPDA produced after recognition of Hg2+. The spectral performance results show that the newly designed fluorescent dye (p-NPDA) can not only emit in the near infrared region after recognizing Hg2+, but also has a large Stokes shift (236 nm). This indirectly reflects that para-substitution is more conducive to Stokes shift, and has become one of the strategies for fluorescent dye design.

A Ratiometric Green Fluorescent Carbazole-Bis(hydrazinobenzothiazole) Probe for the Selective Detection of Toxic Hg2+ Ions in Real Water Samples

A dyad Carbazolyl-bis(hydrazinobenzothiazole) was designed to form a symmetrical structure that containing two-arm active binding sites facilitates coordination with Hg2+ ion. This sensor has imparted a colorimetric and fluorometric changes in presence of Hg2+ ions. The ligand showed a selective blue shift in presence of Hg2+even in co-existence with heavy metal ions with luminescence change from colorless to blue and colorless to green under day light. Enhanced Intramolecular charge transfer process is responsible for fluorescence transformation when ligand interacts with Hg2+ ion. The emission spectra showed a ratiometric response to increasing addition of Hg2+ ions. The sensor is capable of detecting above the lower concentration of 6.8025×10-8 M. The fluorescence efficiency of CBT-2 with Hg2+ ion is quite stable under different co-metal ions and wide range of pH 6 to 9. The sensor CBT-2 forms a 1 : 1 stoichiometric complex with Hg2+ ions and the binding nature is confirmed from the 1H-NMR, FTIR, and mass spectroscopic studies. The sensor CBT-2 and its Hg2+ complex possess good binding nature to protein in Bovine Serum Albumin which could be good in biological applications. Additionally, wedevelop a practical application in real water sample analysis and electrochemical detection via oxidation potential discrimination.

Loading of AuNCs with AIE effect onto cerium-based MOFs to boost fluorescence for sensitive detection of Hg2. Talanta 2024;273:125843. [PMID: 38492285 DOI: 10.1016/j.talanta.2024.125843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Ligand-protected gold nanoclusters (AuNCs) have become promising nanomaterials in fluorescence (FL) methods for mercury ions (Hg2+) monitoring, but low FL efficiency hinders their widespread application. Herein, AuNCs/cerium-based metal-organic frameworks (AuNCs/Ce-MOFs) were prepared by loading 6-aza-2-thiothymine-protected AuNCs (ATT-AuNCs) with aggregation-induced emission (AIE) effect on the surface of Ce-MOFs by electrostatic attraction. This strategy improved the FL intensity of AuNCs through two aspects: (i) the AIE effect of ATT-AuNCs and (ii) the confinement effect of Ce-MOFs, which improved the restriction of intramolecular motion (RIM) of ATT-AuNCs. In addition, Ce-MOFs could adsorb and aggregate Hg2+ during detection, which might increase the local concentration. Therefore, based on the high FL signal of AuNCs/Ce-MOFs and enriched Hg2+, sensitive detection of Hg2+ could be achieved. More importantly, the strong specific recognition between AuNCs and Hg2+ could guarantee selectivity. The developed FL sensor exhibited superior detection performances with a wide linear range of 0.2-500 ng mL-1 and a low detection limit of 0.067 ng mL-1. Furthermore, the FL sensor used for sensitive and selective detection of Hg2+ in real samples, and the results agreed well with the standard method. In summary, this work proposed an effective and generalized strategy for improving the FL efficiency of AuNCs, which would greatly facilitate their application in pollutant monitoring.

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435 nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6 M and 1.733 × 107 M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

Recent Advancements and Future Prospects in NBD-Based Fluorescent Chemosensors: Design Strategy, Sensing Mechanism, and Biological Applications

In recent years, the field of Supramolecular Chemistry has witnessed tremendous progress owing to the development of versatile optical sensors for the detection of harmful biological analytes. Nitrobenzoxadiazole (NBD) is one such scaffold that has been exploited as fluorescent probes for selective recognition of harmful analytes and their optical imaging in various cell lines including HeLa, PC3, A549, SMMC-7721, MDA-MB-231, HepG2, MFC-7, etc. The NBD-derived molecular probes are majorly synthesized from the chloro derivative of NBD via nucleophilic aromatic substitution. This general NBD moiety ligation method to nucleophiles has been leveraged to develop various derivatives for sensing analytes. NBD-derived probes are extensively used as optical sensors because of remarkable properties like excellent stability, large Stoke's shift, high efficiency and stability, visible excitation, easy use, low cost, and high quantum yield. This article reviewed NBD-based probes for the years 2017-2023 according to the sensing of analyte(s), including cations, anions, thiols, and small molecules like hydrogen sulfide. The sensing mechanism, designing of the probe, plausible binding mechanism, and biological application of chemosensors are summarized. The real-time application of optical sensors has been discussed by various methods, such as paper strips, molecular logic gates, smartphone detection, development of test kits, etc. This article will update the researchers with the in vivo and in vitro biological applicability of NBD-based molecular probes and challenges the research fraternity to design, propose, and develop better chemosensors in the future possessing commercial utility.

A ratiometric fluorescent probe with a large Stokes shift for the detection of Hg2+ and its applications in environmental sample and living system analysis

Toxic mercury ions (Hg2+) can cause serious environmental pollution and accumulate in living organisms via the food chain. Therefore, monitoring Hg2+ is crucial in ensuring the safety of ecosystems and organisms. In this work, a novel ratiometric fluorescent probe CMT (5-(4-(diphenylamino)phenyl)-1-(7-hydroxy-coumarin-3-yl)-4-pentene-1,3-dione) based on coumarin was developed for detecting Hg2+, which displayed obvious fluorescence changes, a low detection limit (2.24 × 10-7 M), good selectivity, and a large Stokes shift (255 nm). The CMT probe could detect Hg2+ in real environmental soil and water samples. Furthermore, the CMT probe enabled the naked-eye detection of Hg2+ using test paper experiments. CMT was also applied for fluorescence imaging in living zebrafish and plants. This work provides a highly efficient tool for monitoring Hg2+ in environmental samples and biological systems.

A coumarin-based fluorescent probe for highly selective detection of hazardous mercury ions in living organisms

In recent years, heavy metal mercury (II) pollutants have caused serious harm to human health and ecosystems. It has become critical to develop simple and highly selective sensing solutions for monitoring mercury (II). In this work, we designed and developed a novel fluorescent probe Coa-SH using the Hg2+-induced chemical reaction as a sensing mechanism. The probe Coa-SH showed high selectivity for the detection of Hg2+ by desulfurization reactions in solution. The test strips prepared with this probe could be applied to detect mercury ions in aqueous solutions. In addition, the probe Coa-SH provided a tool to detect Hg2+ in living systems. In living cells and zebrafish, the probe turned on bright red fluorescent signals in the presence of mercury ions. Importantly, the probe Coa-SH enabled Hg2+ detection in plant onion roots. This work provides an effective method for monitoring mercury ions in the environment and in living organisms.

N- and S-codoped carbon quantum dots for enhancing fluorescence sensing of trace Hg2

Carbon-quantum-dot-based fluorescence sensing of Hg2+ is a well-known cost-effective tactic with fast response and high sensitivity, while rationally constructing heteroatom-doped carbon quantum dots with improved fluorescence sensing performances through tuning the electronic and chemical structures of the reactive site still remains a challenging project for monitoring trace Hg2+ in aquatic ecosystems to avoid harm resulting from its high toxicity, nonbiodegradabilty and accumulative effects on human health. Herein, intriguing N,S-codoped carbon quantum dots were synthesized via a facile one-step hydrothermal procedure. As an admirable fluorescent probe with plentiful heteroatom-related functional groups, these N,S-codoped carbon quantum dots can exhibit an absolute fluorescence quantum yield as high as 11.6%, excellent solubility and stability over three months, remarkable sensitivity for Hg2+ detection with an attractive detection limit of 0.27 μg L-1 and admirable selectivity for Hg2+ against thirteen other metal ions. Density functional theory calculations reveal that electron-enriched meta-S of the unique graphitic N with homocyclic meta-thiophene sulfur structure can regulate this N site to have more electrons and preferable affinity towards Hg, hence achieving enhanced fluorescence quenching due to greater charge transfer from N to Hg after the coordination interaction. This strategy provides a promising avenue for precisely designing purpose-made quantum dots with the dedicated fluorescence sensing applications.

Detection of different chemical moieties in aqueous media by luminescent Europium as sensor

Detection of different chemical moieties especially trace metals is important for humans as well as water safety. In this review, different detectors synthesized by the combination of different ligands with luminescent europium complexes were discussed for the separation of metals and chemical moieties in aqueous media. These detectors displayed high sensitivity and selectivity. The limit-of-detection values were very low indicating that these detectors are best suitable for the sensing of chemical moieties and trace metals. These detectors’ luminescent changes could be noticed with the naked eye.

Cost-Effective and Selective Fluorescent Chemosensor (Pyr-NH@SiO2 NPs) for Mercury Detection in Seawater

The release of mercury into the environment has adverse effects on humans and aquatic species, even at very low concentrations. Pyrene and its derivatives have interesting fluorescence properties that can be utilized for mercury (Hg²⁺) ion sensing. Herein, we reported the highly selective pyrene-functionalized silica nanoparticles (Pyr-NH@SiO₂ NPs) for chemosensing mercury (Hg²⁺) ions in a seawater sample. The Pyr-NH@SiO₂ NPs were synthesized via a two-step protocol. First, a modified Stöber method was adopted to generate amino-functionalized silica nanoparticles (NH₂@SiO₂ NPs). Second, 1-pyrenecarboxylic acid was coupled to NH₂@SiO₂ NPs using a peptide coupling reaction. As-synthesized NH₂@SiO₂ NPs and Pyr-NH@SiO₂ NPs were thoroughly investigated by ¹H-NMR, FTIR, XRD, FESEM, EDS, TGA, and BET surface area analysis. The fluorescent properties were examined in deionized water under UV-light illumination. Finally, the developed Pyr-NH@SiO₂ NPs were tested as a chemosensor for Hg²⁺ ions detection in a broad concentration range (0–50 ppm) via photoluminescence (PL) spectroscopy. The chemosensor can selectively detect Hg²⁺ ions in the presence of ubiquitous ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Ag⁺, and seawater samples). The quenching of fluorescence properties with Hg²⁺ ions (LOD: 10 ppb) indicates that Pyr-NH@SiO₂ NPs can be effectively utilized as a promising chemosensor for mercury ion detection in seawater environments.

Ultrasensitive and selective detection of Hg2+ using fluorescent phycocyanin in an aqueous system

Hg²⁺ toxicity is one of the most common chemical poisonings that occurs mainly from drinking polluted water. In the current work, Phycocyanin (PC) was exploited as a fluorescent sensor for sensitive and selective detection of Hg²⁺ in an aqueous system. PC-Hg²⁺ interaction was monitored using a spectro-fluorometer under different buffered solutions at pH values of 6,7,8,9, or 10 above the isoelectric point of PC (5.18). A remarkable decrease of PC fluorescence intensity was observed under Tris-buffer at pH 6 upon the addition of increasing Hg²⁺ concentrations (1-120 nM). Under the maintained experimental conditions, the current sensor showed a good linear relationship with R² = 0.9971 and a limit of detection as low as 0.7 nM was achieved. In addition, a notable selectivity of Hg²⁺ over other nine heavy metals (Cu^2+, Zn^2+, Pb²⁺, Mg^2+, Mn⁴⁺, Li⁺, Fe^3+, Co²⁺, and Al³⁺) was achieved in the presence of 120 nM of each metal. Moreover, the current fluorescent detection assay was also tested in real samples of pond water, and recoveries as well as relative standard deviations within the acceptable limits were recorded.

Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors

Mercury (Hg), this non-essential heavy metal released from both industrial and natural sources entered into living bodies, and cause grievous detrimental effects to the human health and ecosystem. The monitoring of Hg2+ excessive accumulation can be beneficial to fight against the risk associated with mercury toxicity to living systems. Therefore, there is an emergent need of novel and facile analytical approaches for the monitoring of mercury levels in various environmental, industrial, and biological samples. The chromo-fluorogenic chemosensors possess the attractive analytical parameters of low-cost, enhanced detection ability with high sensitivity, simplicity, rapid on-site monitoring ability, etc. This review was narrated to summarize the mercuric ion selective chromo-fluorogenic chemosensors reported in the year 2020. The design of sensors, mechanisms, fluorophores used, analytical performance, etc. are summarized and discussed.

Copillar[5]arene-rhodamine conjugate as a selective sensor for Hg2+ ions

A new copillar[5]arene-coupled rhodamine probe 1 shows selective sensing of Hg²⁺ ions over a series of metal ions in CH₃CN by exhibiting color change of the solution as well as turn on fluorescence. It also shows interaction with Cu²⁺ by exhibiting different color and spectral change. Tetrabutylammonium iodide distinguishes between Hg²⁺ and Cu²⁺ ions.