A novel chemosensor for the distinguishable detections of Cu2+ and Hg2+ by off-on fluorescence and ratiometric UV-visible absorption

Gold nanoparticles-wood nanohybrid as peroxidase-like for simple and selective detection of mercury ion

We present the design and synthesis of a gold nanoparticle-wood nanohybrid (AuNPs@Wood), synthesized via the in-situ growth of gold nanoparticles (AuNPs) within a hierarchical wood flour nanostructure under mild conditions. The AuNPs@Wood exhibited remarkable peroxidase-like activity, attributed to the unique hierarchical architecture of the wood flour. Furthermore, the use of AuNPs@Wood in conjunction with T-rich DNA (P1) results in the development of a label-free colorimetric approach for detecting mercury ions. The peroxidase-like activity of the AuNPs@Wood-P1 system was found to increase with rising concentrations of Hg (II), demonstrating a linear response to Hg (II) concentration with a correlation coefficient of 0.9917. The detection limit for Hg (II) was determined to be 0.016 μM based on three times the standard deviation (σ). Additionally, sensing Hg2+ ions remained unaffected by other metal ions, underscoring the exceptional selectivity of AuNPs@Wood-P1. In comparison to traditional methods, this approach offers advantages such as high selectivity, sensitivity, cost-effectiveness, and ease of operation without requiring complex instrumentation, thereby presenting significant potential for biosensing applications.

Graphene oxide supported MOFs-nanofiber carbon aerogel/SPCE for simultaneous detection of Cd2+ and Pb2+ in seafood

A novel electrochemical sensor for detecting heavy metal ions in seafood was developed to address food safety concerns. The sensor integrates graphene oxide into NH2-UiO-66 loaded nanofiber carbon aerogel, enhanced its three-dimensional conductive network and effective active surface area (0.34 cm2), which improved ion enrichment and oxidation-reduction reaction rates. Using the Box-Behnken design, the sensor was optimized to detect cadmium and lead with LODs of 0.16 μg·L-1 and 0.07 μg·L-1 in the 1 to 150 μg·L-1 linear range. Applied to real seafood samples, the sensor showed results consistent with ICP-OES, confirmed its reliability in complex substrates. This approach offered a promising, low-cost solution for real-time monitoring of heavy metal contamination in seafood, ensuring public food safety.

A dual responsive bis-thiophene affixed thiosemicarbazide based chemosensor for colorimetrically Hg2+ and fluorometrically Cu2+ ions and their applications in live cell imaging

In this work, we developed a fast and straightforward colorimetric and photoluminescent chemosensor probe (P1), featuring bis-thiophene-thiosemicarbazide moieties as its signaling and binding unit. This probe exhibited rapid sensitivity to Hg2+ and Cu2+ ions in a semi-aqueous medium, resulting in distinct colorimetric and photoluminescent changes. In the presence of Cu2+, P1 displayed an impressive 50-fold increase in photoluminescence (PL) at 450 nm (with excitation at 365 nm). The probe P1 formed a 1:1 complex with Hg2+ and Cu2+ ions, featuring association constant values of 4.04 × 104 M-1 and 1.25 × 103 M-1, respectively. P1 has demonstrated its efficacy in the analysis of real samples, yielding promising results. Additionally, the probe successfully visualized copper ions on a mouse fibroblast cell line (NIH3T3), highlighting its potential as an intracellular probe for copper ion detection.

A new Eosin Y-based 'turnon' fluorescent sensor for ratiometric sensing of toxic mercury ion (Hg2+) offering unaided eye detection and its antibacterial activity

A unique fluorescent molecule (ND-S) was obtained from Eosin Y in two simple yet high yielding steps (1). ND-S has special metal ion sensing ability, such that it can selectively detect toxic Hg2+ present in very low concentration in aqueous solutions in the presence of other competing metal ions. The host-guest complexation is ratiometric and is associated with significant increase in fluorescence during the process. Isothermal titration calorimetry (ITC) experiments provided thermodynamic parameters related to interaction between ND-S and Hg2+. Using inductively coupled plasma mass spectrometry (ICP-MS), the Hg2+(aq) removal efficiency of ND-S was estimated to be 99.88%. Appreciable limit of detection (LOD = 7.4 nM) was observed. Other competing ions did not interfere with the sensing of Hg2+ by ND-S. The effects of external stimuli (temperature and pH) were studied. Besides, the complex (ND-M), formed by 1:1 coordination of ND-S and Hg2+ was found to be effective against the survival of Gram-positive bacteria (S. aureus and B. subtilis) with a high selectivity index. Moreover, bacterial cell death mechanism was studied systematically. Overall, we have shown the transformation of a toxic species (Hg2+), extracted from polluted water by a biocompatible sensor (ND-S), into an effective and potent antibacterial agent (ND-M).

Morpholine-modified polyacrylamides with Polymerization-Induced emission and its specific detection to Cu2+ ions

In this work, three morpholine-modified polyacrylamide derivatives (MMPAm) were successfully prepared by free radical polymerization of monomers with morpholine moiety. The intramolecular aggregation of morpholine rings on macromolecular backbone gives MMPAm a significant polymerization-induced emission (PIE). Particularly, poly(N-morpholine acrylamide) (PNMPA) has the characteristics of strong fluorescence at 450 nm, and its fluorescence quantum yield reaches 2.87 %. The introduction of morpholine moiety, the length of CH2 spacer between morpholine ring and the backbone and the molecular weight play the important roles in PIE properties of PNMPA. Interestingly, PNMPA can recognize and detect Cu2+ specifically even in the presence of 12 other metal ions by thorough fluorescence quenching, and the detection limit of PNMPA is 17.3 μM. Furthermore, the dynamic quenching of PNMPA by Cu2+ ions and the complexation ratio of 1:2 according to JOB's working diagram were confirmed by fluorescence titration. Under the assistance of EDTA, a reversible detection system for Cu2+ is achieved, and a portable test paper from PNMPA for the detection of Cu2+ was also made. In conclusion, PNMPA is endowed with a significant PIE effect by the intramolecular aggregation of morpholine rings along the backbone in the polymerization of non-fluorescent monomer, and is expected to be a promising material for specific detection to Cu2+ ions.

A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

A dual channel rhodamine appended smart probe for selective recognition of Cu2+ and Hg2+ via "turn on" optical readout

A new rhodamine-6G hydrazone RHMA has been synthesized using rhodamine-6G hydrazide and 5-Allyl-3-methoxysalicylaldehyde. RHMA has been fully characterized with different spectroscopic methods and single crystal XRD. RHMA can selectively recognize Cu²⁺ and Hg²⁺ in aqueous media amongst other common competitive metal ions. A significant change in absorbance was observed with Cu²⁺ and Hg²⁺ ions with emergence of a new peak at λ_max 524 nm and 531 nm respectively. Hg²⁺ ions lead to "turn-on" fluorescence enhancement at λ_max 555 nm. This event of absorbance and fluorescence marks the opening of spirolactum ring causing visual color change from colorless to magenta and light pink.RHMA-Cu²⁺ and RHMA- Hg²⁺complexes are found to be reversible in presence of EDTA^2-ions. RHMA has real application in form of test strip. Additionally, the probe exhibits turn-on readout-based sequential logic gate-based monitoring of Cu²⁺ and Hg²⁺ at ppm levels, which may be able to address real-world challenges through simple synthesis, quick recovery, response in water, "by-eye" detection, reversible response, great selectivity, and a variety of output for accurate investigation.

Cu2+-assisted sensing of fungicide Thiram in food, soil, and plant samples and the ratiometric detection of Hg2+ in living cells by a low cytotoxic and red emissive fluorescent sensor

Metal ions and pesticides are extensively used in many industries and agriculture. However, they cause significant environmental pollution and various adverse health effects. Therefore, the development of sensitive and selective techniques to detect them is necessary for human health and the ecosystem. In this paper, we report a novel red-emitting fluorescence probe with a large Stokes shift (∼220 nm) based on rhodamine and isophorone units. The probe shows a ratiometric fluorescence response toward Hg²⁺ ions; however, Cu²⁺ ions quench the red fluorescence signal. The decomposition of the probe-Cu²⁺ complex allows detection of Thiram followed by recovery of the red fluorescence signal of the probe. In addition, the probe shows a good linear response to Hg²⁺, Cu²⁺, and Thiram, with detection limits of 122.0 nM, 29.0 nM, and 72.0 nM, respectively. The practical applicability of the probe has been successfully tested in real samples. Moreover, smartphone detection and light-responsive capsule fabrication have been established, for easy and quick detection. The probe possesses very low cytotoxicity and allows visualization of Hg²⁺ and Cu²⁺ ions in HeLa cells. Therefore, the present probe is expected to be an effective tool assisting in easy, quick, and reliable detection of Thiram, Hg²⁺, and Cu²⁺ ions.

A cationic iridium(III) complex containing a thiosemicarbazide unit: Synthesis and application for turn-on chemiluminescent detection of Hg2

A novel cationic iridium(III) complex [(ppy)₂Ir(bPCPC)]PF₆ (ppy: 2-phenylpyridine; bPCPC: 2-([2,2'-bipyridine]-4-carbonyl)-N-phenylhydrazinecarbothioamide) containing a thiosemicarbazide unit was designed and synthesized. The thiosemicarbazide unit was a sensitive functional group to Hg²⁺, when it reacted with Hg²⁺, it was desulphurized and thus led to the formation of 1,3,4-oxadiazole, [(ppy)₂Ir(bPCPC)]PF₆ resultantly was used as a "turn-on" chemodosimeter for luminescent detection of Hg²⁺ in DMF/PBS buffer solution at pH = 7-11. Except for Ag⁺, recognition capability of [(ppy)₂Ir(bPCPC)]PF₆ to Hg²⁺ was not interfered by other common metal ions (Co²⁺, Li⁺, Zn²⁺, Pb²⁺, K⁺, Al³⁺, Na⁺, Mn²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Cr³⁺, Ba²⁺, Mg²⁺, Ni²⁺ and Ca²⁺). The detection limit was 1.83 × 10^-9 mol∙L^-1 (0.37 ppb), which indicated the complex was a highly sensitive chemiluminescent detection reagent of Hg²⁺.

Detection of Heavy Metal Ions by Ratiometric Photoelectric Sensor

In recent years, heavy metal pollution has become increasingly serious. Heavy metals exist in an environment mainly in the form of ions (heavy metal ions, HMs). They can contaminate food, water, soil, and the atmosphere, leading to serious harm to plants and animals. With high bioavailability and nonbiodegradability, HMs can accumulate through biomagnification. Consequently, heavy metal pollution has become the cause of many fatal diseases threatening human health and ecological environment. Therefore, the accurate detection of HMs is vital and necessary. In this paper, the harm and limit standards of heavy metals were systematically summarized and the common analysis methods were overviewed and compared. Specifically, the latest research progress of ratiometric photoelectric sensor, including optical and electrical sensor, were mainly described. The research status and advantages and disadvantages of a photoelectric sensor were summarized. Furthermore, the future directions were proposed, which provided the reference for the further research and application of the ratiometric photoelectric sensor.

Molecular docking and optical sensor studies based on 2,4-diamino pyrimidine-5-carbonitriles for detection of Hg2

An organic chemical sensor based on pyrimidine was successfully produced through the green reaction between aromatic aldehyde, malononitrile, and guanidine carbonate using SBA-Pr-SO3H. This fluorescence intensity of chemosensor (2,4-diamino-6-(phenyl)pyrimidine-5-carbonitrile) decreases by the addition of Hg2+ and its detection limit is about 14.89 × 10-5 M, in fact, through the green synthesis, the ligand was yielded to detect Hg2+ and the importance of ligand was considered in docking studies. The molecular docking of 2,4-diamino-6-(phenyl)pyrimidine-5-carbonitrile compound has been done with the protein selective estrogen receptor 5ACC complexed with (Azd9496), Human Anaplastic Lymphoma Kinase Pdb; 2xp2 complex with crizotinib (PF-02341066) and human wee1 kinase Pdb; 5vc3 complexed with bosutinib. The ligands 2,4-diamino-6-(phenyl)pyrimidine-5-carbonitrile generate very good docking results with the protein Pdb; 2xp2, which is responsible for effective tumor growth inhibition.

"Off-On" typed upconversion fluorescence resonance energy transfer probe for the determination of Cu2+ in tap water

Detection of copper plays a prominent role in the environmental protection and human health. Herein, we firstly design and construct an "off-on" upconversion fluorescence resonance energy transfer (UFRET) probe with low toxicity for the Cu²⁺ determination by using NaYF₄: Yb³⁺, Er³⁺ upconversion nanoparticles (UCNPs) and Au NPs. UCNPs with positive charge and Au NPs with negative charge are respectively employed as the donor and acceptor, and bound together to form UFRET probe. The upconversion fluorescence quenching of UCNPs occurs by Au NPs through FRET (defined as "off" state). When Cu²⁺ exists in samples, Cu²⁺ reacts with 4-mercaptobenzoic acid (4-MBA) capped on the surface of Au NPs to make Au NPs detach from UCNPs, leading to the termination of FRET and the recovery of upconversion fluorescence (defined as "on" state). "Off-on" typed UFRET probe has excellent sensing performances, including linear range of 0.02-1 μM Cu²⁺ concentration, the limit of detection of 18.2 nM, high selectivity to Cu²⁺ and good recovery. The probe has been successfully used to determine Cu²⁺ in spiked tap water with satisfactory results. The probe will provide theoretical and technical support for the design of new sensitive heavy metal ion detection probe.

A NIR fluorescent sensor based on thiazoline-isophorone with low cytotoxicity in living cells for Hg2+ detection through ICT associated hydrogen bonding effect

Mercury (Hg) is a toxic pollutant and may cause serious health and environmental threats even at low concentrations. Thus, sensitive, efficient, and accurate techniques for the detection of Hg²⁺ ions in biological systems are in particular demand. In the current paper, a new, red emitting fluorescence probe (THI) based on electron deficient dicyanovinyl, electron-rich diethylamino, and receptor thiazoline toward Hg²⁺ has been developed. It has been determined that the recognition behavior of the probe toward Hg²⁺ is reversible with S^2-. The probe not only shows perfect selectivity toward Hg²⁺ with a low detection limit over a series of metal ions, but it also displays positive solvato-chromism among the tested solvents via modulation of intramolecular energy transfer from the diethylamino to a dicyanovinyl moiety. Furthermore, it has been shown that the probe can be applied as a fluorescent probe for visualizing Hg²⁺ in living HeLa cells through a confocal laser scanning microscope. Also, the probe THI has not shown any toxic effect in cervical cancer and epithelial cells. Thus, the probe demonstrates high promise for Hg²⁺ detection in biomarker screening, disease diagnosis, and clinical medicine with low cytotoxicity.

Chemosensors based on N-heterocyclic dyes: advances in sensing highly toxic ions such as CN- and Hg2

CN- and Hg2+ ions are harmful to both the environment and human health, even at trace levels. Thus, alternative methods for their detection and quantification are highly desirable given that the traditional monitoring systems are expensive and require qualified personnel. Optical chemosensors (probes) have revolutionized the sensing of different species due to their high specificity and sensitivity, corresponding with their modular design. They have also been used in aqueous media and different pH ranges, facilitating their applications in various samples. The design of molecular probes is based on organic dyes, where the key species are N-heterocyclic compounds (NHCs) due to their proven photophysical properties, biocompatibility, and synthetic versatility, which favor diverse applications. Accordingly, this review aims to provide an overview of the reports from 2016 to 2021, in which fluorescent probes based on five- and six-membered N-heterocycles are used for the detection of CN- and Hg2+ ions.