A dual-channel chemosensor based on 8-hydroxyquinoline for fluorescent detection of Hg2+ and colorimetric recognition of Cu2

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.

"Turn-on" and pinhole-free ultrathin core-shell Au@SiO2 nanoparticle-based metal-enhanced fluorescent (MEF) chemodosimeter for Hg2

This study reports a metal-enhanced fluorescence chemodosimeter for highly sensitive detection of Hg2+ ions. Silica-coated Au nanoparticles (Au@SiO2 NPs) with a pinhole-free 4-5 nm shell were synthesized and functionalized with a monolayer of turn-on fluorescent probes. Compared to other organic fluorescent probes suffering from poor biocompatibility and detection limits, this design of a monolayer of turn-on fluorescent probes immobilized on the Au@SiO2 NPs with a pinhole-free 4-5 nm shell avoids fluorescence quenching and allows the fluorescent probe within the field of the inner Au NPs to experience metal-enhanced fluorescence. With this design, the chemodosimeter permits fluorescence emission in the presence of Hg2+ ions, because they trigger the ring-opening reaction of the fluorescent probe immobilized on the Au@SiO2 NPs. Additionally, the fluorescent probe is distanced by the thin SiO2 shell from directly attaching to the metallic Au NPs, which not only avoids fluorescence quenching but allows the fluorescent probe within the long-ranged field of the inner Au NPs to experience metal-enhanced fluorescence. As a result, the detection limit for the chemodosimeter can reach up to 5.0 × 10-11 M, nearly two orders of magnitude higher than that achieved for the free fluorescent probe. We also demonstrate the acquisition of images of Hg2+ in HTC116 cells and zebrafish using a simple fluorescence confocal imaging technique. The fluorescence response results for HTC116 cells and zebrafish show that the probes can permeate into cells and organisms. Considering the availability of the many organic fluorescent probes that have been designed, the current designed metal-enhanced fluorescence chemodosimeter holds great potential for fluorescence detection of diverse species and fluorescence imaging.

Construction of an optical sensor for copper determination in environmental, food, and biological samples based on the covalently immobilized 2-(2-benzothiazolylazo)-3-hydroxyphenol in agarose

An optical chemical sensor has been developed for the quantitative spectrophotometric analysis of copper. The optode is dependent on covalent immobilization of 2-(2-benzothiazolylazo)-3-hydroxyphenol (BTAHP) in a transparent agarose membrane. The absorbance variation of immobilized BTAHP on agarose as a film upon the addition of 5 × 10-3 M aqueous solutions of Mn2+, Zn2+, Hg2+, Cd2+, Pb2+, Co2+, Ni2+, Fe2+, La3+, Fe3+, Cr3+, Zr4+, Se4+, Th4+, and UO22+ revealed substantially higher changes in the Cu2+ ion content compared to other ions investigated here. The effects of various experimental parameters, such as the solution pH, the reaction time, and the concentration of reagents, on the quality of Cu2+ sensing were examined. Under ideal experimental circumstances, a linear response was achieved for Cu2+ concentrations ranging from 1.0 × 10-9 to 7.5 × 10-6 M with an R2 value of 0.9988. The detection (3σ) and quantification (10σ) limits of the procedure for Cu2+ analyses were 3.0 × 10-10 and 9.8 × 10-10 M, respectively. No observable interference was recorded in the detection of Cu2+ due to other inorganic cations. With no indication of BTAHP leaching, the membrane demonstrated good durability and quick response times. The optode was effectively used to determine the presence of Cu2+ in environmental water, food, and biological samples.

Relay detection of Cu2+ and bovine serum albumin by a dansyl derivative-based fluorescent probe

A dansyl derivative-based fluorescent probe, namely, DGly, was developed for relay detection of Cu²⁺ and bovine serum albumin (BSA) with high selectivity and sensitivity. The fluorescence intensity of DGly at 540 nm displayed "on-off-on" phenomenonafter Cu²⁺ and BSA were added in sequence. Correspondingly, the solution color changed from yellow to dark and then to yellowish white under 365 nm UV light irradiation; thus, the solution could be detected by the naked eye. The association constant of DGly-Cu²⁺ was stronger than that of DGly-BSA and DGly-Cu²⁺-BSA. Hence, BSA was detected after a complex was formed between DGly and Cu²⁺. The relay detection of Cu²⁺ and BSA was not influenced by other competitive interferents, and the detection limits of Cu²⁺ and BSA were 1.32 and 0.26 μM, respectively. Analysis of Cu²⁺ in real water samples validated the detection performance of the method proposed herein; it achieved satisfactory recovery and relative standard deviation values. This work demonstrated that introducing metal ions can be an effective way to improve the sensitivity of BSA detection.

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.

Rational design of a FRET-based ratiometric fluorescent probe with large Pseudo-Stokes shift for detecting Hg2+ in living cells based on rhodamine and anthracene fluorophores

The development of fluorescent dyes has been a continuing attractive research topic in the field of fluorescence sensing and bioimaging technologies, most of them were subject to a single signal change. In this work, a novel colorimetric and ratiometric fluorescent probe 1 based on rhodamine and anthracene groups was designed and synthesized via the fluorescence resonance energy transfer (FRET) mechanism. Probe 1 showed excellent selectivity, higher sensitivity and ratiometric response to Hg²⁺ in the CH₃CN/H₂O (1/1, v/v) system, with a fast response time (less than 30 s); The fluorescent color changed from purple to orange and the solution visible to the naked-eye changed from colorless to pink. The Pseudo-Stokes shift was 174 nm upon addition of Hg²⁺. The limit of detection (LOD) was calculated to be 0.81 μM and 0.38 μM according to fluorescence and UV/vis measurements, respectively. Furthermore, a possible mechanism for the detection of Hg²⁺ by probe 1 was verified by using ¹H NMR, ESI-MS, and HPLC spectra. Meanwhile, probe 1 was successfully used for cell imaging for the detection of Hg²⁺ in living cells.

Interfacially Super-Assembled Benzimidazole Derivative-Based Mesoporous Silica Nanoprobe for Sensitive Copper (II) Detection and Biosensing in Living Cells

Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu²⁺ . DHBM-MSN exhibits an obvious quenching effect on Cu²⁺ in aqueous solutions, and the detection limit can be as low as 7.69×10^-8  M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu²⁺ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications.

Schiff Base Functionalized 1,2,4-Triazole and Pyrene Derivative for Selective and Sensitive Detection of Cu2+ ion in the Mixed Organic- Aqueous Media

We have prepared Schiff base functionalized 1,2,4-triazole and pyrene derivative for selective, sensitive, and naked eye colorimetric detection of Cu²⁺ in the mixed organic- aqueous media. Amongst the 18 different metal ions studied for absorption and fluorescence titration, only Cu²⁺ ion encourages the modification in spectral properties of Schiff base functionalized 1,2,4-Triazole and Pyrene Probe. The stoichiometric ratio of the TP-Cu²⁺ complex was determined to be 2:1 according to Job's plot. The lower detection limit estimated for Cu²⁺ is 0.234 nM which shows excellent sensitivity and selectivity of the present analytical method towards detection of Cu²⁺ ion in the mixed organic-aqueous media. The present approach has been successfully utilized for the quantitative determination of Cu²⁺ ion from environmental aqueous solution.

A novel coumarin-based colorimetric and fluorescent probe for detecting increasing concentrations of Hg2+ in vitro and in vivo

Mercury has complex biological toxicity and can cause a variety of physiological diseases and even death, so it is of great importance to develop novel strategies for detecting trace mercury in environmental and biological samples. In this work, we designed a new coumarin-based colorimetric and fluorescent probe CNS, which could be obtained from inexpensive starting materials with high overall yield in three steps. Probe CNS could selectively respond to Hg²⁺ with obvious color and fluorescence changes, and the presence of other metal ions had no effect on the fluorescence changes. Probe CNS also exhibited high sensitivity against Hg²⁺, with a detection limit as low as 2.78 × 10^-8 M. More importantly, the behavioral tracks of zebrafish had no obvious changes upon treatment with 10 μM probe CNS, thus indicating its low toxicity. The probe showed potential application value and was successfully used for detecting Hg²⁺ in a test strip, HeLa cells and living zebrafish larvae.

An "off-on-off" fluorescence chemosensor for the sensitive detection of Cu2+ in aqueous solution based on multiple fluorescence emission mechanisms

A new organosiloxane precursor ((E)-3-hydroxy-4-((2-(2-hydroxy-4-(3-(3-(triethoxysilyl)propyl)ureido)benzoyl)hydrazono)methyl)phenyl(3-(triethoxysilyl)propyl)carbamate, hereinafter referred to as AHBH-Si) and tetraethylorthosilicate (TEOS) were mixed as the mixed Si source, and bridged periodic mesoporous organic silica (AHBH-PMOs) nanoparticles were obtained through the co-condensation reaction. AHBH-PMO nanoparticles possess mechanisms of "Aggregation Induced Emission" (AIE) and "Intramolecular Charge Transfer" (ICT), which originate from the molecular structure of AHBH having "C[double bond, length as m-dash]N" bond, ortho hydroxyl groups, etc.. Therefore, the optical properties of AHBH are excellent with respect to the solvent effect and enhanced fluorescence. For hybrid materials, the silica framework provides a rigid environment that restricts the rotation of AHBH, thereby turning on the fluorescence of AHBH due to the regulation by the AIE effect. In particular, AHBH-PMOs are no longer restricted by organic solvents and could really achieve the response to Cu2+ with high sensitivity and selectivity in aqueous solutions of a wide pH range. In addition, the detection limit is as low as 3.26 × 10-9 M. Methods such as Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry have shown the coordination interaction between AHBH and Cu2+. The Gaussian 09 software of density functional theory to calculate the reducing changes of energy gaps among AHBH and AHBH-Si before and after the addition of Cu2+ showed that coordination interaction exists in the system. These results indicate that AHBH-PMO hybrid materials have potential applications in the field of environmental monitoring.

Simple and sensitive colorimetric sensors for the selective detection of Cu(ii)

A simple, sensitive colorimetric probe for detecting Cu(ii) ions with fast response has been established with a detection limit of 2.82 μM. UV-Vis spectroscopy along with metal ion response, selectivity, stoichiometry, competition was investigated. In the presence of copper(ii), the UV-Vis spectrum data showed significant changes and the colorimetric detection showed a color change from colorless to yellow. After the selective binding of receptor L with Cu(ii), the UV-visible absorption at 355 nm decreased dramatically, a new absorbance band appeared at 398 nm and its intensity enhanced with the increase in the amount of Cu(ii). Moreover, it exhibited highly selective and sensitive recognition towards Cu(ii) ions in the presence of other cations over the pH range of 7-11. The complex structure was verified by FT-IR spectroscopy, elemental analysis and quantum mechanical calculations using B3LYP/6-31G(d) to illustrate the complex formation between L and Cu(ii). According to the Job plot and the quantum mechanical calculations, the stoichiometric ratio for the complex formation was proposed to be 1 : 1.

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.