Metal Ion Sensors Research Articles

Sensing mechanism of fluorescent sensor to Cu2+ based on inhibiting ultra-fast intramolecular proton transfer process

A novel and efficient chemosensor 1 for detecting Cu2+ has recently been developed. However, the photophysical properties of chemosensor 1 and its response mechanism to Cu2+ are still unclear. Herein, the density functional theory and the time-dependent density functional theory approaches are implemented to investigate the excited state behavior of chemosensor 1 and its sensing mechanism for Cu2+ is revealed. Through constructing the potential energy curve with the dihedral angle of hydroxide radical as a variable, the irreversibility of the adjustment of the hydrogen proton direction is determined. This feature provides a favorable geometric configuration condition for the formation of intramolecular hydrogen bond. Moreover, the reduced density gradient analysis and topological analysis are performed to visualize the hydrogen bond strength, it is found that the hydrogen bond is enhanced in first singlet excited state (S1) compared with that in ground state (S0). The chemosensor 1 has only a low potential barrier in the S1 state, indicating that it could undergo an ultra-fast excited state intramolecular proton transfer (ESIPT) process. Furthermore, the reaction sites of chemosensor 1 and Cu2+ is theoretically predicted by the electrostatic potential analysis and the coordination mode of 1 + Cu2+-H+ is confirmed. Thus, we verify that the deprotonation inhibits the ESIPT behavior and leads to fluorescence quenching to achieve the recognition of chemosensor 1 to Cu2+. In addition, the binding energy of Cu2+ with chemosensor 1 is greater than that of Mg2+ and Zn2+, the high selectivity of chemosensor 1 to Cu2+ is illustrated. Our investigation clarifies the sensing mechanism of chemosensor 1 to Cu2+ based on inhibiting ultra-fast ESIPT process, which provides a theoretical basis for the development of new metal ion sensors.

Differently luminescent sensing abilities for Cu2+ ion of two metal phosphonates with or without the free Lewis basic pyridyl sites

Two metal phosphonates with or without the free Lewis basic pyridyl sites, namely, [Zn1.5(HL)]·2H2O (1) and [Cd0.5(H3L1)]·H2O (2) have been hydrothermally obtained from 4–pyridyl–CH2N(CH2PO3H2)2 (H4L) and 3–pyridyl–CH2N(CH2PO3H2)2 (H4L1). The pyridyl N atom of 1 is uncoordinated with Zn(II) ion, whereas the pyridyl N atom of 2 is coordinated with Cd(II) ion, which leads to the different luminescent sensing abilities for Cu2+ ion. Compound 1 shows a highly selective and sensitive luminescent sensor for sensing Cu2+ with a low detection limit of 2.7 nM in aqueous solution. However, 2 can not be used as a luminescent sensor for metal ions. The result indicates that the presence of the free Lewis basic pyridyl sites in the framework plays an important role in the recognition of metal cations. Meanwhile, the quenching mechanism for 1 is also investigated, which can be attributed to the weak interaction between the free Lewis basic sites from the HL3– ligands and Cu2+ ions.

Dual Luminescent Coordination Polymers Based on Flexible Aliphatic Carboxylate Ligands Supplementing by Rigid Bipyridyl Ligands for 2,4-Dinitrophenol (DNP) and Iron (III) Ion Detections

Based on flexible aliphatic carboxylate ligands supplementing by isomerized structure of rigid bipyridyl ligands, three novel Zn(II) coordination polymers, namely Zn 2 (dpe)(glutarate) 2 (H 2 O) 2 (1), Zn 2 (glutarate) 2 (tdpe) 2 (H 2 O) 2 (2), and Zn(H 2 O)(succinate)(tdpe) 2 (3) (dpe = 1,2-di(4-pyridyl)ethylene, tdpe = trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene)), have been synthesized by appropriate methods. The crystallographic data of all complexes presented the diverse geometries of Zn(II) center such as two independent of square pyramidal and tetrahedral (in (1)), trigonal bipyramidal (in (2)), and octahedral (in (3)). Both the carboxylate ligands act as bridging ligands with the various coordination mode to build up the main structures. While bipyridyl ligand showed only 4-pyridyl site in coordination bond with metal center providing only dpe acted as bridging ligand to build up the principal framework in (1). Whereas tdpe ligand presented monodentate coordination mode in the other. All structures of complexes indicated that the coexistence of two ligand types could support the higher dimensionality in the complexes. Complex 1 was further used as nitro-aromatic compounds (NACs) and heavy metal ion sensors. It shows highly sensitive and selective sensing to 2,4-dinitrophenol (DNP), and Fe(III) ion, respectively based on fluorescence quenching effect.

Selective sensing of CrVI and FeIII ions in aqueous solution by an exceptionally stable TbIII-organic framework with an AIE-active ligand

We herein report a new lanthanide metal-organic framework (MOF) that exhibits excellent chemical stability, especially in the aqueous solution over a wide pH range from 1 to 14. In contrast to many reported lanthanide MOFs, this Tb-based MOF emits cyan fluorescence inherited from the integrated AIE-active ligand, rather than Ln3+ ions. More remarkably, its fluorescence signal features a highly selective and sensitive “turn-off” response toward CrO42−, Cr2O72− and Fe3+ ions, highlighted with the low detection limits down to 68.18, 69.85 and 138.8 ppm, respectively. Thus, the exceptional structural stability and sensing performance render this material able to be a superior luminescent sensor for heavy metal ions in wastewater.

Metal Nanostructures for Environmental Pollutant Detection Based on Fluorescence.

Heavy metal ions and pesticides are extremely dangerous for human health and environment and an accurate detection is an essential step to monitor their levels in water. The standard and most used methods for detecting these pollutants are sophisticated and expensive analytical techniques. However, recent technological advancements have allowed the development of alternative techniques based on optical properties of noble metal nanomaterials, which provide many advantages such as ultrasensitive detection, fast turnover, simple protocols, in situ sampling, on-site capability and reduced cost. This paper provides a review of the most common photo-physical effects impact on the fluorescence of metal nanomaterials and how these processes can be exploited for the detection of pollutant species. The final aim is to provide readers with an updated guide on fluorescent metallic nano-systems used as optical sensors of heavy metal ions and pesticides in water.

Recent advances in carbon based nanomaterials as electrochemical sensor for toxic metal ions in environmental applications

Toxic metal ions are environmental pollutants that are non-biodegradable and hazardous for which World Health Organization has set a maximum permissible limit for safe drinking water. Various spectroscopic techniques are already in practice to monitor these toxic metals but electrochemical sensors have caught our attention because of their portability, low-cost and fast response. The sensitivity of these electrochemical sensors can be further improved by modifying with carbon based nanomaterials (CBNMs) because of their high conductivity, surface area and broad working potential. The review provides recent advances in the use of electrochemical sensors fabricated with CBNMs for detection of toxic metal ions.

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing.

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co2+ and Fe3+ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

Assembly of Two Mesoporous Anionic Metal-Organic Frameworks for Fluorescent Sensing of Metal Ions and Organic Dyes Separation.

Anionic metal-organic frameworks (MOFs) have attracted increasing attention due to the enhanced electrostatic interactions between their anionic frameworks and counter-ionic guests. Owing to these special host-guest interactions, anionic MOFs are beginning to have a large impact in the field of absorption and separation of ionic molecules and selective sensing of metal ions. Herein, two mesoporous anionic metal-organic frameworks, namely, [(CH3)2NH2]6[In6(OX)6(TCA)4]·solvents (JOU-11) and [(CH3)2NH2]6[In6(OX)6(TCPA)4]·solvents (JOU-12) (H3TCA = tricarboxytriphenylamine; H3TCPA = tris((4-carboxyl)phenylduryl)amine; OX = oxalate), have been synthesized by using wheel-type [In6(OX)6(COO)12]6- as building blocks. Structural analyses show that JOU-11 and JOU-12 show isoreticular three-dimensional frameworks with pyr topology. Due to their anionic frameworks and tunable pore window sizes, both compounds can be exploited for absorbing and separating cationic organic dyes. In addition, JOU-11 can be developed as a fluorescence "turn-off" sensor for selectively sensing Fe3+, whereas JOU-12 can be used for fluorescence "turn-on" sensing of Cu2+ and Co2+ ions.

Polyphenol‐Induced Adhesive Liquid Metal Inks for Substrate‐Independent Direct Pen Writing

AbstractSurface patterning of liquid metals (LMs) is a key processing step for LM‐based functional systems. Current patterning methods are substrate specific and largely suffer from undesired imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand‐written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand‐written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise.

Luminescent carbon dots obtained from chitosan: a comparison between different methods to enhance the quantum yield

The preparation of carbon dots (CDs) from different biomass source represents an interesting alternative to obtain these nanoparticles, mainly when they can be prepared using low-cost methods. In this work we have used a nitrogen-rich precursor, chitosan, to obtain CDs using two different methods, acid dehydration (AD) and hydrothermal carbonization (HC), with the aim to study the different characteristics of the obtained nanoparticles. Also, a simple method to functionalize the CDs was applied to enhance the optical properties of the carbon nanoparticles. The obtained CDs were characterized by several techniques including FTIR, Elemental Analysis, TEM, UV-Vis, Fluorescence, and Potentiometric Titration. Size distribution measurements showed that the CDs had a narrow size distribution, with the diameters in the range 1.0–3.6 nm. Also, the CDs obtained by the HC method showed a greater amount of nitrogen functional groups than the nanoparticles prepared by the AD route. The functionalized CDs obtained from the HC method reached 15.3% of quantum yield. Furthermore, the obtained CDs were used as fluorescent sensors for different metal ions. Finally, these results represent an alternative to obtain biomass-derived CDs prepared via a low-cost method, presenting a relatively high quantum yield with potential applications in different areas.

Mechanical Flexibility of DNA: A Quintessential Tool for DNA Nanotechnology.

The mechanical properties of DNA have enabled it to be a structural and sensory element in many nanotechnology applications. While specific base-pairing interactions and secondary structure formation have been the most widely utilized mechanism in designing DNA nanodevices and biosensors, the intrinsic mechanical rigidity and flexibility are often overlooked. In this article, we will discuss the biochemical and biophysical origin of double-stranded DNA rigidity and how environmental and intrinsic factors such as salt, temperature, sequence, and small molecules influence it. We will then take a critical look at three areas of applications of DNA bending rigidity. First, we will discuss how DNA’s bending rigidity has been utilized to create molecular springs that regulate the activities of biomolecules and cellular processes. Second, we will discuss how the nanomechanical response induced by DNA rigidity has been used to create conformational changes as sensors for molecular force, pH, metal ions, small molecules, and protein interactions. Lastly, we will discuss how DNA’s rigidity enabled its application in creating DNA-based nanostructures from DNA origami to nanomachines.

Development of a Simple Fe(II) Ion Colorimetric Sensor from the Immobilization of 1,10-Phenanthroline In Alginate/Pectin Film

An optical analytical sensor was proposed based on the complexation reactions of 1,10-phenanthroline derivative in aqueous solutions. This study aims to synthesize a metal ion sensor for detecting Fe(ll) ion from the immobilization of 1,10-phenanthroline compound in alginate/pectin film. This was carried out by characterizing the films using the Fourier-transform infrared spectrometry (FT-IR) and scanning electron microscope (SEM). The determination of the optimal condition for Fe(II) ion detection and validation of the parameters was conducted by measuring the absorbance of the films using a UV-Vis spectrophotometer. After the addition of Fe(II) ion, the color of the alginate/pectin-phenanthroline film changed from transparent yellow to orange-red, showing its potential as a visual colorimetric sensor for iron(II) ion. It was found that the optimum condition for Fe(II) ion sensing was at 513 nm after 2 min of detection at pH 2. The alginate/pectin-phenanthroline film had good linearity, precision, selectivity, and accuracy with a detection limit as low as 0.446 mg L–1, which was remarkable.

Photophysical Behavior and Sensing Response of Chalcone analogue containing pyrene moeity

D–π–A chalcone composed of pyrene and thiophene units wassynthesized and characterized. The solvatochromic response wasinvestigated in different solvents of various polarities. Additionally, theinclusion characteristic of the investigated dye was studied in differentorganized assemblies of three surfactants. The spectral changessuggested the chalcone would be useful to study the critical micelleconcentrations of the studied assemblies systems. Furthermore, theabsorption and emission spectra are sensitive towards H+, Co2+, Ni2+,Cd2+, Pb2+, and Zn2+ owing to acido- and metallo-chromic behaviors.These results suggest that the investigated chalcone would be potentialcandidate for polarity sensors, probes to characterize microenviromentalpolarity of the surfactants, and sensors for metal ions and H+ proton.

Carbon Dots: An Insight into Their Application in Heavy Metal Sensing

The design of nanomaterials for application in diverse fields ranging from photovoltaic to fluorescence sensing is a research area of increasing interest. Recently, Quantum Dots (QDs), which are classified as semiconductor quantum dots (SQDs) and Carbon dots (CDs), have become a hot topic of investigation, owing to their extraordinary tunable fluorescence emission properties that render them excellent candidates for sensing metal ions. The detection of metal ions in aqueous solutions with high sensitivity is very important as these ions have toxicological and environmental impacts. In this short review, we have described the fluorescence emission properties of CDs and their application for the detection of different metal ions, such as Hg2+, Pb2+, Cu2+, Fe3+, Cd2+, and Cr6+.

Efficient electro-chemical sensor for sensitive Cd2+detection based on novel in-situ synthesized hydrazonoyl bromide (HB)

In this approach, an efficient methodology for synthesis of a novel hydrazonoyl bromide (HB) containing trifluoromethyl moiety by using fluorine-containing building blocks was achieved. The synthesized HB was fully characterized with various methods such as Infra-red spectroscopy (IR), Thin layer chromatography (TLC), 1H NMR, 19F-NMR, 13C NMR, and elemental analyses. In-situ potential examination as reliable technique, an electrochemical sensor based on prepared HB was used for the selective detection of environmental hazardous heavy metal ion, Cd2+. The fabricated sensor was found to perform linearly over the concentration range (linear dynamic range) of 0.1 nM~0.01 mM of Cd2+ ion and the sensitivity (51.12 µAµM−1cm−2) and detection limit (53.85±2.69 pM) of the proposed sensor were estimated from the slope of calibration curve (plot of current versus concentration). Furthermore, the proposed Cd2+ ion sensor was exhibited good analytical performances such reproducibility, stability in phosphate buffer medium and efficiency to detect Cd2+ ion in real environmental samples. This progress in the field of metal ion sensor development might be a cost effective and efficient method in the detection of unsafe and hazardous ions for the safety of environmental and ecological fields in broad scales.

Optical Fiber Sensors for Metal Ions Detection Based on Novel Fluorescent Materials

Recently, novel fluorescent probes based on biomaterials and luminescent nanomaterials for metal ions attract tremendous attentions, owing to their advantages of simple operation, high sensitivity and rapid response for metals detection. Immobilized on the optical fiber sensor, fluorescent probes reveal the advantages while facing outdoor detection challenges. Therefore, numerous fluorescent optical fiber sensors for metal ions have been developed for online and in-situ detection to predict and prevent the environmental problems. Differ from refractometer-based fiber sensors, the structures of the fiber sensors based on fluorescent materials are usually simple, and the characters of the materials and the fabrication processes of fiber sensors are more significant to the sensing performances. This paper summarized the studies of optical fiber sensors for metal detection based on novel fluorescent materials to help researchers get the highlights of recent notable advancements and obtain the better potential prospects.

Colorimetric metal ion (II) Sensors Based on imine boronic esters functionalized with pyridine

The one-step synthesis of three imine boronic esters functionalized with pyridyl groups is described (1a-1c). The presence or absence of a methyl group affects the whole conformation, being bent “L” or linear as determined by X-ray crystal diffraction. C–H⋯O, C–H⋯N, C–H⋯F and C–H … π hydrogen bond interactions support 2D supramolecular arrangements. Ligands were tested as metal ion (M2+) sensors in solution. The addition of metal cations (Fe2+, Co2+ and Cu2+) to 1a using methanol as solvent, showed significant color changes (purple, orange and green, respectively), while for metal cations Ni2+, Zn2+, Cd2+ cations no color changes were observed. The sensitivity of compound 1a towards Fe2+, Co2+ and Cu2+ was monitored by UV–Vis spectroscopy, where the presence of Fe2+ produces new bands at 360 and 566 nm. For Co2+ and Cu2+ a remarkable intensity increase was observed at 290 nm band and new bands appear at 340 and 462 nm, respectively. The stoichiometry of the complexes 1a-Fe2+, 1a-Co2+ and 1a-Cu2+ was determined by Job's plots being 1:3 (metal:ligand, complex [Fe (1a)3]2+), in contrast with the stoichiometry 1:1 observed for 1b-Fe2+. In fact, the computed ΔG formation associated value showed a strong stabilization for the complex [Fe (1a)3]2+ (−65.5 kcal/mol) in comparison with the possible complex [Fe (1b)3]2+ (−29.7 kcal/mol). Detection limits are in the mM range (determined by UV–Vis) and μM range (determined by Fluorescence). An analogous bis-bidentate derivative (2a) also shows similar behavior but stoichiometric interaction changes to 2:3 (metal:ligand) and detection limits are in the mM range obtained by UV–Vis and Fluorescence techniques.

Microchannel–engraved and Cu–dispersed carbon nanocomposite film as a chemiresistive sensor for aqueous metal ions

A Cu-carbon nanocomposite film (2 mm thickness) is fabricated as an efficient chemiresistive sensor for aqueous Cd. The novelty of the study is in fabrication of the laser-ablated vertical microchannels (200 µm wide × 100 µm deep × 200 µm inter-spacing) on both sides of the carbon film. The microchannels speed up sensing by inducing a reproducible capillary action in the film, with a rapid rise of the liquid and wetting of the material, and augmenting exposure of the electroconductive Cu nanoparticles to the analyte through the porous textured walls. Capillary action and wetting are facilitated by hydrophilic functional groups in the material. Notably, the sensor response (electrical resistance of the film) is approximately linear (R2 = 0.977) over the concentration range 10 – 150 ppb. The microfluidics-based approach used in this study can be easily extended to develop fast chemiresistive sensors for biofluids, and the other metals in wastewater.

8-Hydroxyquinoline Fluorophore for Sensing of Metal Ions and Anions.

Among various known hydroxyquinolines, 8-hydroxyquinoline (8-HQ) is the most prevalent moiety due to excellent property for the formation of the complex with different metal ions and anions, and utilized in a wide variety of applications in pharmacological and medicinal fields. 8-Hydroxyquinoline moiety and its analogues acts as fluorophoric ligands on complex formation with alkali and alkaline as well as transition metal ions and anions, thus, considered as an ideal building block in metallo-supramolecular chemistry for recognition, separation, and quantitative investigation of cations. 8-Hydroxyquinoline moiety is also used in various applications for the advancement of novel fluorescent chemosensors in a wide variety of areas viz., material chemistry, bioorganic chemistry, molecular imaging, analytical chemistry, molecular recognition, medical and biological science communities. The present review emphasises on the progress of sensing properties of 8-HQ centred small-molecule fluorescent chemosensors towards several metal ions viz., Fe3+ , Al3+ , Ag+ , Hg2+ , Cu2+ , Pd2+ , Zn2+ , Cr3+ , Cd2+ , Mn2+ , Ca2+ , and K+ and anions such as F- , CN- and PPi, from 2008 to 2020, because of their sensitivity and selectivity in terms of diverse colour changes for different species. This critical and comprehensive review might facilitate the improvement of more prevailing chemosensors for future exciting and broad applications.

Highly sensitive Pb2+ sensor based on rod-like poly-tyrosine/Bi modified glassy carbon electrode combined with electrodeposition to eliminate Cu2+ interference

A rod-like poly-tyrosine membrane modified glassy carbon electrode (p-Tyr/GC) was first prepared and characterized by CV, EIS and SEM, which can improve electroactive area and electron transfer. Then a Bi/p-Tyr/GC composite electrode was prepared by in situ Bi plating. Taking the Bi/p-Tyr/GC’s response to 0.25 μmol·L−1 Pb2+ as reference, the optimal conditions for Bi/p-Tyr/GC preparation and test were obtained with Tyr concentration, scan number, Bi3+ concentration, pH and accumulation potential being 2.0 mmol·L−1, 20, 3.0 μmol·L−1, 6.5 and −1.3 V, respectively. Under optimal conditions, the linear equation of Bi/p-Tyr/GC’s response to Pb2+ (1.0 nmol·L−1 to 3.0 μmol·L−1) was ip (μA) = 0.6184 + 105.5c (μmol·L−1) (R2 = 0.9987) with a detection limit of 0.12 nmol·L−1 (3S/k). For the first time, the elimination of Cu2+ interference for Pb2+ determination was studied by electrodeposition. The Bi/p-Tyr/GC electrode was successfully used for Pb determination in preserved duck eggs with a recovery of 92.1–97.9% and RSD less than 3.5%. The developed Pb2+ sensor has high sensitivity and wide linear range. More importantly, the electrochemical method for eliminating Cu2+ interference has high selectivity and wide application range, which has important reference value for the development of other heavy metal ion sensors in complex samples.