Dual chemosensors for metal ions: A comprehensive review

A highly selective coumarin-based chemosensor for dual sensing of Cu2+ and Zn2+ ions with logic gate integration and live cell imaging

In this paper, a coumarin-based Schiff base chemosensor has been synthesized and developed to detect Cu2+ and Zn2+ ions in nanomolar concentrations. The probe selectively distinguishes Cu2+ and Zn2+ from among several metal ions in DMF : H2O (7 : 3, v/v, pH 7.4) HEPES buffer. The structure of the probe and its sensing behavior were investigated by FT-IR, UV-vis, fluorescence, HRMS, and NMR analyses, along with X-ray crystallography and computational studies. CIH detects Zn2+ and Cu2+ using different strategies: CHEF-induced fluorescence enhancement and paramagnetic fluorescence quenching, respectively. Job's plots show a 1 : 1 binding interaction between CIH and Cu2+ or Zn2+ ions. The binding constant values for Cu2+ (1.237 × 105 M-1) and Zn2+ (1.24 × 104 M-1) suggest a better ability for Cu2+ to interact with CIH than Zn2+. An extremely high sensitivity of the probe was highlighted by its very low detection limits (LOD) of 5.36 nM for Cu2+ and 3.49 nM for Zn2+. The regeneration of the probe with the addition of EDTA in its complexes allows the formation of molecular logic gates. CIH has been successfully employed in mitotracking and intracellular detection of Zn2+ and Cu2+ in SiHa cells.

Colorimetric and Fluorometric N-Acylhydrazone-based Chemosensors for Detection of Single to Multiple Metal Ions: Design Strategies and Analytical Applications

The development of optical sensors for metal ions has gained significant attention due to their broad applications in biology, the environment, and medicine. Colorimetric and fluorometric detection methods are particularly valued for their simplicity, cost-effectiveness, high detection limits, and analytical power. Among various chemical probes, the hydrazone functional group stands out for its extensive study and utility, owing to its ease of synthesis and adaptability. This review provides a comprehensive overview of N-acylhydrazone-based probes, serving as highly effective colorimetric and fluorometric chemosensors for a diverse range of metal ions. Probes are categorized into single-ion, dual-ion, and multi-ion chemosensors, each further classified based on the detected metal(s). Additionally, the review discusses detection modes, detection limits, association constants, and spectroscopic measurements.

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 μM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Synthesis and spectral characterization of the phenothiazine-thiosemicarbazide probe for the optical solid-state detection of Hg2+ and Cu2

In this study, a phenothiazine-thiosemicarbazide (PTZDS) probe was synthesized and characterized. The synthesized PTZDS probe exhibited a yellow color, with a native fluorescence emission at λemission = 550 nm and λexcitation = 450 nm. Over other metal ions, the probe exhibited significant selectivity and sensitivity towards Hg2+ and Cu2+. The probe showed fluorescence quenching along with a minor shift in the absorbance spectra from 400 to 450 nm and 430 nm in the presence of Hg2+ and Cu2+, respectively. In addition, the color of the synthesized probe remarkedly faded with the addition of Hg2+ or Cu2+. Fluorescence measurements, infrared spectroscopy (IR), and density functional theory studies were employed to elucidate the binding process in the PTZDS + Cu2+ and PTZDS + Hg2+ sensor systems. Furthermore, photophysical investigations of the synthesized probe with Hg2+ and Cu2+ were performed. Finally, the probe was successfully employed as a solid-state thin layer chromatography (TLC) optical sensor for detecting Hg2+ and Cu2+ ions.

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 × 10-6 and 2.16 × 10-7 M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 × 10-4 M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Chromene Carbohydrazide- Schiff Base as a Highly Selective Turn-Off Fluorescence Chemosensor for In3+ Ion and its Application

A new 7-(diethylamino)-2-oxo-2 H-chromene-3-carbohydrazide design to synthesize a simple Schiff-base condition. The synthesized molecules' (probe L) photophysical properties were investigated in various solvent systems and solvent-poor-solvent assays. Probe L exhibits the absorbance band at 440 nm and the emission band at 488 nm in DMSO: H2O (7:3, v/v). Further, probe L shows selective turn-off emission recognition of In3+ ions in DMSO: H2O (7:3, pH = 7.4). By Job's plot and ESI mass analysis, probe L forms a 1:2 stoichiometry complex with an estimated association constant of 4.04 × 104 M- 2 with In3+ ions. Metal induces CHEQ (chelation-caused fluorescence quenching) to reduce the intensity of probe L's emission, and the estimated quenching constant was 4.52 × 104 M- 1. The limit of detection was found to be 5.93 nM; the time response of the sensor is instantaneous, and its reversible nature was confirmed using EDTA additions. Solid substrates (test strips) were designed and tested for fast, reliable, user-friendly, and real-time sensing of In3+ ions for on-site applications. The binding mechanism of probe L with In3+ ions was investigated using 1H NMR titration and DFT/TD-DFT studies.

AIE-based ratiometric fluorescent probe for mercury ion, medium-dependent fluorescence color change and optimized sensitivity in solid state

A new AIE-based luminogen TPES, as a ratiometric fluorescence probe for mercury(II) was readily synthesized. The probe combined the advantages of the outstanding specificity of Hg2+-triggered deprotection reaction of thioketal and the brilliant emission of AIEgens in aggregated state. Once encountered aqueous Hg2+, fluorescent color of TPES in THF-H2O (fw = 98%) altered from blue to green rapidly, while other metal cations gave no interference to the probe. And the mechanism of this chemosensor was carefully verified by 1H NMR analysis, FTIR and MS spectra. As expected, TPES exhibits excellent selectivity and sensitivity towards Hg2+ in the solid state. When using filter paper as the solid medium, the fabricated test strips could signify Hg2+ ions with the LOD as 1 × 10-5 M (Hg2+ in aqueous solution), accompanied with a distinct emitting altered from blue to green. Furthermore, by changing the medium from filter paper to silica gel plate, a more significant fluorescence alteration from blue to yellow was achieved, and the LOD was further optimized to 1 × 10-6 M as discerned by naked-eye.

Highly selective, sensitive and biocompatible rhodamine-based isomers for Al3+ detection: A comparative study

Selective detection of a metal ion with high selectivity is of great importance to understand its existence and its role in many chemical and biological processes. We report here the synthesis, characterization and Al3+ sensing properties of two rhodamine-based isomers, (E)-2-((2-(allyloxy)benzylidene)amino)ethyl)-3',6'-bis(ethylamine)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (L-2-oxy) and (E)-2-((4-(allyloxy)benzylidene)amino)ethyl)-3',6'-bis(ethylamine)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (L-4-oxy). L-2-oxyand L-4-oxy show pink coloration, significant enhancement in absorbance at 530 nm and fluorescence intensity at 553 nm in the presence of Al3+ among several cations. Quantum yield and lifetime of the probes increase in the presence of Al3+. LOD values have been determined as low as ∼1.0 nM for both the isomers. DFT study suggests that the cation induces opening of spirolactam ring resulting in the changes of the rhodamine dyes. Additional reason could be Chelation Enhanced Fluorescence (CHEF) effect due to the subsequent chelation of the metal ion. Between two isomers, L-2-oxy displays better sensing ability towards Al3+ in terms of fluorescence enhancement, limit of detection, lifetime enhancement. Both the probes have been utilized in cell imaging studies using rat skeletal myoblast cell line (L6 cell line).

A coumarin hydrazone appended rotatable phenolic scaffold as fluorescent chemosensor for Ag+ ions and its bio imaging applications

A coumarin hydrazone-phenol conjugate, COH4 was designed, synthesized and utilized for the cation sensing studies by fluorimetry studies. The synthesized chemosensor was completely characterized by the usual spectroscopic and analytical studies. The COH4 receptor was examined for the detection of metal ions, in which it had a noticeable blue shifted fluorescence enhancement for Ag+ ions. Upon binding towards Ag+ ions, the photoinduced electron transfer (PET) process is inhibited via intramolecular charge transfer (ICT) process assisted by the arrest of the carbon-carbon single bond rotation. The binding stoichiometry of COH4 + Ag+ complexation ratio is noted to be 1:2, which was further confirmed by jobs plot method. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.41 µM and 0.13 µM respectively. Moreover, COH4 was successfully utilized for the practical applications of Ag+ ion detection in bacterial cell lines.

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 multifunctional fluorescent probe based on Schiff base with AIE and ESIPT characteristics for effective detections of Pb2+, Ag+ and Fe3

In this work, three Schiff-based fluorescent probes with aggregation-induced emission (AIE) and excited intramolecular proton transfer (ESIPT) characters were synthesized by grafting 2-aminobenzothiazole group onto 4-substituted salicylaldehydes. More important, a rare tri-responsive fluorescent probe (SN-Cl) was developed by purposeful variation of substituents in the molecule. It could selectively identify Pb2+, Ag+ and Fe3+ in different solvent systems or with the help of masking agent and show complete fluorescence enhancement without interference of other ions. Meanwhile, the other two probes (SN-ON and SN-N) could only recognize Pb2+ in DMSO/Tris-HCl buffer (3: 7, v/v, pH = 7.4). According to Job's plot, density functional theory (DFT) calculations and NMR analysis, coordination between SN-Cl and Pb2+/Ag+/Fe3+ was determined. The LOD values for three ions were as low as 0.059 μM, 0.012 μM and 8.92 μM, respectively. Ideally, SN-Cl showed satisfactory performance in real water samples detection and test paper experiments for three ions. Also, SN-Cl could be used as an excellent imaging agent for Fe3+ in HeLa cells. Therefore, SN-Cl has the ability to be a "single fluorescent probe for three targets".

Strategies for Improving Selectivity and Sensitivity of Schiff Base Fluorescent Chemosensors for Toxic and Heavy Metals

Toxic cations, including heavy metals, pose significant environmental and health risks, necessitating the development of reliable detection methods. This review investigates the techniques and approaches used to strengthen the sensitivity and selectivity of Schiff base fluorescent chemosensors designed specifically to detect toxic and heavy metal cations. The paper explores a range of strategies, including functional group variations, structural modifications, and the integration of nanomaterials or auxiliary receptors, to amplify the efficiency of these chemosensors. By improving selectivity towards targeted cations and achieving heightened sensitivity and detection limits, consequently, these strategies contribute to the advancement of accurate and efficient detection methods while increasing the range of end-use applications. The findings discussed in this review offer valuable insights into the potential of leveraging Schiff base fluorescent chemosensors for the accurate and reliable detection and monitoring of heavy metal cations in various fields, including environmental monitoring, biomedical research, and industrial safety.

A Novel Rhodamine Probe Acting as Chemosensor for Selective Recognition of Cu2+ and Hg2+ Ions: An Experimental and First Principle Studies

Copper and Mercury ions have vital role to play in biological world as their excess or deficiency can cause different type of diseases in human being as well as biological species including plants and animals. Therefore, their detection at trace level becomes very important in term of biological. The current studies embody the fabrication, structural characterization and recognition behavior of a novel rhodamine B hydrazone formed when hydrazide of rhodamine B was condensed with 5-Allyl-3-methoxy salicylaldehyde (RBMA). RBMA was found to be responsive towards the very trace level of Cu2+ and Hg2+ among other tested cations so far. The sensing procedure is based on the classical opening of the spiroatom ring of rhodamine. The limit of detection (LOD) and binding constant is 5.35 ppm, 2.06 × 104 M-1 and 5.16 ppm, 1.26 × 104 M-1 for Cu2+ and Hg2+ ions respectively. The probable mechanism correlates the specific binding of RBMA with Cu2+ and Hg2+ ions. The 1:1 stoichiometry of RBMA with Cu2+ and Hg2+ ions have been supported by HRMS, FT-IR data, Job's plot, and binding constant data. Reversibility is well exhibited by RBMA by the involvement of CO32- ions via demetallation process. The real time application is well demonstrated by the use of paper strip test. The DFT study also carried out which agrees well with the experimental findings. The results displayed the novelty of this current work towards the trace level analysis of the Cu2+ and Hg2+ of the cations which are play the crucial role in industry.

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.

"Lighting up" fluorescence precise recognition of Al3+ with an effective fluorescence detection using a Bisphenol A-based sensor

Although aluminum is a ubiquitous metal in the ecosystem and has numerous critical roles in both the medicinal and biological fields, human daily life is seriously threatened by its assorted harmful influences. By this virtue, tracking the amount of aluminum byrapid sensitive and selective recognition methodologies is of great importance. Based on this, a novel fluorescent chemosensor 4,4'-(propane-2,2-diyl)bis(2-(((-2-hydroxybenzylidene) hydrazineylidene)-methyl)phenol) (BFASA) capable of recognizing Al³⁺ in a medium was constructed via an easy Schiff-base reaction between bisphenol A-containing molecule and the salicylaldehyde. The metal-binding studies of BFASA indicated a drastically enhanced emission with color alteration from colorless to green establishing the utility of BFASA against monitoring of Al³⁺ and only Cu²⁺/Al³⁺ significantly enhanced the absorbance intensity of the probe solution at 433 and 406, respectively. Its ability to selectively sense Al³⁺ demonstrated "switch-on" fluorescence responses for Al³⁺ with a low detection limit (LOD) of 0.56 μM and good selectivity, and pH adaptation range (5-8). The stoichiometric ratio of BFASA against the Al³⁺ was verified by the Job's plot and TOF-MS analysis and determined as 1:2. To make the recognition process inexpensively, viable and straightforward, Smartphone application of BFASA was effectively applied to Al³⁺ sensing, which could benefit the on-site Al³⁺ recognition. In the fluorescence bio-imaging aspect, the BFASA could effectively monitor Al³⁺ in living cells.

Modulation of aluminum sensing properties of a sulphone group containing chemosensor and its biological applications

A chemosensor with two binding pockets facilitates binding of one metal ion in either of the pockets providing a better chance for the interaction and hence recognition of the cation. We report here a chemosensor, namely 2,2'-(1E)-(5,5'-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H₄L-naph), for selective sensing of Al³⁺ in DMF- HEPES buffer (1:4, v/v, pH 7.4). It shows almost 100-fold fluorescence enhancement at 532 nm (λ_ex = 482 nm) in the presence of Al³⁺. Its quantum yield and excited state lifetime enhances significantly with the cations. H₄L-naph forms a 1:2 complex with Al³⁺ with an association constant value of 2.18 × 10⁴ M^-2. Fluorescence enhancement may be attributed to CHEFF mechanism and restriction of >CN isomerization. Effect of the presence of naphthyl rings instead phenyl ring of a previously reported probe has resulted shifting of excitation/emission peak towards longer wavelength. The probe has been applied to image Al³⁺ in L6 cells with no significant cytotoxicity.

Simple colorimetric copper(II) sensor - Spectral characterization and possible applications

New o-hydroxyazocompound L bearing pyrrole residue was obtained in the simple synthetic protocol. The structure of L was confirmed and analyzed by X-ray diffraction. It was found that new chemosensor can be successfully used as copper(II) selective spectrophotometric regent in solution and can be also applied for the preparation of sensing materials generating selective color signal upon interaction with copper(II). Selective colorimetric response towards copper(II) is manifested by a distinct color change from yellow to pink. Proposed systems were effectively used for copper(II) determination at concentration level 10^-8 M in model and real samples of water.

Macrocyclic chemosensors with anthraquinone signaling unit built into ionophore. Experimental and computational studies (part I) - synthesis and effect of proton binding on spectrophotometric and electrochemical properties

Two macrocyclic chemosensors with anthraquinone signaling unit incorporated into ionophore system (via positions 1 and 8) have been synthesized and subsequently their physicochemical properties became the subject of our extensive research. First ligand, labeled in the paper as AQ-Ncrown is characterized by a cyclic structure of a crown ether, while second one AQ-Ncrypt includes an additional ethoxy bridge, which ensures the bicyclic character of a cryptand. The studied macrocycles possess both oxygen and nitrogen heteroatoms in the ionophore cavity. Dualistic (chromophore and electrophore) signaling nature of described compounds, makes them potentially attractive molecular recognition systems. The aim of our research was to synthesize and analyze the spectroscopic, acid-base and redox properties of aforesaid macrocycles. Furthermore, we have combined experimental approach together with theoretical investigations. The equilibrium structures of AQ-Ncrown and AQ-Ncrypt were determined with the use of DFT calculations. The sensitivity of studied macrocycles towards interactions with protons was scrutinized. The complete pH-spectrophotometric characteristic of studied ligands together with their protolytic forms and corresponding pK_a values were determined. The influence of medium (aprotic and protic solvent) on spectral effects was described. Furthermore, the molecular electrostatic potential maps for ligands and differential electron densities for their mono and dianions were calculated. The redox reactions was investigated at different pHs by cyclic voltammetry. Electrochemical results have presented intriguing phenomenon: the specific stabilization of the reduced form of the protonated molecules. The calculations have revealed that this is a consequence of barrierless intramolecular proton transfer (from the macrocycle cavity onto the anthraquinone moiety) that might occur during the reduction process in acidic medium.

Perylene diimide-based sensors for multiple analyte sensing (Fe2+/H2S/ dopamine and Hg2+/Fe2+): cell imaging and INH, XOR, and encoder logic

In this report, we present our results on the recognition of multiple analytes using trisubstituted PDI-based chemosensors DNP and DNB in 50% HEPES buffered-CH₃CN solution. Upon the addition of Hg²⁺, DNB showed a decrease and increase in absorbance intensity at 560 and 590 nm, respectively, with a detection limit of 7.17 μM and bleaching of the violet color (de-butynoxy). Similarly, the addition of Fe²⁺ or H₂S to the solution of DNP or DNB resulted in ratiometric changes (A_688nm/A_560nm) with respective detection limits of 185 nM and 27.6 nM for Fe²⁺, respectively, and a color change from violet to green. However, the addition of >37 μM H₂S caused a decrease in absorbance at 688 nm with a concomitant blue shift to 634 nm. Upon the addition of dopamine, the DNP + Fe²⁺ assay showed ratiometric (A_560nm/A_688nm) changes within 10 s along with a color change from green to violet. Moreover, DNP has been successfully used for the exogenous detection of Fe²⁺ in A549 cells. Further, the multiple outputs observed with DNP in the presence of H₂S have been used to construct NOR, XOR, INH and 4-to-2 encoder logic gates and circuits.

Fluorescence Properties of ZnOQDs-GO-g-C3N4 Nanocomposites

In this paper, the fluorescence properties of ZnOQD-GO-g-C₃N₄ composite materials (ZCGQDs) were studied. Firstly, the addition of a silane coupling agent (APTES) in the synthesis process was explored, and it was found that the addition of 0.04 g·mL^-1 APTES had the largest relative fluorescence intensity and the highest quenching efficiency. The selectivity of ZCGQDs for metal ions was also investigated, and it was found that ZCGQDs showed good selectivity for Cu²⁺. ZCGQDs were optimally mixed with Cu²⁺ for 15 min. ZCGQDs also had good anti-interference capability toward Cu²⁺. There was a linear relationship between the concentration of Cu²⁺ and the fluorescence intensity of ZCGQDs in the range of 1~100 µM. The regression equation was found to be F₀/F = 0.9687 + 0.12343C. The detection limit of Cu²⁺ was about 1.74 μM. The quenching mechanism was also analyzed.

A rhodamine based chemodosimeter for the detection of Group 13 metal ions

A new rhodamine derivative, HL-CIN, derived from a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and trans-cinnamaldehyde, is reported here for the colorimetric and fluorogenic sensing of Group 13 trivalent cations, namely Al³⁺, Ga³⁺, In³⁺ and Tl³⁺. The absorption intensity of the probe increases significantly at 530 nm whereas the fluorescence intensity enhances massively at 558 nm upon interaction with these metal ions. Other relevant metal ions could not impart any noticeable color change or fluorescence enhancement. The quantum yield or fluorescence life time of HL-CIN increases considerably in the presence of these Group 13 metal ions. Different spectral studies such as ESI-mass, FT-IR, ¹H and ¹³C NMR spectra, establish that HL-CIN undergoes hydrolysis in the presence of the trivalent cations and a rhodamine species in its ring opened form (i.e. N-(2-aminoethyl)-2-((6Z)-3-(ethylamino)-6-(ethylimino)-2,7-dimethyl-6H-xanthen-9-yl)benzamide, (L2)) along with cinnamaldehyde are produced. The rhodamine species in its ring opened form (L2) is responsible for the color change and strong increment in the absorbance and fluorescence of HL-CIN with Group 13 cations. Interaction between L1 and these metal ions could not produce the same outcome. It has been used in test paper strips and to detect these cations in real samples.

Zinc ion detection using a benzothiazole-based highly selective fluorescence "turn-on" chemosensor and its real-time application

A new photochromic fluorescence chemosensor was devised and effectively synthesized using benzothiazole and imidazopyridine derivatives. A "turn-on" fluorescence sensor BIPP for Zn²⁺ detection was developed and has a quick response, excellent sensitivity, and remarkable selectivity over other metal ions. When Zn²⁺ was added to the BIPP solution, a new strong fluorescence emission peak at 542 nm formed with a considerable increase in intensity. The fluorescence color of the BIPP solution changed from blue to bright green. The binding ratio 8 : 2 was found between BIPP and Zn²⁺ by the results of Job's plot, HRMS and ¹H-NMR. The detection limit (LOD) of BIPP towards Zn²⁺ was determined to be 2.36 × 10^-8, which is remarkably low. The ability to detect Zn²⁺ in real water samples demonstrates that BIPP may also be used in environmental systems. Additionally, BIPP can be used to measure Zn²⁺ levels in living cells.

Synthesis and Characterization of a Carbazole-Based Schiff Base Capable of Detection of Al3+ in Organic/Aqueous Media

A new fluorescence probe (L) selectively detecting Al³⁺ ions was synthesized via the condensation reaction, and characterized using UV-Vis, FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The limit of detection for Al³⁺ ions of this synthesized probe was found to be 9.29 × 10^-7 M, while the Ka constant value was determined to be 1.64 × 10⁴ M^-1. The stoichiometric binding ratio of L-Al³⁺ was found to be 2:1 using the Job's plot method, and this ratio was also confirmed by ¹H-NMR titration and mass spectrometry. The recyclability of the chemosensor was found by the fluorescence method through the addition of EDTA to the L-Al³⁺ solution. The obtained data showed that the carbazole-based Schiff base acted as an ideal chemosensor for Al³⁺. Carbazole-based Schiff base as a fluorescent sensor for detection of Al³⁺ was synthesized and characterized. The association constant (K_a) was calculated to be 1.64 × 10⁴ M^-1 and the limit of detection (LOD) value was determined to be 9.29 × 10^-7 M. It was determined that th Schiff base was bound to Al³⁺ ions in 2:1 stoichiometric ratio. In the presence of other competitive metal cations, the selectivity of sensor L to Al³⁺ was not significantly affected.

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

Green-synthesized, pH-stable and biocompatible carbon nanosensor for Fe3+: An experimental and computational study

Brightly fluorescent Carbon Dots (CDs) were synthesized by green hydrothermal method using commonly available biomass (Aloe vera) as carbon precursor. Their physiochemical and optical characterization was done by standard microscopic and spectroscopic techniques. Photophysical features of their aqueous dispersion were investigated in detail. The influence of wide pH range (2–12), high ionic load (2M) and temperature on their photoluminescence behavior was investigated. Their in-vitro cytotoxicity examination was conducted on Human Cervical Cancer Cells (HeLa) using MTT assay. Testing of their ion-recognition property for common metal ions was done in aqueous medium. These CDs exhibited preferential interaction with Fe³⁺ over other tested metal ions, without any functionalization. Interaction between CDs and Fe³⁺ was analyzed in the light of Density Functional Theory (DFT). The work demonstrates that these CDs are acting as nanoprobe for Fe³⁺ and sensing it at ultra-trace level (5 nM).

A visible-light-gated donor–acceptor Stenhouse adduct chemosensor: synthesis, photochromism and naked-eye colorimetric/fluorometric sensing of Al3+ and Zn2+

A visible-light-gated donor–acceptor Stenhouse adduct chemosensor is designed for the colorimetric/fluorometric sensing of Al3+ and Zn2+.

An α-naphtholphthalein-derived colorimetric fluorescent chemoprobe for the portable and visualized monitoring of Hg2+ by the hydrolysis mechanism

An ɑ-naphtholphthalein-derived colorimetric fluorescent chemoprobe was elaborately designed for the portable and visual monitoring of Hg2+ in environmental and biological samples.

A new diformyl phenol based chemosensor selectively detects Zn2+ and Co2+ in the nanomolar range in 100% aqueous medium and HCT live cells

A new diformyl phenol based chemosensor that can sense Zn2+ and Co2+ in the nanomolar range in 100% aqueous solution and in HCT cells was explored.

Discriminatory behavior of a rhodamine 6G decorated mesoporous silica based multiple cation sensor towards Cu2+ and Hg2+vis-à-vis Al3+, Cr3+ and Fe3+: selective removal of Cu2+ and Hg2+ from aqueous media

Selective identification of metal ions as well as their removal is possible when a sensing unit is anchored to a solid support. In this paper, functionalized mesoporous silica with a pendant rhodamine 6G moiety (R6FMS) has been obtained by successive grafting of an aldehyde derivative of bisphenol A followed by rhodamine 6G over a 3-aminopropyl anchored mesoporous silica framework. The materials have been characterized by powder X-ray diffraction, nitrogen sorption and electron microscopy studies, FT-IR and solid state MAS NMR spectral studies, and thermal analysis. In ethanol, the colorless silica material gives pink coloration in the presence of Al3+, Cr3+, Fe3+ and Cu2+ which is also clearly evident from the generation of an absorption peak at 525 nm. Upon excitation at 500 nm, the fluorescence intensity of the probe increases by 36-, 17-, 40- and 89-fold in the presence of Al3+, Cr3+, Fe3+ and Cu2+ ions, respectively. This suggests that R6FMS is a colorimetric and fluorescent chemosensor for these cations in ethanol. However, when the solvent is changed from ethanol to water, it becomes a selective chemosensor only for Cu2+ and Hg2+, by the generation of a pink color and strong fluorescence at ca. 550 nm, thereby discriminating the trivalent cations. Cations induce the opening of the spirolactam ring resulting in pink coloration and strong fluorescence. The quantum yield and lifetime of the probe have been increased considerably in the presence of these cations in ethanol as well as in aqueous media. The detection limit values for these cations range from 10-6 to 10-8 M. R6FMS has been used to remove Hg2+ and Cu2+ from their aqueous solution with a maximum adsorption capacity of 35 mg g-1 and 148 mg g-1 for Cu2+ and Hg2+, respectively.

Synthesis and Characterization of a Mg2+-Selective Probe Based on Benzoyl Hydrazine Derivative and Its Application in Cell Imaging

A simple benzoyl hydrazine derivative P was successfully synthesized and characterized as Mg2+-selective fluorescent probe. The binding of P with Mg2+ caused an obvious fluorescence enhancement at 482 nm. The fluorescent, UV-vis spectra, 1H-NMR, and IR spectra confirmed the formation of P-Mg2+ complex, and the formation of a 1:1 stoichiometry complex was proved by Job's plot and mass spectrometry. The recognition mechanism of P to Mg2+ was owing to the photoinduced electron transfer effect (PET). The fluorescent response was linear in the range of 0.9-4.0 µM with the detection limit of 0.3 µM Mg2+ in water-ethanol solution (1:9, v:v, pH10.0, 20 mM HEPES). In addition, the results of cell imaging of Mg2+ in Hl-7701 cells was satisfying.