A simple, reversible, colorimetric and water-soluble fluorescent chemosensor for the naked-eye detection of Cu2+ in ~100% aqueous media and application to real samples

Highly fluorescent new Schiff base chemosensors for the selective detection of Cu(II) and their application in bioimaging technique

A new symmetrical and a new unsymmetrical Schiff bases are synthesized by condensing 1-(2,4-dihydroxyphenyl)ethanone with, Naphthalen-1-amine and Naphthalen-1,8-diamine under solvent free condition and characterized by IR, UV-visible, 1H NMR, 13C NMR and mass spectral studies. Cation recognizing potentiality of both the Schiff bases is explored-of the Schiff base 4-(1-(naphthalen-1-ylimino)ethyl)benzene-1,3-diol (NEBD) in aqueous methanolic medium and of Schiff base 4,4'-((naphthalene-1,8-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (NDBD) is scrutinized in aqueous ACN medium through dual modes namely absorption and emission methods. Both the Schiff base sensors are found to detect Cu(II) ion selectively. The detection occurs in an off-on mode (increase of emission intensity of the Schiff base in the presence of Cu(II) ion) and on-off mode (decrease of emission intensity of the Schiff base in the presence of Cu(II) ion) for the Schiff bases NEBD and NDBD respectively. For the Schiff base NEBD LOD for Cu(II) ion is 1.528 × 10-6 M and for NDBD it is 2.871 × 10-7 M. The sensing property is applied in bioimaging technique for the detection of human cancer cells HeLa. Both the Schiff bases are screened for their antimicrobial activities. Schiff base NEBD is found to be more potential than the standard drug amphotericin B towards Aspergillus niger. Regarding Schiff base NDBD, it is as potential as the standard drug towards all the organisms studied.

Luminous Insights: Exploring Organic Fluorescent "Turn-On" Chemosensors for Metal-Ion (Cu+2, Al+3, Zn+2, Fe+3) Detection

There are several metal ions that are vital for the growth of the environmental field as well as for the biological field but only up to the maximum limit. If they are present in excess, it could be hazardous for the human health. With the growing technology, a series of various detection techniques are employed in order to recognize those metal ions, some of them include voltammetry, electrochemical methods, inductively couples, etc. However, these techniques are expensive, time consuming, requires large storage, advanced instrumentation, and a skilled person to operate. So, here comes the need of a sensor and it is defined as a miniature device which detects the substance of interest by giving response in the form of energy change. So, from past few decades, many sensors have been formulated for detecting metal ions with some basic characteristics like selectivity, specificity, sensitivity, high accuracy, lower detection limit, and response time. Detecting various metal ions by employing chemosensors involves different techniques such as fluorescence, phosphorescence, chemiluminescence, electrochemical, and colorimetry. The fluorescence technique has certain advantages over the other techniques. This review mainly focuses on the chemosensors that show a signal in the form of fluorescence to detect Al+3, Zn+2, Cu+2, and Fe+3 ions.

Isatin-Schiff base functionalized graphene oxide as a highly selective turn-on fluorescent probe for the detection of Pd(II) via photoinduced electron transfer pathway

We investigated the use of isatin-Schiff base functionalized graphene oxide (ISBGO) as a selective fluorescent chemosensor for the detection of palladium ions. Selectivity tests indicated that over 23 metal ions tested, ISBGO (λex = 340 nm, λem = 504 nm) showed the highest affinity for Pd(II), displaying a 10.1-fold enhancement. Also, interference tests proved that in the presence of both Pd(II) and other metal ions, there was still high fluorescence intensity and no considerable quenching occurred. According to DFT and TD-DFT calculations, photo-induced electron transfer (PET) is responsible for the turn-on response produced by the chemosensor. Coordination of Pd(II) with ISBGO in fact blocks PET from imine nitrogen of 3-iminoindolin-2-one moiety to the benzene ring, which in turn leads to a turn-on response. In addition, Job's plot analysis and Benesi-Hildebrand approach suggest that ISBGO preferably forms a 1:1 complex with Pd(II) with an association constant of 1.020 × 105 M-1. Moreover, FT-IR spectroscopy and DFT study showed that amide oxygen and imine nitrogen of 3-iminoindolin-2-one moiety acted as binding sites of ISBGO. High sensitivity, fast response, great degree of sensitivity, short life time, low detection limit of 32 nM combined with high association constant (Kf) of 1.020 × 105 M-1 and increased fluorescence quantum yield (Φf) of roughly 1.5-fold in the presence of Pd (II), highlight the role of ISBGO as an excellent probe for sensing Pd(II) in aqueous solution.

Anticounterfeiting Feature of a Writable and Self-Erasable Ni(II)-Metallogel Pad via Fluorescent "Turn-On" Detection of Cyanide

A Schiff base 5-(2-hydroxy-3-methoxybenzylidieneamino)-1-H-imidazole-4-carboxamide (HL) comprising multibinding sites has been synthesized with the aim of fabricating a supramolecular gel. The gelator HL was characterized by FT-IR, 1H & 13C NMR, and ESI-MS techniques and also formed a [Ni(L)2] complex. The gelation property of HL was investigated with various metal ions, wherein Ni(II) selectively forms a mechanically and thermally stable supramolecular metallogel (MG) in the presence of a triethylamine base in DMF-MeOH media. Characterization of MG was accomplished with different spectro-analytical techniques such as FT-IR, ESI-MS, powder-XRD, SEM, rheological investigations, UV/vis, and fluorescence. The gelator HL displays moderate emission upon addition of Ni2+ and gives "turn-off" fluorescence output by forming the complex [Ni(L)2] (MG) due to the chelation-enhanced quenching of fluorescence (CHEQ). Job plot and ESI-MS data suggested a 2:1 stoichiometry between HL and Ni(II) in MG. Further, MG exhibited highly selective and ultrasensitive "turn-on" fluorescence signaling with CN- in the background presence of several cations and anions. The limit of detection (LoD) of MG was determined to be 6.9 × 10-9 M for CN- using the fluorescence technique. Notably, MG behaves as a fluorescent writable pad material explicitly with CN- under 365 nm UV light but not under ordinary light and the fluorescent text is self-erased after 15 min. Hence, MG can be used as a metallogel pad in the presence of CN- to communicate secret messages. Overall, the present work explores the fabrication of a thermo- and mechanostable Ni(II)-metallogel (MG), which selectively and ultrasensitively detects CN- both in the solution phase and in the gel form, wherein MG behaves as a writable and self-erasable pad with anticounterfeiting features for practical applications.

Viscosity-sensitive and AIE-active bimodal fluorescent probe for the selective detection of OCl- and Cu2+: a dual sensing approach via DFT and biological studies using green gram seeds

A novel dual-mode viscosity-sensitive and AIE-active fluorescent chemosensor based on the naphthalene coupled pyrene (NCP) moiety was designed and synthesized for the selective detection of OCl- and Cu2+. In non-viscous media, NCP exhibited weak fluorescence; however, with an increase in viscosity using various proportions of glycerol, the fluorescence intensity was enhanced to 461 nm with a 6-fold increase in fluorescence quantum yields, which could be utilized for the quantitative determination of viscosity. Interestingly, NCP exhibited novel AIE characteristics in terms of size and growth in H2O-CH3CN mixtures with high water contents and different volume percentage of water, which was investigated using fluorescence, DLS study and SEM analysis. Interestingly, this probe can also be effectively employed as a dual-mode fluorescent probe for light up fluorescent detection of OCl- and Cu2+ at different emission wavelengths of 439 nm and 457 nm via chemodosimetric and chelation pathways, respectively. The fast-sensing ability of NCP towards OCl- was shown by a low detection limit of 0.546 μM and the binding affinity of NCP with Cu2+ was proved by a low detection limit of 3.97 μM and a high binding constant of 1.66 × 103 M-1. The sensing mechanism of NCP towards OCl- and Cu2+ was verified by UV-vis spectroscopy, fluorescence analysis, 1H-NMR analysis, mass spectroscopy, DFT study and Job plot analysis. For practical applications, the binding of NCP with OCl- and Cu2+ was determined using a dipstick method and a cell imaging study in a physiological medium using green gram seeds.

Development of a method for the detection of Cu2+ in the environment and live cells using a synthesized spider web-like fluorescent probe

A macrocyclic Schiff base fluorescent probe [1,2-phenylenediamine-2,6-pyridinedialdehyde macrocyclic Schiff base] (BP-MSB) based on 2,6-pyridinedialdehyde was synthesized for use in the detection of Cu²⁺ in environmental water samples and live cells imaging by the method of specific recognition. The free fluorescent probe BP-MSB shows strong fluorescence in DMSO/H₂O. The probe shows high sensitivity and selectivity for Cu²⁺ through "turn-off" fluorescence response in DMSO/H₂O buffer solution (pH = 6.5), with a detection limit of 0.83 nM, which is far below the maximum allowable drinking water content of 20.0 μM specified by the US Environmental Protection Agency. The BP-MSB fluorescence quenching method was used for the determination of Cu²⁺ in Xiang Jiang water samples and tap-water. Furthermore, addition of the same number of moles of ethylene diamine tetraacetic acid (EDTA) can realize the reversible recognition of Cu²⁺ by the probe BP-MSB. Most importantly, the fluorescence imaging of live cells after incubation of BP-MSB with GM12878 cells showed good imaging performance, confirming the sensitivity of the fluorescent probe BP-MSB in vivo. The probe was also used to form an analog logic gate. This probe has the advantages of good stability, simple operation and high selectivity, which provides a broad prospect for environmental monitoring, intracellular detection and practical application of POCT.

Using a Modified Polyamidoamine Fluorescent Dendrimer for Capturing Environment Polluting Metal Ions Zn2+, Cd2+, and Hg2+: Synthesis and Characterizations

One of the most pressing global concerns is how to provide a clean environment for future generations given the exacerbation of urban, agricultural, industrial, and economic activities due to the escalating size of the global population. A polyamidoamine (PAMAM) dendrimer peripherally modified with 4-N,N′-dimethylethylenediamine-1,8-naphthalmide as a chromophore was synthesized and utilized to capture hazardous heavy metal ions. This modified fluorescent dendrimer (FCD) was complexed with Group 12 metal ions (Zn2+, Cd2+, and Hg2+) at a 2:1 (metal: FCD) ratio. Electronic absorption, fluorescence emission, Infra-red (IR), and nuclear magnetic resonance (1H NMR) spectroscopies, conductivity, CHN elemental, thermogravimetry, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses were used to characterize the resulting metal complexes. These assays revealed that the synthesized complexes were yellow-colored, thermally stable, nanoscale-sized, and composed of [M2FCD]·4Cl2. Considerable spectral shifts were observed in the emission and absorption spectra of the FCD molecule after binding the Zn2+ ions, which can be used to differentiate the Zn2+ complex from the other two complexes. This work provides basic data to facilitate the detection, quantification, and removal of environmentally hazardous heavy metal ions through complexation with a fluorescent dendrimer.

Four xanthene–fluorene based probes for the detection of Hg2+ ions and their application in strip tests and biological cells

Four new fluorescent probes based on the xanthene structure to detect mercury ions with different colors of fluorescence have been reported.

Novel edaravone-based azo dyes: efficient synthesis, characterization, antibacterial activity, DFT calculations and comprehensive investigation of the solvent effect on the absorption spectra

The present study deals with designing and synthesizing novel dyes using the drug combination of edaravone and azo compounds which can be used as an indicator for anions and cations. The desired product synthesis was accomplished via a two-step process involving diazotizing the aromatic amines followed by the resultant salts coupling with edaravone. The resulting dyes were obtained with high yields under mild conditions. The structures of the dyes were identified with UV-vis, FT-IR, ¹H NMR and ¹³C NMR spectra and CHN analysis. To investigate the solvatochromism effect, the interaction of different solvents with the selected dyes was evaluated using several parameters including the dielectric constant, refractive index, hydrogen bond donating ability, hydrogen bond accepting ability and dipolarity/polarizability scale. To achieve deep understanding about the stability and geometrical characteristics of the azo–hydrazo tautomers of the synthesized dyes and their UV-visible spectra prediction, some DFT calculations were also carried out on the synthesized dyes. The antibacterial activities of some synthesized compounds were also evaluated using the disk diffusion method. The results revealed different activity of the selected synthesized dyes for antibacterial tests against selected Gram positive and Gram negative bacteria.

The present study deals with designing and synthesizing novel dyes using the drug combination of edaravone and azo compounds which can be used as an indicator for anions and cations.

A dual-functional probe for sensing pH change and ratiometric detection of Cu2

A series of benzothiazole-based compounds were synthesized and characterized. Among them, probe Z showed significant dual-functional performance which was capable of sensing pH change and Cu²⁺. Probe Z displayed fluorescent turn-on under alkaline conditions due to deprotonation of the hydroxyl group along with the obviously color change from colorless to mint green. Interestingly, it further achieved in ratiometric detection of Cu²⁺ through absorbance or fluorescence signals in strong alkaline condition. The limit of detection was calculated correspondingly as 0.37 μM and 1.35 μM, respectively. Especially, the combination of the XNOR and INHIBIT logic gates could be used to confirm that one medium was in neutrality or alkalinity condition. Moreover, Z was successfully used in real water samples and test paper for fast identification of Cu²⁺, respectively.

Bithiophene-based fluorescent sensor for highly sensitive and ultrarapid detection of Hg2+ in water, seafood, urine and live cells

Using Hg²⁺-promoted deprotection reaction, we have developed a new fluorescent turn-on sensor 2TS based on bithiophene fluorophore for Hg²⁺ detection. The sensing mechanism of 2TS towards Hg²⁺ was strongly proved by ¹H NMR, FTIR, HRMS, UV-vis and fluorescence spectra. Remarkly, 2TS towards Hg²⁺ in 100% aqueous solution shows high sensitivity with a low detection limit of 19 nM, superior selectivity and ultra-rapid response of 20 s during a wide sensing pH range from 4 to 10. Taking advantage of the excellent properties, the low-cost sensor 2TS-based filter paper/TLC test strips were fabricated for visual, immediate and quantitative detection of Hg²⁺ in water, proving its applicability towards sensitive in-situ and on-site detection. Meanwhile, 2TS showed high analytical performance for Hg²⁺ detection in water, seafood as well as human urine samples. Moreover, thanks to the good water solubility, negligible cytotoxicity, good biocompatibility and cell-membrane permeability, 2TS was further applied to effectively image Hg²⁺ in live cells. Furthermore, the developed sensor 2TS acted as good fluorescent display material for Hg²⁺ with obvious color change.

Highly Selective and Sensitive Colorimetric and Fluorimetric Sensor for Cu2

A newly designed fluorescent and colorimetric probe was synthesized and selective detection of cu²⁺ was successful in aqueous medium. The design strategy exhibited strongly fluorescent when binding with cu²⁺ based on the change in structure between spirocyclic to a non-cyclic form of rhodamine based dye. The UV visible spectra of probe (6GS2) exhibited three absorption peaks at 229, 309 and 530 nm respectively. The emission spectra of fluorescent probe exhibited wavelength at 550 nm. The peak intensity increases during the addition of copper ion to probe through n-π transition. The probe characterized by different techniques like NMR, absorption, emission, mass and test strips methods. Graphical Abstract .

A novel chromone based colorimetric sensor for highly selective detection of copper ions: Synthesis, optical properties and DFT calculations

In this work, a new chromone based colorimetric sensor (ChrCS) was developed for highly selective detection of copper ions in semi-aqueous media. Evaluation of color and spectral changes displayed by the developed sensor shows that the sensor can be applied to detect copper ions in the presence of other competing metal ions and anions. The developed sensor, which contains biologically active chromone ring, shows excellent selectivity at microlevel for Cu²⁺ with a color change from colorless to yellow. Job's plot based on spectroscopic data showed the complex formation between ChrCS and Cu²⁺ ions has the stoichiometric ratio of 1:1 (ChrCS-Cu²⁺ complex). In addition, the binding constant of the ChrCS to Cu²⁺ was determined using the Benesi-Hildebrand equation. Furthermore, the test papers of the developed ChrCS were successfully prepared and employed to detect different concentration Cu²⁺ (10^-3 M to 10^-7 M) in aqueous solution. Importantly, sensor ChrCS was applied to detect Cu²⁺ ions in real water samples. To better understand the optical character of ChrCS and the effect of metal ion titration, density functional theory (DFT) calculations at the B3LYP/6-31 + G(d,p) level were performed for ChrCS and its complex ChrCS-Cu²⁺. Furthermore, on the basis of the Job's plot analysis DFT calculations, and reversible nature of the developed sensor, the sensing mechanism was demonstrated.

Diaminomaleonitrile-based Fluorophores as Highly Selective Sensing Platform for Cu2

A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu²⁺ detection. It showed high selectivity and sensitivity towards Cu²⁺ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu²⁺ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu²⁺ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu²⁺-promoted hydrolysis reaction, which was confirmed by ¹H NMR, ¹³C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.

A novel boronic acid-based fluorescent sensor for selectively recognizing Fe3+ ion in real time

Boronic acid provides faster fluorescence response to Fe3+ compared to other reported sensors, which is critical for continuous dynamic detection. Herein, we reported a novel boronic acid-based sensor 4 that could recognize Fe3+ ion in real time. After 10 equiv. of Fe3+ ion (1 mM) was added, the fluorescence of sensor 4 was immediately quenched by 96%. While other ions, including Ba2+, Ca2+, Cr2+, Cd2+, Co2+, Cs2+, Cu2+, Fe2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+ or Zn2+, respectively, did not change the fluorescence significantly. Further tests indicated that the high selectively sensing Fe3+ ion benefits from the two boronic acid functionalities in the structure. Moreover, interference experiments showed this sensor has an excellent anti-interference ability. In addition, we performed binding activity test in rabbit plasma and other real samples for practical applications, obtaining similar results. And the thin layer loading sensor 4 was also successfully applied to recognize Fe3+ ion among various ions. Therefore, 4 may serve as a potential sensor for continuous monitoring and detecting Fe3+ ion in real time.

A new fluorescent-colorimetric chemosensor based on a Schiff base for detecting Cr3+, Cu2+, Fe3+ and Al3+ ions

A new Schiff base derivative fluorescence-colorimetric chemosensor 2-hydroxy-5-[(2-hydroxy-1-naphthyl)methylideneamino]benzoic acid (H₃L), has been designed and synthesized. H₃L displayed high selectivity and sensitivity for detecting Cr³⁺, Cu²⁺, Fe³⁺ and Al³⁺ ions in DMF/H₂O (v/v = 1/1) solution. When Cr³⁺, Cu²⁺ or Fe³⁺ ions were added, the solution of H₃L in DMF/H₂O exhibited different color changes. While with the addition of Fe³⁺ or Al³⁺ ions, the solution of H₃L in DMF/H₂O displayed different fluorescence responses. The bonding modes and bonding ratios of H₃L and metal ions were explored by the Job's plot, ¹H NMR titration, and electrospray ionization mass spectrometry (ESI-MS). The detection limits of H₃L with Cr³⁺, Cu²⁺, Fe³⁺and Al³⁺ ions were 3.37 × 10^-7 M, 4.65 × 10^-7 M, 3.58 × 10^-7 M and 4.89 × 10^-7 M, respectively.

A fast, highly selective and sensitive colorimetric and fluorescent sensor for Cu2+ and its application in real water and food samples

A new oligothiophene functionalized Schiff base sensor 3TDC has been successfully designed and synthesized. Sensor 3TDC exhibited "naked-eye" colorimetric and selective "on-off" fluorescence response toward Cu²⁺ with high selectivity and sensitivity within a wide pH range. The binding ratio of the sensor 3TDC and Cu²⁺ was determined to be 1:1 through fluorescence titration, Job's plot, ¹H NMR titration, FTIR and DFT studies. The detection limit is calculated to be as low as 2.81 × 10^-8 M, which is much lower than the allowable level of Cu²⁺ in drinking water set by U.S. Environmental Protection Agency (~20 μM) and the World Health Organization (~30 μM). The binding constant (K_a) of Cu²⁺ to sensor 3TDC was found to be 2.52 × 10⁴ M^-1. Sensor 3TDC for Cu²⁺ detection exhibited fast fluorescence response within 30 s and high anti-interference performance. Moreover, sensor 3TDC could be used as an effective fluorescent sensor for detecting Cu²⁺ ions in various real water and food samples with good accuracy and high precision.

Water-Soluble Sulfonate Schiff-Base Ligands as Fluorescent Detectors for Metal Ions in Drinking Water and Biological Systems

The ability to detect and selectively identify trace amounts of metal ions is of major importance for drinking water identification and biological studies. Herein, we report a series of water-soluble Schiff-base ligands capable of being fluorescent and colorimetric sensors for metal ions. Upon coordination of the metal ion to the ligand, quenching of fluorescence is observed, typically in a 1:1 ratio. The selectivity of metal ions Cu²⁺, Ni²⁺, Cr₃₊, and Co₂₊ is exhibited via fluorescence quenching accompanied by colorimetric changes, whereas that of Ag⁺ and Co²⁺ is observed through colorimetric changes alone. Additionally, pH sensing studies were performed for the potential use of these ligands in biological applications.

A viscochromic, mechanochromic, and unsymmetrical azine for selective detection of Al3+ and Cu2+ ions and its mitotracking studies

A mechanoresponsive, viscochromic, and unsymmetrical azine NDEA probes Al³⁺ and Cu²⁺ ions and also co-localizes in the mitochondria of C6 glioma cell lines.

Novel thiophene-based colorimetric and fluorescent turn-on sensor for highly sensitive and selective simultaneous detection of Al3+ and Zn2+ in water and food samples and its application in bioimaging

A novel bifunctional thiophene-based Schiff base TS as a colorimetric and fluorescent turn-on sensor for rapid and simultaneous detection of Al³⁺ and Zn²⁺ ions with high selectivity and sensitivity has been developed. The sensor shows remarkable fluorescence enhancement response for Al³⁺ and Zn²⁺ over a broad pH range with good anti-interference capability, which accompanied with an obvious color change easily detected by naked eyes. Sensor TS can detect as low as 3.7 × 10^-9 M for Al³⁺ and 3.0 × 10^-8 M for Zn²⁺, whereas respective association constants are 1.16 × 10⁴ M^-1 and 2.08 × 10⁴ M^-1. With the help of fluorescence titration and Job's plot, the stoichiometric ratio of TS with Al³⁺/Zn²⁺ was determined to be 1:1. The sensing mechanism of sensor TS with Al³⁺/Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) was analyzed in detail through ¹H NMR titration, FTIR, HRMS and DFT studies. Moreover, sensor TS has been applied to the detection of Al³⁺ and Zn²⁺ in real environmental water and food samples as well as the filter paper-based test strips. Furthermore, sensor TS has good cell-permeability and can be used to selectively sense intracellular Al³⁺ and Zn²⁺ by bioimaging.

A new high selective and sensitive turn-on fluorescent and ratiometric absorption chemosensor for Cu2+ based on benzimidazole in aqueous solution and its application in live cell

A new benzimidazole base turn-on fluorescent and ratiometric absorption chemosensor (L) bearing bidentate ligand for detection of Cu²⁺ was designed and synthesized. Fluorescence and UV-vis spectra studies demonstrated that L can detect Cu²⁺ ions in aqueous solution using fluorescence enhancement and ratiometric absorption sensing over a wide pH range. Both fluorescent and ratiometric absorption sensing of L for Cu²⁺ possessed high selectivity and sensitivity over other competitive metal ions and had low detection limit. Job's plot, mass spectra and DFT calculation indicated the sensing mechanism is the complex formation between L and Cu²⁺ with 1:2 stoichiometry. Fluorescence images of HepG2 in the absence and presence of Cu²⁺ displayed L had cell permeability and detection ability for Cu²⁺ in live cells.

Highly selective and sensitive determination of Cu2+ in drink and water samples based on a 1,8-diaminonaphthalene derived fluorescent sensor

A new simple and efficient fluorescent sensor L based on 1,8‑diaminonaphthalene Schiff-base for highly sensitive and selective determination of Cu²⁺ in drink and water has been developed. This Cu²⁺-selective detection over other tested metal ions displayed an obvious color change from blue to colorless easily detected by naked eye. The detection limit is determined to be as low as 13.2 nM and the response time is very fast within 30 s. The 1:1 binding mechanism was well confirmed by fluorescence measurements, IR analysis and DFT calculations. Importantly, this sensor L was employed for quick detection of Cu²⁺ in drink and environmental water samples with satisfactory results, providing a simple, rapid, reliable and feasible Cu²⁺-sensing method.

A peptide-based multifunctional fluorescent probe for Cu2+, Hg2+ and biothiols

A peptide-based fluorescent probe (Dansyl-His-Pro-Gly-Trp-NH₂, D-P4) bearing the dansyl fluorophore and tryptophan residue has been developed for the detection of Hg²⁺, Cu²⁺ and biothiols (–SH).