Highly chemoselective colorimetric/fluorometric dual-channel sensor with fast response and good reversibility for the selective and sensitive detection of Cu2+

A novel colorimetric and fluorometric dual-channel sensor DA with a favorable optical property and high specificity via a facile synthesis for Cu²⁺ was developed. DA showed a remarkably rapid response and high selectivity for Cu²⁺ over other metal ions with low detection limit of 15.1 nM. The sensing mechanism of DA for Cu²⁺ was based on the chelation-enhanced fluorescence quenching (CHEQ) mechanism, and further confirmed by optical measurements, FTIR, HRMS and DFT calculations. Importantly, DA for sensing Cu²⁺ possessed excellent sensing performances including colorimetric and fluorometric dual-mode detection, fast response, good reversibility, wide pH response range and strong anti-interference ability. Moreover, the DA could be not only applied to quantitatively detect Cu²⁺ in environmental water, food and drink samples, but also show highly colorimetric detection of Cu²⁺ on test strips and silica, indicating its possibility to be utilized as a convenient and low-cost sensor for environment and food monitoring.     

Coumarinyl aldehyde as a Michael acceptor type of colorimetric and fluorescent probe for cyanide in water

A simple aldehyde-functionalized coumarin (1) was utilized as a doubly activated Michael acceptor type of chemodosimeter for cyanide in water. The probe has shown a selective and sensitive response to the cyanide anion over other various anions through the Michael addition reaction of the cyanide to 1. When cyanide anions were added, the prominent color changes as well as fluorescence changes of 1 were observed so that millimolar concentrations of cyanides were detectable by the naked eye.     

Highly selective colorimetric sensor for cysteine and homocysteine based on azo derivatives

A simple colorimetric method for the determination of cysteine and homocysteine has been developed. The reaction of the azo dyes containing an aldehyde group with cysteine or homocysteine afforded very stable derivatives thiazolidines or thiazinanes under neutral pH conditions. The method is selective and sensitive for cysteine and homocysteine detection without the interference of other amino acids. Importantly, the recognition of Cys and Hcy could be observed by naked eyes.     

Highly selective and sensitive fluorescent chemosensor for Hg in aqueous solution

A new indole-based fluorescent chemosensor 1 was prepared and its metal ion sensing properties were investigated. It exhibits high sensitivity and selectivity toward Hg²⁺ among a series of metal ions in H₂O-EtOH (7:1, v/v). The association constant of the 1:1 complex formation for 1-Hg²⁺ was calculated to be 9.57 × 10³ M⁻¹, and the detection limit for Hg²⁺ was found to be 2.25 × 10⁻⁵ M. Computational results revealed that 1 and Hg²⁺ ion formed with a central tetrahedron-coordinated Hg²⁺.     

A high selective anion colorimetric sensor based on salicylaldehyde for fluoride in aqueous media

A new and simple salicylaldehyde-based sensor 1 designed for fluoride sensing has been investigated in DMSO and even in the 9/1 DMSO/H₂O (v/v) mixtures. The affinity constants of receptor 1 for anionic species in the 9/1 DMSO/H₂O (v/v) reveal that it is sensitive to F. Also, the color changes induced by anions can provide a way of detection by ‘naked-eye’. These result can be substantiated by the spectrum changes upon the addition of 25 equiv. anions to 1 in the 9/1 DMSO/H₂O solution. The further insights to the nature of interactions between the sensor 1 and F⁻ were investigated by ¹H NMR titration experiments in 9/1 DMSO-d₆/H₂O (v/v). In addition, the proposed binding mode between 1 and F⁻ was suggested.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

Two closely related iridium(III) complexes as colorimetric and fluorometric chemodosimeters for nitrite in aqueous solution operating along different modes of action

Two closely related dual-channel chemodosimeters for nitrite in buffered aqueous acetonitrile were developed using [(pq)(2)IrCl](2) (1) and [(ppy)(2)IrCl](2) (2). In the UV-vis channel, the addition of nitrite caused visibly distinct color changes with both probes as a result of sizable absorption intensity enhancements. In the photoluminescence channel, the probes behaved oppositely upon the addition of nitrite. The emission was increased with 1, while it was quenched with 2. NMR and X-ray studies indicated that structurally very different η(1)-nitrito-N and η(2)-nitrito-O,O' complexes were formed. Linear relationships for the quantification were obtained in both channels, allowing one to analyze for NO(2)(-) in a range from 5 × 10(-5) to 2 × 10(-2) M.     

Colorimetric and fluorometric dual-modal probes for cyanide detection based on the doubly activated Michael acceptor and their bioimaging applications

In this study, we synthesized CTB and CB probes based on doubly activated Michael acceptors to selectively detect cyanide (CN⁻) anions through a one-step condensation reaction of coumarinyl acrylaldehyde with the corresponding derivatives of malonyl urea (thiourea). Through the conjugated addition of CN⁻ to the β-site of the Michael acceptor, both probes displayed colorimetric and fluorometric dual-modal responses that were highly reactive and selective. CTB generates an active fluorescent response, whereas CB displays a ratiometric fluorescent response. The fluorescent signal of the probes reached its maximum given only 1 CN⁻ equivalent and the signal change was linearly proportional to CN⁻ concentrations ranging from 0 to 5 μM with the detection limits 18 and 23 nM, respectively. The reaction rate of the probes is highly dependent on the methylene acidity of malonyl urea derivatives. Thus, the response rate of CTB to CN⁻ is 1.2-fold faster than that of CB, and the response rate of CB to CN⁻ is 1.2-fold faster than that of the previously examined CM. We then verified the highly reactive nature of the β-site of the probes through density functional reactivity theory calculations. In addition, according to proof-of-concept experiments, these probes may be applied to analyze CN⁻ contaminated water and biomimetic samples. Finally, cell cytotoxicity and bioimaging studies revealed that the probes were cell-permeable and could be used to detect CN⁻ with low cytotoxicity.     

Ratiometric fluorescent and colorimetric sensors for Cu based on 4,5-disubstituted-1,8-naphthalimide and sensing cyanide via Cu displacement approach

Two 4,5-disubstituted-1,8-naphthalimide derivatives 1 and 2 were synthesized as ratiometric fluorescent and colorimetric sensors for Cu²⁺, respectively. In 100% aqueous solutions of 1, the presence of Cu²⁺ induces a strong and increasing fluorescent emission centered at 478 nm at the expense of the fluorescent emission of 1 centered at 534 nm. Compound 2 senses Cu²⁺ by means of a colorimetric (primrose yellow to pink) method with a thorough quench in emission attributed to the deprotonation of the secondary amine conjugated to the naphthalimide fluorophore. 1-Cu²⁺ and 2-Cu²⁺ sense cyanide in ratiometric way via colorimetric and fluorescent changes.     

A novel colorimetric chemosensor based on quinoline for the sequential detection of Fe3+ and PPi in aqueous solution

A novel quinoline-functionalized Schiff-base derivative PY was designed and synthesized. Sensor PY displayed highly selective and sensitive fluorescence enhancement and naked-eye color change to Fe³⁺ in the presence of other competing cations. The mechanisms have been supported by Job’s plot evaluation, FT-MS and theoretical calculations. The in situ generated PY-Fe³⁺ complex solution exhibited a high selectivity toward PPi via Fe³⁺ displacement approach. The detection limits of sensor PY to Fe³⁺ and PY-Fe³⁺ complex to PPi were estimated to be 4.24 × 10^?8 M and 8.18 × 10^?8 M, respectively. This successive recognition feature of sensor PY makes it has a potential utility for Fe³⁺ and PPi detection in aqueous solution. A B3LYP/6-31G(d,p) basis set was employed for optimization of PY and PY-Fe³⁺ complex.     

Novel,highly selective detection of Cr(III) in aqueous solution based on a gold nanoparticles colorimetric assay and its application for determining Cr(VI)

A simple, rapid, sensitive and field-portable colorimetric technique for the determination of Cr(III) in aqueous solution based on an aggregation-induced color transition of gold nanoparticles (AuNPs) has been developed. AuNPs were first functionalized with a dithiocarbamate-modified N-benzyl-4-(pyridin-4-ylmethyl)aniline ligand (BP-DTC). Chelation of Cr(III) by several of these ligands, bound to different nanoparticles, led to nanoparticle aggregation in solution. This gave rise to a color change from wine-red to blue that was discernible by the naked eye and an easily measurable alteration in the extinction spectrum of the particles. The method could be used to determine Cr(III) with a detection limit of 31 ppb. Furthermore, selective detection of trace Cr(III) in aqueous solution in the presence of 12 other transition metal ions has been achieved. Toward the goal of practical applications, the sensor has been further evaluated with a view to monitoring Cr(III) in nutritional supplements and the blood of diabetes patients and also applied in the indirect determination of Cr(VI) in waste water.     

Highly selective recognition of monosaccharide based on two-component system in aqueous solution

A highly selective switch for d-fructose was formed by water-soluble conjugated polymer PP-S-BINOL and tetraboronic acid functionalized benzyl viologen ToBV. The two-component system showed a high selectivity and sensitivity only for d-fructose in familiar d-monosaccharides. The high selectivity of the sensing system for d-fructose may be depended on stable pyranose ester form of d-fructose with ToBV. A desirable linear response of the sensing system to low concentrations of d-fructose (<10.0 mM) was observed with 0.9936 linear dependent coefficient at pH 7.4.     

A selective detection of fluoride ions in DMSO by fluorescent and colorimetry competition assays based on 4-bromo-2,6-bis-(hydroxymethyl)phenol

A novel and very simple colorimetric and fluorometric method for selectively sensing F^- was proposed based on 4-bromo-2,6- bis（hydroxymethyl）phenol（BBHMP）,which is a simple and available phenolic receptor the absence of any special chromophoric function and with over wide range of anions（Cl^-,Br^-,I^-,AcO^-,HSO₄^-,NO₃^- and BzO^-） in DMSO media.The colorimetric method is described for naked-eye detection of F^- in the presence of the BBHMP.The BBHMP was found to show selective and sensitive fluorescence quenching response toward fluoride over than Cl^-,Br^-,I^-,AcO^-,HSO₄^-,NO₃^- and BzO^-.     

A colorimetric and ratiometric fluorescent chemosensor based on furan-pyrene for selective and sensitive sensing Al3+

A new pyrene derivative BF bearing a furan group was synthesized via a one-step reaction as a colorimetric and ratiometric chemosensor for Al³⁺in ethanol-H₂O (9:1,v/v,pH 7.2,HEPES buffer) solution.This chemosensor could selectively recognize Al³⁺ in the presence of other competing ions.Low limit of detection (LOD) and high association constant revealed its superior sensitivity and binding affinity toward Al³⁺.Besides,the probe BF performed perfectly in a reversibility test using EDTA.The mechanism of the interaction has been confirmed by ¹H NMR titration.Importantly,chemosensor BF has also been utilized to detect Al³⁺ on test paper strips,which showed its potential for practical applications.     

A highly selective colorimetric probe based on 2,2′,2″-trisindolylmethene for cysteine/homocysteine

The interaction and colorimetric sensing properties of receptor 1, tris(3-methylindole-2-yl)methene as the perchlorate salt, with amino acids in aqueous MeCN at neutral pH were investigated using UV-vis spectroscopic techniques. Specifically, receptor 1 behaves as a colorimetric probe for selective and sensitive detection of cysteine (Cys)/homocysteine (Hcy) based on the nucleophilic addition reaction between the sulphydryl group of Cys/Hcy and the meso carbon-carbon double bond of receptor 1, leading to clear color change from violet to colorless. A more quantitative determination for Cys/Hcy was preliminary performed by flow injection analysis (FIA) coupled with spectrophotometry. The selective binding ability of receptor 1 toward Cys/Hcy has also been evaluated by electrochemical techniques.     

A novel fluorescent and chromogenic probe for cyanide detection in water based on the nucleophilic addition of cyanide to imine group

A fluorescent and colorimetric probe bearing salicylaldehyde hydrazone functionality has been prepared for cyanide sensing. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the imine group of the probe with a 1:1 binding stoichiometry, which could be confirmed by ¹H NMR and MS studies. The specific reaction results in a prominent fluorescence enhancement and a color change from colorless to yellow.     

Paper test strip for silver ions detection in drinking water samples based on combined fluorometric and colorimetric methods

In this study, a portable silver ion (Ag⁺) sensor was fabricated based on a dual signal output system using black phosphorus quantum dots (BPQDs) as probes. It is the first work for Ag⁺ detection using paper test strip based on BPQDs. The color change of BPQDs paper sensor for the determination of Ag⁺ was easily identified by naked eye. BPQDs were synthesized from bulk black phosphorus (BP) by mechanical exfoliation combined with a solvothermal method. BPQDs exhibited blue fluorescence with a quantum yield of 8.82 %. The fluorescence of BPQDs can be quenched by Ag⁺, and the absorbance of BPQDs is increased with increasing Ag⁺ concentration. The mechanism of the interaction between BPQDs and Ag⁺ involving fluorescence quenching and bonding was investigated by experimental and computational methods. The detection limit of Ag⁺ was 1.56 μg/mL and 0.19 μg/mL using fluorometry and colorimetry methods, respectively. A portable visual sensor based on paper test strip was constructed for Ag⁺ detection using the colorimetric approach. The strategy was employed to determine Ag⁺ successfully in drinking water samples. Therefore, the proposed portable Ag⁺ sensor can be potentially utilized for the lab-free analysis of drinking water and even dietary samples.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

Colorimetric detection of Ni2+ based on an anionic triphenylmethane dye and a cationic polyelectrolyte in aqueous solution

The combination of xylenol orange (XO) and poly(diallyldimethylammonium chloride) (PDADMAC) has been utilized as a colorimetric sensor for selective recognition of Ni²⁺ in aqueous solution. Upon addition of Ni²⁺, the chemosensor exhibited the significant color change from red to purple with a bathochromic shift, whereas these change was not induced by other metal ions. XO alone did not recognize Ni²⁺ colorimetrically, indicating that PDADMAC was required for detecting Ni²⁺. This study can provide the facile method for the construction of new chemosensors by a simple mixture of an anionic water-soluble dye and cationic polyelectrolyte.