Colorimetric Fluorescent Sensor Research Articles

Selective fluoride ion sensing using novel quinoline chemosensor insights into kinetics and molecular logic gate functions

CQHC, a novel colorimetric fluorescent sensor, developed for the selective sensing of ions and well characterised, including SC-XRD. It demonstrated selective sensing for Co2+, Zn2+, Hg2+ and F– using absorbance titration at 420 nm, 446 nm and the binding constants estimated follows the order F– > Co2+ > Hg2+ > Zn2+. On light of this, molecular logic gate was built for CQHC’s selective multi-ion detection. However, fluorescence titration analysis revealed that CQHC is solely selective for F– ions. This conclusion was validated by 1H–NMR titration, clearly showed deprotonation occurs from N3–H. Fluorescent decay titration, kinetic investigations and computational studies all contributed to the selective sensing of F–. According to TD–DFT calculations, added fluoride ion interacts with N3–H proton and deprotonates to generate F–H in the excited state.

Anchor carbon dots inside NH2-MIL-88B via ship-in-a-bottle strategy for dual signal enhancement in colorimetric-fluorescent sensors

The increase in oxytetracycline (OTC) pollution has become a significant risk to ecological stability and human health because of excessive use. Therefore, developing a precise and reliable sensor for trace OTC detection is critical. In this work, a dual-mode sensor of colorimetric-fluorescent (CL-FL) with dual signal-on was developed for OTC detection. Firstly, a novel carbon dots encapsulating in cavities of MOFs composite (CDs@NH2-MIL-88B) was constructed by the ship-in-a-bottle approach, which enhanced peroxidase-like activity and fluorescent intensity. Further, combining with surface molecularly imprinted polymer (MIP), the dual-mode sensor was constructed to develop selectivity (CDs@NH2-MIL-88B@rMIP). Finally, the dual signal enhancement mechanism of the sensor comes from the interaction between OTC and identifying binding site involving strong hydrogen bonding and metal complexation from imprinted cavity and CDs@NH2-MIL-88B, respectively. The prepared sensor has a linear detection range of 1.00 × 10−9 - 1.00 × 10−5 M with the limit of detection (LOD) of 1.47 × 10−10 M for the CL mode and a detection range of 1.00 × 10−11 −1.00 × 10−7 M with the LOD of 1.84 × 10−12 M for the FL mode. Meanwhile, the sensor shows high sensitivity, accuracy and reliability in OTC detection. Overall, this work provides a promising CL-FL dual-mode sensing systems with signal-on in the detection of antibiotics and other hazardous pollutants.

Ratiometric fluorescence sensor based on deep learning for rapid and user-friendly detection of tetracycline antibiotics

The detection of tetracycline antibiotics (TCs) in food holds great significance in minimizing their absorption within the human body. Hence, this study aims to develop a rapid, convenient, real-time, and accurate detection method for detecting antibiotics in an authentic market setting. A colorimetric fluorescence sensor was devised for tetracycline detection utilizing PVA aerogels as the substrate. Its operating principle is based on the IFE effect and antenna effect. A detection device is designed to capture fluorescence images while deep learning was employed to aid in the detection process. The sensor exhibits high responsiveness with a mere 60-s requirement for detection and demonstrates substantial color changes(blue to red), achieving 99% accuracy within the range of 10–100 μM with the assistance of deep learning (Resnet18). Real sample simulation tests yielded recovery rates between 95% and 130%. Overall, the proposed strategy proved to be a simple, portable, reliable, and responsive solution for rapid real-time TCs detection in food samples.

A chromone-based colorimetric fluorescence sensor for selective detection of Cu2+ions, and its application for in-situ imaging

A chromone-based chemosensor Probe 1 was synthesized, and characterized by FTIR, UV-vis, 1H NMR, 13C NMR, and mass spectrometric studies. Probe 1 exhibited high selectivity and sensitivity for the Cu2+ions over various metal ions (Al3+, Cr3+, Co2+, Cd2+, Mn2+, Fe3+, Ni2+, Zn2+) that was investigated by colorimetric, absorption, and fluorescence titrations. The binding mode of Probe 1 with the Cu2+ ion was derived from Job's plot measurements, and it showed 2:1 stoichiometry. Probe 1 revealed an association constant value of 8.48 × 108 M−2 as determined by employing non-linear least square fit data. The detection limit of Probe 1 for the Cu2+ion was found to be 0.273 × 10−6 mol L−1. Furthermore, Probe 1 was implemented to detect Cu2+ ions in different tissues of the liver fluke, infected and non-infected bovine liver. DFT studies were performed to support the sensing mechanism. The results of these experiments demonstrate that Probe 1 could be a promising chemosensor for the instant naked eye and fluorescence detection of Cu2+ ions in different biological samples.

Determination of hypochlorite and bisulfite in water by bifunctional colorimetric sensor based on octupolar conjugated merocyanine dyes

In this study, we developed a bifunctional colorimetric fluorescent sensor based on three merocyanine structures for the detection of hypochlorite (ClO−) and bisulfite (HSO3−). In MeOH solution and under special conditions, this sensor shows high selectivity on fluorescence and UV–Vis spectra for the detection of ClO− and HSO3−, respectively. The sensor solution exhibits a strong red fluorescence emission at 638 nm, which was quenched and the blue color turned to purple pink rapidly upon the addition of ClO−. The mechanism of the detection of ClO− was confirmed via ESI-MS that the CC groups were induced to produce ethylene oxide and ethylene glycol derivatives by hypochlorite. The fluorescence emission at 638 nm in the concentration range of ClO− from 0 to 24 μM showed a good linear relationship (R2 = 0.9919), and the LOD of the sensor for ClO− was 0.42 μM. Interestingly, the sensor can also detect HSO3− in acid condition (pH less than 7.4). The blue shift of UV–Vis spectra of the solution of sensor were observed after addition of HSO3− and irradiation with visible light for about 4 min. The HSO3− concentration showed a good linear relationship (R2 = 0.9987) at 275 nm in the range of 12–42 μM, and thus its LOD was calculated to be 1.14 μM. Finally, the sensor has important value for detecting ClO− and HSO3− in tap water and lake water.

Near infrared and colorimetric fluorescence sensor for ultra-selective detection of Cu2+ level with applications in diverse water samples, brain tumor cell and flow injection analysis

A new colorimetric NIR fluorescence sensor based on heptamethine cyanine connected to 2-(4-(2-aminoethylsulfanyl)butylsulfanyl)ethanamine (Cy7C4) was successfully synthesized and characterized in this work. The sensor possessed high sensitivity to discriminate Cu2+ from other interfering ions with colorimetric change and NIR-fluorescence quenching. Cy7C4 formed a complex with Cu2+ in 1:1 ratio (Cy7C4:Cu2+) derived by Job’s plot analysis and the possible structure of Cy7C4:Cu2+ complex was predicted using molecular modeling. The detection limit was calculated to be 1.56 ppb, which was lower than the highest of Cu2+ level in safe drinking water defined by the U.S. EPA. In addition, Cy7C4 was capable to detect Cu2+ in diverse real water samples and brain tumor cells. Moreover, this sensor was adopted in flow injection analysis (FIA) for automated monitoring Cu2+ in dual channels of UV–Vis absorption and fluorescence signaling.

A high-performance colorimetric fluorescence sensor based on Michael addition reaction to detect HSO3− in real samples

Based on the Michael addition mechanism, a colorimetric fluorescence sensor (E)-2-(2-(9-benzyl-9H-carbazol-3-yl)vinyl)-3-methylbenzo[d]thiazol-3-ium iodide (BCVTI) that specifically recognizes HSO3− was constructed with benzothiazole iodide as the acceptor unit and benzylcarbazole as the donor unit. The sensor BCVTI exhibited orange-red fluorescence by itself due to the intramolecular charge transfer (ICT) effect. When HSO3− was added, BCVTI underwent nucleophilic addition, which destroyed the ICT effect and quenched the fluorescence. At the same time, the color of the BCVTI solution changed from orange-red to colorless, which can detect HSO3− by naked eyes. BCVTI had high selectivity, and its sensing mechanism had been studied by nuclear magnetism and mass spectrometry. In addition, BCVTI can complete the detection of HSO3− within 4 min, with a detection limit as low as 3.3 nM. Finally, the fluorescence sensor BCVTI was also applied to the trace detection of HSO3− in mineral water, wine, and white sugar with satisfactory results. All these results showed that BCVTI could be as a practical sensing platform for analysis of HSO3− in food samples.

Dual functions of pH-sensitive cation Zr-MOF for 5-Fu: large drug-loading capacity and high-sensitivity fluorescence detection.

Nanomaterials, as carriers of small molecular drugs, have been a focal point in recent years. In this work, a carbazolyl functionalized metal-organic framework, UiO-67-CDC, was successfully synthesized employing the ligand 9H-carbazole-2,7-dicarboxylic acid (9H-2,7-CDC). Postsynthetic approaches targeted the cationization and replacement of the Lewis base carbazole site with two methyl groups, resulting in the positively charged skeleton, which has proven to be a promising carrier for the anticancer drug 5-fluorouracil (5-Fu). The prepared cationic framework UiO-67-CDC-(CH3)2 showed moderately high surface area, hierarchical pore structures, and positive surface characteristics, which effectively and selectivity encapsulated the electron-rich 5-Fu molecules through electrostatic attraction, with a relatively high loading of up to 56.5% (wt%). The drug delivery in simulated blood environment (pH = 7.4) exhibited a more effective release, demonstrating a physiological pH-responsive sustained release. Significantly, the electron-deficient Zr-MOF itself, as a kind of high-sensitivity fluorescence detector, has a unique fluorescence "turn-on" effect with 5-Fu. These results pave the way towards designing surface-engineered MOF materials of interest in drug delivery and fluorescent sensing applications.

Organophilic Carbon Nanodots with Multi-Band Emission and their Application as a Ratiometric and Colorimetric Fluorescent Sensor

In this work, organophilic carbon nanodots (CNDs) were synthesized in acetone from organic extract of plant leaves. The as-prepared CNDs showed multi-band emission, and could be well dispersed in acetone and ethanol. The photoluminescence (PL) of the CNDs at 520[Formula: see text]nm was excitation-independent. The PL in the blue region could be tuned from 420 to 480[Formula: see text]nm through changing of the excitation wavelength. The multi-emissive CNDs were used as a ratiometric and colorimetric sensor for curcumin detection in ethanol. The blue PL of the CNDs at 420[Formula: see text]nm was quenched by curcumin through inner filter effect. Meanwhile, the green PL at 495[Formula: see text]nm and 535[Formula: see text]nm were enhanced with additional fluorescence of curcumin. The value of I[Formula: see text]/I[Formula: see text] and I[Formula: see text]/I[Formula: see text] both increased linearly with the curcumin concentration in the range of 0–15[Formula: see text][Formula: see text]M. The fluorescence color of the mixed solution changed from blue to yellow, and the detection limit reached 36.7[Formula: see text]nM. The sensitive and visual detection of the CNDs probe toward curcumin showed their high potential in practical applications.

Cu2+-selective NIR fluorescence sensor based on heptamethine cyanine in aqueous media and its application.

A near-infrared (NIR) colorimetric fluorescence sensor, Cy7C3, based on heptamethine cyanine dye was synthesized for determining the presence of Cu2+ ions. The sensor showed highly sensitive fluorescence quenching toward Cu2+ ions in acetonitrile/buffer solution at physiological pH with long emission wavelength of 718nm. Cy7C3 also provided an excellent selectivity to Cu2+ ions over other competing metal ions, with a low detection limit of 9ppb, which was lower than the maximum concentration of Cu2+ ions in drinking water of U.S. EPA. Cy7C3 could achieve naked-eye detection of Cu2+ ions via the color change from blue to colorless, which allowed determination of Cu2+ ions in hydroponic fertilizers. Additionally, the sensor was developed to detect Cu2+ ions in HepG2 cancer cells via fluorescence imaging.

Highly Stable Lanthanide Metal-Organic Framework as an Internal Calibrated Luminescent Sensor for Glutamic Acid, a Neuropathy Biomarker.

Glutamic acid (Glu) is the most abundant excitatory neurotransmitter in the central nervous system, and an elevated level of Glu may indicate some neuropathological diseases. Herein, three isomorphic microporous lanthanide metal-organic frameworks (MOFs) [(CH3)2NH2]2[Ln6(μ3-OH)8(BDC-OH)6(H2O)6]·(solv)x (ZJU-168; ZJU = Zhejiang University, H2BDC-OH = 2-hydroxyterephthalic acid, Ln = Eu, Tb, Gd) were designed for the detection of Glu. ZJU-168(Eu) and ZJU-168(Tb) suspensions simultaneously produce the characteristic emission bands of both lanthanide ions and ligands. When ZJU-168(Eu) and ZJU-168(Tb) suspensions exposed to Glu, the fluorescence intensity of ligands increases while the emission of lanthanide ions is almost unchanged. By utilizing the emission of ligands as the detected signal and the emission of lanthanide ions as the internal reference, an internal calibrated fluorescence sensor for Glu was obtained. There is a good linear relationship between fluorescence intensity ratio and Glu concentration in a wide range with the detection limit of 3.6 μM for ZJU-168(Tb) and 4.3 μM for ZJU-168(Eu). Major compounds present in blood plasma have no interference for the detection of Glu. Furthermore, a convenient analytical device based on a one-to-two logic gate was constructed for monitoring Glu. These establish ZJU-168(Tb) as a potential turn-on, ratiometric, and colorimetric fluorescent sensor for practical detection of Glu.

Colorimetric fluorescent paper strip with smartphone platform for quantitative detection of cadmium ions in real samples

Instrument-free, portable and direct read-out mini-devices have wider application prospects in various fields, especially for real-time/on-site detection in environmental science. Herein, a colorimetric fluorescent sensor for detecting cadmium ions (Cd2+) based on aggregation-induced emission (AIE) was established, fluorescent paper strips integrated with smartphone platform was further designed for the visualization, on-site and quantitative detection of Cd2+. The colorimetric fluorescent sensor was prepared by mixing orange emission glutathione-stabilized gold nanoclusters (AuNCs) with blue emission ethylenediamine functionalized graphene oxide (EDA-GO), and introducing copper ions (Cu2+) to quench the orange emission of AuNCs while the blue emission served as a background reference without color change. The Cd2+ can induce Cu2+-GSH-AuNCs to aggregation and emit orange fluorescence, causing the fluorescent color of the sensor changed from blue to red with the limit of detection (LOD) as low as 33.3 nM in solution. Moreover, fluorescent paper strips integrated with smartphone platform has a sensitive detection of Cd2+ with the LOD of 0.1 μM in rice samples. The method reported here might have great application prospects in real-time monitoring of foods safety and environmental protection.

An AIE+TICT activated colorimetric and ratiometric fluorescent sensor for portable, rapid, and selective detection of phosgene

Colorless and highly toxic phosgene has long been considered to be a great menace to human health and national security. Excellent AIE + TICT characteristic ratiometric and colorimetric fluorescent sensor TPE-CI was constructed with the combination of the TICT based 3-benzo[d]imidazole-chromen-2-imine unit and AIE based tetraphenylethene (TPE) unit. TPE-CI can detect phosgene not only in organic solvent through a change from the TICT process to the AIE process, but also in solid-state through a new change from the AIE + TICT process to the AIE process. TPE-CI exhibited convenient to use as a test strip, rapid response (less than 6 s in solvent and 2 min in air atmosphere), excellent selectivity and fair sensitivity for visual inspection of trace phosgene in the organic solvent and in the gas phase. The limit of detection (LOD) was calculated and derived as 0.36 μM in solvent and 0.27 ppm in the air atmosphere, which was far below the acute phosgene exposure level of human response. The satisfactory results indicate that this AIE + TICT strategy may offer valuable thinking to develop convenient solid-state optical sensors with dual ratiometric and colorimetric fluorescence response for gaseous phosgene identification.

Dual colorimetric and ratiometric fluorescent pH sensors for neutral and alkaline pH ranges

Dual colorimetric and ratiometric fluorescent pH sensors for neutral and alkaline pH ranges

Selective optical detection of HSO4− via hydrolysis of a simple Schiff Base

A very simple Schiff Base derived from 1-Naphthylamine and 4-(Trifluoromethy) benzaldehyde (L) was prepared as a selective colorimetric and turn-on fluorescent sensor for hydrogen sulfate. In the CH3CN:H2O (3:2, v/v) solvent system, L shows a highly selective colorimetric response to HSO4− ions by changing its color from yellow to colorless immediately. In addition, the weakly fluorescent receptor L shows a highly selective enhancement of fluorescence intensity at 425 nm for HSO4− upon excitation at 320 nm. The recognition process is proven to be hardly influenced by the other tested competitive anions. The sensing is suggested to involve a hydrolysis process promoted by HSO4− which has been further supported by UV–Vis, 1H NMR and HRMS spectroscopic studies. Applicability of L to detect HSO4− in tap water has been demonstrated. An easy-to-prepare test strip of L has also been made for the naked-eye detection of HSO4− in real samples.

A highly selective visible light excitable boron dipyrromethene probe for cysteine over homocysteine and glutathione based on a Michael addition reaction

A new reaction-based, colorimetric fluorescent sensor of BODIPY derivative (1) for cysteine (Cys) has been designd and synthesized. This probe shows highly selective detection of Cys over homocysteine (Hcy), glutathione (GSH) as well as other amino acids with a dramatic color change from wine red to fluorescence green because of the significant increase of the visible light excitable fluorescence intensity with the addition of Cys, due to their different reaction rates of the Michael addition reaction. The detection limit for Cys was 8.57×10−7M. Possible mechanism for sensing of Cys by BODIPY 1 was studied by NMR and HRMS. Probe 1 has been successfully applied to the biological imaging of Cys in living cells.

A novel colorimetric fluorescence sensor for Fe3+ based on quinoline Schiff base.

A novel fluorescent sensor bearing a quinoline and an anisidine moiety has been developed for highly selective detection of Fe3+ , which shows photo-induced electron transfer (PET) behavior induced by Fe3+ . Binding of Fe3+ to the sensor induced the electron of C=N group transfer from quinoline to iron, the result exhibits fluorescent enhancement. With the features of easy synthesis, simple structural skeleton and excellent sensing ability, the newly synthesized chemosensor also applied as a highly selective fluorescent probe in complex samples containing various competitive metal ions. The probe could fulfill various needs in biological and environmental fields.

Rhodamine Diaminomaleonitrile Conjugate as a Novel Colorimetric Fluorescent Sensor for Recognition of Cd2+ Ion.

Rhodamine diaminomaleonitrile linked probe (RD-1) shows highly sensitive colorimetric and selective turn-on fluorescent response to Cd2+ over other metal ions. The fluorescence intensity and absorbance of the probe RD-1 showed a good linearity, with very low detection limits of 18.5nm. The probe RD-1 was preliminarily applied to the determination of Cd2+ ion in water samples from river and tap water with satisfying results. The live cell image confocal microscopy, HeLa cell demonstrated that RD-1 had low cytotoxicity with good membrane permeable property is successfully applied to fluorescence microscopic imaging for the detection of Cd2+ ions.

A schiff-base receptor based naphthalimide derivative: Highly selective and colorimetric fluorescent turn-on sensor for Al3+

A new schiff-base receptor L based on naphthalimide had been investigated as a selective and sensitive chemosensor for Al3+ in CH3OH. Upon addition of Al3+, L showed a 39-fold enhancement at 508nm with colorimetric and fluorometric dual-signaling response which might be induced by the integration of ICT and CHEF. A 1:1 stoichiometry for the L-Al3+ complex was formed with an association constant of 1.62×104 M−1, and the limit of detection for Al3+ was determined as 7.4nM. In addition, the potential utility of L in sensing Al3+ was also examined in real water samples.

An RGH–MOF as a naked eye colorimetric fluorescent sensor for picric acid recognition

A novel RGH–MOF system was prepared for ratiometric sensing of picric acid. The color changes can be observed by the naked eye.