Turn-on Fluorescent Sensor Research Articles

Real-time imaging of intracellular cysteine level fluctuations during Cu2+ or H2O2 induced redox imbalance using a turn-on fluorescence sensor

Redox balance is a necessary guarantee to maintain the normal physiological activities of organisms. Cysteine (Cys), a critical biological thiol, has the effect of maintaining redox balance in the body. The concentration of intracellular Cys is abnormal under redox imbalance, thereby resulting in multiple diseases. Additionally, studies have revealed that Cu2+ can stimulate the body to produce excess reactive oxygen species (ROS, similar to H2O2), and the generated ROS will consume reducing substances (such as Cys) in the body, leading to redox imbalance. Thus, finding a simple and effective method to monitor Cys under redox imbalance is pressing. Here, a turn on probe (DDNO) was proposed by connecting SBD-Cl to a red dye (HDM). The probe can specifically recognize Cys with rapid response (180 s) and low detection limit (0.61 μM) through substitution-rearrangement reaction between sulfhydryl and chlorine atom. Bioimaging experiments indicated that the probe has good biocompatibility and cell membrane permeability, which can be applied to monitor the fluctuation of Cys levels in live cells and zebrafish under the redox imbalance induced by Cu2+ or H2O2.

An ultralow concentration of Al-MOFs for turn-on fluorescence detection of aflatoxin B1 in tea samples

A turn-on fluorescent sensing platform based on an ultralow concentration of Al-metal organic frameworks for the detection of aflatoxin B1 has been developed for the first time. This fluorescence turn-on sensor exhibits the largest fluorescence enhancement (or quenching) constant value of 179404 M−1 among all luminescence-based chemical sensors reported till date. Moreover, the sensor afforded a rapid detection of aflatoxin B1, with a linear response in the concentration range of 0.05–9.61 μM and a low detection limit of 11.67 ppb. Additionally, the fabricated sensor showed good repeatability, reproducibility, stability, and selectivity. Most importantly, the practical application of this sensor has been demonstrated by detecting aflatoxin B1 in complex tea samples with low relative standard deviation (≤7.72%; n = 3) and satisfactory recoveries. In summary, the proposed method has great potential as a simple, sensitive and selective strategy for monitoring aflatoxin B1 in food samples.

Selective cyanide sensing using a Fe(III) complex of pyridoxal-beta alanine Schiff base

Fluorogenic chemosensors using pyridoxal derivatized ligands as fluorophore is a rapidly growing field of research. Here we report a new Fe(III) complex, [Fe(HBala-pydx)(Bala-pydx)] (H2Bala-pydx is the Schiff base of pyridoxal with beta-alanine), which can serve as a sensitive and selective turn-on fluorescent sensor for the detection of cyanide(CN−) in micromolar concentrations (L.O.D. is 1.134 µM), via the ligand displacement approach, in aqueous-acetonitrile medium. The Fe(III) complex is adequately characterized by analytical and spectroscopic methods along with X-ray crystal structure determination.

Colorimetric and selective turn-on fluorescent sensor for cyanide via aggregation-induced enhanced emission (AIEE)

Colorimetric and selective turn-on fluorescent sensor for cyanide via aggregation-induced enhanced emission (AIEE)

Turn-on and blue-shift fluorescence sensor toward L-histidine based on stable CdII metal-organic framework with tetranuclear cluster units.

A novel CdII-based two-fold interpenetrated metal-organic framework (MOF), namely {[Cd2(BTDB)2(4,4-bpy)]·DMF}n (JXUST-14), (H2BTDB = 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid and 4,4-bpy = 4,4-bipyridine), has been prepared and characterized. Single-crystal structure determination reveals that JXUST-14 has a tetranuclear cluster based 6-connected pcu topological network with Schlafli symbol {412·63}. When soaked in common organic solvents and aqueous solutions with diverse pH values of 2-12 for 48 h, JXUST-14 remains stable. JXUST-14 is a highly selective and sensitive luminescent sensor for L-histidine (His) with a detection limit of 11.1 ppm. JXUST-14 is the first CdII-based MOF for the detection of His via turn-on and fluorescence blue-shift effects. Experimental study and theoretical calculation suggest that the sensing process can be mainly attributed to a charge transfer and energy transfer mechanism. More interestingly, LED lamps of JXUST-14 and JXUST-14@His were successfully developed, which endowed efficient sensitivity for His detection and thus provide great potential for future applications.

Stable terbium metal-organic framework with turn-on and blue-shift fluorescence sensing for acidic amino acids (L-aspartate and L-glutamine) and cations (Al3+ and Ga3+).

A terbium-based metal-organic framework, namely {[Tb2(ADIP)(H2ADIP)(HCOOH)(H2O)2]·2DMF·2H2O}n (Tb-MOF, H4ADIP = 5,5'-(anthracene-9,10-diyl) diisophthalic acid), was synthesized and characterized. The single-crystal structure analysis shows that the Tb-MOF crystallizes in the C2/C space group in the monoclinic system and its asymmetric unit contains two TbIII ions, one ADIP4-, one H2ADIP2-, one coordinating formic acid and two coordination water molecules. Tb-MOF has a three-dimensional porous structure with a porosity of 41.5%. Tb-MOF is a highly selective and sensitive fluorescence turn-on and blue-shift sensor for L-aspartate (Asp), L-glutamine (Glu), Al3+ and Ga3+with detection limits of 0.25, 0.23, 0.069 and 0.079 μM, respectively. Experimental studies and theoretical calculations show that the sensing process is mainly attributed to the energy transfer and the absorbance caused enhancement (ACE) mechanism. Therefore, Tb-MOF is a good multi-response fluorescence sensor for acidic amino acids and Al3+, Ga3+cations.

Turn-on fluorescent sensor based on curcumin@MOF-5 for the sensitive detection of Al3.

Two fluorescent chemosensors based on MOF-5 and curcumin (A-curcumin@MOF-5 and B-curcumin@MOF-5) were designed and synthesized. The two curcumin@MOF-5 materials retained the framework structure of MOF-5 and the fluorescence properties of curcumin. Importantly, both curcumin@MOF-5 materials in ethanol displayed highly selective fluorescence enhancement responses toward Al3+ with the special pore structure of MOF-5 as the main reason for the high selectivity. The fluorescence intensities of the two curcumin@MOF-5 materials showed a good linear relationship with Al3+ concentration with low detection limits of 3.10 μM for A-curcumin@MOF-5 and 2.84 μM for B-curcumin@MOF-5, respectively. The complexation of curcumin with Al3+ inhibited the photoinduced electron-transfer (PET) process and further enhanced the fluorescence of the curcumin molecules. Both the curcumin@MOF-5 materials can be used as fluorescent sensors to identify and detect Al3+ in water samples.

A Turn-On Fluorescent Sensor for Hydrazine Based on Conjugated D-Π-A Molecule

A Turn-On Fluorescent Sensor for Hydrazine Based on Conjugated D-Π-A Molecule

Turn-on fluorescent sensors for Cu-rich amyloid β peptide aggregates.

Protein misfolding and metal dishomeostasis are two key pathological factors of Alzheimer's disease. Previous studies have shown that Cu-mediated amyloid β (Aβ) peptide aggregation leads to the formation of neurotoxic Aβ oligomers. Herein, we report a series of picolinic acid-based Cu-activatable sensors, which can be used for the fluorescence imaging of Cu-rich Aβ aggregates.

A covalent organic polymer for turn-on fluorescence sensing of hydrazine

A polymer, COP-Ta, was designed and synthesized. It served as a turn-on fluorescent sensor for hydrazine detection with high performance.

In situ ligand-induced Ln-MOFs based on a chromophore moiety: white light emission and turn-on detection of trace antibiotics

Series novel 3D Ln-MOFs containing both carboxyphenyl and pyridinyl moieties have been constructed. Tb-MOF fluorescence turn-on sensor of levofloxacin solution with highly sensitive and excellent selective was achieved through d-PET approach.

Molecular phosphonic acid-tethered tetraphenylethene AIEgen based highly selective fluorescent turn-on sensor for neomycin

We demonstrated highly selective and sensitive tetraphenylethene -tetraphosphonic acids for the facile detection of aminoglycoside antibiotic neomycin for the first time. Neomycin was found to effectively induce aggregate formation of (4-(1,2,2-tris(4-phosphonophenyl)vinyl)phenyl)phosphonic acid octasodium salt (TPPE) in aqueous solution. The aggregation-induced emission (AIE) response of TPPE was realized upon addition of neomycin in Milli-Q water at pH 7. The detection mechanism relies on electrostatic and hydrogen bonding interactions. The TPPE-based sensor system exhibited a detection limit 2.088 × 10−10 M of neomycin. Further, we demonstrate use of TPPE system for visual detection of neomycin as thin layer chromatography (TLC) sensor to develop kits for real world applications.

A Pyrazolo Imine-based Colorimetric and Turn-on Fluorescent Sensor Probe for Determination of Hg2+ Ion and its Application in Test Paper Strips.

In this work, we synthesized diethylamino substituted pyrazolo imine (3) fluorescent probe for recognition of Hg2+ ion.The sensor probe 3 can detect Hg2+ by colorimetric method, and there is a 10-fold enhancement in fluorescence response. When the fluorescent probe bound with Hg2+ ion, turn-on fluorescence was observed via the coordination. Probe 3 has an excellent selectivity toward Hg2+ in the CH3 CN/H2 O (8:2, v/v) solution with low limit of detection and high binding association constant of 551 parts per billion (ppb) and 6.6067 × 106 m-1 for 3+Hg2+ , respectively. Furthermore, the formation of 3+Hg2+ complex with 1:1 binding mode was evidenced by Job's plot, 1 H NMR spectroscopy and Mass analysis. In addition, probe 3 is a feasible option to detect Hg2+ in various sources of water samples. Bio-imaging experiments have demonstrated that probe 3 can be used to monitor Hg2+ in Escherichia coli bacterial cell. The sensor 3 was also used for paper strip application to detect Hg2+ ion.

Highly sensitive and cost-effective fluorescent turn-on sensors based on octamethylcalix[4]pyrrole receptor for the detection of fluoride anion

Cost-effective fluorescence turn-on indicator-displacement-assay (IDA) sensors based on octamethylcalix[4]pyrrole receptor and tetrabutylammonium salts of 4-methylumbelliferone and fluorescein indicators were developed for highly sensitive detection of fluoride anion. The IDA sensor assembly relies on the hydrogen bonding between calix[4]pyrrole and carboxylate units of indicators and further displacement replacement of receptors with target analyte. While all the sensors displayed rapid and selective sensitivity towards fluoride over the other anions, 4-methylumbelliferone based IDA system was also found to have a visual color change for the sensing of fluoride anion. The experimental results revealed that fluorescein-based IDA sensor could be used for the sensing of fluoride anion with a detection limit as low as 3.2 nM.

A novel boronic acid-based fluorescence turn on sensor for specific detection of adenosine in urine

Three simple fluorescence turn-on sensors have been designed for the selective detection of adenosine (AD) based on a boronic acid receptor and a coumarin fluorophore (NLC, NJC, NDC). In the absence of AD, the fluorescence emission intensity of the sensors was relatively weak due to the effective electronic transfer from the to the coumarin to the boronic acid moiety. When the AD was introduced into the system, an obvious fluorescence enhancement was observed. It was attributed to the boronic acid covalently binding to the cis-diol unit of the AD resulting in the electronic transfer process being inhibited. Under the optimal conditions, these fluorescent sensors not only could perform good selectivity and fast response (< 30 s), but also show good water solubility. Finally, the proposed sensor NLC has been utilized for the AD determination in urine without any complicated pretreatment and the recovery was in the range of 95–103%. As a result, it is promising for application on the AD detection in complex biological samples. Moreover, there are no small molecular sensors detecting AD have been reported, yet, it is promising for providing a new platform to detect AD by small molecular sensor.

Adenosine triphosphate (ATP) and zinc(II) ions responsive pyrene based turn-on fluorescent probe and its application in live cell imaging.

A novel highly selective and sensitive turn-on fluorescent chemosensor PCE to recognize Zn2+ has been developed. The sensor PCE displays a remarkable fluorescent enhancement at 456nm (λex=340nm) with Zn2+ without the interference of other biologically important relevant metal ions in aqueous acetonitrile solution. Job's plot and mass spectral studies divulge such the interaction of PCE by Zn2+ was 1:1 binding stoichiometry. The association constant and detection limit of PCE to recognize Zn2+ was found to be 0.948×104M-1 and 4.82×10-7M respectively. The nature of turn-on fluorescence sensor was supported by TD-DFT calculations. And the synthesized probe PCE was able to image intracellular Zn2+ in living cells using confocal imaging techniques. PCE-Zn ensemble showed the remarkable fluorescence enhancement with ATP selectively among other biologically important phosphates. 31P NMR experiments suggesting that the triphosphates unit of ATP is intact with the PCEZn. PCE-Zn ensemble can be utilized for monitoring ATP in live cells.

Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn2+ and Colorimetric Chemosensors for Zn2+, Cu2+, and Ni2+ Ions.

Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn2+, Cu2+, and Ni2+. The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn2+, Cu2+, and Ni2+ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Fe2+, Fe3+, Mg2+, K+, and Na+). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn2+ ions and turn off response for Cu2+ and Ni2+ ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn2+, while it was 0.30 ppm and 0.34 ppm for Ni2+ and Cu2+, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn2+, Cu2+, and Ni2+ ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn2+ ions in live cells.

Turn-on, photostable, nontoxic and specific, iron(II) sensor

The pressing need to develop a specific analytical sensor that can identify and quantify Fe(II) without a cytotoxic response was the major motivation drive in this work. The turn-on fluorescent sensor here described can successfully detect Fe(II) and discriminate this ion from other analytes that commonly act as interferents in biological media. Moreover, this reduced fluoresceinamine-based sensor has a high photostability and high dissociation constant, which is an indication that the complex obtained between reduced fluoresceinamine (RFL) and Fe(II) is highly stable. This fluorescence-based sensor has a binding mechanism of 1:1 and a positive cooperativity was found between analyte and sensor. The detection, quantification and sensitivity parameters of the sensor were determined: 21.6 ± 0.1 μM; 65.6 ± 0.1 μM and 48 ± 3 (×107) μM, respectively. To evaluate a possible cytotoxicity effect an erythrocyte assay was performed and the obtained data were evaluated considering CdTe Quantum Dots (QDs) passivated with mercaptoacetic acid has experimental control. According to the resulting data RFL is not cytotoxic even when used in high concentrations, 660 mM. On the other hand QDs are quite different. Indeed it was proven that these heavy metal-based nanoparticles are responsible for 40% erytrocytes hemolysis in concentrations of 600 mM.

A turn-on fluorescence sensor for rapid sensing of ATP based on luminescence resonance energy transfer between upconversion nanoparticles and Cy3 in vivo or vitro

Adenosine triphosphate (ATP) is an energy molecule of significant importance, and, the monitoring of ATP in living cells is considerable for the clinical diagnosis of many related diseases, including cancer. Upconversion nanoparticles (UCNPs) have recently been attracting widespread interest in biomedical applications due to their chemical and thermal stability, high sensitivity, good biocompatibility, and excellent tissue penetration. Herein, a Cy3-aptamer-cDNA- UCNPs nanosensor was synthesized, based on the luminescence resonance energy transfer (LRET) between UCNPs and Cy3 for monitoring ATP in living cells. It showed a selective sensing ability for ATP levels by changes of fluorescence intensity of UNCPs at 536 nm. The investigated biosensor showed a precise, efficient detection with sufficient selectivity which was achieved through the optimization of conditions. In the range of 1–1000 μM, the ATP-induced changes of the fluorescence intensity were linearly proportional to the ATP concentrations. Furthermore, the cytotoxicity assay revealed that the UCNPs sensor exhibited favorable biocompatibility, implicating the use of UCNPs in vivo imaging. This study highlights the potential of using a combination of UCNPs and ATP-binding aptamer to design an ATP-activatable probe for fluorescence-mediated imaging in living cells. These results implied that the nanosensor can be applicable for the monitoring of intracellular ATP by fluorescence imaging and the quantitative analysis of biological liquids.

Design of fluorescence turn-on sensors with novel response mechanism based on C[dbnd]N isomerization

A series of new type naphthalimide-based fluorescent molecules linking aniline-like groups via a coupling chain with –CN– structure were developed as novel fluorescence chemosensors with high sensitivity and selectivity toward H+ in solution and acidic atmosphere as well as Al3+ in the presence of other cations. The fluorescence turn-on mechanism was studied and proved to be based on the CN isomerization. For these fluorescent molecules with donor-acceptor structure, their luminescent wavelength and photophysical properties can be dominated by adjusting the structure of aniline-like groups and the chain length connecting with naphthalimide. All of these fluorescent molecules emitted strong solid-state fluorescence due to their inherent twisted geometries, and exhibited excellent thermal stability, which is beneficial for their application at high temperature.