Fluorescence Turn-on Research Articles

Highly sensitive and selective fluorescent "turn-on" sensor for Ag+ detection using MAPbBr3@PCN-221(Fe): An efficient Ag+-bridged energy transfer from perovskite to MOF.

Metal ion-induced water pollution is attracting increasing public attention. Perovskite quantum dots and metal-organic frameworks (MOFs), owing to their outstanding properties, hold promise as ideal probes for detecting metal ions. In this study, a composite material, MAPbBr3@PCN-221(Fe), was prepared by encapsulating MAPbBr3 quantum dots with PCN-221(Fe), demonstrating high chemical stability and good reusability. The composite material shows a sensitive fluorescence turn-on signal in the presence of silver ions. The fluorescence intensity of the composite material exhibits a linear relationship with the concentration of Ag+ in the solution, with a low detection limit of 8.68 µM. Moreover, the fluorescence signal exhibits a strong selectivity for Ag+, enabling the detection of Ag+ concentration. This fluorescence turn-on signal originates from the Ag+-bridged energy transfer from the conductive band of MAPbBr3 to the excited state of the MOF, which is directly proportional to the concentration of silver ions. Simultaneously, this finding may open up a new possibility in artificial controlled energy transfer from perovskite to MOF for future development.

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample.

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6M and 1.733 × 107M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

Disaggregation-Activated pan-COX Imaging Agents for Human Soft tissue Sarcoma.

Cancer stem cells are pivotal players in tumors initiation, growth, and metastasis. While several markers have been identified, there remain challenges particularly in heterogeneous malignancies like adult soft tissue sarcomas, where conventional markers are inherently overexpressed. Here, we designed BODIPY scaffold fluorescence probes (BD-IMC-1, BD-IMC-2) that activate via disaggregation targeting for cyclooxygenase (COX), a potential marker for CSCs in sarcoma in clinical pathology. Based on their structures, BD-IMC-1 showcased higher susceptibility to disaggregation compared to BD-IMC-2, consistent with their selective interaction with COX. Notably, the BD-IMC-1 revealed positive cooperativity binding to COX-2 at sub-micromolar ranges. Both probes showed significant fluorescence turn-on upon LPS or PMA triggered COX-2 upregulation in live RAW264.7, HeLa, and human sarcoma cell line (Saos-LM2) up to 2-fold increase with negligible toxicity. More importantly, the BD-IMC-1 demonstrated their practical imaging for COX-2 positive cells in paraffin-fixed human sarcoma tissue. Considering the fixed tissues are most practiced pathological sample, our finding suggests a potential of disaggregation activated chemosensor for clinical applications.

Influence of Solvents and Halogenation on ESIPT of Benzimidazole Derivatives for Designing Turn-on Fluorescence Probes

Influence of Solvents and Halogenation on ESIPT of Benzimidazole Derivatives for Designing Turn-on Fluorescence Probes

Fluorescence Turn-on Detection of Perfluorooctanoic Acid (PFOA) by Perylene Diimide-Based Metal-Organic Framework.

A novel, water-stable, perylene diimide (PDI) based metal-organic framework (MOF), namely, U-1, has been synthesized for selective and sensitive detection of perfluorooctanoic acid (PFOA) in mixed aqueous solutions. The MOF shows highly selective fluorescence turn-on detection via the formation of a PFOA-MOF complex. This PFOA-MOF complex formation was confirmed by various spectroscopic techniques. The detection limit of the MOF for PFOA was found to be 1.68 μM in an aqueous suspension. Upon coating onto cellulose paper, the MOF demonstrated a significantly lower detection limit, down to 3.1 nM, which is mainly due to the concentrative effect of solid phase extraction (SPE). This detection limit is lower than the fluorescence sensors based on MOFs previously reported for PFAS detection. The MOF sensor is regenerable and capable of detecting PFOA in drinking and tap water samples. The PDI-MOF-based sensor reported herein represents a novel approach, relying on fluorescence turn-on response, that has not yet been thoroughly investigated for detecting per- and polyfluoroalkyl substances (PFAS) until now.

Dual function Schiff-base as a selective fluorescence “Turn-on” sensor for Zn2+ and a colorimetric sensor for Cu2+ and Fe3+ ions

A simple and adaptable salen-based Schiff base receptor (L = 6,6′-((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol))was employed in the current study for colorimetric detection of Cu2+, Fe3+, and fluorescence detection of Zn2+ ions in a semi-aqueous solution. L could identify the three target ions among the many different cations and anions in the solution. The turn-on fluorescence signal of L to Zn2+ ions was boosted by the restriction of the intramolecular charge transfer process, and the resulting chelation enhances the fluorescence signal. The sensing mechanisms were validated using a Job’s plot, Electrospray Ionization Mass Spectrometry (ESI-MS) analysis, Nuclear Magnetic Resonance (NMR) titration experiment, and theoretical calculation investigations. The detection limits for Zn2+ were determined to be 0.038 μM, whereas Cu2+ and Fe3+ detection limits were 0.58 μM and 0.62 μM, respectively. Next, L was used to develop solid silica gel and test strips for instantaneous colorimetric and fluorescent detection of the three target ions in real time. The trace level of Cu2+ and Fe3+ in the tap and drinking water samples could be quantitatively measured using L. Eventually, applications for keypad locks and molecular logic gates were developed utilizing the receptor L.

Sensitive and rapid detection of ciprofloxacin and ofloxacin in aqueous samples by a facile and green synthesized copper nanocluster as a turn-on fluorescent probe

The present method reports a rapid, inexpensive and sensitive sensing system based on fluorescence turn-on strategy for trace detection of ciprofloxacin (CIP) and ofloxacin (OFL) in aqueous samples. In a one pot method, copper nanocluster whose dimensions are less than 15 nm, were easily prepared and decorated with sodium gluconate (Gl@CuNCs) as a biocompatible material.The Gl@CuNCs were characterized with XRD, TEM, DLS, TG-DTA techniques as well UV–Vis, FT-IR and fluorescence spectroscopies.The maximum fluorescence emission of Gl@CuNCs at 414 nm with excitation at 322 nm shifted to higher wavelength upon addition of CIP and OFL. A good linear relationship between fluorescence emission and drug concentration was achieved in the concentration range of 0.005–0.3 μg mL−1 (15–900 nM for CIP and 14–830 nM for OFL). The limits of detection (LOD) for the determinations of CIP and OFL were calculated to be 9 and 8 nM, respectively. Furthermore, even a 100-fold higher concentration of interfering species had no significant effect on the detection of CIP and OFL. The proposed method was successfully used to determine CIP and OFL in drinking water, cow milk, human urine and serum samples with satisfactory recoveries.

Tuning the sensing properties of isophthalic dihydrazide-based receptor via formation of organic–inorganic hybrid and metal complex: An enhanced sensing activity for Hg2+ and CN− detection in semi-aqueous medium

A Schiff base receptor H2L has been synthesized through a condensation reaction between 2-hydroxy-3-methoxybenzaldehyde and isophthalic dihydrazide. The compound has been characterized by various characterization techniques such as 1H, FT-IR, CHNS and single crystal X-ray crystallography. Despite its limited solubility in water, a strategy was employed to enhance its effectiveness in aqueous environment by forming fluorescent nanoaggregates of H2L through a re-precipitation method. The fluorescent nanoaggregates of H2L show strong recognition ability towards Hg2+ ions through a fluorescence turn-on mechanism in H2O–DMSO (90 %, v/v). The study has been extended by developing a hybrid nano-assembly of H2L as Ag@H2L which exhibits higher sensitivity for Hg2+ ions with an improved detection limit 9.3 × 10−9 M as compared to that of organic nanoaggregates having 7.9 × 10−8 M in H2O–DMSO (90 %, v/v). Further Hg2+ complex of H2L has also been synthesized and characterized using elemental analysis, mass spectrometry and IR, UV–Vis spectroscopic techniques. The findings have been complimented by density functional theory (DFT) computations. The synthesized H2L-Hg complex is able to detect CN− ion using UV–Vis spectroscopy in H2O–DMSO (80 %, v/v) with a detection limits of 1.04 × 10−6 M.

A turn-on fluorescent probe based on pyrene for hydrazine detection

This paper presents a novel fluorescent probe (GNEM) based on a pyrene fluorophore, with dicarboximide as the recognition unit for hydrazine. The fluorescence probe can be synthesized in a simple one-step process. A highly selective and sensitive fluorescence turn-on GNEM synthesized. GNEM react with hydrazine through nucleophilic addition, leading to the deprotection of dicarboximide and the release of dicarboximide hydrazine, resulting in significant blue fluorescence. This enhanced emission is attributed to the intramolecular charge transfer (ICT) sensing mechanism of GNEM. In addition, detection of hydrazine in soil and water is conducted. By designing a simple detection device, the hydrazine content in the air can be quantitatively measured.

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO− with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO− with high fluorescent selectivity. DBT-Cl quickly detected ClO− in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO−. Detection mechanism of DBT-Cl toward ClO− was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO− in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO− through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO− probe in environmental and living organism systems.

A phenothiazine coumarin based fluorescent probe with AIE feature for real-time detecting lysosomal ClO– in living cell

A new phenothiazine coumarin based probe WX-Lyso for detection of ClO– was developed. The probe showed obvious aggregation-induced emission (AIE) characteristic and exhibited a highly selective and sensitive turn-on fluorescence signal at 544 nm for ClO– with a large Stokes shift of 144 nm. The limit of detection (LOD) of ClO– was measured as low as 0.99 μM and a good line equation was obtained in the 0–50 μM concentration range. The detection mechanism was elucidated FT-IR, ESI-MS analysis and DFT. Furthermore, the probe had been demonstrated successfully has good lysosomal-targeting and high-contrast imaging abilities, which has the potential to become a new chemical tool and provide help for detecting ClO– in living systems.

Iron modified hydrogen-bonded organic framework as fluorescent sensor for ascorbic acid detection

Herein, iron modified hydrogen-bonded organic framework (Fe-HOF) was successfully prepared by introducing the yellow-green fluorescent ligand 2,5-dihydroxyterephthalic acid into HOF and then modifying Fe3+. A simple turn-on fluorescence strategy is proposed for the detection of ascorbic acid (AA) based on Fe-HOF. Fe3+ could effectively quench fluorescence emission of HOF. In the presence of AA, Fe3+ was reduced to Fe2+, which led to the fluorescence recovery of HOF, thus realizing the fluorescence quantitative detection of AA. These fluorescence responsive behaviors of Fe-HOF ensure fluorescence assay of AA within 0.5 − 8 μM, along with a limit of detection (LOD) of 0.14 μM. The sensing platform could realize the rapid detection of ascorbic acid in vitamin C pills, tablets and beverages in the detection of ascorbic acid with good recoveries.

Turn-on fluorescence of mirabegron for its sensitive detection in human plasma: Box-Behnken-Design for optimization

Here, a novel fluorescence strategy was established for the detection of mirabegron (MBG) sensitively on the basis of hantzsch dihydropyridine synthesis. The developed method adopts turn-on fluorescence of MBG for the first time, permitting its selective determination in spiked human plasma at 486 nm after excitation at 410 nm. The developed method exhibited a good linear range from 0.5 μgmL-1 to 2.0 μgmL-1 with detection and quantification limits of 0.05 and 0.2 (μgmL-1), respectively. The profitable applicability of the developed method in spiked human plasma samples was demonstrated, achieving limit of detection below the previously levels reported by spectroscopic methods, allowing application of the developed method for selective determination of MBG in its tablets and spiked human plasma samples with good recovery.

A Water-Soluble Wavy Coordination Polymer of Cu(II) as a Turn-On Luminescent Probe for Histidine and Histidine-Rich Proteins/Peptides.

Histidine plays an essential role in most biological systems. Changes in the homeostasis of histidine and histidine-rich proteins are connected to several diseases. Herein, we report a water-soluble Cu(II) coordination polymer, labeled CuCP, for the fluorimetric detection of histidine and histidine-rich proteins and peptides. Single-crystal structure determination of CuCP revealed a two-dimensional wavy network structure in which a carboxylate group connects the individual Cu(II) dimer unit in a syn-anti conformation. The weakly luminescent and water-soluble CuCP shows turn-on blue emission in the presence of histidine and histidine-rich peptides and proteins. The polymer can also stain histidine-rich proteins via gel electrophoresis. The limits of quantifications for histidine, glycine-histidine, serine-histidine, human serum albumin (HSA), bovine serum albumin, pepsin, trypsin, and lysozyme were found to be 300, 160, 600, 300, 600, 800, 120, and 290 nM, respectively. Utilizing the fluorescence turn-on property of CuCP, we measured HSA quantitatively in the urine samples. We also validated the present urinary HSA measurement assay with existing analytical techniques. Job's plot, 1H NMR, high-resolution mass spectrometry (HRMS), electron paramagnetic resonance (EPR), fluorescence, and UV-vis studies confirmed the ligand displacement from CuCP in the presence of histidine.

Rapid detection of hypobromous acid by a tetraphenylethylene-based turn-on fluorescent AIE probe and its applications

BackgroundSimilar to hypochlorous acid (HClO), hypobromous acid (HBrO) is one of the most notable reactive oxygen species (ROS). Overexpression of HBrO is linked to various diseases causing organ and tissue loss. Due to HBrO's role in the oxidation of micropollutants, real-time monitoring of HBrO in water-based systems is essential. Tetraphenylethylene (TPE)-based organic aggregation-induced emission luminophores (AIEgens) are an emerging category of fluorescent probe materials that have attracted considerable attentions. However, AIE probes are rarely applied to detect HBrO. Developing faster, more precise, and more sensitive AIE probes is thus crucial for detecting biological and environmental HBrO. ResultsA small molecule fluorescent probe 4-(1,2,2-triphenylvinyl)benzamidoxime (SWJT-21) was synthesized for the sensitive and selective detection of hypobromous acid (HBrO) based on aggregation-induced emission (AIE). The amidoxime unit of SWJT-21 would undergo an oxidation reaction with HBrO, leading to a structure differentiation between the probe and the product, and therefore the turn-on fluorescence by the AIE effect. The probe could recognize hypobromous acid rapidly (less than 3 s) in high aqueous phase (99 % water) with a turn-on fluorescence response. It was determined that the limit of detection for HBrO was 5.47 nM. Moreover, SWJT-21 demonstrates potential as a test strip for the detection of HBrO. SWJT-21 was also successfully used for the monitoring of HBrO in water samples and for the detection of endogenous/exogenous HBrO in living cells and zebrafish. SignificanceA special AIE fluorescence turn-on probe SWJT-21 based on tetraphenylethylene was designed for detecting HBrO in the environmental and biological systems. This probe has an extremely low detection limit of 5.47 nM and is able to detect HBrO in 99 % aqueous phase in less than 3 s.

Medium-dependent selectivity for Cu2+ and glutathione by a near-infrared fluorescent probe

A novel near-infrared Schiff base fluorescent probe was synthesized. The probe displayed medium-dependent selectivity and could specifically recognize Cu2+ in EtOH/H2O (9:1, v/v) while respond to glutathione (GSH) in THF/H2O (9:1, v/v). Addition of Cu2+ to the probe solution caused obvious fluorescence quenching and color change. The detection limit was calculated to be 37 nM. The probe could specifically detect GSH through fluorescence turn-on in THF/H2O (9:1, v/v) medium based on GSH-induced hydrolysis of the probe, with the detection limit as low as 20 nM. The sensing mechanism of the probe was verified by spectral analysis and density functional theory (DFT) calculations. Application of the probe to real water samples analysis and bioimaging was achieved.

Visualized Enzyme-Activated Fluorescence Probe for Accurately Detecting β-Gal in Living Cells and BALB/c Nude Mice.

Colorectal cancer was one of the major malignant tumors threatening human health and β-Gal was recognized as a principal biomarker for primary colorectal cancer. Thus, designing specific and efficient quantitative detection methods for measuring β-Gal enzyme activity was of great clinical test significance. Herein, an ultrasensitive detection method based on Turn-on fluorescence probe (CS-βGal) was reported for visualizing the detection of exogenous and endogenous β-galactosidase enzyme activity. The test method possessed a series of excellent performances, such as a significant fluorescence enhancement (about 11.3-fold), high selectivity as well as superior sensitivity. Furthermore, under the optimal experimental conditions, a relatively low limit of detection down to 0.024 U/mL was achieved for fluorescence titration experiment. It was thanks to the better biocompatibility and low cytotoxicity, CS-βGal had been triumphantly employed to visual detect endogenous and exogenous β-Gal concentration variations in living cells with noteworthy anti-interference performance. More biologically significant was the fact that the application of CS-βGal in BALB/c nude mice was also achieved successfully for monitoring endogenous β-Gal enzyme activity.

Promising optical chemical sensor for detecting Al(III) ions in water based on organic fluorophore

In the present work, an optical sensing scheme was designed to detect the Al(III) ions based on a fluorescent probe. The synthesized probe N-(3-chloro)-salicylaldimine CSI receptor was developed using turn-on fluorescence enhancement. During the treatment process of Al(III) ions, the emission of the CSI probe was increased at 545 nm due to the formation of a 1:1 complex between the chemosensor and the Al(III) ions at room temperature. The gradual addition of Al(III) ions to the studied solution gradually enhanced the CSI emission. The other metal ions, including alkali, alkaline metal ions, and some transition metal ions, had no noticeable impact on the fluorescent intensity. The limit of detection (LOD) and (LOQ) were determined as 0.427 nM and 1.28 nM, respectively. The detection limit for this sensor is very low, demonstrating its remarkable selectivity and ultra-sensitivity. These impressive characteristics allow the detection of Al(III) ions at concentrations as low as 1.28 × 10−3 to 1 μM while highly selective even in the presence of other metal ions. EDTA solution at a concentration of 1 µM was used to make the sensor reversible. We also provide the fact that the CSI probe can be a promising optical chemical for detecting Al(III) ions in real samples.

Development of Paper-Based Fluorescent Molecularly Imprinted Polymer Sensor for Rapid Detection of Lumpy Skin Disease Virus.

Lumpy Skin Disease (LSD) is a notifiable viral disease caused by Lumpy Skin Disease virus (LSDV). It is usually associated with high economic losses, including a loss of productivity, infertility, and death. LSDV shares genetic and antigenic similarities with Sheep pox virus (SPV) and Goat pox (GPV) virus. Hence, the LSDV traditional diagnostic tools faced many limitations regarding sensitivity, specificity, and cross-reactivity. Herein, we fabricated a paper-based turn-on fluorescent Molecularly Imprinted Polymer (MIP) sensor for the rapid detection of LSDV. The LSDV-MIPs sensor showed strong fluorescent intensity signal enhancement in response to the presence of the virus within minutes. Our sensor showed a limit of detection of 101 log10 TCID50/mL. Moreover, it showed significantly higher specificity to LSDV relative to other viruses, especially SPV. To our knowledge, this is the first record of a paper-based rapid detection test for LSDV depending on fluorescent turn-on behavior.

A novel coumarin-linked tetraphenylethene fluorescent probe for simultaneous sensing of ATP and GSH

Adenosine triphosphate (ATP) as the intracellular energy currency, and glutathione (GSH) as the regulator of redox homeostasis in the cell microenvironment, are all closely associated with numerous important physiological processes in living organisms. However, the fluorescent probes that can simultaneously detect ATP and GSH are rarely reported. Herein, a bifunctional coumarin-linked tetraphenylethene (TPE) probe P1 was successfully developed, which exhibits a red emission at 633 nm owing to the fluorescence resonance energy transfer (FRET) from energy donor coumarin to energy acceptor TPE. P1 can detect ATP with a fluorescence turn-on response at 633 nm in the red channel by complexation-enhanced aggregation mechanism, and showed a ratiometric detection toward GSH through the disruption of the FRET process, accompanied by an increase in the blue channel at 467 nm and a decrease in the red channel at 633 nm. P1 also displays a superior sensitivity and high selectivity to ATP and GSH, with a detection limit of 20.80 nM for ATP and 3.47 µM for GSH. Significantly, P1 can discriminate GSH from ATP and other analytes due to the different response times. Furthermore, P1 can localize mitochondria and has been discovered to be capable of imaging ATP and GSH in living cells and zebrafish.