Turn-on Fluorescent Probe Research Articles

Eu-doped carbon dots-MOF based turn-on fluorescent probe for trace Hg2+ and Pb2+ and construction of the simultaneous detection model

Multiple trace heavy metal pollutants present a serious threat to the aquatic environment, and their coexistence also affected the detection efficiency. This work prepared Eu doped metal organic framework (MOF) complexed with S-containing carbon dots (CD(s)) exhibited dual-emission fluorescence. Its chelation-enhanced fluorescence with heavy metals replaced the original agglomerative fluorescence quenching of pure CD(s), which was utilized to construct a “turn on” fluorescence sensing probe. Based on the XPS, DFT and fluorescence lifetime results, the N, S functional groups on the surface of the materials could bind specifically to Hg2+ and Pb2+ with enhanced sensitivity. The limit of detection reached 76.67 nM for Hg2+ and 5.12 nM for Pb2+ within 2 min detection time. Furthermore, due to the different response mechanism of the two signal peaks to Hg2+ and Pb2+, a three-dimensional data model was developed for simultaneous detection in the co-existence system. The model had been successfully applied to actual Hg2+-Pb2+ containing water samples with recoveries ranged from 93.15 ∼ 105.08 %. The results provided a new strategy for simultaneous detection of trace environmental pollutants.

Selective Recognition of the Dimeric NG16 Parallel G-Quadruplex Structure Using Synthetic Turn-On Red Fluorescent Protein Chromophore.

Red fluorescent protein (RFP)-based fluorescent probes that can selectively interact with specific nucleic acids are of great importance for therapeutic and bioimaging applications. Herein, we have reported the synthesis of RFP chromophores for selective recognition of G-quadruplex nucleic acids in vitro and ex vivo. We identified DFHBI-DM as a fluorescent turn-on probe that binds to the dimeric NG16 parallel quadruplex with superior selectivity and sensitivity over various parallel, antiparallel, and hybrid topologies. The binding of DFHBI-DM to NG16 exhibited excellent photophysical properties, including high binding affinity, large Stokes shift, high photostability, and quantum yield. The MD simulation study supports the 1:1 binding stoichiometry. It confirms the planar conformation of DFHBI-DM, which makes strong binding interactions with a flat quartet of NG16 compared to other antiparallel and hybrid topologies. The cell imaging and MTT assays revealed that DFHBI-DM is a biocompatible and efficient fluorescent probe for intracellular imaging of NG16. Overall, these results demonstrated that DFHBI-DM could be an effective fluorescent G4-stabilizing agent for the dimeric NG16 parallel quadruplex, and it could be a promising candidate for further exploration of bioimaging and therapeutic applications.

Rational design of an ultrabright quinolinium-fused rhodamine turn-on fluorescent probe for highly sensitive detection of SO2 derivatives: Applications in food safety and bioimaging

Sulfur dioxide (SO2) is an essential signaling molecule involved in various physiological processes within living organisms. Bisulfite (HSO3−) possesses antioxidant, antimicrobial, and preservative properties, making it a common food additive. However, elevated levels of SO2 or excessive HSO3− intake can lead to a range of diseases, highlighting the importance of detecting SO2 and its derivatives (HSO3−/SO32−). This study presents a quinolinium-fused rhodamine fluorogenic probe (RQB-R) for ultrafast, highly selective, and sensitive detection of HSO3−. The probe operates via a dual-response mechanism, exhibiting a visible color change and a transition from nonemissive to intense red fluorescence upon interaction with HSO3−. The detection mechanism involves a 1,4-nucleophilic addition reaction of HSO3− at the 4-position of the quinolinium unit, which bypasses the photoinduced electron-transfer fluorescence quenching pathway and activates the intramolecular charge transfer mechanism, thereby enhancing fluorescence emission. Practical applications of the RQB-R probe include rapid quantification of HSO3− levels in sugar samples and integration into smartphone-assisted detection platforms. This method demonstrates excellent biocompatibility and enables visualization of both exogenous and endogenous HSO3− within MCF-7 cells, with a specific focus on targeting mitochondria.

A near-infrared fluorescent probe with a large Stokes shift for the detection and imaging of biothiols in vitro and in vivo.

In this study, a new near-infrared (NIR) fluorescent turn-on probe featuring a large Stokes shift (198nm) was developed for the detection of biothiols. The probe was based on a dicyanoisophorone derivative serving as the fluorophore and a 2,4-dinitrobenzenesulfonyl (DNBS) group functioning as both a recognition site and a fluorescence quencher. In the absence of biothiols, the fluorescence of the probe was low due to the photoinduced electron transfer (PET) effect between the fluorophore and DNBS. Upon the presence of biothiols, the DNBS group underwent a nucleophilic aromatic substitution reaction with the sulfhydryl group of biothiols, leading to the release of the fluorophore and a notable emission peak at 668nm. This developed probe exhibited exceptional selectivity and sensitivity to biothiols in solution, with an impressive detection limit of 28nM for cysteine (Cys), 22nM for homocysteine (Hcy), and 24nM for glutathione (GSH). Furthermore, the probe demonstrated its applicability by successfully visualizing both endogenous and exogenous biothiols in living systems.

A novel dialdehyde cellulose-based colorimetric and turn-on fluorescent probe for H2S detection and its application in red wine

Hydrogen sulfide (H2S) is considered one of the most important gaseous transmitters in the metabolic system, and the abnormal concentration of H2S is associated with a variety of diseases. Up to now, it is still a challenge to develop a portable assay for H2S even though the research about the detection of H2S is booming. Herein, a novel bifunctional dialdehyde-cellulose fluorescent probe DAC-DPD was prepared with high selectivity and sensitivity to H2S with colorimetric and fluorescent “turn-on” characteristics, and the limit of detection (LOD) of DAC-DPD for H2S was 0.831 μM. The sensing mechanism of DAC-DPD's to H2S was a Michael addition reaction confirmed by HRMS, 1H NMR and density-functional theory (DFT) calculations. DAC-DPD can be used to detect H2S in red wine samples. In Addition, the prepared DAC-DPD embedded fluorescent membrane can be used as a reliable sensing platform for rapid detection of H2S. It provided a convenient and rapid detection material, simplifying the detection process of H2S, which is of great significance for the development of cellulose-based fluorescent smart material.

Highly selective peptide-based fluorescent turn-on probe with large Stokes shift for the detection of Cd(II) and its applications in bio-imaging and smartphone-assisted recognition

Cadmium ions (Cd2+) is a ubiquitous environmental pollutant that endangers all forms of life, and it has become critical to develop simple and highly selective detection methods for monitoring Cd2+. Herein, a new fluorescent turn-on probe DPGC with dansyl fluorophore labelled tripeptide (ProGlyCys-NH2) was successfully synthesized using solid-phase peptide synthesis technology with Fmoc chemistry. Interestingly, DPGC showed high specificity and fluorescence “turn on” response towards Cd2+ in 100% aqueous solution. In addition, the limit of detection (LOD) for Cd2+ recognition by DPGC was calculated to be 12.4 nM. The pH test showed that DPGC had a wide detection range of 7–11 for Cd2+, and the response time was also less than 30 s. Notably, the DPGC-Cd2+ complex forms a 2:1 binding stoichiometry was determined using fluorescence titration, Job's plot, ESI-HRMS and DFT calculations. Additionally, the binding of DPGC with Cd2+ was found fluorescence reversible on addition of EDTA. Meanwhile, DPGC has excellent membrane permeability and low cytotoxicity, and was successfully employed for detecting Cd2+in living cells and zebrafish. More importantly, the colour change of Cd2+ solution with different concentrations under 365 nm UV light was detected by a smartphone App to achieve semi-quantitative visual analysis of Cd2+ ions.

A Dicyanoisophorone-based Fluorescent Turn-on Probe for Rapid Detecting Thiophenol in Aqueous Medium and Living Cell Imaging

A novel colorimetric and fluorescent thiophenol probe based on dicyanoisophorone has been successfully achieved, which has low-cost, easy operation, high selectivity, sensitivity and stability. The chemosensor shows a large Stokes shift and approximately 170 nm when excited at 510 nm. ISO-DiNO2 could be utilized as “Turn-on” and a naked-eyes chemosensor to detect PhSH, which is accompanied by a distinct color shift from red to dark purple with strong red fluorescence at 365 nm UV-light. Its limit of detection was determined to be 1.15 μM. More importantly, ISO-DiNO2 can react instantaneously (<10 s) with PhS−. In addition, ISO-DiNO2 has been utilized in test paper strips, water sample together with imaging of PhS− in living Raw264.7 cells, demonstrating that ISO-DiNO2 has excellent and promising applications.

Endoplasmic reticulum-targeting fluorescence turn-on probe for nitric oxide detection in living cells and serum samples

Nitric oxide (NO) is an important gas signaling molecule, and endoplasmic reticulum (ER) stress induced by NO may be related to the pathogenesis of many diseases. Therefore, the development of ER-targeted fluorescent probes for NO is of great significance to investigate the relationship between ER stress and NO concentration changes in related diseases. Herein, an ER-targeted fluorescent probe (ER-Np) for sensing NO was constructed. ER-Np was served as an excellent tool for detection NO with high selectivity, sensitivity and ER-targetable ability. Moreover, fluorescence imaging experiments indicated that ER-Np is capable of imaging NO in living cells. Impressively, visualization of endogenous NO production during dithiothreitol (DTT)-induced ER stress in living cells was successfully observed. In addition, we found that serum NO levels were upregulated in epilepsy children, which opens up a new avenue for further understanding the relationship between the diagnostic of epilepsy.

A 1,3,4-thiadiazole based turn-on probe with large Stoke’s shift and ESIPT effect for fluorescent detection of H2S and its applications

Based on a useful 1,3,4-thiadiazole scaffold in our lab, a turn-on fluorescent probe for sensing H2S in environment, biological imaging and food analysis was rationally designed and synthesized. In this probe, 1,3,4-thiadiazole unit was used as fluorophore with ESIPT effect and 2,4-dinitrophenyl moiety was used as recognition fragment and fluorescent bursting agent to inhibt ESIPT. Thus, a PET process was formed and an “off–on” procedure arose after added target analyte. These brought the probe could specifically detect H2S without being interfered by other biological thiols. It showed high sensitivity (LOD=60.8 nM), large Stoke’s shift (133 nm) and had a stable performance over pH range of 6.0–9.0 in H2S monitoring system. More importantly, probe could be used for detection of H2S in real water, three beer samples and red wine sample. Furthermore, probe was successfully utilized for visualizing H2S in HeLa cells and applied for real-time monitoring of H2S during food spoilage by “naked eye” and smartphone colorimetric analysis.

Construction of novel π-bridged fluorescent probes for Fe2+ monitoring in living cells and foods.

Fe2+ plays a crucial role in biological systems as an essential trace element in the body. Iron is absorbed by the body through food and Fe2+ is also an important component of living cells; therefore, quantitative testing of Fe2+ in food and in living cells is of great importance. This paper presents the development of a novel π-bridge EDOT-based N-oxide turn-on fluorescent probe, designated as FeE, for the detection of Fe2+. The probe has been shown to exhibit excellent sensitivity, a favorable linear relationship between fluorescence signal intensity and Fe2+ concentration, and an effective immunity to interference. The probe has low cytotoxicity and has been successfully used to detect Fe2+ in cells using laser confocal fluorescence microscopy. It is also possible to determine the presence of Fe2+ in animal blood, spinach, apple juice, red wine, mineral water and metal cans.

Near-Infrared Fluorescent Turn-On Probe for Selective Detection of Hypochlorite in Aqueous Medium and Live Cell Imaging.

Hypochlorite, as an important reactive oxygen species (ROS), plays a vital role in many physiological and pathological processes, but an excess concentration of hypochlorite (ClO-) may become toxic to humans and cause disease. Hence, the selective and rapid detection of hypochlorite (ClO-) is necessary for human safety. Here, we report a novel near-infrared (NIR) fluorescence "turn-on" and highly selective benzophenoxazinium chloride-based fluorescent probe, BPH (benzophenoxazinium dihydroxy benzaldehyde), for hypochlorite detection. Due to hypochlorite-induced vicinal diol oxidation to the corresponding ortho benzoquinone derivative, the photoinduced electron transfer (PET) process, which was operating from vicinal diol to the benzophenoxazinium chloride receptor moiety, was suddenly inhibited, as a result of which strong NIR fluorescence "turn-on" emission was observed. The detection limit of BPH was found to be 2.39 × 10-10 M, or 0.23 nM. BPH was successfully applied for exogenous and endogenous hypochlorite detection in live MDA-MB 231 cells.

Synthesis and photophysical properties of 3-aryl-2-cyanoacrylamides: Design of a turn-on fluorescent probe for cyanide ion detection

Three 3-aryl-2-cyanoacrylamide derivatives were synthesised in 71−79 % yields from cheap reagents and mild reaction conditions using the Et3N-mediated Knoevenagel condensation of fluorescent arylaldehydes (e.g., triphenylamine and anthracene) with cyanoacetamide. These dyes' photophysical properties and anions-recognizing behaviour were studied, revealing that the 9-anthracenyl derivative can "turn on" fluorescence in cyanide presence, with high selectivity and a detection limit (LOD) of 710 nM. Initially, there is fluorescence quenching by the energy transfer (ET) from the anthracene ring to the 2-cyanoacrylamide moiety due to the non-coplanarity of these fragments and, upon the cyanide addition to Cβ of the receptor unit, the intrinsic fluorescence of anthracene is restored. HRMS and NMR experiments and TD-DFT calculations were performed to confirm the detection mechanism and fluorescence properties of the design chemodosimeter; fluorescent test paper was also used to detect cyanide in an aqueous medium.

Theoretical insights into a turn-on fluorescence probe based on naphthalimide for peroxynitrite detection

Compared with other reactive oxygen species, peroxynitrite (ONOO−) has diversified reactions and transformations in organisms, and its specific action mechanism is not very clear. The study of reactive oxygen species is of great significance in the field of physiology and pathology. Recently an effective on/off fluorescent probe HCA-OH was designed by Liu et al. through tethering p-aminophenol to 1,8-naphthalimide directly. The probe HCA-OH could release the fluorophore HCA-NH2 with good photostability and high fluorescence quantum yield under oxidation of ONOO− via dearylation process. In this work, the sensing mechanism and spectrum character of probe HCA-OH were studied in detail under quantum chemistry calculation. The electronic structures, reaction sites and fluorescent properties of the probe were theoretically analyzed to benefit us for in-depth understanding the principle of detection on reactive oxygen species (ONOO−) with the fluorescent probe HCA-OH. These theoretical results could inspire the medical research community to design and synthesize highly efficient fluorescent probe for reactive oxygen species detection.

A fluorescence turn-on organosilane-coated Cyst/QDs nanocomposites for highly sensitive and selective monitoring silver ions in living organisms

The practical applications of Cd-based quantum dots (QDs) in biological systems have been restricted by their high toxicity and poor biocompatibility. Herein, we constructed a new water-soluble Cyst/QDs nanocomposites composed of silicon-functionalized CdSe/CdS QDs and cystine as a turn-on fluorescent probe for the imaging and detection of Ag+ in living organisms. CdSe/CdS-Si-NH2 QDs with rich amino groups (-NH2) on their surface were firstly synthesized by reacting 3-aminopropyltrimethoxysilane with CdSe/CdS QDs capped with 2-mercaptoethanol. CdSe/CdS-Si-NH2 QDs emit the bright green fluorescence at 575 nm in aqueous solution with quantum yield of 10.6 % and superior photo-stability. Meanwhile, their fluorescence intensity can be effectively enhanced by cystine based on its strong affinity towards Cd2+ on the surface of Cd-based QDs. Besides, the addition of Ag+ results in a strongly enhanced fluorescence of as-prepared Cyst/QDs nanocomposites in aqueous solution. Under the optimal conditions, the response was linearly proportional to natural logarithm of Ag+ concentration ranging from 4.0×10−9 to 1.0×10−6 mol/L with a detection limit of 1.65 nM. Furthermore, Cyst/QDs nanocomposites can be exploited as a possible fluorescent probe for in vivo imaging based on its excellent luminescent properties, low toxicity and great biocompatibility. Bio-imaging study also revealed that Cyst/QDs nanocomposites could be applied to detecting Ag+ in live cells and organisms (zebrafish). Thus, our research provides an efficient method for creating low-toxic and biocompatible Cd-based QDs nanoprobe for a sensitive and selective detection of Ag+ in live cells and organisms.

A water-soluble colorimetric and turn-on fluorescence sensor for fast and sensitive detection of sulfite/bisulfite ions in real samples and live cells

Consuming an excessive amount of sulfites can have detrimental effects on human health. Therefore, it is essential to develop an effective technique to detect the presence of HSO3− in food samples and live cells. Herein, we have developed a colorimetric and turn-on fluorescent probe PI capable of efficiently detecting sulfite/ bisulfite (SO32− /HSO3−) in aqueous PBS buffer (pH 7.4). This probe PI is non-fluorescent due to intramolecular charge transfer (ICT), but becomes fluorescent in the presence of HSO3−. The reaction between SO32− /HSO3− and the probe disrupts π - conjugation by a nucleophilic addition mechanism, resulting in the inhibition of intramolecular charge transfer (ICT). This leads to changes in both the fluorescence and absorption spectra. The color of the probe PI changed from blue to colorless, making it easier to detect HSO3−with the naked eye. Our probe also demonstrates excellent sensitivity, selectivity, fast (reaction completed in 300 s), and a low limit of detection (LOD = 8.4 nM). Furthermore, it is effective in detecting levels of SO32− /HSO3− in water, sugar, and MDA-MB-231 live cancer cells.

A metal–organic framework composite loaded with coumarin guests as a turn-on luminescent sensor for detection of cysteine in aqueous solution

In this work, a composite material (ACE@UiO-66-NH2) has been synthesized conveniently by loading a cysteine-responsive molecular probe Acrylic acid 3-acetyl-2-oxo-2H-chromen-7-yl ester (ACE) on a UiO-type zirconium-based metal–organic framework (UiO-66-NH2). Furthermore, the resulting ACE@UiO-66-NH2 demonstrated to be a fluorescent turn-on probe for selective recognition of Cys from other amino acids in aqueous HEPES buffer systems. Additionally, the proposed recognition mechanism has been confirmed by 1H NMR and TLC. The study provided a promising approach to rationally design MOF-based fluorescent sensor for Cys in aqueous system.

Synthesis and application of a novel turn-on fluorescent probe for the determination of sulfur ions in real samples

A novel and highly selective reactive sulfur ions (S2-) probe, 4′-(benzo[d]thiazol-2-yl)-3′-((7-nitrobenzo[c][1,2,5] oxadiazol-4-yl) oxy)-N, N-diphenyl-[1,1′-biphenyl]-4-amine (DBA), has been synthesized through covalent bonding of a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) unit with 4-(benzo[d]thiazol-2-yl)-4′-(diphenylamino)-3-phenylphenol (BO-OH). The structure was meticulously characterized using a combination of IR, NMR, HRMS, and LC-MS techniques. Notably, upon the addition of S2-, the fluorescence of the probe DBA solution underwent a marked enhancement, transitioning from nearly colorless to brilliant yellow-green luminescence. The Ultraviolet–visible absorption spectrum and fluorescence emission were utilized to assess the probe DBA efficacy in detecting and identifying S2-. It exhibited a substantial fluorescence amplification, enabling quantitative detection within a concentration range of 0 to 17.1 μM, and possessed a low detection limit of 66.89 nM. Moreover, this method boasts a high recovery rate, excellent accuracy, and usefulness for analysis when tracking S2- in real samples.

Simple turn-on fluorescent probe for ultrafast and highly selective detection of hydrogen sulfide in aqueous solutions

5H-Benzimidazo[1,2-c]quinazoline-6-thione (BI–QT), was synthesized as a benzimidazole-based probe to detect H2S. BI–QT exhibits a fluorescent “turn-on” response in DMSO/H2O (9:1, HEPES 10 mM, pH 7.4) upon the addition of H2S. The BI–QT probe can determine micromolar (0–600 µM) H2S concentrations in aqueous systems, with a detection limit of 1.12 µM. Interestingly, BI–QT exhibited an ultrafast response to H2S, with maximum intensity achieved almost instantly when exposed to H2S. BI–QT is largely unaffected by pH and responds reliably over the wide 4–11 pH range, which highlights its applicability to various physiological scenarios. UV–vis, fluorescence, and 1H NMR spectroscopic analyses investigated the sensing mechanism. The practicality of the probe was demonstrated using water samples and living cells.

A highly efficient coumarin-based turn-on fluorescent probe for specific and sensitive detection of exogenous and endogenous Nitroxyl in vivo and in vitro

Nitroxyl (HNO) is documented to be closely concerned with diverse pathological and physiological processes within living organisms. This research showcased the creation of a smart fluorescent turn-on probe, CCA-HNO, which is based on coumarin. It is designed to specifically detect HNO in the presence of metal ions, anions, biothiols, and reactive oxygen species (ROS). The probe CCA-HNO exhibited low detection limit of 34 nM and wide pH applicable range of 2–12 in the detection process of HNO. In view of its low cytotoxicity and admirable cell permeability, the probe CCA-HNO was utilized for high-contrast imaging of exogenous and endogenous HNO fluctuations in living cells. Moreover, the probe CCA-HNO also can effectively realize the real-time visualization of exogenous and endogenous HNO in living zebrafish. We anticipated that this finding can provide an excellent method for knowing the biological function of HNO in relevant pathological processes.

Mitochondrial Targetable Turn-On Fluorescent Probe for Fast Detection of NAD(P)H in Living Cells and In Vivo.

Using colorimetric and fluorescent probes has garnered significant interest in detecting NAD(P)H within practical systems and biological organisms. Herein, we synthesized a mitochondrial targetable fluorescent probe (ISQM) for fast NAD(P)H detection in <1 min. The ISQM is positively impacted because of the quinolinium reduction facilitated by NAD(P)H. It consequently liberates the push-pull fluorophore ISQM-H with a large Stokes shift (110 nm). This release leads to a turn-on response of red-emitting fluorescence, accompanied by a meager detection limit of 59 nM. To compare the differences in the NAD(P)H levels of tumor cells and normal cells, we used ISQM to measure the fluorescent signal intensities of HeLa cells (tumor cells) and RAW 264.7 cells (normal cells), respectively. Surprisingly, the experiment, including the measurement of colocalization over time, indicated that the probe exhibits a reaction with mitochondrial NAD(P)H and trace NAD(P)H in hypoxia conditions in cancer cells. Moreover, we effectively used the probe ISQM to identify the NAD(P)H in tumor mice.