Fluorescence Turn-on Research Articles

Fluorescent probes for formaldehyde based on formaldehyde-promoted C-N cleavage of azanyl carbamates.

Formaldehyde (FA) is an endogenous one-carbon metabolite and an environmental pollutant and carcinogen. Elevated FA levels are associated with many diseases. Methods for the convenient and in situ detection of FA levels are of great significance for understanding FA's biofunctions and signalling pathways. Herein, the NAP-FAP2 series of fluorescent probes for FA detection were developed based on FA-promoted C-N cleavage of 3-nitrophenylazanyl N-arylcarbamate via FA-induced intramolecularity, where the aryl group is the fluorophore 1,8-naphthalimide-4-yl. The 3-nitrophenylazanyl containing reactive group also functions as a fluorescence quenching group via a photo-induced electron transfer mechanism to generate turn-on fluorescence response upon reaction with FA. The probes were applied to explore FA level changes in erastin-induced ferroptosis, and it was found that the FA level increases intracellularly, but not in the endoplasmic reticulum, suggesting that the FA level increases in ferroptosis are not derived from lipid peroxidation.

Tuning sensing efficacy of anthraimidazoledione-based charge transfer dyes: nitro group positioning impact.

Anthraimidazoledione-based optical sensors have been designed by varying the position of the nitro functional group. All three positional isomers showed highly colored, photostable optical signals owing to intramolecular charge transfer interactions. Despite having the same anion-binding site (imidazole unit), the selectivity and sensitivity of the compounds depend on the positioning of the nitro group. The selectivity was fairly good for the meta isomer, followed by the ortho and para isomers, respectively. In contrast, the sensitivity towards anions followed a completely opposite trend, with the para isomer being the most sensitive one towards anions. Interestingly, the color changing response along the turn-on fluorescence signal was observed only with CN- ions in a semi-aqueous environment. Though the introduction of water as a co-solvent could improve the selectivity, the sensitivity was found to be slightly less than that observed in pure organic medium. Mechanistic studies indicated hydrogen bonding interactions between the imidazole -NH proton and cyanide, which further facilitated the extent of intramolecular charge transfer.

BODIPYs α-appended with distyryl-linked aryl bisboronic acids: single-step cell staining and turn-on fluorescence binding with D-glucose.

Small-molecule sensors that are selective for particular sugars are rare. The synthesis of BODIPYs appended with two boronic acid units is reported, alongside cellular staining/labelling and turn-on fluorescence binding data for carbohydrates. The structural frameworks were designed using computational methods, leaning on the chelation characteristics of bis(boronic acids) and the photophysical properties of BODIPYs. Selective binding to glucose is demonstrated via emission and absorption methods, and the challenges of using NMR data for studying carbohydrate binding are discussed. Furthermore, crystal structures, cell permeability and imaging properties of the BODIPYs appended with two boronic acid units are described. This work presents boronic-acid-appended BODIPYs as a potential framework for tunable carbohydrate sensing and chemical biology staining.

A thiophene-linked terpyridine based phenanthridine chemoreceptor for Cd2+ and Cr3+ selective ratiometric fluorescence detection in environmental water and rice samples

BackgroundThe studied materials, Cadmium (Cd2+) and Chromium (Cr3+) are highly toxic, and it focuses on investigating various environmental sources, such as industrial processes and waste water. When quantities of Cr3+ and Cd2+ exceed the allowable limit, biological toxicity and hazardous environmental pollution are unavoidable. In order to address this problem, we introduce 5-(5-(4-([2,2':6′,2″-terpyridin]-4′-yl) phenyl) thiophen-2-yl)-7,8,13,14-tetrahydrodibenzo [a,i] phenanthridine (TPTP), a dual-emission response chemosensor that employs a colorimetric and fluorescence turn-on approach for the rapid, sensitive, and discriminate detection of Cr3+ and Cd2+ ions. ResultsWe created a newly designed luminous TPTP sensor based on intramolecular charge transfer (ICT). TPTP sensor probe specifically determined Cr3+ and Cd2+ ions with an immediate colour shift from cyan to green and orange in CH3CN: H2O (6:4) solvent solution. The permissible level set by the Environmental Protection Agency (EPA) of the United States for the presence of Cr3+ and Cd2+ ions in drinking water was higher than the detection level of 3.5 and 9.7 nM, by this sensor respectively. NMR titrations, HRMS, and theoretical calculation methods were employed to examine the accurate sensing processes of TPTP and complexes. SignificanceThis is an effective method of detecting Cr3+ and Cd2+ ions in an environmental system using a ratiometric methodology. In addition, TPTP was used to determine the concentration of Cr3+ and Cd2+ ions in natural water and food samples. Fluorescent bio-imaging studies revealed that the present sensor TPTP could identify Cr3+ and Cd2+ ions inside living HeLa cells. A paper kit analysis has been done on TPTP, which has a time-to-result of less than 1 s and offers a cost-effective assay. As a result, the platform offers portability.

A turn-on fluorescence molecularly imprinted sensor based on covalent organic framework for specific and visual detection of α-dicarbonyl compounds

In this paper, a turn-on fluorescence sensor (COFTPDD@ILMIPs) was prepared for the detection and removal of the α–dicarbonyl compound 3-deoxyglucosone (3-DG) in milk. The sensor uses ultra-high quantum yield green fluorescent covalent organic frameworks (COFs) as the fluorescence center, and introduces ionic liquids to improve its fluorescence performance and mass transfer rate, and the selectivity and anti-interference ability of the sensor were improved by molecular imprinted technique. In addition, the sensor was combined with a smartphone sensing platform to achieve real-time quantitative detection of 3-DG in the field. The quantitative detection of 3-DG in a good linear range (0.5–100 μg/L) was observed, and the low limit of detection was 0.31 μg/L. The spiked recoveries of 3-DG in milk samples ranged from 81.96–117.39 %, which provided an effective strategy for the accurate and rapid detection of hazardous substances in milk.

Fluorescent and Electrochemical Sensor Based on Basic Red 9 Dye Functionalised Graphene Oxide-Montmorillonite Composite for Selective Detection of Cerium (III) Ion.

In this work, graphene oxide (GO) has been prepared from used dry cells using modified Hummer's method and encapsulated with montmorillonite clay. To enhance its electrical property, the GO-MMT composite has been functionalised with Basic Red 9 dye. The sensor was characterized by various spectroscopic techniques like FT-IR spectroscopy, PXRD, SEM analysis, etc. Basic Red 9 dye functionalised GO-MMT composite has been employed for fluorescent and electrochemical detection of Ce3+ ion. The fluorescent turn-on sensing is sensitive, reversible and free from interference from other metal ions. The detection of Ce3+ ion by the sensor was also conducted in bovine serum albumin (BSA) medium. Pt electrode modified with the hybrid sensor produces excellent electrochemical change in presence of Ce3+ ion through cyclic voltammetry and square wave voltammetry technique. The limit of detection (LOD) from fluorescence spectroscopy, cyclic voltammetry and square wave voltammetry were calculated to be 0.6556 × 10- 9 M, 1.232 × 10- 9 M and 1.923 × 10- 9 M respectively.

Real-Time Live Imaging of Osteoclast Activation via Cathepsin K Activity in Bone Diseases.

Intravital fluorescence imaging of functional osteoclasts within their intact disease context provides valuable insights into the intricate biology at the microscopic level, facilitating the development of therapeutic approaches for osteoclast-associated bone diseases. However, there is a lack of studies investigating osteoclast activity within deep-seated bone lesions using appropriate fluorescent probes, despite the advantages offered by the multi-photon excitation system in enhancing deep tissue imaging resolution. In this study, we report on the intravital tracking of osteoclast activity in three distinct murine bone disease models. We utilized a cathepsin K (CatK)-responsive two-photon fluorogenic probe (CatKP1), which exhibited a notable fluorescence turn-on response in the presence of active CatK. By utilizing CatKP1, we successfully monitored a significant increase in osteoclast activity in hindlimb long bones and its attenuation through pharmacological intervention without sacrificing mice. Thus, our findings highlight the efficacy of CatKP1 as a valuable tool for unraveling pathological osteoclast behavior and exploring novel therapeutic strategies.

Self-Report Amphiphilic Polymer-Based Drug Delivery System with ROS-Triggered Drug Release for Osteoarthritis Therapy.

The development of drug delivery systems with real-time cargo release monitoring capabilities is imperative for optimizing nanomedicine performance. Herein, we report an innovative self-reporting drug delivery platform based on a ROS-responsive random copolymer (P1) capable of visualizing cargo release kinetics via the activation of an integrated fluorophore. P1 was synthesized by copolymerization of pinacol boronate, PEG, and naphthalimide monomers to impart ROS-sensitivity, hydrophilicity, and fluorescence signaling, respectively. Detailed characterization verified that P1 self-assembles into 11 nm micelles with 10 μg mL-1 CMC and can encapsulate hydrophobic curcumin with 79% efficiency. Fluorescence assays demonstrated H2O2-triggered disassembly and curcumin release with concurrent polymer fluorescence turn-on. Both in vitro and in vivo studies validated the real-time visualization of drug release and ROS scavenging, as well as the therapeutic effect on osteoarthritis (OA). Overall, this nanotheranostic polymeric micelle system enables quantitative monitoring of drug release kinetics for enhanced treatment optimization across oxidative stress-related diseases.

Flexible metallosalen complex for pyrophosphate sensing in biological milieu: Use disassembly strategy for signal amplification

In the present work, we have designed and synthesized two dimeric fluorescein derivatives with flexible salen (1) or a rigid salophen (2) linker unit. The Fe(III) complexes of these compounds ([1.Fe]+ and [2.Fe]+) showed changes in solution color specifically upon addition of inorganic pyrophosphate (PPi) at pH 7.0 in PBS buffer. Along this, we also observe appearance of green fluorescence (turn-on) in the prescence of PPi. The mechanistic studies suggested PPi-induced demetallation process, which led to disassembly for molecular structure in the aqueous medium and release of highly fluorescent fluorescein aldehyde. The disassembly process was found to be dependent on electronic structure, rigidity of the linker unit, temperature, and local pH etc. The selectivity as well as sensitivity of [1.Fe]+ towards PPi was also found to be superior than that observed with [2.Fe]+. Since each disassembly process released two signalling unit (fluorescein), we could observe a huge increment in FL intensity even with small quantity of PPi (<10 µM). Finally, the sensory system was utilized for detection of PPi in diluted blood serum samples and inside living mammalian cells (HeLa, cervical cancer cells). Chemically-modified paper strips have been developed for the detection of PPi in water samples at outside laboratory conditions.

A magnetic molecular imprinting-based fluorescence probe for sensitive and selective detection of 2,4-D herbicide.

A new magnetic molecular imprinting-based turn-on fluorescence probe (Fe3 O4 NPs@SiO2 @NBD@MIPs) has been synthesized via a facile sol-gel polymerization for the detection of 2,4-dichlorophenoxyacetic acid (2,4-D). Based on the photoinduced electron transfer (PET) of nitrobenzoxadiazole (NBD), 2,4-D can be recognized by enhancement of NBD fluorescence. With the presence of Fe3 O4 in the core of the probe, this sensor can also be reused many times using magnetic aggregation methods. After the addition of various concentrations of 2,4-D, the fluorescence peak at 530 nm (excitation of 468 nm) increased linearly ranging from 0.1 to 3μM with a detection limit of 0.023 μM. This sensing system is believed to be available for detecting 2,4-D in real samples, with high recovery rates ranging from 94% to 108% for three spike levels of 2,4-D with precisions below 5%.

Detection of pioglitazone based on dual-emission ratiometric fluorescence probe consisting of ZIF8 and to L-ASC-AuNP/DA nanoparticles.

Asimple and sensitive dual-emission ratiometric fluorescent probe was developed using zeolitic imidazolate framework 8 (ZIF8) and L-ascorbic acid Au-doped dopamine nanoparticles (ZIF8/L-ASC-AuNP/DA NP) for the determination of pioglitazone (Pio), an oral hypoglycemic agent and insulin sensitizer, in real samples. The prepared system was based on the Pio-enhanced dual-emission intensity of ZIF8/L-ASC-AuNP/DA NP. The potential impact of various parameters on the system's emission intensity was tested. According to the findings, there is a strong linear correlation between the system's turn-on fluorescence intensity and Pio concentrations in the range 0.3nM to 30.0μM. The obtained value for the limit of detection (LOD) was 0.14nM. In addition, the intra- and inter-day accuracy of the nanoprobe was studied and the findings revealed satisfactory precision and accuracy of the system. The short-term and freeze-thaw stability of Pio in plasma samples was evaluated and the results indicated the high stability of the developed nanoprobe under the test conditions. Pio was accurately detected in human plasma samples under ideal conditions with analytical recoveries in the range 86.0 - 109.3%. The results showed that the devised probe may be employed as an easy, sensitive, and precise approach for detecting Pio in real samples.

Synthesis and characterization of the reactivity of new far-red fluorescent dyes and a boronate probe containing a tricyanopyrroline skeleton

Probes that exhibit turn-on fluorescence in the far-red region (600–750 nm) are in high demand because their use causes minimal autofluorescence and cellular damage. Here, we present a practical microwave-assisted synthesis of dyes containing a tricyanopyrroline (TCP) unit and a new boronate probe based on the TCP chemical scaffold. The proposed microwave-assisted method performs better in an eighteenth of the time than condensation in ethanol. We also present the simple methodology to detect peroxynitrite using the TCP-BOR redox probe in three different ways. First, the TCP-OH dye, which absorbs far-red light, is a major oxidation product that can be used for fluorescent detection. Second, peroxynitrite-specific products, nitrated TCP-NO2, and reduced TCP-H derivatives can easily be detected and quantified with HPLC due to a significant difference in the position of their absorption bands. Furthermore, the EPR signal recording of the spin adducts of the phenyl radical formed in the reaction of TCP-BOR with peroxynitrite and mass spectrometric analyses of these adducts can also be used to confirm the oxidation of the probe by peroxynitrite. TCP-OH was also detected in macrophages RAW 264.7 activated for the ONOO− production.

Green-emitting carbon dots as a "turn on" fluorescence bio-probe for highly sensitive and selective detection of lipase in human serum.

Enzyme activity assays play a crucial role in numerous fields, including biotechnology, the food industry, and clinical diagnostics. Lipases are particularly important enzymes due to their widespread use in lipid metabolism and esterification reactions. Here, we present a pioneering method for the sensitive and selective determination of lipase activity using green carbon dots (G-CDs) for first time. G-CDs are a fascinating class of carbon nanomaterials with unique optical properties and biocompatibility, making them ideal candidates for enzyme activity assays. This approach eliminates the need for traditional fluorophores or chromogenic substrates, reducing costs, fast response time (1 min), and environmental impact with a quantum yield (QY) of 7.42%. As designed, the G-CDs fluorescent probe turn-on demonstrated a reliable linear detection range from 0 to 9 mg/mL under ideal conditions, with detection limit of 0.01 mg/mL and limit of quantification (LOQ) of 0.045 mg/mL, respectively. Furthermore, the G-CDs system was thoroughly evaluated in human serum samples, showing recoveries ranging from 100.0 to 105.0%. These findings highlight the promising applicability of the G-CDs probe for lipase detection, yielding highly favorable results.

A practical chromogenic and fluorogenic dual-mode sensing platform for rapid quantification of sulfite in food

Sulfur dioxide (SO2) and its derivatives (HSO3− and SO32−) are widely used in food-processing. Whereas excessive consumption of sulfur dioxide and its derivatives (>0.70 mg·kg−1day−1) severely endangers human health. In this work, we rationally constructed a practical dual-mode probe (dicyanomethylene)-1-methyl-1,4-dihydroquinolin-2-yl)vinyl)-1-methylquinolinium (QMN), which underwent a specific 1, 4-Michael addition with sulfite to afford a noticeable color change from pale yellow to red along with a high-contrast fluorescence turn-on response at 598 nm. QMN has the advantages of rapid response, high signal-to-noise ratio, excellent selectivity, good water-solubility, large Stokes shift and low detection limit (LOD = 31.9 nM). QMN has been successfully used to on-site visually determine sulfite in a diversity of foods with satisfactory recoveries (91.33–111.33 %) and high accuracy (93.74–98.71 %). Furthermore, a portable smartphone-based fluorescence sensing platform was fabricated for on-site determination of sulfite in food with good performance.

Co-crystal of caffeic acid and bipyridyl ethylene as a selective fluorescence sensor for Al3+ and its coordination geometry – Combined experimental and theoretical investigations

Herein, the caffeic acid and bipyridyl ethylene-based co-crystal (CA-BPE) have been developed as a fluorescent turn-on sensor for Al3+ ions in MeOH: H2O (8:2, v/v) media. The free CA-BPE co-crystal shows an absorbance band at 297 nm and emission at 445 nm. The probe forms a 1:1 stoichiometry complex with an estimated association constant of 9.17 × 104 M−1 by Job's and BH plots, respectively. The CA-BPE detects Al3+ down to 30.4 nM with a pH range of 3 to 6 without interfering with other metal ions. Further, the binding mechanism between CA-BPE and Al3+ was studied by FTIR and DFT studies. Interestingly, the PXRD, SEM, EDX, and DFT-based computational studies reveal the formation of 2D layers of a metal–organic framework (MOF)-like structure.

Novel &amp; Smart Sensing of Acetate and Hypochlorite Ions With Relay Recognition of Cr3+ Ion With Fluorescence Turn-on: Application in Bio-imaging &amp; Real Sample Analysis

Novel &amp; Smart Sensing of Acetate and Hypochlorite Ions With Relay Recognition of Cr3+ Ion With Fluorescence Turn-on: Application in Bio-imaging &amp; Real Sample Analysis

Multi-analyte fluorescence sensing based on a post-synthetically functionalized two-dimensional Zn-MOF nanosheets featuring excited-state proton transfer process

Covalent post-synthetic modification of metal–organic frameworks (MOFs) represents an underexplored but promising avenue for allowing the addition of specific fluorescent recognition elements to produce the novel MOF-based sensory materials with multiple-analyte detection capability. Here, an excited-state proton transfer (ESPT) active sensor 2D-Zn-NS-P was designed and constructed by covalent post-synthetic incorporation of the excited-state tautomeric 2-hydroxypyridine moiety into the ultrasonically exfoliated amino-tagged 2D Zn-MOF nanosheets (2D-Zn-NS). The water-mediated ESPT process facilitates the highly accessible active sites incorporated on the surface of 2D-Zn-NS-P to specifically respond to the presence of water in common organic solvents via fluorescence turn-on behavior, and accurate quantification of trace amount of water in acetonitrile, acetone and ethanol was established using the as-synthesized nanosheet sensor with the detection sensitivity (<0.01% v/v) superior to the conventional Karl Fischer titration. Upon exposure to Fe3+ or Cr2O72−, the intense blue emission of the aqueous colloidal dispersion of 2D-Zn-NS-P was selectively quenched even in the coexistence of common inorganic interferents. The prohibition of the water-mediated ESPT process and local emission, induced by the coordination of ESPT fluorophore with Fe3+ or by Cr2O72− competitively absorbs the excitation energy, was proposed to responsible for the fluorescence turn-off sensing of the respective analytes. The present study offers the attractive prospect to develop the ESPT-based fluorescent MOF nanosheets by covalent post-synthetic modification strategy as multi-functional sensors for detection of target analytes.

Off-label use of molecular glue: 3-hydroxythalidomide derived fluorescent probe for selective detection of palladium based on Tsuji-Trost reaction

3-Hydroxythalidomide draws more and more attentions as a molecular glue in the field of biomedicine and analysis, due to its unique bonding mode to CRBN protein and the novel fluorescent properties. However, there is rare reports about the application in the field of chemosensor. Herein, we designed and synthesized a fluorescence turn-on probe using 3-hydroxythalidomide as a fluorophore for the detection of palladium based on Tsuji-Trost reaction. The mechanism of the chemosensor for palladium and the effects of the phosphine ligands were investigated systematically. The results indicated that the probe displayed an excellent linear relationship with palladium concentration (region factor, R2 = 0.998) over the range of 1 × 10−7 M − 4 × 10−6 M, presenting a low detection limit of 1.2 nM. Furthermore, it was successfully applied to the determination of palladium in the samples of pharmaceutical wastewater and spiked water with different oxidation states.

A strategy for constructing novel red emitting fluorescent probes for neutrophil elastase tracking based on self-immolative linker and TICT effect

Neutrophil elastase (NE) is a crucial biomarker for the diagnosis of lung related diseases. Until now, most of the basic structure of the reported NE fluorescent probes is connected by the amide bond between the pentafluoropropionyl recognition group and the fluorophore containing an amino group, which extremely limited the application of the fluorophores containing hydroxyl groups. To address this limitation, we have rationally constructed a red emitting NE fluorescent probe, namely SNARF-NE, which consists of a hydroxyl containing rhodamine derivative SNARF-OH and pentafluoropropionyl, connected by a self-immolative linker. As we expected, SNARF-NE was successfully used to detect NE activity in a red emitting fluorescence turn-on model along with favorable sensitivity and ultrahigh selectivity. Furthermore, in order to further improve the response ability of SNARF-NE, a novel fluorophore TSNARF-OH has been redesigned by restricting the TICT effect of SNARF-OH to construct the NE fluorescent probe TSNARF-NE. When used to detect NE levels, as we expected, TSNARF-NE exhibited faster response time, higher quantum yield, longer fluorescence lifetime, lower detection limit and higher catalytic efficiency than SNARF-NE. Most importantly, TSNARF-NE has shown an ability to image and track endogenous NE levels in lung cancer cells and zebrafish model much faster compare with SNARF-NE. All the experimental results clearly demonstrate that the utilization of self-immolative linker and TICT blocking methods is highly valuable for designing a wide range of NE fluorescent probes with outstanding optical properties.

Near-infrared fluorescent probe with large Stokes shift for specific detection of lysine

A new near-infrared (NIR) fluorescent probe CL based on coumarin- dicyanoisophorone was synthesized. Addition of Lys to probe CL solution in DMF/H2O (9:1, v/v) medium resulted in noticeable enhancement in the intensity of the fluorescence emission at 702 nm, accompanying distinct color change from yellow to pink. While addition of other amino acids and biothiols (Gly, Hcy, GSH, Glu, Val, Tyr, Arg, Trp, Lys, His, Leu, Phe, Asp and Met) did not bring about substantial changes in both fluorescence emission and color. The detection limit was calculated to be 0.51 μM. Job’s plot test revealed that probe CL and Lys formed a complex of 1:1 stoichiometry. Probe CL showed high stability and could be used to recognize Lys in a wide pH range of 4.0–10.0. The sensing mechanism was proposed and verified by 1H NMR spectral measurement. The dual-modal fluorescence turn-on and colorimetric NIR probe with an extremely large Stokes shift of 280 nm may be utilized for highly specific and practical sensing of Lys.