Turn-on Fluorescent Sensor Research Articles

Turn-on fluorescent sensors based on post-modified Zr-MOF for enantioselective recognition of phenylalanine

Chiral enantiomers, particularly amino acids, frequently display distinct physiological activities and biological functions. Consequently, it is crucial to distinguish their absolute conformations. Herein, a pair of chiral sensors, UiO-L-Pro and UiO-D-Pro, were obtained by immobilizing the chiral center l-proline (L-Pro) and d-proline (D-Pro) into a Zr-based metal−organic framework (MOF) via a condensation reaction. Fluorescence analyses revealed a notable difference in the enhancement of fluorescence intensity between UiO-L-Pro and UiO-D-Pro when treated with l-phenylalanine (L-Phe) or d-phenylalanine (D-Phe), demonstrating enantioselective luminescence properties. Differences based on hydrogen bond interaction give them significant enantioselectivity factors α. The enantioselectivity factors α (α = KBH(D-Phe)/KBH(L-Phe)) for UiO-L-Pro and UiO-D-Pro were 4.15 and 0.47, respectively. Thus, the chiral material could be employed to identify different configurations of phenylalanine.

AIE active hydroxycoumarin-anthranilic acid coupled enamine: Sequential detection of Cu2+/S2− ions and live cell imaging application

In this contribution, we designed and developed 7-diethylamino-4-hydroxycoumarin coupled anthranilic acid-based enamine (DHCBA) and its Cu2+ complex (DHCBA-Cu)via simple synthetic strategy. DHCBA shows solvatochromic effect, aggregation induced emission feature at 80 % methanol–water mixture and colorimetric as well as fluorescence turn-off sensing features towards Cu2+ ions. The DHCBA-Cu2+ ensemble has been utilized as a turn-on fluorescence sensor for the detection of S2− through a decomplexation approach. The formation of a 1:1 DHCBA-Cu2+ ensemble was further supported by 1H NMR studies, HRMS analysis and Density Functional Theory (DFT) calculation. The detection limit for Cu2+ was found to be 6.5 nM and then the binding affinity and binding stoichiometry of the probe towards Cu2+ ion was calculated using the online BindFit v0.5 supramolecular software. Moreover, the 1:1 stoichiometric ratio between DHCBA and Cu2+ ions were confirmed via single crystal X-ray analysis. The structural analysis of DHCBA-Cu2+ indicates that it forms an interesting one-dimensional coordination polymeric chain-like structure, further transformed into a two-dimensional polymeric network through hydrogen bonding interactions. The reversible on–off–on emission character of the probe, DHCBA was successfully applied for the construction of the IMPLICATION logic gate as well as on-site detection applications using paper strip and cotton-swab tests. Furthermore, the sensing feature of the enamine against Cu2+/S2− ions were validated by intracellular imaging applications.

A "Turn-On" Fluorescent Probe for the Visual Detection of Total Iron in Wine.

A turn-on fluorescent sensor (E)-4-((4-(5-fluoro-1H-benzo[d]imidazol-2-yl)benzylidene)amino)phenol (FBAP) for the detection of Fe3+/2+ was synthesized. The fluorescence intensity of probe FBAP solution gradually increased with increased Fe3+ concentration. The low detection limit (LOD) was calculated to be 0.17 nM. The optimized structure and luminescent properties of FBAP were calculated by time-dependent density functional theory (TD-DFT) and Solvation Model Density (SMD). The rotation of the dihedral angle and ICT in the imine probe turned off the emission of the benzimidazole, which was restored upon cleaving the imine. Probe FBAP was successfully applied to determine whether Fe3+/2+ in wine exceeded the standard by phone and the rapid detection of Fe3+/2+ in the form of test strips was also conducted.

A Fluorescence Enhancement Sensor Based on Silver Nanoclusters Protected by Rich-G-DNA for ATP Detection.

In this study, a turn-on fluorescence sensor for the detection of adenosine 5'-triphosphate (ATP) was developed and tested using ATP-DNA2-Ag NCs. The results showed that the fluorescence of ATP-DNA2-Ag NCs was significantly enhanced with the addition of ATP. The fluorescence enhancement was a result of the specific binding activity of the ATP aptamer and ATP, which caused G-rich sequences to approach the dark DNA-Ag NCs, owing to the alteration in ATP aptamer conformation. The proposed sensor demonstrated a good linear range of 18-42 mM and a limit of detection (LOD) of 2.8 μM. The sensor's features include sensitivity, selectivity, and simple operation. In addition, the proposed sensor successfully measured ATP in 100-fold diluted fetal bovine serum.

A highly stable, rapid and sensitive fluorescent probe for Al3+ and pefloxacin based on enhanced fluorescence of a Co(II) coordination polymer

Fabricating functional coordination polymer (CP) architectures and exploiting it as fluorescence sensors for detecting diverse metal ions and antibiotics, have attracted extensive attention. Based on a rarely-used benzimidazole-derived ligand 2,2′-bis-(2-pyridin-3-yl-vinyl)-3H,3′H-[5,5]bibenzoimidazole (L), a new CP {[Co(L)0.5(tbip)]·H2O}n (H2tbip =5‑tert-butylisophthalic acid) (1) was synthesized under solvothermal condition and characterized. Complex 1 reveals a two-dimensional network with the type of topology of 3,4,5L7. Complex 1 possesses excellent thermal and chemical stability. The fluorescence detection ability of complex 1 was explored and demonstrated that complex 1 can be used as the first fluorescent turn-on sensor to sense Al3+ and pefloxacin (PEF) with a low detection limit and fast response. The fluorescence enhancement mechanism was investigated in detail.

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 simple turn-on fluorescent sensor for Cu2+ detection based on Schiff base via restricted ICT and fabrication of paper strips for on-site visual sensing applications

Herein, Sensor RN2 was prepared by condensation of 2‑hydroxy-1-naphthaldehyde and 2-chloroaniline and well characterized by FTIR, PXRD, 1H NMR, and 13C NMR. Photophysical investigation reveals that sensor RN2 exhibits remarkable colorimetric and fluorometric “turn-on” behavior towards Cu2+ with high selectivity and sensitivity in the presence of other examined metal ions. The stoichiometric ratio was determined to be 2:1 for RN2 and Cu2+ based on the Job plot, DFT and HRMS analysis. The detection limit for Cu2+ reached the nM level. The binding constant of RN2 with Cu2+ was 2.55 × 1011M−2. RN2 was successfully applied for quantitative recognition of Cu2+ in biological and environmental samples. The test strips based on RN2 were fabricated, which could act as an efficient and convenient Cu2+test kit.

Highly selective fluorescence turn-on sensor for·thiol compounds detection

As a kind of commonly-used synthetic materials for many pesticides, thiol compounds, once being leaked, can cause serious harm to the environment and humans. Therefore, the efficient detection of thiol compounds is essential. In this study developed a turn-on fluorescent probe (Cu@Zn-CP) for the highly sensitive fluorescence detection of thiol compounds. The probe was constructed based on a zinc coordination polymer (Zn-CP), whose fluorescence was quenched through the effective doping of Cu2+ ions. After the introduction of methyl thioglycolate (MTC), a rapid fluorescence turn-on response was generated within 90 s with a low detection limit of 23 ppb. Even after being reused for five cycles, the sensor maintains excellent detection performance and demonstrates good recyclability. It can also detect MTC in river water, with a spike recovery rate between 98–103 %. Furthermore, the designed Cu@Zn-CP exhibits good universality for detecting multifarious thiol compounds, including L-cysteine, glutathione, monothioglycerol, and 2-hydroxy-1-ethanethiol. This result provides a potential recyclable fluorescent sensor for thiol compounds.

New G-Triplex DNA Dramatically Activates the Fluorescence of Thioflavin T and Acts as a Turn-On Fluorescent Sensor for Uracil-DNA Glycosylase Activity Detection.

G-triplexes are G-rich oligonucleotides composed of three G-tracts and have absorbed much attention due to their potential biological functions and attractive performance in biosensing. Through the optimization of loop compositions, DNA lengths, and 5'-flanking bases of G-rich sequences, a new stable G-triplex sequence with 14 bases (G3-F15) was discovered to dramatically activate the fluorescence of Thioflavin T (ThT), a water-soluble fluorogenic dye. The fluorescence enhancement of ThT after binding with G3-F15 reached 3200 times, which was the strongest one by far among all of the G-rich sequences. The conformations of G3-F15 and G3-F15/ThT were studied by circular dichroism. The thermal stability measurements indicated that G3-F15 was a highly stable G-triplex structure. The conformations of G3-F15 and G3-F15/ThT in the presence of different metal cations were studied thoroughly by fluorescent spectroscopy, circular dichroism, and nuclear magnetic resonance. Furthermore, using the G3-F15/ThT complex as a fluorescent probe, a robust and simple turn-on fluorescent sensor for uracil-DNA glycosylase activity was developed. This study proposes a new systematic strategy to explore new functional G-rich sequences and their ligands, which will promote their applications in diagnosis, therapy, and biosensing.

Pyrene excimer-based fluorescent chemosensor for cascade detection of Zn(II) and phosphate ions and its applications

There is growing research on developing fluorescent chemosensors that can detect multiple analytes. Herein, a pyrene-naphthaldehyde based Schiff base PNY was synthesized, characterized, and employed for the cascade fluorescent ‘Off-On-Off’ detection of Zn2+ and phosphate ions. The interaction of PNY with Zn2+ led to a distinct fluorescence enhancement at 450 nm, and the fluorescent color of PNY was changed from blue to cyan-blue due to the complexation-induced formation of a pyrene excimer. PNY, as a fluorescent turn-on sensor can be employed to detect Zn2+ down to 2.20 × 10−7 M. Subsequently, the in-situ formed PNY-Zn2+ complex gets decomplex upon the addition of phosphate ion among other tested anions with a detection limit of 3.42 × 10−7 M. With the addition of phosphate ion, fluorescence intensity of PNY-Zn2+ at 450 nm was quenched with the concomitant formation of an emission peak at around 396 nm. The excimer-monomer mechanism was used to explain the sensing ability of PNY. Further, to complement the phosphate ion selectivity, the ability of PNY-Zn2+ to detect adenosine triphosphate (ATP) was explored. At last, the analytical novelty of PNY and PNY-Zn2+ was explored by quantifying Zn2+ and phosphate ions in real environmental and biological samples.

A Dual Fluorescence Turn-On Sensor Array Formed by Poly(para-aryleneethynylene) and Aggregation-Induced Emission Fluorophores for Sensitive Multiplexed Bacterial Recognition.

Bacterial infections have emerged as the leading causes of mortality and morbidity worldwide. Herein, we developed a dual-channel fluorescence "turn-on" sensor array, comprising six electrostatic complexes formed from one negatively charged poly(para-aryleneethynylene) (PPE) and six positively charged aggregation-induced emission (AIE) fluorophores. The 6-element array enabled the simultaneous identification of 20 bacteria (OD600=0.005) within 30s (99.0 % accuracy), demonstrating significant advantages over the array constituted by the 7 separate elements that constitute the complexes. Meanwhile, the array realized different mixing ratios and quantitative detection of prevalent bacteria associated with urinary tract infection (UTI). It also excelled in distinguishing six simulated bacteria samples in artificial urine. Remarkably, the limit of detection for E. coli and E. faecalis was notably low, at 0.000295 and 0.000329 (OD600), respectively. Finally, optimized by diverse machine learning algorithms, the designed array achieved 96.7 % accuracy in differentiating UTI clinical samples from healthy individuals using a random forest model, demonstrating the great potential for medical diagnostic applications.

Surfactant-based supramolecular dye assembly: A highly selective and economically viable platform for quantification of heparin antidote

Herein, we have employed a supramolecular assembly of a cationic dye, LDS-698 and a common surfactant sodium dodecyl sulfate (SDS) as a turn-on fluorescent sensor for protamine (Pr) detection. Addition of cationic Pr to the solution of dye-surfactant complex brings negatively charged SDS molecules together through strong electrostatic interaction, assisting aggregation of SDS way before its critical micellar concentration (CMC). These aggregates encapsulate the dye molecules within their hydrophobic region, arresting non-radiative decay channels of the excited dye. Thus, the LDS-698•SDS assembly displays substantial enhancement in fluorescence intensity that follows a nice linear trend with Pr concentration, providing limit of detection (LOD) for Pr as low as 3.84(±0.11) nM in buffer, 124.4(±6.7) nM in 1% human serum and 28.3(±0.5) nM in 100% human urine. Furthermore, high selectivity, low background signal, large stokes shift, and emission in the biologically favorable deep-red region make the studied assembly a promising platform for Pr sensing. As of our knowledge it is the first ever Pr sensory platform, using a very common surfactant (SDS), which is economically affordable and very easily available in the market. This innovative approach can replace the expensive, exotic and specialized chemicals considered for the purpose and thus showcase its potential in practical applications.

Covalently construction of C-GSH-AuNCs@UiO-66-NH2 composites as an efficient turn-on fluorescence sensor for UO22+

Due to the continuous expansion of the nuclear power industry, the exploitation of uranium resources has led to the discharge of large quantities of uranium-rich wastewater into the environment, which poses a major threat to the environment and human health. Rapid detection of uranium in water bodies is of great significance for early warning of uranium contamination in the environment, safe discharge and real-time regulation of nuclear waste, and sustainable development of energy and ecological environment. Herein, we report a new “turn-on” fluorescent sensor for the detection of UO22+ in aqueous solutions. The fluorescent sensor was obtained by covalently bonding UiO-66-NH2 with gold nanoclusters GSH-AuNCs and showed a sensitive fluorescence enhancement response to UO22+ at low solid-liquid ratio, with a detection limit of 15.3 nmol L−1. With the advantages of intuitive visual detection, reusability and easy separation, the sensitive fluorescence sensor has great potential for the detection of UO22+ in aqueous solutions.

A novel turn-on fluorescence sensor based on the Nd (III) complex for the ultrasensitive detection of 6-mercaptopurine

6-mercaptopurine (6MP) is a chemotherapeuticdrug widely used for treating inflammatory bowel diseases and several cancers. Nevertheless, determining and monitoring its concentration in the human body is highly important because over or under-doses of 6MP can lead to critical health issues. In this paper, we have developed a turn-on fluorescent probe for the determination of the anticancer drug 6-mercaptopurine (6-MP) based on coordination complex [Nd (Anth)3 (H2O)3]. [Nd (Anth)3 (H2O)3] has been synthesized through a simple precipitation process taking the stoichiometric ratio of Nd (III) nitrate hexahydrate and 2-aminobenzoic acid (2-ABA), commonly known as anthranilic acid (Anth). The synthesis and structure have been investigated and validated by different characterizations like UV–visible spectroscopy, FT-IR, HRMS, XPS, and SEM. The synthesized complex displayed excellent fluorescence properties, and the fluorescence intensity was enhanced with the addition of 6MP in the form of a [Fe (6MP)3]2+ mixed complex (Fe-6MP), which is formed by dissolving it in FeCl3. The fabricated sensors displayed the best linear response in a wide range of concentrations from 2.55 μM to 45.51 μM of 6MP. The lower limit of detection (LOD) of the developed sensor was found to be 0.26 μM with a linear correlation coefficient (R2) of 0.99. The synthesized probe gives an acceptable response for the sensing of 6MP in the presence of several interfering agents.

A turn-on fluorescence sensor for highly selective detection of chlortetracycline based on AIE effect enhanced by citrate modified graphitic carbon nitride nanodots

In this study, the novel graphitic carbon nitride (g-C3N4) nanodots etched with citrate (CCNDs) were synthesized successfully. And the result CCNDs exhibited an obvious aggregation emission effect (AIE) by forming a fluorescence complex with chlortetracycline (CTC) and significantly enhanced the fluorescence intensity of CCNDs. On the strength of this, the synthesized CCNDs demonstrated remarkable sensitivity and selectivity to CTC, which has been effectively studied and utilized for selectively and sensitively detecting CTC by AIE-based fluorescence-enhanced effect with a detection range spanning from 0 to 15 μM and a limit of detection (LOD) as low as 13 nM. The CCNDs were viably used for actually detecting CTC in real samples including chicken and feed, and further extended to detecting CTC in living cells. Finally, the bonding mechanism of CCNDs towards CTC was investigated in detail by dynamic light scattering (DLS), zeta(ζ) potential, TEM, ultraviolet-visible absorption spectrometry (UV-Vis), resonance light scattering (RLS) and fluorescence lifetime. It is due to the combination of a special fluorescent complex between CCNDs and CTC, which distinguishes CTC from other TCs.

A novel dual-functional half salamo-based fluorescent turn-on sensor for selectively recognition and differentiation of Zn2+ and Al3+ ions

Efficient detection of cationic pollutants released into the environment has become a matter of necessity and challenging task for the health of human beings. To address this, a novel half salamo-based fluorescent sensor JQS was developed and the sensing behavior toward various metal ions was comprehensively studied. The spectroscopic results demonstrated a prominent fluorescence enhancement upon Zn2+ and Al3+ ions were introduced into the sensor solution, and the response occurred at different emission wavelengths (451 nm for Zn2+, 426 nm for Al3+) with different colors, which could be easily distinguished by naked-eye. Various experimental analyses combined with theoretical calculation, the sensing mechanism was proposed. The selective recognition of Zn2+ and Al3+ by JQS was achieved through coordination binding, which leads to the inhibits of photoinduced electronic transfer effect and chelation enhanced fluorescent process. The detection limits of JQS toward Zn2+ and Al3+ were separately calculated to be 0.21 & 0.097 μM. Additionally, the sensing of Zn2+ & Al3+ in real water samples proved its potential for practical utility.

Bromine atom introduction improves the F- sensing ability of an indolo[3,2-b]carbazole-salicylaldehyde-based fluorescence turn-on sensor.

The heavy-atom effect usually quenches fluorescence, but scarcely enhances it. Herein, fluorescence turn-on sensors without or with a bromine atom for F- detection are presented, achieving fast response time within 1 min, and the LODs of 1.9 × 10-7 and 8.5 × 10-8 M, reflecting that halogen atom introduction is beneficial for F- detection ability improvement. The sensing mechanism of -OH unit deprotonation is confirmed based on the results of a 1 : 2 stoichiometric ratio, 1H NMR titration and TD-DFT calculation. The water environment F- detection and spiked recovery experiments demonstrate their potential for real sample detection.

Surfactant-induced alterations in optoelectronic properties of perylene diimide dyes: modulating sensing responses in the aqueous environment.

The compartmentalization effect of microheterogeneous systems, like surfactant aggregates, showcases altered optoelectronic properties of a perylene diimide-based chromogenic dye (PDI-Ala) compared to bulk water. The relatively hydrophobic microenvironment, poor hydration, and exceptionally large local concentration of dye molecules in the confined environment affect their interaction with target analytes. This realization intrigued us to investigate if micellization can modify the sensing properties (selectivity, sensitivity, response kinetics, output signal, etc.) of the encapsulated dye molecules in the aqueous medium. Response comparisons of PDI-Ala to the ionic analyte (Fe3+) and biomolecule (heparin) in aqueous and surfactant-bound states highlighted significant variations. Fe3+ interaction exhibited a "turn-off" fluorescence response in a water medium, while surfactant-bound conditions triggered "turn-on" fluorescence, enhancing selectivity at the micelle-water interface. Conversely, the native probe showed no interaction with heparin in water but displayed a turn-on fluorescence response in cetyltrimethylammonium bromide (CTAB) micelles, indicating the transformation of a silent molecule into a turn-on fluorescence sensor. This study underscores the influence of micellar environments on dye molecules, altering the sensing responses and selectivity toward analytes, crucial for applications in understanding cellular pathways and toxicity mechanisms.

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications.

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

A versatile sensor capable of ratiometric fluorescence detection of trace water and turn-on detection of Cu2+ modulating the binding interaction of a Cu(II) complex with BSA and DNA complemented by docking studies.

A fluorescent molecule, pyridine-coupled bis-anthracene (PBA), has been developed for the selective fluorescence turn-on detection of Cu2+. Interestingly, the ligand PBA also exhibited a red-shifted ratiometric fluorescence response in the presence of water. Thus, a ratiometric water sensor has been utilized as a selective fluorescence turn-on sensor for Cu2+, achieving a 10-fold enhancement in the fluorescence and quantum yield at 446 nm, with a lower detection limit of 0.358 μM and a binding constant of 1.3 × 106 M-1. For practical applications, sensor PBA can be used to detect Cu2+ in various types of soils like clay soil, field soil and sand. The interaction of the PBA-Cu(II) complex with transport proteins like bovine serum albumin (BSA) and ct-DNA has been investigated through fluorescence titration experiments. Additionally, the structural optimization of PBA and the PBA-Cu(II) complex has been demonstrated by DFT, and the interaction of the PBA-Cu(II) complex with BSA and ct-DNA has been analyzed using theoretical docking studies.