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Glutathione (GSH) serves several vital biological functions and its abnormal levels are associated with many diseases. Simple and sensitive methods capable of detecting GSH are desired for better understanding the mechanism of diseases. In this work, a label-free MnO 2 nanosheets assisted aggregation-induced emission (AIE)-silica nanospheres (SiO 2 NPs) nanoprobe for fluorescent "turn-on" detection of GSH with high sensitivity was reported for the first time. The anionic tetraphenylethylene derivative 3 (TPE3) was synthesized and employed as the AIE-active probe, which can be aggregated on the uncoated amino-functionalized SiO 2 NPs to form AIE-SiO 2 NPs and emitted strong fluorescence. Negatively charged MnO 2 nanosheets were employed as both positive charge protectors for amino-functionalized SiO 2 NPs and recognition units for GSH. The presence of GSH could selectively reduce MnO 2 nanosheets to Mn 2+ , thus releasing the amino-functionalized SiO 2 NPs and exposure its positive charges. Accordingly, the TPE3 could be aggregated on the exposured amino-functionalized SiO 2 NPs to form AIE-SiO 2 NPs and emitted strong fluorescence. The proposed assay is simple, fast, low cost, and highly sensitive with a detection limit of 200nM for GSH. The assay was further applied in human serum samples for the detection of GSH with satisfactory results, demonstrating its promising application in practical biological samples., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Using sterculia lychnophora seeds as precursors for the first time, fluorescent carbon dots (CDs) were synthesized by simple hydrothermal treatment. The quantum yield of as-synthesized CDs was 6.9% by using quinine sulfate as the reference. The fluorescence of CDs could be effectively quenched by a MnO 2 nanosheet based on fluorescence resonance energy transfer (FRET). Ascorbic acid (AA) could reduce MnO 2 to Mn 2+ and result in the destruction of the MnO 2 nanosheets, which could induce the fluorescence recovery of the CDs. In particular, alkaline phosphatase (ALP) could bio-catalyze acid 2-phosphate (AAP) hydrolysis to AA. Here, an efficient fluorescence probe based on a CDs-MnO 2 nanosheet for rapid and selective detection of ALP was reported for the first time. Excellent performance for the detection of ALP was observed with high sensitivity and a detection limit of 0.4U/L owing to the low background. The detection of ALP in human serum was conducted with satisfactory results, demonstrating its potential applications in clinical diagnosis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A new ratiometric fluorescent probe for efficient determination of ALP was developed. The probe was constructed by combining Ce3+-crosslinked copper nanoclusters (Ce3+-CuNCs) which exhibit the aggregation-induced emission (AIE) feature with carbon dots (CDs). The introduction of phosphate (Pi) induced the generation of CePO4 precipitation, resulting in significant decrease of fluorescence emission of CuNCs at 634 nm. At the same time, the fluorescence of CDs at 455 nm was obviously enhanced, thus generating ratiometric fluorescence response. Based on the fact that the hydrolysis of pyrophosphate (PPi) by ALP can produce Pi, the CD/Ce3+-CuNCs ratiometric probe was successfully used to determine ALP. A good linear relationship between the ratiometric value of F455/F634 and ALP concentrations ranging from 0.2 to 80 U·L− 1 was obtained, with a low detection limit of 0.1 U·L− 1. The ratiometric responses of the probe resulted in the visible fluorescence color change from orange red to blue with the increase of ALP concentration. The smartphone-based RGB recognition of the fluorescent sample images was used for ALP quantitative determination. A novel ratiometric fluorescent system based on Ce3+-CuNCs with AIE feature and CDs were constructed for efficient detection of ALP. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescence nanoprobe based on long-wavelength emission carbon dots (CDs) was designed for high sensitive and selective detection of Zn2+. The CDs were conveniently prepared by a one-step solvothermal treatment of formamide and glutathione (GSH). Under single excitation wavelength (420 nm), the obtained CDs exhibit three emission peaks at 470, 650, and 685 nm, respectively. For the long-wavelength emission region of the CDs, the fluorescence at 685 nm can be quenched with different levels upon the addition of most metal ions. However, the presence of Zn2+ not only results in the fluorescence quenching at 685 nm effectively but also enhances at 650 nm remarkably, which may be due to the formation of CD-Zn2+ chelate complex inducing the dispersion of CDs aggregates and changes in the group distribution on the surface of CDs. Taking the advantage of the unique fluorescence response induced by Zn2+, the prepared CDs were successfully employed as nanoprobe for self-ratiometric fluorescence determination of Zn2+ with F650/F685 as signal output. A good linear relationship in the concentration range 0.01 to 2 μM, and a detection limit as low as 5.1 nM has been obtained. The ratiometric nanoprobe was successfully applied to Zn2+ determination in human serum samples. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescence nanoprobe based on carbon dots (CDs) and Cu nanoclusters (CuNCs) was designed for the label-free determination of uric acid (UA). The metal-organic framework (MOF) encapsulated CuNCs (ZIF-CuNC), and nitrogen-doped CDs can self-assemble into well-defined spherical nanocomposites (CD@ZIF-CuNC) due to physical adsorption. Under the excitation wavelength of 360 nm, the CD@ZIF-CuNC nanocomposites exhibit two evident intrinsic emissions peaked at 460 nm (CDs) and 620 nm (ZIF-CuNC), respectively. In the presence of H2O2, the fluorescence of CD@ZIF-CuNC at 620 nm is quenched remarkably within 1 min, while little effect on the emission at 460 nm is observed. Therefore, taking the fluorescence at 620 nm as the report signal and 460 nm as the reference signal, ratiometric quantitative determination of H2O2 was achieved with a linear range of 1–100 μM and a detection limit of 0.30 μM. The CD@ZIF-CuNC nanoprobe was successfully applied to the determination of UA that is catalyzed by uricase to produce H2O2, obtaining the linear range of 1–30 μM and the detection limit of 0.33 μM. Eventually, this strategy has been successfully applied to the determination of UA in human urine samples. [ABSTRACT FROM AUTHOR]

Heparin (Hep) is widely used as a major anticoagulant in surgery. Simple and sensitive methods capable of quantitative detection of Hep are desired for better regulating its clinical use. Herein, a novel nanoassembly of amino-functionalized mesoporous silica nanoparticle–gold nanoclusters (MSN–AuNCs) with remarkable emission enhancement characteristics for sensitive fluorescence detection of Hep is developed. The electrostatic interaction between the positively charged amino-functionalized MSNs and the AuNC-stabilizing surface ligands triggers the self-assembly of MSN–AuNC nanocomposites which exhibit more than 5-fold fluorescence emission enhancement. However, the presence of negatively charged Hep inhibits the emission enhancement phenomenon due to the effective wrapping of Hep on the surface of MSNs, which blocks the interaction between AuNCs and MSNs. Benefitting from the remarkable emission enhancement and the competing binding of Hep, facile and ultrasensitive detection of Hep can be realized with a detection limit as low as 2 nM. Moreover, the successful application of the proposed method for detection of Hep in human serum samples shows promise for clinical applications. [ABSTRACT FROM AUTHOR]

Since bleomycins (BLMs) play a prominent role in the clinical treatment of various cancers, the development of convenient and sensitive detection assays for BLM is of great significance in cancer therapy and related biological mechanism research. Here, taking advantage of the easily controllable and excitation of the G-triplex DNA structure, we reported a facile, label-free G-triplex based functional molecular beacon (G3MB) sensing system for fluorescence “turn-on” detection of BLM based on BLM-Fe(ii) mediated DNA strand scission. In the presence of BLM, the stable hairpin structure of G3MB undergoes an irreversible cleavage in the loop region that contains a 5′-GT-3′ recognition site for BLM. The released G-tract DNA fragment self-assembles into a G-triplex–ThT complex showing a strong fluorescence. Owing to the effective locking of G-tracts in the stem of the G3MB and the specific DNA strand scission by BLM which is like a key for the release of G-tracts, the assay shows high sensitivity and selectivity with a detection limit of 0.2 nM. In addition, satisfactory results were obtained for the detection of BLM in human serum samples. Critically, the convenient “mix-and-detect” protocol, fast response and no need for modifying DNA offered a potential application of the proposed strategy for BLM assay in biomedical and clinical studies. [ABSTRACT FROM AUTHOR]

In this study, a coumarin-based probe (probe 1) bearing a maleimide group was used to rapidly and selectively detect thiols. After inducing thiols, this probe presented a significant fluorescence enhancement (≥22-fold), whereas other amino acids that had no sulfhydryl group just generated slight changes. The detection limits were determined to be as low as 7.41 nM for Cys, 6.06 nM for GSH, and 7.73 nM for Hcy based on S/N = 3. Furthermore, this probe possessed excellent water solubility and successfully detected thiols in PBS (pH 7.4, 99.5%). More importantly, the practical application of probe 1 for the selective detection of thiols was successfully demonstrated in living T24 cells. [ABSTRACT FROM AUTHOR]

A novel amplified fluorescence graphene oxide (GO) sensing platform for sensitive detection of T4 polynucleotide kinase (PNK) activity and inhibition was developed based on the exonuclease III (ExoIII) reaction. The efficient digestion capacity of ExoIII and the super quenching ability of GO both contribute to the detection sensitivity. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescence nanoprobe based on long-wavelength emission carbon dots (CDs) was designed for high sensitive and selective detection of Zn2+. The CDs were conveniently prepared by a one-step solvothermal treatment of formamide and glutathione (GSH). Under single excitation wavelength (420 nm), the obtained CDs exhibit three emission peaks at 470, 650, and 685 nm, respectively. For the long-wavelength emission region of the CDs, the fluorescence at 685 nm can be quenched with different levels upon the addition of most metal ions. However, the presence of Zn2+ not only results in the fluorescence quenching at 685 nm effectively but also enhances at 650 nm remarkably, which may be due to the formation of CD-Zn2+ chelate complex inducing the dispersion of CDs aggregates and changes in the group distribution on the surface of CDs. Taking the advantage of the unique fluorescence response induced by Zn2+, the prepared CDs were successfully employed as nanoprobe for self-ratiometric fluorescence determination of Zn2+ with F650/F685 as signal output. A good linear relationship in the concentration range 0.01 to 2 μM, and a detection limit as low as 5.1 nM has been obtained. The ratiometric nanoprobe was successfully applied to Zn2+ determination in human serum samples. [ABSTRACT FROM AUTHOR]

• Novel turn-on fluorescent probe RhB@MOF-5 for β-glucuronidase is firstly fabricated. • The reason of β-glucuronidase responses is depend on the synergistic effect of IFE and SQE. • The probe exhibits high selectivity and real human serum testing. • The theoretical limit of detection of this platform is low to 0.03 U L−1. β-Glucuronidase (β-GCU) is closely related to the occurrence of multiple diseases, and it has been applied as a biomarker and therapeutic target in clinical diagnosis. However, reliable methods with high selectivity and sensitivity for monitoring β-GCU are still lacked. Herein, we designed a novel fluorescent nanoprobe, rhodamine B encapsulated MOF-5 (RhB@MOF-5) for the first time, to detect β-GCU through the synergistic effect of inner filter effect (IFE) and static quenching effect (SQE) by employing 4-nitrophenyl-β-D-glucuronide (PNPG) as the substrate. After encapsulating into MOF-5, the fluorescence emission of RhB at 550 nm excited by 320 nm was greatly enhanced. The major overlap between the fluorescence excitation spectrum of RhB@MOF-5 (about 320 nm) and the ultraviolet absorption spectrum of PNPG (about 310 nm) lead to PNPG being a good IFE absorber in this sensing system. Under the optimized conditions, the excitation spectrum of the RhB@MOF-5 could be absorbed by PNPG, resulting in the dramatically decrease of fluorescence emission. After adding β-GCU into the system, the substrate of PNPG would be enzymatic hydrolyzed to p -nitrophenol (PNP) and glucose, then the IFE disappearance and the fluorescence recovered. The current sensing platform was interference-free and exhibited a broad linearity relationship for β-GCU range of 0.1–10 U L−1 (R2 = 0.9957) with a limit of detection as low as 0.03 U L−1, which was reduced by more than one orders compared with the reported methods. Moreover, the encapsulation of dyes using porous nanoparticles to achieve some tailor-made characteristics will enrich experimental design inspiration. [ABSTRACT FROM AUTHOR]

Nitrite ion (NO 2 -) is a typical contaminant that can cause severe damage to the human body. Diazotization-based fluorimetric methods used for the efficient and selective detection of NO 2 - under a strong acidic condition remain a huge challenge. In this study, a specific nanoprobe was developed through the functionalization of the luminescent MOF of NH 2 -MIL-101 with Polyvinylidene fluoride/polyvinylpyrrolidone (PVDF/PVP) for detecting NO 2 - based on diazotization reaction. After functionalization, the resultant NH 2 -MIL-101 @PVDF/PVP exhibited enhanced stability even under a strong acidic condition and featured higher fluorescence intensity. Because NO 2 - reacted with the -NH 2 group of the probe to form diazonium salt, a significant fluorescence signal was obtained. With the addition of N-(1-Naphthyl) ethylenediamine, the diazonium salt significantly changed from colorless to a purple-red color under direct sunlight. The developed dual-signal readout sensor exhibited high sensitivity, high selectivity, and good linearity in the range of 0.67–20 μM with a limit of detection of 0.67 μM. Owing to the unique properties of MOFs, the proposed sensor was characterized by simple preparation, high sensitivity, and fast response kinetics compared with the traditional sensing reagents. This study provides a potential strategy for fabricating smart fluorimetric probes used for nitrite detection. • A specific sensor for NO 2 - was developed by functionalizing NH 2 -MIL-101 with PVDF/PVP. • Both stability and fluorescence of the probe enhanced greatly even under the NO 2 - sensing condition of strong acid of H 2 SO 4. • Both fluorescent and clorimetric signal were achieved with high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Transformation of renewable bio-feedstock to fine chemicals and functional materials are much desirable in chemistry and chemical engineering. Herein, a series of AIE dyes (compounds a-o ) with thermo/pressure dependent fluorescence were revealed. Fifteen compounds ( a-o ) with the ortho- carboxyl diarylamine key structure were obtained from the renewable biomass molecule shikimic acid and ten of them exhibited typical AIE behavior. By changing the substituent groups that might affect the AIE property, the fluorescent emission of the AIE dyes could be changed from white to green or blue. Thermo/pressure dependent fluorescence emission was observed for the tested AIE molecules and the fluorescent intensity changes could be used as a quantified signal for the surrounding temperature. Moreover, substituent moderating effect for the AIE property of compounds a-o was revealed by using DFT calculation. In addition, organic nanoparticle fluorescent probe (ONFP) was prepared based on compound o and used in the selective and sensitive detection of arginine in real water. [Display omitted] • A series of AIE dyes with adjustable fluorescence emission was derived from shikimic acid. • Thermo/pressure dependent fluorescence emission was observed for the revealed AIE dyes. • Organic nanoparticle fluorescent probe (ONFP) was prepared and used for fluorescent sensing. • Substituent moderating effect and the mechanism for fluorescent sensing of arginine were revealed. [ABSTRACT FROM AUTHOR]

A novel CDs-Ag+-OPD system was conveniently prepared as ratiometric fluorescent nanoplatform for sensitive and selective detection of ALP. [Display omitted] • CDs-Ag+-OPD based nanoplatform was constructed for ratiometric detection of ALP. • Ag+ regulated the generation of DAP that emits fluorescence at 570 nm and was used as reporter signal. • The fluorescence of CDs at 454 nm were used as reference signal. • Good performance was obtained with a detection limit of 0.1 U/L for ALP. • Favorable results were achieved for detecting ALP in human serum samples. In this work, a novel silver ion (Ag+)-regulated ratiometric fluorescence method for the effective and sensitive determination of alkaline phosphatase (ALP) was established based on carbon dots (CDs) and o -phenylenediamine (OPD). OPD can be oxidized by Ag+ to generate fluorescent 2, 3-diaminophenazine (DAP). Thus, based on inner-filter effect (IFE) or/and fluorescence resonance energy transfer (FRET) between CDs and DAP, the CDs-Ag+-OPD system can generate dual-emission at 454 nm and 570 nm respectively when excited at 360 nm. The introduction of ascorbic acid (AA) can react with Ag+ to produce dehydroascorbic acid (DHAA), which inhibits the generation of DAP, resulting in the fluorescence decrease at 570 nm and fluorescence recovery of CDs at 454 nm. Meanwhile, DHAA can react with OPD to generate quoxaline (QX), which emits strong blue fluorescence at 440 nm, further inhibiting the IFE or/and FRET between CDs and DAP. An obvious ratiometric fluorescence response was observed with the increase of the concentration of AA introduced. Due to the fact that AA can be generated by the enzyme catalysis reaction between ALP and 2-phospho- l -ascorbic acid (AAP), the CDs-Ag+-OPD ratiometric system was applied to the determination of ALP successfully. The ratiometric fluorescence value of F 454 / F 570 increases with increasing ALP concentration, with a linear range of 0.2 to 40 U/L and detection limit of 0.1 U/L. In addition, the CDs-Ag+-OPD ratiometric system was successfully applied to the detection of ALP in human serum samples. [ABSTRACT FROM AUTHOR]

Abstract: A universal amplified sensing strategy based on endonuclease was developed for designing fluorescence aptasensors. By employing hairpin-structured design for both recognition and reporter probes to decrease background signal, and a nicking endonuclease to perform target-triggered enzymatic recycling amplification, the proposed biosensor showed high sensitivity to target protein. To demonstrate the feasibility of the design, immunoglobulin E (IgE) was studied as a model target. Upon the addition of target protein, the specific formation of IgE/aptamer complex induced the releasing of the 37-mer fragment which partially hybridized with the molecular beacon (MB) probe. In the presence of endonuclease Nt.BbvCI, the MB was cleaved into two parts. Then, the released 37-mer fragment hybridized with another MB, and triggered the second cycle of cleavage, leading to an accumulation of fluorescence signals. Under the optimal conditions, a detection limit of 5pM was obtained. The proposed sensing system was used for detection of IgE in complex biological samples with satisfactory results. [Copyright &y& Elsevier]

This study demonstrates a novel and convenient ratiometric fluorescent method for the detection of alkaline phosphatase (ALP) activity. Amino-functionalized mesoporous silica nanoparticle-gold nanoclusters (MSN-AuNCs) nanocomposites were integrated with o-phenylenediamine (OPD) to form a ratiometric fluorescence nanoplatform. The presence of ALP induced the generation of quinoxaline (QX) derivative which called 3-(dihydroxyethyl)furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission at 450 nm, while the orange-red fluorescence of MSN-AuNCs at 580 nm was slightly quenched. Meanwhile, an obvious fluorescence color change from orange-red to purple and finally to blue can be observed by naked eyes with the increasing of ALP concentration. Therefore, employing the fluorescence emission of DFQ at 450 nm as the reporter signal and the fluorescence emission of MSN-AuNCs at 580 nm as a reference signal, a sensitive ratiometric detection method for ALP was developed. Quantitative detection of ALP activity in the linear range from 0.2 to 80 U/L with a detection limit of 0.1 U/L can be realized in this way, which endows the assay with high sensitivity enough for practical detection of ALP in human serum samples. Image 1 • OPD/MSN-AuNCs based nanoplatform was constructed for ratiometric detection of ALP. • The Fe3+ mediated generation of DFQ with strong emission was used as reporter signal. • The fluorescence of MSN-AuNCs at 580 nm were used as reference signal. • Good performance was obtained with a detection limit of 0.1 U/L for ALP. • Favorable results were achieved for detecting ALP in human serum samples. [ABSTRACT FROM AUTHOR]

G-triplexes have been reported recently with the similar function to G-quadruplex that can combine with thioflavin T (ThT) and emit strong fluorescence but easier to be controlled and excited. In this work, we report an Hg2+-mediated stabilization of G-triplex based functional molecular beacon (G3TMB) sensing system for the label-free detection of Hg2+, reduced glutathione (GSH), and glutathione reductase (GR) activity. In the presence of Hg2+, the extended G-triplex sequence containing the "T" bases can form a stable hairpin structure due to the strong interactions of "T-Hg2+-T", resulting in the locking of G-tracts in the stem of the G3TMB effectively. However, the hairpin structure of the G3TMB can be opened by the introduction of GSH through the stronger "GSH-Hg2+" interaction. Therefore, by employing the fact that GR can catalyze the reduction of oxidized glutathione (GSSG) into GSH, this concept can be applied to fluorescence "off-on" detection of GR activity, with a linear range of 0.02–30 mU/mL and detection limit of 0.01 mU/mL. This work may expand a new perspective of G-triplex based functional molecular beacon as the label-free fluorescent probes in the detection of small biomolecule and enzyme activity. A label-free G3TMB sensing system containing "T" bases was constructed for the fluorescence detection of Hg2+, GSH, and GR activity. Unlabelled Image • A label-free G3TMB sensing system containing "T" bases was constructed. • The extended G-triplex sequence can form stable hairpin structure via Hg2+ mediation. • The G3TMB sensing system was used to detection of Hg2+ with high sensitivity. • GSH and GR could also be detected via the stronger "GSH-Hg2+" interaction. [ABSTRACT FROM AUTHOR]

The level of alkaline phosphate (ALP) is a significant biomarker index in organism. In this work, a label-free and sensitive G-quadruplex fluorescence assay for monitoring ALP activity has been developed with the assistance of Cu2+ based on the competitive binding effect between pyrophosphate (PPi) and G-quadruplex-N-methylmesoporphyrin (G4/NMM) complex to Cu2+. In the sensing assay, the G4/NMM complex is employed as a signal indicator, while the Cu2+ as a quencher and the PPi as recovery agent as well as the hydrolytic substance for ALP. In details, the fluorescence of the G4/NMM complex was efficiently quenched by introducing Cu2+ due to the proximal carboxylate groups of NMM coordinating with the Cu2+ as well as the unfolding of G-quadruplex by Cu2+, while the higher affinity between PPi and Cu2+ could lead to the fluorescence recovery. However, in the presence of ALP, the PPi was hydrolyzed to phosphate ions (Pi) which cannot integrate with Cu2+, resulting in the fluorescence quenching once again. Thus, a simple and facile way to inspect ALP has been exploited. The proposed assay shows a good linear relationship in the range from 0.5 to 100 U/L with the detection limit of 0.3 U/L. Moreover, the fabricated method is succeeded in detecting ALP in human serum samples, indicating the potential as a profitable candidate in biological and biomedical application. Label-free and sensitive fluorescence detection of ALP based on G-quadruplex/NMM complex with the assistance of Cu2+ was reported. Image 1 • PPi can inhibit the fluorescence quenching effect of Cu2+ to G4/NMM complex. • The G4/NMM complex was used for label-free fluorescence detection of ALP. • Good performance was obtained with a detection limit of 0.3 U/L for ALP. • Favorable results were achieved for detecting ALP in human serum samples. [ABSTRACT FROM AUTHOR]