Search

Abstract The accurate quantification of hydrogen peroxide (H 2 O 2) and glucose is essential significance in clinical diagnosis. Herein a selective and sensitive ratiometric fluorescent nanosensor was developed for the determination of H 2 O 2 and glucose by integrating peroxidase–like catalytic and fluorescent bifunctional properties of glutathione protected gold nanoclusters (GSH–AuNCs). The GSH–AuNCs exhibit inherent peroxidase–like activity and accelerate the decomposition of H 2 O 2 into hydroxyl radicals. The produced hydroxyl radicals oxidize terephthalic acid (TA), a typical non–fluorescent substrate of peroxidase, to a highly fluorescent product hydroxyterephthalate (TAOH). Upon excitation with single–wavelength at 315 nm, dual–emission fluorescence peaks were recorded at 430 and 600 nm simultaneously. The fluorescence signal of TAOH at 430 nm continuously increased with increasing the concentration of H 2 O 2 while the fluorescence signal of GSH–AuNCs at 600 nm remained unchangeable. Based upon on these facts, a ratiometric fluorescent nanosensor was fabricated for H 2 O 2 assay with TAOH as response unit and GSH–AuNCs as reference, respectively. By converting glucose into H 2 O 2 with catalytic oxidation of glucose oxidase (GOx), this nanosensor was further exploited for glucose assay. Under the optimum conditions, the detection limits of 10 nmol/L H 2 O 2 and 20 nmol/L glucose were acquired. The relative standard deviations were less than 5% for both H 2 O 2 and glucose (5.0 μmol/L solution, n = 11). The practicability of the nanosensor was verified by the determination of glucose in human serum samples. This nanosensor can be easily expanded as a general platform for the detection of other substances involving H 2 O 2 produced or consumed. Graphical abstract fx1 Highlights • Intrinsic peroxidase–like activity of GSH–AuNCs was demonstrated in fluorescent system. • A ratiometric fluorescent nanosensor was constructed with catalytic and fluorescent bifunctional properties of GSH–AuNCs. • Quantitative analysis of glucose in human serum samples was demonstrated. • The nanosensor can be easily adapted to measure other physiological substances with appropriate oxidases. [ABSTRACT FROM AUTHOR]

Abstract In this work, a sulfone-functionalized metal organic frameworks (MOFs) (CAU-11) formulated as [Al(OH)(SDBA)]·0.25DMF (H 2 SDBA = 4, 4′-sulfonyldibenzoic acid) has been successfully constructed under solvothermal conditions. Next, a europium ion post-functionalized compound (Eu3+@CAU-11) with bright red fluorescence has been obtained by postsynthetic modification (PSM). Because of its excellent luminescence and robust framework, we design this compound as a ratiometric fluorescent probe (I L / I Eu) for sensing application. In the investigation process, what is surprising is that Fe3+ can quench the fluorescence of Eu3+@CAU-11 both in aqueous solutions and in N, N-dimethylformamide (DMF) while Cu2+ can only quench the fluorescence of it in DMF. It represents a rare example of a sensor based on a metal-organic framework which can dually sense and distinguish two quenching metal ions in different solutions simultaneously. To better explain this phenomenon, the probable sensing mechanism of the two metal ions has also been discussed in this paper. More importantly, we have designed this ratiometric fluorescent sensor as a combinational molecular logic gate for further logical application because of its sample synthesis process and favorable luminescent properties. Graphical abstract fx1 Highlights • A Eu3+ postsynthetic modified (PSM)a sulfone-functionalized MOFs (CAU-11) as probe. • A ratiometric fluorescent probe (I L / I Eu) for sensing metal ions both in aqueous solutions and in DMF (N, N-dimethylformamide). • An effective sensor for detecting Fe3+ and Cu2+. • Cu2+ has different fluorescence responses in different solvents. • A combinational logic gate to distinguish these two quenching ions. [ABSTRACT FROM AUTHOR]

Abstract Tyrosinase is the key enzyme in the treatment of vitiligo. Development of rapid, simple, and visual methods for screening bioactive compounds with tyrosinase activity from natural compounds is interesting for new drug discovery. Herein, a novel visual ratiometric fluorescent assay for screening tyrosinase activators and/or inhibitors based on silicon nanoparticles (Si NPs) was explored. Inspired by the changes in both of the solution color and the fluorescence emission due to the sensing between Si NPs and dopamine (DA), we employed tyramine as the model substrate, which can transfer into DA by tyrosinase. It was found that the tyrosinase-incubated tyramine solution exhibited pale yellow under nature light or yellow fluorescence under UV light in the presence of Si NPs, where the color/fluorescence intensity were directly related to the concentration of tyrosinase. The established method showed good detection selectivity, and the LOD for tyrosinase was 0.14 U mL−1. Eventually, this assay was successfully applied to screen tyrosinase activators or inhibitors from a natural product-like library, and a tyrosinase activator with EC 50 of 2.62 μM, more potent than the commonly used tyrosinase activator 8-MOP, was discovered. Graphical abstract fx1 Highlights • The ratiometric fluorescent assay exhibited good selectivity, adequate sensitivity, and excellent tolerance to sample matrix. • The ratiometric fluorescent assay simultaneously realized visualization and quantitative analysis of tyrosinase activity. • A compound with potent tyrosinase activation (EC 50 = 2.62 μM) was found. [ABSTRACT FROM AUTHOR]

Abstract Here, we report Nd3+-doped Y 2 O 3 nanoparticles suitable for luminescence thermal sensing in the first and second biological windows. The nanoparticles were synthesized via the combined Pechini-foaming method. A ratiometric approach, based on the relative changes in the intensities of different emission bands corresponding to the Stark sublevels or excited levels, was applied to determine local temperature. The evaluated thermal sensitivities differed 5-fold times depending on the choice of transitions for the luminescence intensity ratio calculation. The temperature uncertainty was determined to be below 1 °C, which allows to perform sub-degree thermal sensing. The results of ex vivo experiment indicate that Nd3+-doped Y 2 O 3 nanoparticles are promising candidates for real biological applications. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

A label-free ratiometric fluorescent platform has been developed for the detection of 3′–5′ exonuclease utilizing two individual DNA conformation-specific dyes. Initially, the DNA substrate maintains a stable HP (hairpin probe) structure, resulting in bright fluorescence at 455 nm for 4′,6-diamidino-2-phenylindole (DAPI), which is able to insert into A–T base pairs of the HP structure. Upon the addition of 3′–5′ exonuclease (exonuclease III), the HP structure was digested to single-stranded DNA (ssDNA), and the fluorescence intensity at 455 nm was decreased. However the emission of N-methyl mesoporphyrin IX (NMM) at 610 nm was increased significantly due to the formation of G-quadruplex. This label-free method is realized by facile design and shows good selectivity for Exo III detection. More importantly, it also shows its potential as a platform for Exo III inhibitor screening. [ABSTRACT FROM AUTHOR]

A novel highly selective chemosensor Z based on rhodamine B hydrazone derivatives was designed and synthesized, and it showed both colorimetric and “turn-on” fluorescence responses for CN− in an aqueous solution. The results showed that after adding CN− ions in aqueous solution, the chemosensor Z showed significant color change from colorless to pale-yellow, which was visible to the naked eye, and it rapidly produced strong green fluorescence. The probe could distinguish CN− by deprotonation and intramolecular charge transfer (ICT) mechanisms, as evidenced by 1H-NMR titration and DFT calculations. In addition, the detection limit of the fluorescence response of the sensor for CN− was 5.81 × 10−8 M, which was measured by titration. The chemosensor Z has been successfully used to detect CN− in sprouting potatoes. Z-containing test strips have also been prepared, and they can be used as a colorimetric tool for CN− detection in potential applications. [ABSTRACT FROM AUTHOR]

Taking advantage of the special Hg 2+ -promoted deprotection reaction of dithioacetals and the well-known coumarin chromophore, novel reactive fluorescent probes ( C3 and C4 ) towards mercury ions were designed and synthesized. Upon the addition of mercury ions, probe C3 displayed remarkable fluorescence quenching, which was beneficial to the production of a high signal output during sensing process. Differently, compound C4 displayed dramatic red-shift in both fluorescence (60 nm) and absorption (60 nm) spectra, with the detection limit of 90 nM. By virtue of this unique chemical reaction, compound C4 had selective response towards Hg 2+ over other metal ions and only the addition of Hg 2+ could lead to apparent emission and absorption spectra changes. Moreover, C4 was successfully applied to microscopic imaging for the detection of Hg 2+ in HeLa cells with ratiometric fluorescent methods. [ABSTRACT FROM AUTHOR]

Specific modification of carbon dots (CDs) exhibit excellent properties and are suitable for numerous applications. The exploitation of multifunctional CDs in the area of fluorescent assay is still urgent and attractive. Herein, using a simple two-step heating procedure, positive charged carbon dots (P-CDs) were prepared with the co-doping of the elements of N and S. The morphology, optical properties and stability of P-CDs was investigated. Furthermore, P-CDs show the dual functions of unprecedented quenching performance toward fluorophore-modified DNA coupling the retaining fluorescence of P-CDs self. The quenching effect and mechanism of P-CDs to fluorophore-modified DNA was investigated. The fluorescence and quenching properties of P-CDs were used to design a ratiometric fluorescence platform for DNA based on the complex of P-CDs and FAM-labeled ssDNA. The ratiometric method allows the detection of target DNA because of the different affinities of P-CDs to ssDNA and dsDNA with acceptable sensitivity and improved reproducibility, when using sequence fragment of the gene of Gardnerella vaginalis as model. This method provides a new approach to widen the future of the biological applications based on some special CDs. [ABSTRACT FROM AUTHOR]

A palygorskite (Pal)-based ratiometric fluorescent nanoprobe is designed in order to establish a real time, on-site visual, and highly sensitive detection method for tetracyclines (TCs). The nanoprobe comprises the green emissive dye molecules embedded in the natural Pal, which serve as the internal reference signal. The potential red-emissive seed-europium (Eu 3+ ) ions are covalently bound on the surface of modified Pal, and they can act as the specific recognition element. The emission intensity of Eu 3+ ions significantly increases upon TC addition. The nanoprobe fluorescence changes from green to yellow, orange, or red, thereby accomplishing the visual ratiometric fluorescent detection. This nanoprobe exhibits a high sensitivity with a detection limit of 7.1 nM and an excellent selectivity in monitoring the levels of TCs in milk samples. In addition, this nanoprobe is useful for quantitative determination of TCs, and it is not affected with intensity fluctuations due to instrumental or environmental factors. The nanoprobe-immobilized test paper realizes real-time TCs analysis by using a smartphone with an easy-to-access color-scanning APP as the detection platform. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea, that is, from nature, for nature, and into the nature. [ABSTRACT FROM AUTHOR]

Most quantitative fluorescence measurements report emission quantum yields by referring the integrated fluorescence profile to that of a well-known standard compound measured under carefully controlled conditions. This simple protocol works well provided an appropriate standard fluorophore is available and that the experimental conditions used for reference and unknown are closely comparable. Commercial fluorescence spectrophotometers tend to perform very well at wavelengths between 250 and 650 nm but are less responsive at longer wavelengths. There are no recognized emission standards for the far-red region. We now report fluorescence quantum yields for a series of commercially available cyanine dyes in methanol solution at room temperature. The compounds are selected to span the wavelength region from 600 to 850 nm, with absolute emission quantum yields being determined by thermal blooming spectrometry. Calibration of the instrument is made by reference to aluminium(iii) phthalocyanine tetrasulfonate and aza-BODIPY in methanol. [ABSTRACT FROM AUTHOR]

A two-photon ratiometric fluorescent probe (Mito-N) has been developed for monitoring mitochondrial nitric oxide (NO) in vivo. Mito-N exhibited excellent selectivity and sensitivity toward NO among various ROS/RNS. The successful two-photon imaging of mitochondrial NO proved that Mito-N is a powerful noninvasive imaging tool in living systems. [ABSTRACT FROM AUTHOR]

A novel compound 1 based on phenanthro[9,10-d]imidazole platform has been unveiled as an effective ratiometric fluorescent probe for selective and rapid detection of NaCN. The sensing behavior was demonstrated by UV-vis, fluorescence experiments and NMR studies. This sensory system exhibited prominent visual emission color change toward CN − over other testing anions in CH 3 CN-PBS buffer (v/v, 3:1, pH 7.2) solution, with a 1:1 binding stoichiometry. Detection limit of the new cyanide-sensing probe 1 was 1.8 × 10 −9 mol L −1 , which was much lower than the World Health Organization (WHO) recommended level drinking water. The experimental results revealed that the formation of anionic species from the deprotonation of imidazole moiety by the CN − ion was responsible for the spectral changes. Calculations of the transition energies also verified such process. The spectral responses of probe could be switched back and forth alternatively by adding CN − and H + anions into the CH 3 CN-PBS buffer (v/v, 3:1, pH 7.2) solution, which indicated that compound 1 was stable and could be used in reversible manner. [ABSTRACT FROM AUTHOR]

We report here a ratiometric pH probe (Z)−2-(2-(2-(4-hydroxyphenyl)−2-(pyrrolidin-1-yl)vinyl) −4H-chromen-4-ylidene)-malononitrile over the pH range of 2.44–6.00. It was synthesized by Knoevenagel Reaction from dicyanomethylene-4H-chromene and pyrrolidine. This is the first example of pyrrolidine as a part of the product structure in Knoevenagel condensation. High selectivity and sensitivity for pH variation were observed with significant fluorescent ratiometric responses and a remarkable Stokes shift (about 138 nm). The probe was stable in the studied solvent and no obvious fluorescence changes were detected in acidic media within one month at room temperature. [ABSTRACT FROM AUTHOR]

pH-dependent protein adsorption on mesoporous silica nanoparticle (MSN) was examined as a unique means for pH monitoring. Assuming that the degree of protein adsorption determines the distance separating protein molecules, we examined the feasibility of nanoscale pH probes based on fluorescence resonance energy transfer (FRET) between two fluorescent proteins (mTurquoise2 and mNeonGreen, as donor and acceptor, respectively). Since protein adsorption on MSN is pH-sensitive, both fluorescent proteins were modified to make their isoelectric points (pIs) identical, thus achieving comparable adsorption between the proteins and enhancing FRET signals. The adsorption behaviors of such modified fluorescent proteins were examined along with ratiometric FRET signal generation. Results demonstrated that the pH probes could be manipulated to show feasible sensitivity and selectivity for pH changes in hosting solutions, with a good linearity observed in the pH range of 5.5-8.0. In a demonstration test, the pH probes were successfully applied to monitor progress of enzymatic reactions. Such an 'in situ-assembling' pH sensor demonstrates a promising strategy in developing nanoscale fluorescent protein probes. [ABSTRACT FROM AUTHOR]

Fluorescent probe UREA-TP undergoes nearly 600% increase in emission intensity at 310 nm on addition of 1 equivalent of TNT, but the emission band centered at 440 nm remains unchanged. UREA-TP acts as a ratiometric fluorescence “turn-on” probe and can detect TNT between 10 −9 to 10 −5 M with limit of detection as low as 100 pM. Paper strips coated with UREA-TP on interaction with TNT become fluorescent purple under 365 nm light and can determine both qualitatively and quantitatively as low as 10 μl solution of 10 −13 M TNT, which accounts for 2.27 × 10 −16 g cm −2 TNT, significantly lower than the TNT concentration allowed in drinking water by EPA. The common nitroaromatic derivatives 2,4-DNT, 2,6-DNT, picric acid and 2,4-DNP, the pain killers, food supplements and inorganic anions show insignificant interference in the determination of TNT using UREA-TP . The aggregate size determination using dynamic light scattering analysis and morphological studies using TEM investigations reveals that UREA-TP in H 2 O-DMSO (98:2) remains in aggregate state with average size of 200 nm, which undergo further aggregation to larger size aggregates with increasing amounts of TNT. [ABSTRACT FROM AUTHOR]

A novel mitochondria-targeted ratiometric near-infrared fluorescence probe NDMBT for Sulfur dioxide (SO 2 ) derivatives was constructed based on the SO 2 derivatives-triggered Michael addition reaction. It displayed ultrafast response time (within 10 s), large hypsochromic shift (260 nm), high photostability, excellent selectivity and high sensitivity in aqueous media with a detection limit of 43 nM. More importantly, it was successfully applied to imaging of the enzymatically generated SO 2 derivatives in mitochondria of live cells. [ABSTRACT FROM AUTHOR]

In this work, a novel and facile ratiometric fluorescence probe was prepared for the visual detection of dopamine (DA). In this detection system, red-emission CdTe@SiO 2 (r-QDs@SiO 2 ) was used as steady core of the probe and inverse microemulsion method was applied to synthesize uniform r-QDs@SiO 2 , this step could protect CdTe from contacting with human skin directly. Polydopamine (PDA) acted as response signal to detect DA, a very handy method which just combined polyethyleneimine (PEI) with DA together to synthesize PDA, this way for synthesis of PDA was much time-saving and non-toxic than any other methods. Differently from traditional analysis processes, the products of this experiment were also the analysis substances in final. Under optimum measurement conditions, the dual-emission ratiometric fluorescence probe was used for detections of DA in a concentration ranged from 10 μM to 80 μM with a detection limit of 0.12 μM, with addition of DA the color of the probe changed from red to green watched by naked eyes. In addition, the developed probe was also used for detections of DA in human serum samples successfully. This study provides a simple, time-saving and non-toxic approach for detections of DA without the requirement of complex equipment. [ABSTRACT FROM AUTHOR]

Ratiometric sensors generally couple binding events or chemical reactions at a distal site to changes in the fluorescence of a core fluorophore scaffold. However, such approaches are often hindered by spectral overlap of the product and reactant species. We provide a strategy to design ratiometric sensors that display dramatic spectral shifts by leveraging the chemoselective reactivity of novel functional groups inserted within fluorophore scaffolds. As a proof-of-principle, fluorophores containing a borinate ( RF620) or silanediol ( SiOH2R) functionality at the bridging position of the xanthene ring system are developed as endogenous H2O2 sensors. Both these fluorophores display far-red to near-infrared excitation and emission prior to reaction. Upon oxidation by H2O2 both sensors are chemically converted to tetramethylrhodamine, producing significant (≥66 nm) blue-shifts in excitation and emission maxima. This work provides a new concept for the development of ratiometric probes. [ABSTRACT FROM AUTHOR]

Zinc is essential for normal growth and development, and hence selective recognition and detection for zinc has been a significant area of research. Here 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine is described for the ratiometric fluorescence quantification of zinc ion with high selectivity. The fluorescence of 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine at 406 nm was quenched in the presence of zinc, and a new emission band appeared at 452 nm. The ratiometric method for the determination of zinc ion was based on the dual fluorescence measurements at 406 and 452 nm. This fluorescence response is caused by the formation of a 1:1 complex between 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine and the zinc(II) ion. The analytical figures of merit for the protocol were obtained. The linear dynamic range extended for zinc concentrations from 3.0 to 40.0 µmol/L with a limit of detection of 0.28 µmol/L. Zinc was determined in water with satisfactory results. [ABSTRACT FROM PUBLISHER]

Special functionalization of semiconducting polymer dots (Pdots) is highly desired to expand their applications in chemo/biosening. Herein, carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadiazole)] dots covalently tagged with aminated β-cyclodextrin (NH2-CD) have been designed to construct a ratiometric sensor for cholesterol (Cho). Using CD-Pdots as energy donors with rhodamine B (RB) as energy acceptors, a fluorescence resonance energy transfer (FRET) pair has been built because the host-guest interaction between RB and CD attached to Pdots brings donors and acceptors into close proximity. In the presence of Cho, the acceptors will depart from the donors because of the competitive inclusion interaction between Cho and RB with CD, resulting in the hindering of the FRET process between CD-Pdots and RB. On the basis of the turn-on fluorescence of CD-Pdots and turn-off fluorescence of RB, a sensitive ratiometric method for the determination of Cho in the concentration range from 25 to 350 nM with a detection limit of 4.9 nM was achieved. The proposed method was validated to determine free Cho in human serum samples with satisfactory results. [ABSTRACT FROM AUTHOR]

In this work, 2-naphthol ( 1 ) and its derivative 1-(2-hydroxynaphthalen-1-yl)naphthalen-2-ol (BINOL) ( 2 ) as two ratiometric fluorescence probes are used to detect hypochlorite, which is one of the biologically important reactive oxygen species (ROS), by UV–vis and fluorescent spectrometers. The fluorescence intensity of probe 1 and 2 were gradually decreased when addition of ClO − . Also, the detailed signal mechanism was elucidated by 1 H NMR and ESI-MS. In addition, the detection limits of probe 1 and 2 for ClO − were found to be 81 nM and 49 nM. Both two probes showed high selectivity for hypochlorite. [ABSTRACT FROM AUTHOR]

We show that mixed-phase titanium dioxide (TiO2) can be effectively employed as an unconventional, inorganic, dual-emitting, and ratiometric optical sensor of O2. Simultaneous availability of rutile and anatase TiO2 photoluminescence (PL) and their peculiar "anti-correlated" PL responses to O2 allow using their ratio as a measurement parameter associated with the O2 concentration, leading to an experimental responsivity being by construction larger than the one obtainable for single-phase PL detection. A proof of this concept is given, showing a two-fold enhancement of the optical responsivity provided by the ratiometric approach. Besides the peculiar ratiometricenhanced responsivity, other characteristics of mixed phase TiO2 can be envisaged as favorable for O2 optical probing, namely (a) low production costs, (b) absence of heterogeneous components, and (c) self-supporting properties. These characteristics encourage experimenting with its use for applications requiring high indicator quantities at a competitive price, possibly also tackling the need to develop supporting matrixes that carry the luminescent probes and avoiding issues related to the use of different components for ratiometric sensing. [ABSTRACT FROM AUTHOR]

We report a platform for the ratiometric fluorescent sensing of endogenously generated gaseous transmitter H2S in its aqueous form (bisulfide or hydrogen sulfide anion) based on the alteration of Forster resonance energy transfer from an emissive semiconductor quantum dot (QD) donor to a dithiol-linked organic dye acceptor. The disulfide bridge between the two chromophores is cleaved upon exposure to bisulfide, resulting in termination of FRET as the dye diffuses away from the QD. This results in enhanced QD emission and dye quenching. The resulting ratiometric response can be correlated quantitatively to the concentration of bisulfide and was found to have a detection limit as low as 1.36 ± 0.03 µM. The potential for use in biological applications was demonstrated by measuring the response of the QD-based FRET sensor microinjected into live HeLa cells upon extracellular exposure to bisulfide. The methodology used here is built upon a highly multifunctional platform that offers numerous advantages, such as low detection limit, enhanced photochemical stability, and sensing ability within a biological milieu. [ABSTRACT FROM AUTHOR]

Tetraamide-based receptors bearing hydroxy groups from serine and threonine side chains showed suitable ratiometric fluorescence responses upon the addition of basic oxoanions such as phosphate by pendant pyrenyl groups in aqueous MeCN. Receptor 3 is the first example of an artificial anion receptor bearing threonine residues as recognition sites. [ABSTRACT FROM AUTHOR]

A BODIPY-based ratiometric fluorescent probe for HOCl has been designed based on the transduction of thioether to sulfoxide function. This probe features a marked absorption and emission blue-shift upon the HOCl-promoted rapid transduction, enabling the highly selective and ratiometric detection. In addition, the probe works excellently within a wide pH range of 4–10, addressing the existing pH dependency issue. Living cells studies demonstrate that the probe is cell membrane permeable and can be employed successfully to image endogenous HOCl generation in macrophage cells. [ABSTRACT FROM AUTHOR]

A simple Cu 2+ -selective ratiometric fluorescence signaling probe based on the hydrolysis of dansylhydrazine was developed. Dansylhydrazine 1 showed prominent ratiometric fluorescence signaling behavior toward Cu 2+ ions in a 50% aqueous (pH 7.4) acetonitrile solution. The ratiometric signaling behavior was due to the Cu 2+ -assisted hydrolysis of the yellow-colored fluorescent dansylhydrazine to strongly blue-fluorescent dansyl acid. The Cu 2+ -selective signaling of probe 1 was not affected by the presence of biologically important metal ions. The ratiometric signaling of Cu 2+ by 1 was possible with a detection limit of 6.0 × 10 −8 M (3.8 ppb). In addition, the signaling of Cu 2+ in biological samples using synthetic urine was also tested. [ABSTRACT FROM AUTHOR]

Herein, Eu 3+ doped Gd 2 Ti 2 O 7 nanoparticles were tested for application in ratiometric luminescence thermometry. It is shown that two combinations of emissions: one that uses two emissions of Eu 3+ ions and one that uses one emission of Eu 3+ ions and trap emission of Gd 2 Ti 2 O 7 provide thermometry over the 303–423 K temperature range with relative sensitivities between 0.14% K −1 and 0.95% K −1 . Thermometry based on two Eu 3+ emissions from 5 D 0 to 5 D 1 levels has a higher relative sensitivity, but lower absolute sensitivity than thermometry based on one Eu 3+ emission and trap emission of Gd 2 Ti 2 O 7 . The tested material is prepared by Pechini-type polymerized complex route and is composed of agglomerated nanoparticles of ~30–50 nm in size with pure-phase cubic structure (space group Fd-3m) as evidenced from electron microscopy and X-ray diffraction measurements. [ABSTRACT FROM AUTHOR]

In this work, we developed a sensitive and efficient ratiometric electrochemical method for lipopolysaccharide (LPS) detection using Cu-based metal-organic frameworks (Cu-MOFs) as a catalyst and target-triggered quadratic cycles for signal amplification. First, in the presence of target LPS, the conformation change of the specifically designed hairpin probes 1 (HP1) triggered the target cyclic-induced polymerization to produce the output DNA with the aid of phi29 DNA polymerase (phi29). Then, the obtained output DNA hybridized with ferrocene-labeled hairpin probes 2 (Fc-HP2, which were immobilized on the electrode) to generate a nicking endonuclease (N.BstNBI) cleavage site. Thus, with N.BstNBI, the original signal molecules of Fc left from the electrode, and the single-stranded capture-probe-modified sensing interface was obtained. At this time, signal probes conducted by Au-nanoparticles-functionalized Cu-MOFs and labeled hairpin probes 3 (HP3/AuNPs/Cu-MOFs) were hybridized with capture probes for hairpin assembly. Herein, AuNPs/Cu-MOFs were not only used as nanocarriers for immobilizing HP3 but also acted as electroactive materials for signal reporting. With the proposed target-triggered quadratic cycles, the cleavage sites of Fc-HP2 were cut, and capture probes were obtained to hybridize with HP3/AuNPs/Cu-MOFs, which caused the signal decrease of Fc. Then Cu-MOFs were closed to the electrode for the signal increase of Cu-MOFs. Furthermore, when glucose was present in the detection solution, AuNPs/Cu-MOFs catalyzed the oxidation of glucose to realize the enzyme-free signal amplification. By measuring the peak currents ratio of the Cu-MOFs and Fc, the proposed aptasenor for LPS detection showed a low detection limit (0.33 fg/mL) and a wide linear range from 1.0 fg/mL to 100 ng/mL with high accuracy and sensitivity. This ratiometric electrochemical approach is expected to be a valuable strategy for detection of other analytes. [ABSTRACT FROM AUTHOR]

A chlorinated coumarin-aldehyde was developed as a colorimetric and ratiometric fluorescent probe for distinguishing glutathione (GSH), cystenine (Cys) and homocysteine (Hcy). The GSH-induced substitution-cyclization and Cys/Hcy-induced substitution-rearrangement cascades lead to the corresponding thiol-coumarin-iminium cation and amino-coumarin-aldehyde with distinct photophysical properties. The probe can be used to simultaneously detect GSH and Cys/Hcy by visual determination based on distinct different colors – red and pale-yellow in PBS buffer solution by two reaction sites. From the linear relationship of fluorescence intensity and biothiols concentrations, it was determined that the limits of detection for GSH, Hcy and Cys are 0.08, 0.09 and 0.18 μM, respectively. Furthermore, the probe was successfully used in living cell imaging with low cell toxicity. [ABSTRACT FROM AUTHOR]

A type of N-unsubstituted-1,2,3-triazole-decorated conjugated polymer (P3), with the feature of aggregation-induced emission enhancement (AIEE), was successfully synthesized via a Cu+-catalyzed click reaction between an acetylene-substituted precursor polymer (P2) and azidotrimethylsilane. Except for Ag+, the introduction of other metal ions had only a slight influence on the optical properties of P3. With the introduction of aqueous Ag+, the fluorescence of P3 in a THF–water mixture (vTHF/vwater = 4/1) (buffered with Tris–CA, 1 mM, pH = 7.4) displayed a ratiometric alteration at the blue (∼420 nm) and green (∼495 nm) bands. The corresponding I495/I420 ratio values maintained an upward trend throughout the titration process of Ag+. The detection limit of Ag+ reaches ∼1.4 μM (3σ/k), as evaluated from the corresponding relationship between I495/I420 and [Ag+]. The aggregation between the polymer chains induced by a Ag+–triazole interrelation is the plausible reason for the alteration of P3's optical properties. [ABSTRACT FROM AUTHOR]

Since its introduction in 1998, genetically encoded pH-sensitive sensor ratiometric pHluorin proved to be a valuable tool for cell physiology studies. Here, we show how the sensitivity of pHluorin-based monitoring of intracellular pH changes performed with cell suspensions can be enhanced by using synchronously scanned fluorescence spectroscopy. In the suspensions of S. cerevisiae cells subjected to varying extracellular pH values, we have been able to measure statistically significant changes in intracellular pH of less than 0.1 unit, which were not detectable using a standard ratiometric approach. [ABSTRACT FROM AUTHOR]

A coumarin–rhodamine based ratiometric fluorescent probe was designed and successfully synthesized. The probe can detect Hg 2+ with high selectivity over other metal ions and high sensitivity with the most sensitive readout signal in aqueous solution. There is a good linear relationship between the fluorescence ratio I 587 /I 478 and the concentration of Hg 2+ ranging from 0.5 u M to 1.5 u M and the detection limit was calculated to be as low as 3.2 n M. In addition, the probe can quickly detect Hg 2+ over a wide pH range from 4 to 11. Furthermore, the probe is cell membrane permeable and can detect Hg 2+ in living cells. [ABSTRACT FROM AUTHOR]

The fluorescent probe is constructed by incorporating an α, β-unsaturated pyridinium to a pyrene fluorophore. The chemodosimeter has shown a selective and sensitive response to sulfite anion over other various anions and biological thiol through a Michael addition of the sulfite to the alkene of the probe. Meanwhile, it can be easily observed that the color of the probe for sulfite changes from yellow to colorless by the naked eye, and from yellow to blue under UV lamp immediately after the sulfite is added. [ABSTRACT FROM AUTHOR]

This paper presents an ultra low-power and low-voltage pulse-width modulation based ratiometric capacitive sensor interface. The interface was designed and fabricated in a standard 90 nm CMOS 1P9M technology. The measurements show an effective resolution of 10 bits using 0.5 V of supply voltage. The active occupied area is only 0.0045 mm2 and the Figure of Merit (FOM), which takes into account the energy required per conversion bit, is 0.43 pJ/bit. Furthermore, the results show low sensitivity to PVT variations due to the proposed ratiometric architecture. In addition, the sensor interface was connected to a commercial pressure transducer and the measurements of the resulting complete pressure sensor show a FOM of 0.226 pJ/bit with an effective linear resolution of 7.64 bits. The results validate the use of the proposed interface as part of a pressure sensor, and its low-power and low-voltage characteristics make it suitable for wireless sensor networks and low power consumer electronics. [ABSTRACT FROM AUTHOR]

A novel ratiometric electrochemical sensor for sensitive and selective determination of deoxyribonucleic acid (DNA) had been developed based on signal-on and signal-off strategy. The target DNA hybridized with the loop portion of ferrocene (Fc) labeled hairpin probe immobilized on the gold electrode (GE), the Fc away from the surface of GE and the methylene blue (MB) was attached to an electrode surface by hybridization between hairpin probe and MB labeled primer. Such conformational changes resulted in the oxidation peak current of Fc decreased and that of MB increased, and the changes of dual signals are linear with the concentration of DNA. Furthermore, with the help of strand-displacement polymerization, polymerase catalyzed the extension of the primer and the sequential displacement of the target DNA, which led to the release of target and another polymerization cycle. Thus the circular strand displacement produced the multiplication of the MB confined near the GE surface and Fc got away from the GE surface. Therefore, the recognition of target DNA resulted in both the “signal-off” of Fc and the “signal-on” of MB for dual-signal electrochemical ratiometric readout. The dual signal strategy offered a dramatic enhancement of the stripping response. The dynamic range of the target DNA detection was from 10 −13 to 10 −8 mol L −1 with a detection limit down to 28 fM level. Compared with the single signaling electrochemical sensor, the dual-signaling electrochemical sensing strategy developed in this paper was more selective. It would have important applications in the sensitive and selective electrochemical determination of other small molecules and proteins. [ABSTRACT FROM AUTHOR]

In this paper, we report a highly selective and sensitive ratiometric NIR fluorescent probe that can be used for real-time detection of the biologically important hypochlorite with colorimetric and significant NIR fluorescent turn-on signal changes at NIR excitation wavelength. In addition, experiments showed that this probe can be applied to detect hypochlorite in tap water, serum samples, and living cells with low cytotoxicity. [ABSTRACT FROM AUTHOR]

An ultrasensitive method for the detection of protein is critically important in fundamental research and practical applications due to the low abundance of disease markers in body fluids or tissues. To detect the trace levels of disease markers with high sensitivity and specificity, a sensitive colorimetric biosensor for protein assay was developed using gold nanoparticles (AuNPs) and rolling circle amplification (RCA). After binding the biotinylated primer/circular template to the streptavidin-conjugated sandwich ELISA immunocomplex, the biotinylated primer was isothermally extended to generate single-stranded DNA (ssDNA). Sequentially, the padlock DNA was added and hybridized with the RCA products. The aggregation of the additional AuNPs in the supernatant containing the surplus padlock DNA and a certain concentration of salt could then be observed. The established sensor allowed for the specific detection of α-fetoprotein (AFP) with a detection limit of 33.45 pg mL−1. It was also demonstrated that this method could distinguish 500 pg mL−1 AFP with the naked eye. In addition, this biosensor could be applied to complex sample analysis and could be further used as a universal method for any protein or virus determination by changing the corresponding antibodies. [ABSTRACT FROM AUTHOR]

In the present work two different approaches, a semi-quantitative and a Derringer function approach, were developed to assist column selection for method development in targeted metabolomics. These approaches were applied in the performance assessment of three HILIC columns with different chemistries (an amide, a diol and a zwitterionic phase). This was the first step for the development of a HILIC UPLC–MS/MS method that should be capable to analyze a large number of polar metabolites. Two gradient elution profiles and two mobile phase pH values were tested for the analysis of multi-analyte mixtures. Acquired chromatographic data were firstly treated by a ratiometric, “semi-quantitative” approach which quantifies various overall analysis parameters (e.g. the percent of detected compounds, retentivity and resolved critical pairs). These parameters were used to assess chromatographic performance in a rather conventional/traditional and cumbersome/labor-intensive way. Secondly, a comprehensive and automated comparison of the three columns was performed by monitoring several well-known chromatographic parameters (peak width, resolution, tailing factor, etc.) using a lab-built programming script which calculates overall desirability utilizing Derringer functions. Derringer functions exhibit the advantage that column performance is ultimately expressed in an objective single and quantitative value which can be easily interpreted. In summary, results show that each column exhibits unique strengths in metabolic profiling of polar compounds. The applied methodology proved useful for the selection of the most effective chromatographic system during method development for LC–MS/MS targeted metabolomics, while it could further assist in the selection of chromatographic conditions for the development of multi-analyte methods. [ABSTRACT FROM AUTHOR]

A luminescent probe for determination of pH was designed based on a Förster resonance energy transfer (FRET) system, combining a europium chelate as the donor and carboxynaphtho-fluorescein as a pH sensitive acceptor. The FRET system enables referenced pH detection in an exceptional broad dynamic range from pH 3 to 9. [ABSTRACT FROM AUTHOR]

A new visible-light-excitable fluorescence ratiometric probe for OCl- has been developed based on a triphenylamine-diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single-crystal X-ray analysis. It behaves as a highly selective and sensitive probe for OCl- over other analytes with a fast response time (~100 s). OCl- reacts with the probe leading to the formation of the corresponding aldehyde in a mixed-aqueous system. The detection limit of the probe is in the 10-8m range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non-polar to polar, the emission band of TAM largely red-shifted. Moreover, the probe shows an excellent performance in real-life application in detecting OCl- in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl- were studied by DFT and TDDFT computational calculations. [ABSTRACT FROM AUTHOR]

A new ‘‘naked-eye’’ ratiometric colorimetric and fluorometric chemodosimeter (PBF) was constructed to enable trace vapor detection of hydrazine. This probe utilizes an irreversible and fast hydrazine-promoted cleavage of the ester linkage in PBF. This probe was shown to be highly selective for hydrazine, and showed real time response as well as a positive linear relationship to hydrazine concentration. The probe also shows an excellent performance in the ‘‘dip stick’’ method. [ABSTRACT FROM AUTHOR]

A ratiometric pH probe composed of a fluorescein moiety and an ionic near-infrared-emitting phosphorescent cyclometalated iridium(III) complex bis(6-(benzo[b]thien-2-yl)phenanthridinato)(4-(3-carboxypropyl)-4′-methyl-2,2′-bipyridine)iridium(III) was synthesized. With good cell permeability, the probe demonstrated a linear ratiometric response to the pH variation in the physiological range in HeLa cell assay. [ABSTRACT FROM AUTHOR]

We have described two “OFF–ON electrochemical latent ratiometric redox chemodosimeters”, 1,4-Bis(tert-butyldimethylsiloxy)benzene (H 2 Q′) and 1,4-Bis (tert-butyldimet hylsiloxy)-2-methoxybenzene (MH 2 Q′) for the selective detection of inorganic fluoride. The electrochemical signals of hydroquinone (H 2 Q) and o -methoxy hydroquinone (MH 2 Q) within this latent redox probes (H 2 Q′ and MH 2 Q′) were completely masked by protecting their hydroxyl group as silylether (OFF state). The externally added fluoride ions triggered the deprotection of H 2 Q′ and MH 2 Q′ and unmasked the electrochemical properties of H 2 Q and MH 2 Q respectively. The electrochemical reporters (H 2 Q and MH 2 Q) presented a pair of redox peaks at the electrode surface (ON state) and the peak currents are linearly dependent with the concentration of fluoride which leading to the ratiometric detection of fluoride. The limit of detection (signal-to-noise ratio=3) observed for the probes are 23.8 µM and 2.38 µM for H 2 Q′ and MH 2 Q′ respectively. The deprotection is highly selective for fluoride over other anions investigated. The probes are highly stable and the proposed approach offers rapid response time and promising practical applicability. The proposed strategy holds great promise for the commencement of new H 2 Q based electrochemical probes by tuning the electrochemical behavior of H 2 Q. [ABSTRACT FROM AUTHOR]

This paper reported a facile method for fabricating a functionalized fluorescent graphene oxide (GO) by covalently grafting the amine-modified mesoporous silica nanoparticles (MSNs) containing poly(p-phenylenevinylene) (PPV) and lactam of Rhodamine 6G (SRh6G) inside the channel of MSNs. The resulted GO-PPV@MSN-NH 2 @SRh6G fluorescent hybrid nanoparticles had a good dispersion and strong green fluorescence in aqueous solution. This hybrid material can be used as a fluorescent ratiometric probe to detect Hg 2+ in the water through fluorescence resonance energy transfer (FRET). Upon the addition of only Hg 2+ ions, the mission corresponding to the ring-opened form of rhodamine appeared at 550 nm with a simultaneous emission quenching of PPV at 494 nm. This ratiometric fluorescence change indicated that an FRET from the PPV to rhodamine was triggered by Hg 2+ ions. The hybrid nanoparticles of GO-PPV@MSN-NH 2 @SRh6G could be used as a novel fluorescent probe to carry out the quantitative detection of Hg 2+ with a detection limit of 7.1 × 10 −8 M. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent probe, 2-(7-diethylamino-2-oxo-2H-1-benzopyran-3-yl)-7-hydroxyl-1-benzopyrylium ( 1 ), has been developed for sulfite sensing. The method employs the nucleophilic addition of sulfite to the electrically positive benzopyrylium moiety of 1 to block the π-conjugated system of the whole molecule, which in turn results in significant blue shifts in the absorption and emission spectra of the sensing system. The fluorescence intensity ratio at 485 and 640 nm ( I 485 / I 640 ) increases linearly with sulfite concentration in the range of 0.05–10 μM. The proposed probe shows excellent selectivity toward sulfite over other common anions and biothiols. The bioimaging experiment demonstrates the potential of probe 1 for the ratiometric fluorescent imaging of sulfite in living cells. [ABSTRACT FROM AUTHOR]

The (13E,19E)-N1′,N3′-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide ( L ) has been developed for the detection of Th 4+ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L –Th 4+ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L –Th 4+ . The detection limit of L for Th 4+ recognition is to a concentration down to 0.1 μM (0.023 μg g −1 ). The present sensing system is also successfully applied for the detection of Th 4+ ion present in soil near nuclear atomic plants. [ABSTRACT FROM AUTHOR]

Developments of ratiometric bioprobes are highly appealing due to the superiority of their self-calibration capability for the quantitative biotracking. In this work, we designed and synthesized a novel lanthanide complex-based ratiometric luminescence probe, [4'-(2,4-dinitrophenyloxy)-2,2':6',2"-terpyridine-6,6"-diyl]bis(methylenenitrilo) tetrakis(acetate)-Eu3+/Tb3+ (NPTTA-Eu3+/Tb3+), for the specific recognition and quantitative time-gated luminescence detection of hydrogen sulfide (H2S) in aqueous and living cell samples. Due to the presence of the photoinduced electron transfer (PET) process from the terpyridine-Eu3+/Tb3+ moiety to 2,4-dinitrophenyl (DNP), the probe itself is weakly luminescent. In physiological pH aqueous media, the reaction of NPTTA-Eu3+/Tb3+ with H2S leads to the cleavage of DNP moiety from the probe molecule, which affords the deprotonated (4'-hydroxy-2,2':6',2"-terpyridine-6,6"-diyl)bis(methylenenitrilo) tetrakis(acetate)-Eu3+/Tb3+ and terminates the PET process. Meanwhile, the intensity of Tb3+ emission at 540 nm is remarkably increased, while that of the Eu3+ emission at 610 nm is slightly decreased. After the reaction, the intensity ratio of Tb3+ emission to Eu3+ emission, I540/I610, was ~220-fold increased, and the dose-dependent enhancement of I540/I610 showed a good linearity upon the increase of H2S concentration with a detection limit of 3.5 nM. This unique luminescence response allowed NPTTA-Eu3+/Tb3+ to be conveniently used as a ratiometric probe for the time-gated luminescence detection of H2S with I540/I610 as a signal. In addition, the applicability of the probe for the quantitative time-gated luminescence imaging of intracellular H2S in living cells was investigated. The results demonstrated the efficacy and advantage of the new probe for the time-gated luminescence cell imaging application. [ABSTRACT FROM AUTHOR]

Highlights: [•] A ratiometric two-photon fluorescent probe (MQ) for cysteine (Cys) and homocysteine (Hcy) was developed. [•] MQ exhibited a large two-photon absorption cross-section at 710nm (265GM). [•] MQ responded to Cys/Hcy much faster than previous reported two-photon fluorescent probes for Cys/Hcy. [•] MQ was cell-permeable and could be used to detect Cys with low cytotoxicity under two-photon excitation. [Copyright &y& Elsevier]

Abstract: A novel ratiometric colorimetric and NIR fluorescent probe for Cu2+ was designed based on the Cu2+ induced spirocyclic-opening reaction accompanied with activating the photo-induced transfer (PET) process of cyanine to Cu2+-metal ligand centers, by which well-resolved peaks and sensitivity could be obtained. The probe CyRh–Cu was also successfully applied to the determination of Cu2+ in water samples. [Copyright &y& Elsevier]

An organic salt as a fluorescent probe based on intramolecular charge transfer for Ca2+ determination is developed. Ca2+ can be detected by ratiometric emission at 490 and 594 nm with an excitation wavelength of 405 nm. This probe is highly selective for Ca2+ over other divalent metal cations and displays a large Stokes shift of 189 nm that can avoid interference of the excitation light beam and autofluorescence of biological samples. The dissociation constant for Ca2+ is 2.25 ± 0.47 μM and pertinent to Ca2+ detection in cellular resting and dynamic states. The probe demonstrates its application in monitoring Ca2+ in living cells under confocal microscopic imaging. [ABSTRACT FROM AUTHOR]