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]

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]

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]

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]