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Abstract: The design and synthesis of a porphyrin-appended terpyridine, 5-(4-([2,2′:6′,2″]-terpyridin-4-yl-carboxyamidyl)phenyl)-10,15,20-triphenylporphyrin (H2TPPTPy) and its application as potential fluoroionophore for recognition of metal ions are reported. For preparation of the fluoroionophore, a novel simple strategy with improved total yield has been applied for the synthesis of 2,2′:6′,2″-terpyridine-4′-carboxylic acid as a ligand. H2TPPTPy shows chelation-enhanced fluorescence effect with cadmium ion via the interruption of photoinduced electron transfer (PET) process, which has been utilized as the basis of the fabrication of the Cd(II)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Cd(II)-sensitive chemosensor were investigated. It shows a linear response toward Cd(II) in the concentration range of 3.2×10−6 to 3.2×10−4 M with a limit of detection of 1.2×10−6 M. The chemosensor shows good selectivity for Cd(II) over a large number of cations, such as alkali, alkali earth and transitional metal ions except Cu(II) and Zn(II). The sensor has been used for determination of Cd(II) in water samples with satisfactory recoveries. [Copyright &y& Elsevier]

Abstract A novel ratiometric and reversible chemosensor 4-((2-(Benzo[d]thiazol-2-yl)phenyl)ethynyl)- N,N -diethylaniline (BT-1) based on ortho -arylethynyl benzothiazole with large Stokes shift (Δλ≈190 nm) was designed and synthesized to recognize Cu2+. Copper ion induces a remarkable fluorescence enhancement and causes formation of a BT-1-Cu complex. The clamp-on coordination mode of BT-1 to Cu2+ was demonstrated using Job's plot, mass spectrum (MS) and DFT calculations. The calculations also indicate that Cu2+ was chelated to BT-1 through N and alkyne instead of S and alkyne. The probe could quantify Cu2+ with the detection limit of 3.2 × 10−9 M. The in vitro imaging results indicated that the probe BT-1 was membrane-permeable and could be applied into the recognition of Cu2+ ions in living cells. Graphical abstract Image 1 Highlights 1. A novel ratiometric and reversible fluorescence probe with a large stokes shift based on a new clamp-on unit. 2. It is the first example that utilizes aryl alkyne coordination in the determination of copper ions. 3. The probe BT-1 was membrane-permeable and could be applied into the recognition of Cu2+ ions in living cells. [ABSTRACT FROM AUTHOR]

Superoxide anion radical (O 2 − ), the “primary” reactive oxygen species (ROS) in living systems, is linked to a variety of physiological and pathological processes. Therefore, developing an effective strategy to monitor the fluctuation of O 2 − in biological systems is of great importance. This paper describes a new turn-on two-photon fluorescent probe for endogenous O 2 − detection and imaging, which was rationally designed and synthesized via a non-redox strategy. In the presence of O 2 − , the probe exhibited notable fluorescence enhancement (∼235-fold) with a low detection limit down to 1 nM, indicating a high signal-to-background ratio and excellent sensitivity. In addition, short response time, good biocompatibility, low cytotoxicity, long-term stability against light illumination, specificity to O 2 − over general reductants, and pH stability were demonstrated, indicating that the requirements for cellular O 2 − determination are met. Furthermore, the probe was successfully applied in two-photon fluorescence imaging of endogenous O 2 − in living cells and tissues and showed high imaging resolution and a deep-tissue imaging depth of ∼150 μm, illustrating the promising potential for practical applications in complex biosystems and providing a valuable theoretical basis and technical support for the study of physiological and pathological functions of O 2 − . [ABSTRACT FROM AUTHOR]

Two-dimensional graphitic carbon nitride nanosheets (CNNSs) with planar graphene-like structure have stimulated increasingly research interest in recent years due to their unique physicochemical properties. CNNSs possess superior stability, high fluorescence quantum yield, low-toxicity, excellent biocompatibility, unique electroluminescent and photoelectrochemical properties, which make them appropriate candidates for biosensing. In this review, we first introduce the preparation and unique properties of CNNSs, with emphasis on their superior properties for biosensing. Then, recent advances of CNNSs in photoelectrochemical biosensing, electrochemiluminescence biosensing and fluorescence biosensing are highlighted. An additional attention is paid to the marriage of CNNSs and nucleic acids, which exhibits great potentials in both biosensing and intracellular imaging. Finally, current challenges and opportunities of this 2D material are outlined. Inspired by the unique properties of CNNSs and their advantages in biological applications, we expect that more attention will be drawn to this promising 2D material and extensive applications can be found in bioanalysis and diseases diagnosis. [ABSTRACT FROM AUTHOR]

SO 2 and its derivatives (bisulfite/sulfite) play crucial roles in several physiological processes. Therefore, development of reliable analytical methods for monitoring SO 2 and its derivatives in biological systems is very significant. In this paper, a FRET-based two-photon fluorescent turn-on probe, A-HCy , was proposed for specific detection of SO 2 derivatives through the bisulfite/sulfite-promoted Michael addition reaction. In this FRET system, an acedan (2-acetyl-6-dialkylaminonaphthalene) moiety was selected as a two-photon donor and a hemicyanine derivative served as both the quencher and the recognition unit for bisulfite/sulfite. A-HCy exhibited excellent selectivity and rapid response to HSO 3 − with a detection limit of 0.24 μM. More importantly, probe A-HCy was first successfully applied in two-photon fluorescence imaging of biological SO 2 derivatives in living cells and tissues, suggesting its great potential for practical application in biological systems. [ABSTRACT FROM AUTHOR]

In this work we use a water-soluble cationic perylene derivative (compound 1) as the G-quadruplex (G4) structure fluorescence indicator to construct a fluorescent biosensor for simple, rapid and label-free detection of Pb 2+ . In the absence of Pb 2+ , strong electrostatic interactions between compound 1 and the G-rich DNA probe (PW17) induced the aggregation of compound 1 and resulted in the fluorescence quenching. In the presence of Pb 2+ , the PW17 formed Pb 2+ -stabilized G4 structure, which reduced the aggregation of compound 1 and gave rise to high fluorescence. This allowed us to use convenient “mix-and-detect” protocol for quantitative analysis of Pb 2+ . Since Pb 2+ can specially induce PW17 to form compact DNA fold, our proposed biosensor displayed high selectivity for Pb 2+ . It also exhibited a high sensitivity to Pb 2+ , with a limit of detection of 5.0 nM observed. Furthermore, the biosensor was applied for the detection of Pb 2+ in urine and paint samples, and both showed satisfactory results. [ABSTRACT FROM AUTHOR]

DNAzyme-based catalytic beacons have been widely studied for both in vivo and in vitro molecular detection. However, only a few label-free catalytic beacons with excellent analytical performance have been reported so far. In this work, by combining a catalytic DNAzyme for amplified sensing through enzymatic turnover with cleavage-induced G-quadruplex formation, a label-free DNAzyme biosensor was developed for amplified “turn-on” fluorescence detection of Pb 2+ with a detection limit of 3 nM. The method is very competitive compared to many other labeled or label-free methods with or without signal amplification. Due to the inherent specificity of the GR-5 DNAzyme, the method also exhibits excellent selectivity. This biosensor successfully detected Pb 2+ in river water samples with high sensitivity and selectivity. Such a method might provide a universal DNAzyme-based sensing platform for sensitive detection of various targets both in environmental and biomedical fields. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescent sensing systems based on the quenching of fluorophores have found wide applications in bioassays. An efficient quencher will endow the sensing system a high sensitivity. The frequently used quenchers are based on organic molecules or nanomaterials, which usually need tedious synthesizing and modifying steps, and exhibit different quenching efficiencies to different fluorophores. In this work, we for the first time report that aggregated perylene derivative can serve as a broad-spectrum and label-free quencher that is able to efficiently quench a variety of fluorophores, such as green, red and far red dyes labeled on DNA. By choosing nucleases as model biomolecules, such a broad-spectrum quencher was then employed to construct a multiplexed bioassay platform through a label-free manner. Due to the high quenching efficiency of the aggregated perylene, the proposed platform could detect nuclease with high sensitivity, with a detection limit of 0.03U/mL for EcoRV, and 0.05U/mL for EcoRI. The perylene quencher does not affect the activity of nuclease, which makes it possible to design post-addition type bioassay platform. Moreover, the proposed platform allows simultaneous and multicolor analysis of nucleases in homogeneous solution, demonstrating its value of potential application in rapid screening of multiple bio-targets. [Copyright &y& Elsevier]

Abstract: In this work, based on the fact that pyrophosphate (PPi) could regulate the activity of Zn2+-dependent DNAzyme, we for the first time report a fluorescence turn-on sensing system for alkaline phosphatase (ALP) with improved sensitivity via nonprotein-enzymatic signal amplification. A catalytic and molecular beacon (CAMB) design was employed to further improve its sensitivity. Taking advantage of the strong interactions between PPi and the Zn2+, the cofactor Zn2+ was caged, and the DNAzyme activity was effectively inhibited. The introduction of ALP, however, could catalyze the hydrolysis of PPi and release free Zn2+, resulting in the activation of DNAzyme to catalyze the cleavage of the molecular beacon substrate with a remarkable increase of fluorescent signal. These optimized designs together allow a high sensitivity for ALP, with a detection limit of 20pM observed, much lower than previously reported methods. It has also been used for detection of ALP in human serum with satisfactory results, demonstrating its potential applications in clinical diagnosis. [Copyright &y& Elsevier]