A highly selective and sensitive fluorescence sensing system for distinction between diphosphate and nucleoside triphosphates

Advancing Glucose Sensing Through Auto-Fluorescent Polymer Brushes: From Surface Design to Nano-Arrays

Designing smart (bio)interfaces with the capability to sense and react to changes in local environments offers intriguing possibilities for new surface-based sensing devices and technologies. Polymer brushes make ideal materials to design such adaptive and responsive interfaces given their large variety of functional and structural possibilities as well as their outstanding abilities to respond to physical, chemical, and biological stimuli. Herein, a practical sensory interface for glucose detection based on auto-fluorescent polymer brushes decorated with phenylboronic acid (PBA) receptors is presented. The glucose-responsive luminescent surfaces, which are capable of translating conformational transitions triggered by pH variations and binding events into fluorescent readouts without the need for fluorescent dyes, are grown from both nanopatterned and non-patterned substrates. Two-photon laser scanning confocal microscopy and atomic force microscopy (AFM) analyses reveal the relationship between the brush conformation and glucose concentration and confirm that the phenylboronic acid functionalized brushes can bind glucose over a range of physiologically relevant concentrations in a reversible manner. The combination of auto-fluorescent polymer brushes with synthetic receptors presents a promising avenue for designing innovative and robust sensing systems, which are essential for various biomedical applications, among other uses.

Zn-dipicolylamine-based reactive oxygen species-responsive lipids for siRNA delivery and in vivo colitis treatment

The reduction of ROS and inflammatory factor levels plays important role in the treatment of colitis. A series of ROS-responsive lipids (ZnDPA-R) based on the thioketal structure were designed and synthesized. It was hoped that the lipidic materials could combine ROS consumption and siRNA delivery capacity to achieve synergistic treatment of colitis. The target liposomes could combine with the phosphate backbone of siRNA to form lipoplexes with the size of ∼100 nm, and could deliver siRNA cargo into the cell. The results of in vitro anti-inflammatory experiments showed that the lipids may effectively consume ROS in cells. Meanwhile, the lipoplexes significantly reduced the expression levels of TNF-α mRNA and related inflammatory factors in macrophages. After PEGylation, the lipoplex was used for the treatment of mouse colitis, and biodistribution results proved that the lipoplexes effectively aggregated in the intestine. The delivery system could not only response to the high ROS level at colitis via thioketal breaking, but also could assist in the treatment of inflammation by ROS consumption. The treatment results revealed that the levels of TNF-α mRNA and related inflammatory factors at the colon lesion were largely reduced, and the inflammatory symptoms were significantly relieved. Hematology test results indicated that the treatment was safe and induced no obvious side effects on mice. This study may shed light on the synergistic treatment for colitis via anti-inflammatory siRNA delivery and ROS depletion strategies. STATEMENT OF SIGNIFICANCE: Downregulation of inflammatory factors and reactive oxygen species (ROS) levels is critical in treating colitis. In the present study, a series of ROS-responsive lipid molecules based on the Zn-DPA headgroup and thioketal linkage were synthesized for delivering TNF-α siRNA and for treating colitis. In addition to silencing the expression of TNF-α mRNA and the related inflammatory factors, the material also achieved synergistic treatment by simultaneous consumption of ROS in the colon lesion. In vitro cell experiments and in vivo colitis treatment in mice showed that the lipoplex exerted a satisfactory therapeutic effect on colitis, and the symptoms of colitis in mice were significantly alleviated. The present study may shed light on the synergistic treatment for colitis through anti-inflammatory siRNA delivery and ROS depletion strategies.

A Dual-Control Strategy by Phosphate Ions and Local Microviscosity for Tracking Adenosine Triphosphate Metabolism in Mitochondria and Cellular Activity Dynamically

Adenosine triphosphate (ATP) acts as the main energy source for growth and development in organisms, and the disorder reflects the mitochondrial damage to a large extent. Therefore, an efficient tool for the evaluation of the ATP metabolic level is important to track mitochondrial health, providing an additional perspective for an in-depth long-term study on living activities. Herein, a twisted intramolecular charge transfer (TICT) framework is utilized to build up a sensitive receptor, Mito-VP, with a negligible background to target mitochondrial ATP metabolism by monitoring the phosphate ion (Pi) level upon ATP hydrolysis under the overall consideration of the structural and functional features of mitochondria. The responsive fluorescence could be lighted on under the dual control of Pi and local microviscosity, and the two steps of ATP hydrolysis could be captured through fluorescence. In addition to the well-behaved mitochondrial targeting, the energy metabolism at cellular and organism levels has been clarified via mitosis and zebrafish development, respectively.

Azulene-based fluorescent chemosensor for adenosine diphosphate

AzuFluor® 435-DPA-Zn, an azulene fluorophore bearing two zinc(II)-dipicolylamine receptor motifs, exhibits fluorescence enhancement in the presence of adenosine diphosphate. Selectivity for ADP over ATP, AMP and PPi results from appropriate positioning of the receptor motifs, since an isomeric sensor cannot discriminate between ADP and ATP.

Efficient synthesis of 6,6′-diamido-2,2′-dipicolylamine ligands for potential phosphate anion sensing

Through retrosynthetic analysis, functionalized 6,6′-diamido-2,2′-dipicolylamines (DA-DPAs) have been efficiently synthesized, which may accelerate the development of selective probes towards phosphate anions.

Monitoring inorganic pyrophosphatase activity with the fluorescent dizinc(ii) complex of a macrocycle bearing one dansylamidoethyl antenna

The dizinc(ii) complexes of L were used for the recognition of anions by fluorescence spectroscopy (L is a heteroditopic hexaazamacrocycle with two diethylenetriamine coordination heads with 2-methylpyridyl and dansylamido ethyl arms, and m-xylyl spacers). The protonation of L and stability constants of its zinc(ii) complexes were determined in aqueous solution, at 298.2 ± 0.1 K and I = 0.10 ± 0.01 M in KNO₃. At a 2 : 1 Zn²⁺/L ratio, the dinuclear complexes clearly dominate. The ligand alone does not display fluorescence changes upon increasing the pH value, but in the presence of Zn²⁺ the emission reaches a maximum at pH ≅ 7.5, at which 95% of the ligand is in the dinuclear complex form. The emission appears concomitantly with the [Zn₂H_-1L]³⁺ species formation, which supports that the latter complex corresponds to the metal-promoted deprotonation of dansylamide NH. The [Zn₂H_-1L]³⁺ complexes were used for the recognition of phosphate and polyphosphate anions in aqueous solution buffered at pH 7.5 with 2 mM PIPPS, at 298.2 K. The binding of anions causes a decrease of the emission. The association constant determination revealed that HPPi^3- is the strongest bound anion (log K_app = 5.57), followed by HATP^3- (two times weaker), and the remaining anions show lower binding constants, with HPO₄^2- having the weakest uptake by the receptor. The observed selectivity of the [Zn₂H_-1L]³⁺ receptor for PPi in relation to HPO₄^2-, and the fact that the formation of the [Zn₂H_-1L]³⁺ complex is not disturbed by the presence of Mg²⁺, allowed monitoring of the PPi hydrolysis by using inorganic pyrophosphatase in real-time.

Selective sensing of ATP by hydroxide-bridged dizinc(ii) complexes offering a hydrogen bonding cavity

This work illustrates the highly selective fluorescence detection of ATP in the presence of other competing anions, such as AMP, ADP, PPi and other phosphates by using a set of hydroxide-bridged dizinc(ii) complexes offering a cavity lined with hydrogen bonds and other interactive forces. ATP, as a whole, was recognized by the synergic combination of Zn-phosphate bonding, ππ stacking between the adenine ring of ATP and the pyridine ring of the dizinc complex and hydrogen bonding interactions that modulate the cavity structure of the dizinc complexes.

Spectrophotometric, fluorimetric and electrochemical selective pyrophosphate/ATP sensing based on the dimethyltin(IV)-tiron system

Sensing of pyrophosphate anion (PPi) in the presence of nucleotide triphosphates allows the real time monitoring of the polymerase chain reaction. To get a deeper understanding of the factors involved in PPi/nucleotide triphosphate discrimination, a detailed study on the performance of a dimethyltin (IV)-catecholate complex capable of both separate fluorimetric or electrochemical detection of PPi in the presence of adenosine triphosphate (ATP) has been undertaken. Dimethyltin (IV) tightly binds PPi or ATP, and forms a stable 1:1 complex with tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid) in water. The complexation equilibria with all components are characterized quantitatively by potentiometric and spectroscopic titrations. Pyrophosphate anion can be detected owing to its ability to release free tiron from the complex by measuring either a fluorimetric or an electrochemical signal. On the contrary, ATP does not displace tiron but causes an interference with PPi in the fluorimetric detection method due to the formation of a ternary Me₂Sn(IV)-tiron-ATP complex with optical properties intermediate between those of free and bound tiron. In the electrochemical (square wave voltammetry) method, the ternary ATP complex shows a separate peak which does not coincide with the peaks of neither free nor bound tiron, thus making possible the simultaneous detection of ATP in addition to PPi.

Are two better than one? Comparing intermolecular and intramolecular indicator displacement assays in pyrophosphate sensors

Peptide receptors with Zn(ii)-DPA units and a covalently bound fluorescent coumarin indicator on an oxazole-containing scaffold are shown to function as more selective pyrophosphate sensors than the analogous chemosensing ensembles in indicator displacement assays.

A Schiff base platform: structures, sensing of Zn(ii) and PPi in aqueous medium and anticancer activity

A Schiff base platform was explored to present structural aspects of its Zn(ii) and Cd(ii) coordination compounds, sensing behavior towards Zn(ii) and PPi in aqueous medium and anticancer activity.

Di- and Triphosphate Recognition and Sensing with Mono- and Dinuclear Fluorescent Zinc(II) Complexes: Clues for the Design of Selective Chemosensors for Anions in Aqueous Media

The synthesis of a new ligand (L1) containing two 1,4,7-triazacyclononane ([9]aneN₃ ) moieties linked by a 4,5-dimethylenacridine unit is reported. The binding and fluorescence sensing properties toward Cu²⁺ , Zn²⁺ , Cd²⁺ , and Pb²⁺ of L1 and receptor L2, composed of two [9]aneN₃ macrocycles bridged by a 6,6''-dimethylen-2,2':6',2''-terpyridine unit, have been studied by coupling potentiometric, UV/Vis absorption, and emission measurements in aqueous media. Both receptors can selectively detect Zn²⁺ thanks to fluorescence emission enhancement upon metal binding. The analysis of the binding and sensing properties of the Zn²⁺ complexes toward inorganic anions revealed that the dinuclear Zn²⁺ complex of L1 selectively binds and senses the triphosphate anion (TP), whereas the mononuclear Zn²⁺ complex of L2 displays selective recognition of diphosphate (DP). Binding of TP or DP induces emission quenching of the Zn²⁺ complexes with L1 and L2, respectively. These results are exploited to discuss the role played by pH, number of coordinated metal cations, and binding ability of the bridging units in metal and/or anion coordination and sensing.

Cd(II)-terpyridine-based complex as a ratiometric fluorescent probe for pyrophosphate detection in solution and as an imaging agent in living cells

The terpyridine anthracene ligand was synthesized and characterized. is a ratiometric fluorescent probe for Cd(2+) with a recognition mechanism based on intramolecular charge transfer (ICT). An complex was isolated, and its structure was established using single-crystal XRD. The complex was able to serve as a novel reversible chemosensing ensemble to allow ratiometric response to pyrophosphate (PPi) in aqueous media. Moreover, the fluorescence imaging in living cells from these two emission channels suggested that was a ratiometric probe for Cd(2+), and the in situ generated complex was also a ratiometric ensemble for PPi detection in living cells.

Tetraphenylethene-pyridine salts as the first self-assembling chemosensor for pyrophosphate

We presented a novel approach for pyrophosphate (PPi) sensing. Two tetraphenylethene (TPE)-functionalised pyridine salts (TPM and TPH) were designed and synthesized. Both of them exhibited weak emission in the solution state that originates from intramolecular charge transfer (ICT) from TPE to the pyridine; the addition of PPi into the TPM aqueous solution would enhance the fluorescence intensity, which eliminates the emission quenching effect of the iodide ion by the formation of PPi-sensor nanoparticles. The detection limit of TPM was determined to be as low as 133 nM. Meanwhile, a thin solid film of TPM that could detect PPi rapidly was conveniently prepared.

Making pyrophosphate visible: the first precipitable and real-time fluorescent sensor for pyrophosphate in aqueous solution

An in situ generated Zn²⁺ complex of di-2-(picoly) amine BINOL–DPA was presented as a precipitable and real-time fluorescent sensor for PPi with a detection limit of 95 nm, and it could be successfully applied in imaging PPi in living cells.

Fluorescent and colorimetric chemosensors for pyrophosphate

In this review, we will cover the fluorescent and colorimetric chemosensors developed for the detection of pyrophosphate (PPi) since 2010.

Phosphate ion targeted colorimetric and fluorescent probe and its use to monitor endogeneous phosphate ion in a hemichannel-closed cell

Fluorescent probe 1, the first inorganic phosphate (Pi) targeted colorimetric and fluorescent probe to detect endogenous Pi in hemichannel-closed cells, has been developed. Probe 1 undergoes a unique Pi induced hydrolytic reaction in DMSO-HEPES (V/V = 9:1) buffered (0.02 M, pH 7.4) solutions that produces a colorimetric change associated with a 62 nm red-shift in the UV-vis absorption maximum and up to a 780-fold enhancement in the fluorescence intensity. The mechanistic proposal that these spectroscopic changes are associated with reaction Pi with 1 to form coumarin gains support from the results of theoretical calculations and mass spectrometry studies. Observations made in fluorescence imaging studies with HeLa cells and C. elegans show that 1 can be employed to monitor Pi production in vivo caused by apyrase-catalyzed ATP hydrolysis. Moreover, probe 1 was utilized to show that apoptosis of hemichannel-closed Sf9 cells is caused by Inx3 promoted dephosphorylation of Akt (RAC serine/threonine-protein kinase), leading to an elevation of the concentration of Pi. Overall, the study has produced the first fluorescent sensor 1 for endogenous inorganic phosphate. Moreover, the utility of 1 for measuring Pi release in vitro has been demonstrated and utilized to elucidate the mechanism of Inx3 action in hemichannel-closed Sf9 cells.

A nanoparticle formula for delivering siRNA or miRNAs to tumor cells in cell culture and in vivo

To improve RNA delivery, we present a protocol to produce an RNA carrier based on a Zn(II)-dipicolylamine (Zn-DPA) analog, which is an artificial receptor for phosphate anion derivatives. We further functionalized this Zn-DPA analog to hyaluronic acid (HA)-based self-assembled nanoparticles (HA-NPs) with a hydrodynamic diameter of 100 nm by conjugating amine-functionalized Zn-DPA molecules onto the HA-NPs through amide formation, resulting in efficient tumor-targeted delivery of RNAs (siRNAs, miRNA or other short oligoribonucleotides) and small-molecule drugs. The functional group of Zn-DPA can be converted into other groups such as a carboxylic or thiol group, and the DPA analog can be covalently attached to a variety of existing and novel platforms or formulations for the development of multifunctional materials via standard bioconjugation techniques. Protocols for RNA formulation and delivery into tumor tissues and tumor cells are also described. Our design strategy offers a versatile and practical method for delivering both RNA and chemotherapeutics to tumor cells and expands existing nanomaterial capabilities to further the field of drug and gene delivery.

Pyrophosphate selective recognition by a Zn2+ complex of a 2,2′-binaphthalene derivative bearing di(2-pyridylmethyl)aminomethyl groups in aqueous solution

A dinuclear zinc complex of a 2,2′-binaphthalene derivative selectively recognized a pyrophosphate anion.

Focused fluorescent probe library for metal cations and biological anions

A focused fluorescent probe library for metal cations was developed by combining metal chelators and picolinium/quinolinium moieties as combinatorial blocks connected through a styryl group. Furthermore, metal complexes derived from metal chelators having high binding affinities for metal cations were used to construct a focused probe library for phosphorylated biomolecules. More than 250 fluorescent probes were screened for identifying an ultraselective probe for dTTP.

Molecular recognition with boronic acids-applications in chemical biology

Small molecules have long been used for the selective recognition of a wide range of analytes. The ability of these chemical receptors to recognise and bind to specific targets mimics certain biological processes (such as protein-substrate interactions) and has therefore attracted recent interest. Due to the abundance of biological molecules possessing polyhydroxy motifs, boronic acids-which form five-membered boronate esters with diols-have become increasingly popular in the synthesis of small chemical receptors. Their targets include biological materials and natural products including phosphatidylinositol bisphosphate, saccharides and polysaccharides, nucleic acids, metal ions and the neurotransmitter dopamine. This review will focus on the many ways in which small chemical receptors based on boronic acids have been used as biochemical tools for various purposes, including sensing and detection of analytes, interference in signalling pathways, enzyme inhibition and cell delivery systems. The most recent developments in each area will be highlighted.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011

This review focuses on examples reported in the years 2010-2011 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions.

Studies on acedan-based mononuclear zinc complexes toward selective fluorescent probes for pyrophosphate

We have demonstrated that mononuclear Zn(II)-dipicolylamine (DPA) complexes with an auxiliary ligand can fluorescently discriminate pyrophosphate over ATP with as high selectivity as the known fast responding dinuclear bis(ZnDPA) complexes.

Highly selective visual distinction of pyrophosphate from other phosphate anions with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene in the presence of copper(II) ions

Pyrophosphate (PPi), as a biologically related phosphate anion, plays very important roles in organisms. Here, a highly selective visual method for distinction of PPi was made with commercial available 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) in the presence of copper(II). The yellow solution of 5-Cl-PADAB exhibits strong absorption at 450.5 nm, and addition of Cu(II) results in a red solution with a new absorption band at 506.0 nm. Upon titration with PPi, the absorption band at 506.0 nm decreases with blueshift, while another new absorption band in the region from 562.0 nm to 750.0 nm appears which gradually splits into two peaks, and the color accordingly changes from red to cyan. Further addition of PPi, the new absorption peaks gradually disappear, and the mixture shows the absorption of 5-Cl-PADAB and recovers to yellow from cyan. This process is highly selective for PPi since other phosphate anions such as nucleotides cannot induce such spectral and color changes. With this method, the detection of PPi concentration in human urine was made with satisfactory results.

Highly selective colorimetric sensing pyrophosphate in water by a NBD-phenoxo-bridged dinuclear Zn(II) complex

A novel NBD-phenoxo-bridged dinuclear Zn(II) complex is found to be an effective colorimetric sensor for pyrophosphate (PPi) in pure aqueous solution over a wide pH range. This sensor shows high binding affinity (K(a)≈ 3 × 10(8) M(-1)) and high selectivity for PPi, and can be also used to assay the activity of pyrophosphatase in real time.

Anion recognition and sensing with Zn(II)-dipicolylamine complexes

This critical review covers the developments in anion recognition and sensing using Zn(II)-dipicolylamine functionalized receptors over the past decade with emphasis on recent rapid advances in the last five years.

Sticky nanoparticles: a platform for siRNA delivery by a bis(zinc(II) dipicolylamine)-functionalized, self-assembled nanoconjugate

Delivering the goods: Multifunctional, self-assembled, polymeric nanoparticles for the simultaneous delivery of small-molecule drugs and siRNA have been synthesized. The nanoparticles are composed of biodegradable hyaluronic acid, for tumor targeting and cellular delivery, and a high siRNA binding affinity is provided by a Zn(II)-dipicolylamine analogue as an artificial phosphate-binding receptor (see scheme).