Ratiometric Detection of Nanomolar Concentrations of Heparin in Serum and Plasma Samples Using a Fluorescent Chemosensor Based on Peptides

Dwyer J. Editors' Choice-Perspective-Deciphering the Glycan Kryptos by Solid-State Nanopore Single-Molecule Sensing: A Call for Integrated Advancements Across Glyco- and Nanopore Science

Glycans, or complex carbohydrates, are information-rich biopolymers critical to many biological processes and with considerable importance in pharmaceutical therapeutics. Our understanding, though, is limited compared to other biomolecules such as DNA and proteins. The greater complexity of glycan structure and the limitations of conventional chemical analysis methods hinder glycan studies. Auspiciously, nanopore single-molecule sensors-commercially available for DNA sequencing-hold great promise as a tool for enabling and advancing glycan analysis. We focus on two key areas to advance nanopore glycan characterization: molecular surface coatings to enhance nanopore performance including by molecular recognition, and high-quality glycan chemical standards for training.

d-type peptides based fluorescent probes for "turn on" sensing of heparin

Developing "turn on" fluorescent probes was desirable for the detection of the effective anticoagulant agent heparin in clinical applications. Through combining the aggregation induced emission (AIE) fluorogen tetraphenylethene (TPE) and heparin specific binding peptide AG73, the promising "turn on" fluorescent probe TPE-1 has been developed. Nevertheless, although TPE-1 could achieve the sensitive and selective detection of heparin, the low proteolytic stability and undesirable poor solubility may limit its widespread applications. In this study, seven TPE-1 derived fluorescent probes were rationally designed, efficiently synthesized and evaluated. The stability and water solubility were systematically estimated. Especially, to achieve real-time monitoring of proteolytic stability, the novel Abz/Dnp-based "turn on" probes that employ the internally quenched fluorescent (IQF) mechanism were designed and synthesized. Moreover, the detection ability of synthetic fluorescent probes for heparin were systematically evaluated. Importantly, the performance of d-type peptide fluorescent probe XH-6 indicated that d-type amino acid substitutions could significantly improve the proteolytic stability without compromising its ability of heparin sensing, and attaching solubilizing tag 2-(2-aminoethoxy) ethoxy) acid (AEEA) could greatly enhance the solubility. Collectively, this study not only established practical strategies to improve both the water solubility and proteolytic stability of "turn on" fluorescent probes for heparin sensing, but also provided valuable references for the subsequent development of enzymatic hydrolysis-resistant d-type peptides based fluorescent probes.

Construction of a highly sensitive detection platform for heparin based on a "turn-off" cationic fluorescent dye

A highly sensitive detection platform for heparin was constructed via the utilization of a commercially available cationic fluorescent dye (cresyl violet acetate, CV) as a fluorescence probe. The electrostatic binding between CV and heparin quenched the fluorescence in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic (HEPES) buffer solution (10 mM, pH 7.1). CV was highly selective towards heparin over other potential inferring substances. The detection limit of heparin detection was 5.19 ng/mL, and the linear working range was 0 ∼ 1 μg/mL in HEPES solution. In 1 % serum, the detection platform based on the fluorescence "turn-off" behavior of CV was also successfully constructed with a detection limit of 5.86 ng/mL in the linear range of 0 ∼ 0.8 μg/mL. Moreover, the CV-heparin complex was considered a potential sensor platform for the detection of protamine because of its stronger affinity for heparin and protamine.

Development of peptide-based ratiometric fluorescent probe for sensing heparan sulfate and heparin in aqueous solutions at physiological pH and quantitative detection of heparan sulfate in live cells

Heparan sulfate (HS) plays a critical role in various biological processes as a vital component of the extracellular matrix. In this study, we synthesized three fluorescent probes (1-3) comprising Arg-rich peptides as HS receptors and a fluorophore capable of exhibiting red-shifted emissions upon aggregation. All three probes demonstrated ratiometric responses to HS and heparin in aqueous solutions. Remarkably, probe 3 exhibited a unique ratiometric response to HS in both aqueous solutions at physiological pH and HS proteoglycans on live cells. Probe 3 displayed exceptional sensing properties, including high biocompatibility, water solubility, visible light excitation, a large Stokes shift for ratiometric detection and remarkable selectivity and sensitivity for HS (with a low limit of detection: 720 pM). Binding mode studies unveiled the crucial role of charge interactions between probe 3 and negatively charged HS sugar units. Upon binding, the fluorophore segments of the probes overlapped, inducing green and red emission changes through restricted intramolecular rotation of the fluorophore moiety. Importantly, probe 3 was effectively employed to quantify the reduction of HS proteoglycan levels in live cells by inhibiting HS sulfation using siRNA and an inhibitor. It successfully detected decreased HS levels in cells treated with doxorubicin and irradiation, consistent with results obtained from western blot and immunofluorescence assays. This study presents the first ratiometric fluorescent probe capable of quantitatively detecting HS levels in aqueous solutions and live cells. The unique properties of peptide-based probe 3 make it a valuable tool for studying HS biology and potentially for diagnostic applications in various biological systems.

Pyrene-Based Self-Assembling Peptide for Ratiometric Detection of Heparin

Heparin is a commonly used anticoagulant in clinical practice; however, excessive heparin can cause serious adverse reactions. Convenient and accurate detection of heparin levels is thus very important. In this research, a pyrene-based self-assembling fluorescent peptide PyFFRRR was designed for simple, selective, and efficient heparin detection. The guanidine groups in the arginine residues of PyFFRRR bind tightly with heparin, which is highly sulfated, through electrostatic interactions. Charge neutralization facilitated the self-assembly of PyFFRRR, resulting in its spectral response changing from deep blue monomer fluorescence to green excimer fluorescence. PyFFRRR exhibited excellent sensitivity and selectivity for ratiometric detection of heparin. The binding mechanism was investigated by using spectral and simulation tools, and structural observation. Finally, PyFFRRR was employed in human serum samples for ratiometric detection of heparin.

Luminescence Sensing of Biomacromolecules Heparin and Protamine in 100% Human Serum and Plasma by Supramolecular Polymeric Assemblies

Heparin, an anionic biomacromolecule, is routinely used as an anticoagulant during medical surgery to prevent blood clot formation and in the treatment of several heart, lung, and circulatory disorders having a higher risk of blood clotting. We herein report supramolecular polymeric nanoassemblies of cationic pyrene-tagged bis-imidazolium amphiphiles for heparin detection with high sensitivity and selectivity in aqueous buffer, plasma, and serum media. The nano-assemblies exhibited cyan-green excimeric emission in aqueous media, and their multivalent array of positive surface charges allowed them to form co-assemblies with heparin, resulting in significantly enhanced emission. This provided a convenient method for heparin detection in buffer at nanomolar concentrations, and most notably, a ratiometric fluorescence response was obtained even in highly competitive 100% human serum and 100% human plasma in a clinically relevant concentration range. Moreover, using the heparin-based luminescent co-assemblies, protamine sulfate, a clinically administered antidote to heparin, was also detected in 100% human serum and 100% human plasma at sub-micromolar concentrations.

Efficient imidazolium-biomolecule interaction-assisted amplified quenching for ultrasensitive detection of heparin

Detection of Heparin (HP) under physiological conditions is difficult due to the presence of biological obstructions including proteins and lipids. Thus, it is highly challenging to selectively detect HP and to increase its sensitivity in complex systems. Here, we report the detection of HP at nanomolar levels via efficient imidazolium-HP interaction-assisted fluorescence quenching amplification. The self-assembled pyrenyl aggregates are devised as a conduit for efficient exciton transport, which induces amplified fluorescence quenching for HP detection. This amplified quenching is enhanced by introducing an imidazolium receptor designed to have high affinity to HP via electrostatic and/or additional interactions with C2 protons, resulting in a very high Stern-Volmer quenching constant of approximately 1.17 ☓ 10 8 M -1 .

Highly sensitive and ratiometric luminescence sensing of heparin through templated cyanostilbene assemblies

The assembly of organic dyes on bio-molecular templates is an attractive strategy for the creation of bio-materials with intriguing optical properties. This principle is exploited here for the detection of polyanion heparin, a known anticoagulant, by employing di-cationic cyanostilbene derivatives with inherent aggregation induced emission (AIE) features. The cyanostilbene derivatives exhibited weak cyan-blue monomeric emissions in solutions but upon electrostatic co-assembly with heparin, formed highly luminescent clusters on the polyanion surface. The cyanostilbene chromophores in the clusters exhibited greenish-yellow excimer emissions with remarkably longer life-times (up to 70-fold) and higher quantum yields (up to 85-fold) compared to their aqueous solutions. This led to heparin detection in aqueous buffer in low nanomolar concentrations. Additionally, and more importantly, a ratiometric detection of heparin was achieved in highly competitive media such as 50% human serum and 60% human plasma in medically relevant concentrations.

Novel fluorescence immunoassay for the detection of zearalenone using HRP-mediated fluorescence quenching of gold-silver bimetallic nanoclusters

In the presented study, a horseradish peroxidase (HRP)-mediated ratiometric fluorescence enzyme-linked immunosorbent assay (ELISA) for zearalenone (ZEN) was reported based on fluorescence quenching of gold-silver bimetallic nanoclusters (Au-Ag NCs). HRP-antibody was used as a bridge in this immunoassay, linking the ratiometric fluorescence signal to the ZEN concentration. HRP catalyzed the oxidization of o-phenylenediamine in the presence of H₂O₂, leading to the formation of 2,3-diaminophenazine, which not only delivered a new peak at 580 nm but also quenched Au-Ag NCs fluorescence at 690 nm. Under optimal conditions, the detection limit for the proposed ELISA was 0.017 ng/mL, which was approximately 6.6-fold lower than conventional ELISA. Moreover, analytical performances were evaluated fully including specificity, accuracy, precision, and practicability, and showed that this method provides a potential platform for sensitive and reliable detection of ZEN.

A colorimetric and fluorometric based dual readout approach for effective heparin sensing

Devising fluorescence-based turn-on probes for the specific and sensitive detection of Heparin is of utmost clinical importance. In this contribution, we have identified a molecular rotor based asymmetric cyanine probe, thiazole orange (TO), which enables an efficient colorimetric and fluorimetric detection of Heparin. TO undergoes the formation of emissive H-aggregates upon interaction with Heparin that display an impressive emission enhancement of ~22 fold together with drastic changes in the absorption spectra that yields a prominent colour change in the solution from orange to yellow. These seldom reported emissive H-aggregates of TO, serve as an efficient platform for Heparin detection with a LOD of 19 nM, fluorometrically and 34 nM, colorimetrically. The TO-Heparin complex is also accompanied by a large change in the excited-state lifetime. The TO-Heparin complex has been further utilized for the detection of Protamine, which is the only medically affirmed antitoxin of Heparin. Overall, our sensing system offers several advantages, such as, simple, dual read-out, economic and specific detection of Heparin with longer excitation and emission wavelength, rapid naked eye detection and utilizes an in-expensive commercially available fluoprophore, TO. Most importantly, our sensing system also displays a good performance in the biologically complex human serum matrix.

Micellization-induced amplified fluorescence response for highly sensitive detection of heparin in serum

Fluorescence-based assays should be feasible in aqueous media for effectively detecting the biological factors. However, numerous sensors have limited signal transductions and low fluorescence quantum yields due to the ingerently reduced excited state energy of fluorophores in aqueous solution, which reduces their sensitivity. This necessitates a smart sensing approach with an amplified fluorescence response for analytes in aqueous solution. Herein, a new building block which self-assembles in aqueous media, giving a micellar sturcuture with the hydrophobic π-extended conjugated system at the core and hydrophilic groups at the periphery, was devised for the first time. We demonstrated that the aggregated fluorophores in a micelle induce amplified fluorescence quenching, in which the excited electron efficiently migrates through π-extended conjugated system in a micelle, as in a polymeric system. Such feature differentiates this sensing approach from the numerous fluorescence-based tools previously developed for sensitive detection. This new system exhibited highly sensitive signal transduction for specific analytes even under actual bioanalytical conditions.

Chemically tailoring nanopores for single-molecule sensing and glycomics

A nanopore can be fairly-but uncharitably-described as simply a nanofluidic channel through a thin membrane. Even this simple structural description holds utility and underpins a range of applications. Yet significant excitement for nanopore science is more readily ignited by the role of nanopores as enabling tools for biomedical science. Nanopore techniques offer single-molecule sensing without the need for chemical labelling, since in most nanopore implementations, matter is its own label through its size, charge, and chemical functionality. Nanopores have achieved considerable prominence for single-molecule DNA sequencing. The predominance of this application, though, can overshadow their established use for nanoparticle characterization and burgeoning use for protein analysis, among other application areas. Analyte scope continues to be expanded, and with increasing analyte complexity, success will increasingly hinge on control over nanopore surface chemistry to tune the nanopore, itself, and to moderate analyte transport. Carbohydrates are emerging as the latest high-profile target of nanopore science. Their tremendous chemical and structural complexity means that they challenge conventional chemical analysis methods and thus present a compelling target for unique nanopore characterization capabilities. Furthermore, they offer molecular diversity for probing nanopore operation and sensing mechanisms. This article thus focuses on two roles of chemistry in nanopore science: its use to provide exquisite control over nanopore performance, and how analyte properties can place stringent demands on nanopore chemistry. Expanding the horizons of nanopore science requires increasing consideration of the role of chemistry and increasing sophistication in the realm of chemical control over this nanoscale milieu.

o-Phenylenediamine/gold nanocluster-based nanoplatform for ratiometric fluorescence detection of alkaline phosphatase activity

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

Chemical sensors for selective and quantitative heparin sensing

In this review article, chemical sensors for selective and quantitative heparin sensing are discussed with detailed examples.

Lost in (Clinical) Translation: Recent Advances in Heparin Neutralization and Monitoring

The heparin family, which includes unfractionated heparin, low-molecular heparin, and fondaparinux, is a class of drugs clinically used as intravenous blood thinners. To date, issues related to both the reversal of anticoagulation and the blood level determination of the anticoagulant at the point-of-care remain: while the only U.S. Food and Drug Administration (FDA) approved antidote for heparin displays serious efficacy and safety drawbacks, the current assays for heparin monitoring are indirect measurements subject to their own limitations and variations. Herein, we provide an update on the numerous recent chemical approaches to tackle these issues, from which it is clear that some new antidotes and sensors for heparin certainly have the potential to exceed current clinical standards. This review aims to review a field that requires close collaborations between physicians, biologists, and chemists in order to foster advances toward clinical translation.

Surveying silicon nitride nanopores for glycomics and heparin quality assurance

Polysaccharides have key biological functions and can be harnessed for therapeutic roles, such as the anticoagulant heparin. Their complexity—e.g., >100 monosaccharides with variety in linkage and branching structure—significantly complicates analysis compared to other biopolymers such as DNA and proteins. More, and improved, analysis tools have been called for, and here we demonstrate that solid-state silicon nitride nanopore sensors and tuned sensing conditions can be used to reliably detect native polysaccharides and enzymatic digestion products, differentiate between different polysaccharides in straightforward assays, provide new experimental insights into nanopore electrokinetics, and uncover polysaccharide properties. We show that nanopore sensing allows us to easily differentiate between a clinical heparin sample and one spiked with the contaminant that caused deaths in 2008 when its presence went undetected by conventional assays. The work reported here lays a foundation to further explore polysaccharide characterization and develop assays using thin-film solid-state nanopore sensors.

The complexity of polysaccharides significantly complicates their analysis in comparison to other biopolymers. Here, the authors demonstrate that solid-state silicon nitride nanopore sensors can be used to reliably detect native polysaccharides and to perform a simple quality assurance assay on a polysaccharide therapeutic, heparin.

Differential calixarene receptors create patterns that discriminate glycosaminoglycans

A well-designed fluorescence displacement sensing array based on calixarene receptors realizes the discrimination of glycosaminoglycans.

SERS spectral study of HAuCl4-cysteine nanocatalytic reaction and its application for detection of heparin sodium with label-free VB4r molecular probe

In the presence of nanocatalyst, L-cysteine reduce HAuCl₄ rapidly to form gold nanoparticles (AuNP), and a quick nanocatalytic preparation procedure was established for Au/AuNP sol with highly active surface enhanced Raman scattering (SERS) effect and good stability. The nanoreaction was also studied by absorption, resonance Rayleigh scattering (RRS), transmission electron microscopy (TEM) and energy spectra. In the selected conditions, the analyte heparin sodium (HS) could react with victoria blue 4 R (VB4r) to form associated complexes which have very weak SERS effect to make the SERS signals decrease. The SERS signals at 1617 cm⁻¹ reduced linearly with HS concentration increasing. Upon addition of FeCl₃, it hydrolyzed to form stable Fe(OH)₃ sol platform that carried SERS active Au/AuNPs to enhance the sensitivity. Accordingly, we established a SERS quantitative analysis method in the sol substrate of Fe(OH)₃-Au/AuNPs, with a linear range of 0.5–75 ng/mL HS and a detection limit of 0.2 ng/mL. HS in real samples was determined, with a relative standard deviation of 2.65–7.63% and a recovery of 99.3–101%.

Sensing Active Heparin by Counting Aggregated Quantum Dots at Single-Particle Level

Developing highly sensitive and highly selective assays for monitoring heparin levels in blood is required during and after surgery. In previous studies, electrostatic interactions are exploited to recognize heparin and changes in light signal intensity are used to sense heparin. In the present study, we developed a quantum dot (QD) aggregation-based detection strategy to quantify heparin. When cationic micelles and fluorescence QDs modified with anti-thrombin III (AT III) are added into heparin sample solution, the AT III-QDs, which specifically bind with heparin, aggregate around the micelles. The aggregated QDs are recorded by spectral imaging fluorescence microscopy and differentiated from single QDs based on the asynchronous process of blue shift and photobleaching. The ratio of aggregated QD spots to all counted QD spots is linearly related to the amount of heparin in the range of 4.65 × 10 ^-4 U/mL to 0.023 U/mL. The limit of detection is 9.3 × 10 ^-5 U/mL (∼0.1 nM), and the recovery of the spiked heparin at 0.00465 U/mL (∼5 nM) in 0.1% human plasma is acceptable.

A pyrene-based fluorescent sensor for ratiometric detection of heparin and its complex with heparin for reversed ratiometric detection of protamine in aqueous solution

An imidazolium-modified pyrene derivative, IPy, was used for ratiometric detection of heparin, and its complex with heparin was used for reversed ratiometric detection of protamine in both aqueous solution and serum samples. The cationic fluorescent probe could interact with anionic heparin via electrostatic interaction to bring about blue-to-green fluorescence changes as monomer emission significantly decreases and excimer increases. The binary combination of IPy and heparin could be further used for green-to-blue detection of protamine since heparin prefers to bind to protamine instead of the probe due to its stronger affinity with protamine. The cationic probe shows high sensitivity to heparin with a low detection limit of 8.5nM (153ng/mL) and its combination with heparin displays high sensitivity to protamine with a detection limit as low as 15.4nM (107.8ng/mL) according to the 3σ IUPAC criteria. Moreover, both sensing processes are fast and can be performed in serum solutions, indicating possibility for practical applications.

Rapid and visual detection of heparin based on the disassembly of polyelectrolyte-induced pyrene excimers

A sensor based on polyelectrolyte-induced pyrene excimers has been developed for the visual detection of heparin with high sensitivity and selectivity.

Highly selective and sensitive detection of heparin based on competition-modulated assembly and disassembly of fluorescent gold nanoclusters

A simple and economical fluorescence assay for heparin using glutathione-protected gold nanoclusters via competitive binding was developed.

An Ionic 1,4-Bis(styryl)benzene-Based Fluorescent Probe for Mercury(II) Detection in Water via Deprotection of the Thioacetal Group

Highly sensitive and selective mercury detection in aqueous media is urgently needed because mercury poisoning usually results from exposure to water-soluble forms of mercury by inhalation and/or ingesting. An ionic conjugated oligoelectrolye (M1Q) based on 1,4-bis(styryl)benzene was synthesized as a fluorescent mercury(II) probe. The thioacetal moiety and quaternized ammonium group were incorporated for Hg²⁺ recognition and water solubility. A neutral Hg²⁺ probe (M1) was also prepared based on the same molecular backbone, and their sensor characteristics were investigated in a mixture of acetonitrile/water and in water. In the presence of Hg²⁺, the thioacetal group was converted to aldehyde functionality, and the resulting photoluminescence intensity decreased. In water, M1Q successfully demonstrated highly sensitive detection, showing a binding toward Hg²⁺ that was ~15 times stronger and a signal on/off ratio twice as high, compared to M1 in acetonitrile/water. The thioacetal deprotection by Hg²⁺ ions was substantially facilitated in water without an organic cosolvent. The limit of detection was measured to be 7 nM with a detection range of 10–180 nM in 100% aqueous medium.

Phenazine-Based Ratiometric Hg2+ Probes with Well-Resolved Dual Emissions: A New Sensing Mechanism by Vibration-Induced Emission (VIE)

Phenazines exhibit intriguing vibration-induced emission (VIE) owing to the fast intrinsic vibration of benzo[a,c]phenazine moiety. For the first time, a phenazine-based ratiometric fluorescent probe DBPST is developed for recognizing Hg²⁺ via restriction of VIE. Upon binding with Hg²⁺ , DBPST demonstrates two well-resolved emission peaks (over 130 nm) with a wide tuning color and affords a large signal-to-background ratio.

Emissive H-Aggregates of an Ultrafast Molecular Rotor: A Promising Platform for Sensing Heparin

Constructing "turn on" fluorescent probes for heparin, a most widely used anticoagulant in clinics, from commercially available materials is of great importance, but remains challenging. Here, we report the formation of a rarely observed emissive H-aggregate of an ultrafast molecular rotor dye, Thioflavin-T, in the presence of heparin, which provides an excellent platform for simple, economic and rapid fluorescence turn-on sensing of heparin. Generally, H-aggregates are considered as serious problem in the field of biomolecular sensing, owing to their poorly emissive nature resulting from excitonic interaction. To the best of our knowledge, this is the first report, where contrastingly, the turn-on emission from the H-aggregates has been utilized in the biomolecule sensing scheme, and enables a very efficient and selective detection of a vital biomolecule and a drug with its extensive medical applications, i.e., heparin. Our sensor system offers several advantages including, emission in the biologically advantageous red-region, dual sensing, i.e., both by fluorimetry and colorimetry, and most importantly constructed from in-expensive commercially available dye molecule, which is expected to impart a large impact on the sensing field of heparin. Our system displays good performance in complex biological media of serum samples. The novel Thioflavin-T aggregate emission could be also used to probe the interaction of heparin with its only clinically approved antidote, Protamine.

Development of new peptide-based receptor of fluorescent probe with femtomolar affinity for Cu(+) and detection of Cu(+) in Golgi apparatus

Developing fluorescent probes for monitoring intracellular Cu(+) is important for human health and disease, whereas a few types of their receptors showing a limited range of binding affinities for Cu(+) have been reported. In the present study, we first report a novel peptide receptor of a fluorescent probe for the detection of Cu(+). Dansyl-labeled tripeptide probe (Dns-LLC) formed a 1:1 complex with Cu(+) and showed a turn-on fluorescent response to Cu(+) in aqueous buffered solutions. The dissociation constant of Dns-LLC for Cu(+) was determined to be 12 fM, showing that Dns-LLC had more potent binding affinity for Cu(+) than those of previously reported chemical probes for Cu(+). The binding mode study showed that the thiol group of the peptide receptor plays a critical role in potent binding with Cu(+) and the sulfonamide and amide groups of the probe might cooperate to form a complex with Cu(+). Dns-LLC detected Cu(+) selectively by a turn-on response among various biologically relevant metal ions, including Cu(2+) and Zn(2+). The selectivity of the peptide-based probe for Cu(+) was strongly dependent on the position of the cysteine residue in the peptide receptor part. The fluorescent peptide-based probe penetrated the living RKO cells and successfully detected Cu(+) in the Golgi apparatus in live cells by a turn-on response. Given the growing interest in imaging Cu(+) in live cells, a novel peptide receptor of Cu(+) will offer the potential for developing a variety of fluorescent probes for Cu(+) in the field of copper biochemistry.

Studies on the interaction of heparin with lysozyme by multi-spectroscopic techniques and atomic force microscopy

The interaction between heparin (Hep) and lysozyme (Lyso) in vitro was studied by fluorescence, UV-vis, circular dichroism (CD), resonance Rayleigh scattering (RRS) spectroscopy and atomic force microscopy (AFM) under normal physiological conditions. UV-vis spectra of Lyso showed the absorbance was significantly increased with the addition of Hep. Fluorescence studies revealed that the emission quenching of Lyso with Hep was initiated by static quenching mechanism. CD spectral studies showed that Hep induced conformational changes in the secondary structure of Lyso. RRS spectra of Lyso showed the intensity of scattering was significantly increased with the addition of Hep and the enhanced RRS intensities were proportional to the concentration of Hep in a certain range. Thus, a new RRS method using Lyso as a probe could be used for the determination of Hep. The detection limit for Hep was 3.9 ng mL(-1). In addition, the shape of the complex was characterized by AFM. The possible reaction mechanism and the reasons for the enhancement of RRS intensity had been discussed through experimental results.

Pyrene-based heparin sensors in competitive aqueous media – the role of self-assembled multivalency (SAMul)

Simple functionalised pyrene derivatives can achieve ratiometric sensing of heparin with the precise sensing mechanism depending on whether the sensor self-assembles into a multivalent ligand display.

Chromo/Fluorogenic Detection of Co(2+), Hg(2+) and Cu(2+) by the Simple Schiff Base Sensor

Herein, we reported the ditriazole Schiff base derivative 1 and evaluated its photophysical properties on induction of varieties of metal ions including Na(+), Ag(+), Ni(2+), Mn(2+), Pd(2+), Co(2+), Hg(2+), Cu(2+), Pb(2+), Cd(2+), Zn(2+), Sn(2+), Fe(2+), Fe(3+), Cr(3+) and Al(3+), in order to figure out its potential as ion sensor. The ligand 1 exhibited the strong colorimetric change in the reaction solution as well as absorption spectral shifting with the concomitant appearance of well-defined isosbestic points only upon Co(2+), Hg(2+) and Cu(2+) addition corroborates its applicability as multichannel ion detector. The different extent of spectral shifting as well as unique chromogenic change in the probe solution upon Co(2+), Hg(2+) and Cu(2+) introduction can be used as the discrimination tool for these metal ions. The ligand-metal binding stoichiometry was assessed by their optical response which was further supported by the FT-IR, NMR and mass spectrometric analysis. The association constant and the detection limits of the ligand toward Co(2+), Hg(2+) and Cu(2+) ions were calculated to be 1.52 × 10(-8), 3.26 × 10(-9), 1.16 × 10(-8) and 3.87 × 10(-10), 5.47 × 10(-11), 8.91 × 10(-11) M, respectively, employing the Benesi-Hilderbrand equation and 3 σ slope(-1) methods. Furthermore, the successive addition of Co(2+), Hg(2+) and Cu(2+) induce the constant decline in the fluorescence emission signal intensity of the probe. The quenching efficiency of the probe upon metallic induction was fitted to the Stern-Volmer equation which yielded the upward curvature in case of all the three metals ions (Co(2+), Hg(2+) and Cu(2+)) when (Io/I-1) was plotted against the quencher concentration indicating the occurrence of both the dynamic and static quenching process in the system with the average Stern-Volmer quenching constant values of 9.25 × 10(-7), 1.14 × 10(-7), 1.829 × 10(-7), respectively.

A "turn on" fluorescent probe for heparin and its oversulfated chondroitin sulfate contaminant

Designing "turn on" fluorescent probes for heparin (Hep), a widely used anticoagulant in clinics, is of great importance but remains challenging. By introducing a Hep specific binding peptide AG73 to a typical aggregation induced emission (AIE) fluorogen, tetraphenylethene (TPE), a sensitive and selective "turn on" fluorescent probe named TPE-1 for Hep was developed. TPE-1 was able to detect Hep in a wide pH range of 3-10 without obvious interference from tested anions and biomolecules, especially Hep analogues known as chondroitin sulfate (Chs) and hyaluronic acid (HA). The detection limit of Hep sensing was 3.8 ng mL-1, which was far below the clinically demanded concentration of Hep. The probe was applicable to both unfractionated Hep and low molecular weight Hep, the two main heparin products clinically used. Besides, the fluorescence of Hep bound TPE-1 can be turned off via sequential treatment with heparinases. Importantly, this phenomenon allows us to develop an enzyme assisted strategy for "turn on" sensing of oversulfated chondroitin sulfate (OSCS) with a detection limit of 0.001% (w%), which is the main contaminant in Hep and may cause severe adverse reactions including death.

Pyrene Excimer-Based Peptidyl Chemosensors for the Sensitive Detection of Low Levels of Heparin in 100% Aqueous Solutions and Serum Samples

Fluorescent chemosensors (1 and 2, Py-(Arg)nGlyGlyGly(Arg)nLys(Py)-NH2, n = 2 and 3) bearing two pyrene (Py) labeled heparin-binding peptides were synthesized for the sensitive ratiometric detection of heparin. The peptidyl chemosensors (1 and 2) sensitively detected nanomolar concentrations of heparin in aqueous solutions and in serum samples via a ratiometric response. In 100% aqueous solutions at pH 7.4, both chemosensors exhibited significant excimer emission at 486 nm as well as weak monomer emission in the absence of heparin. Upon the addition of heparin into the solution, excimer emission increased with a blue shift (10 nm) and monomer emission at 376 nm decreased. The chemosensors showed a similar sensitive ratiometric response to heparin independent of the concentration of the chemosensors. The peptidyl chemosensors were applied to the ratiometric detection of heparin over a wide range of pH (1.5-11.5) using the excimer/momomer emission changes. In the presence of serum, 1 and 2 displayed significant monomer emission at 376 nm with relatively weak excimer emission and the addition of heparin induced a significant increase in excimer emission at 480 nm and a concomitant decrease in monomer emission. The enhanced ratiometric response to heparin in the serum sample was due to the interactions between the peptidyl chemosensors and serum albumin in the serum sample. The detection limits of 2 for heparin were less than 1 nM in 100% aqueous solutions and serum samples. The peptidyl chemosensors bearing two heparin-binding sites are a suitable tool for the sensitive ratiometric detection of nanomolar concentrations of heparin in 100% aqueous solutions and serum samples.