Reversible Sensing of the Anticoagulant Heparin with Protamine Permselective Membranes

Surfactant-based supramolecular dye assembly: A highly selective and economically viable platform for quantification of heparin antidote

Herein, we have employed a supramolecular assembly of a cationic dye, LDS-698 and a common surfactant sodium dodecyl sulfate (SDS) as a turn-on fluorescent sensor for protamine (Pr) detection. Addition of cationic Pr to the solution of dye-surfactant complex brings negatively charged SDS molecules together through strong electrostatic interaction, assisting aggregation of SDS way before its critical micellar concentration (CMC). These aggregates encapsulate the dye molecules within their hydrophobic region, arresting non-radiative decay channels of the excited dye. Thus, the LDS-698•SDS assembly displays substantial enhancement in fluorescence intensity that follows a nice linear trend with Pr concentration, providing limit of detection (LOD) for Pr as low as 3.84(±0.11) nM in buffer, 124.4(±6.7) nM in 1% human serum and 28.3(±0.5) nM in 100% human urine. Furthermore, high selectivity, low background signal, large stokes shift, and emission in the biologically favorable deep-red region make the studied assembly a promising platform for Pr sensing. As of our knowledge it is the first ever Pr sensory platform, using a very common surfactant (SDS), which is economically affordable and very easily available in the market. This innovative approach can replace the expensive, exotic and specialized chemicals considered for the purpose and thus showcase its potential in practical applications.

Dielectric polarization-based separations in an ionic solution

A novel non-electrophoretic, electric field-based separation mechanism capable of transporting ions based on their dielectric properties is presented here for the first time. Though this polarization-based mechanism behaves similarly to dielectrophoresis, the separation mechanism is remarkably very efficient at small length scales compared to any dielectrophoretic separation mechanism for particles. For an applied electric field of strength as low as ∼0.75 MV m^-1 across a 100 μm channel, the working solute - sodium fluorescein - is shown to decrease in its concentration by ≈20% in electric field region relative to the non electric field region. The existing macroscopic theoretical models like electrohydrodynamics and equilibrium thermodynamics are shown to underestimate the concentration change by two orders of magnitude for the same electric field strength. This surprisingly large difference between theory and experimental results suggests that the electric field-based equilibrium thermodynamic model lacks a key physics.

Deep Learning-Enhanced Potentiometric Aptasensing with Magneto-Controlled Sensors

Bioelectronic sensors that report charge changes of a biomolecule upon target binding enable direct and sensitive analyte detection but remain a major challenge for potentiometric measurement, mainly due to Debye Length limitations and the need for molecular-level platforms. Here, we report on a magneto-controlled potentiometric method to directly and sensitively measure the target-binding induced charge change of DNA aptamers assembled on magnetic beads using a polymeric membrane potentiometric ion sensor. The potentiometric responses of the negatively charged aptamer, serving as a receptor and reporter, were dynamically controlled and modulated by applying a magnetic field. Based on a potentiometric array, this non-equilibrium measurement technique combined with deep learning algorithms allows for rapidly and reliably classifying and quantifying diverse small molecules using antibiotics as models. This potentiometric strategy opens new modalities for sensing applications.

Nanoclay-based sensor composites for the facile detection of molecular antioxidants

A paper-based sensor containing nanoclay particles, a polyelectrolyte and a metal complex as sensing elements was developed for the facile detection of molecular antioxidants.

Reagentless Acid-Base Titration for Alkalinity Detection in Seawater

Herein, we report on a reagentless electroanalytical methodology for automatized acid–base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (WiorekA.Anal. Chem.2019, 91, 14951−1495931691565), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid–base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid–base titrations to obtain high-resolution data on alkalinity in water resources.

Ultrafine fluorene-pyridine oligoelectrolyte nanoparticles for supersensitive fluorescence sensing of heparin and protamine

A new fluorene-pyridine oligoelectrolyte (OFP) is rationally proposed and readily synthesized via a simple one-pot Sonogashira approach. Hence, an unexpectedly small cationic oligomer nanosensor (i.e. OFPNPs, ∼ 1.2 nm in diameter) was conveniently fabricated owing to the enhanced flexibility endowed by the meta-substituted pyridyl unit. Inspiringly, this facile nanoplatform with low cytotoxicity favors the ultrasensitive fluorescence assay for heparin and protamine with a detection limit (LOD, S/N = 3) as low as 1.2 ng mL^-1 and 0.5 ng mL^-1, respectively, involving heparin-induced aggregation of OFPNPs through electrostatic interaction or competitive rebinding of protamine to heparin.

Translating potentiometric detection into non-enzymatic amperometric measurement of H2O2

The developments of alternative signal readout strategies for the ion-selective electrodes (ISEs) are necessary in order to break through the limitation of the Nernst equation. In this work, a simple, convenient and easily operated strategy based on the non-enzymatic amperometric measurement of H₂O₂ is proposed to read out the potentiometric responses for the ISEs. The proposed amperometric signal readout based on H₂O₂ is carried out in a two compartment electrochemical cell configuration containing a detection cell and a sample cell, physically connected by a salt bridge. A glassy carbon (GC) electrode is placed in the detection cell to monitor the oxidation current of H₂O₂, and an ISE is placed in the sample cell to act as both the reference electrode and the potentiometric sensor for obtaining the ion activities. The oxidation of H₂O₂ is induced by a constant potential applied between the GC electrode and the ISE, and subsequently modulated by the potential change of the ISE in the presence of the primary ion. The proposed amperometric signal readout based on H₂O₂ shows the satisfied slope sensitivity and detection limit, which are better than or compared to those for the potentiometric responses for the ISEs. This work provides a general strategy for transforming the potential response of the ISEs into the amperometric readout, and is promising for detection of cations (eg., Ca²⁺) and anions (eg., NO₃^-) with high sensitivity and excellent selectivity.

Quantitative determination of dextran sulfate and pentosan polysulfate and their binding with protamine using chronopotentiometry with polyion-selective electrodes

We report for the first time a chronopotentiometric measurement of polyanions based on localized ion depletion at the sample/membrane interface at a characteristic transition time τ, using polymer membrane polyanion-selective electrodes. Chronopotentiometric transduction of polyions based on the measurement of transition time has analytically more attractive applications compared to the controlled-current reversible pulsed chronopotentiometric transduction based on electromotive force (emf) measurement. This is because traditional polyion-selective electrodes based on emf measurement intrinsically give nonlinear (sigmoidal) calibration curves. While these can be used for indirect determination of polyions via polyanion-polycation titrations, they are not convenient for direct quantitation. However, under chronopotentiometric measurement based on the measurement of transition time, the square root of the transition time τ is linearly related to the concentration of the polyion according to the Sand equation and can be used for a direct calibration-free rapid determination. In this work, we have measured the concentrations of dextran sulfate (DS) and pentosan polysulfate (PPS) using polyanion selective electrodes under chronopotentiometric method where the transition time was measured and controlled-current pulsed chronopotentiometric transductions, where the phase boundary potential (emf) was measured. In addition, the protamine-DS and the protamine-PPS binding ratios have been determined using both transductions. The protamine-PPS binding ratio was determined to be 1.51:1 by the titration method and 1.54:1 by chronopotentiometry. The protamine-DS binding ratio was determined to be 1.37:1 by the titration method and 1.41:1 by chronopotentiometry, showing excellent agreement between the two methods. These simple measurement methods of binding ratios between polysaccharides and polypeptides may become important tools for screening safer and more reliable antidotes for the newer and safer anticoagulants such as Low Molecular Weight Heparins(LMWHs) and also to determine the dosages of antidotes needed to neutralize the anticoagulant activity.

Photoelectric current as a highly sensitive readout for potentiometric sensors

The photocurrent at a working electrode coated with a ZnSe/r-GO composite can be modulated by a polymeric membrane ion-selective electrode that works as a reference electrode.

Dual-Analyte Chronopotentiometric Aptasensing Platform Based on a G-Quadruplex/Hemin DNAzyme and Logic Gate Operations

Conventional potentiometric ion sensors that rely on a specific ion carrier in a polymeric membrane can hardly achieve multianalyte detection. Inspired by the remarkable ability of built-in logic gate sensors for multianalyte detection, herein we report a potentiometric aptasensing platform based on a G-quadruplex/hemin DNAzyme and logic gate operations for determination of two analytes using a single membrane electrode. A bifunctional probe with two aptamer units and a signal reporter oligonucleotide with a DNAzyme sequence are assembled on the magnetic beads to form a DNA hybrid structure. The "OR" and "INHIBIT" logic functions can be performed by using the two aptamers and their targets as inputs, and using the chronopotentiometric response based on the G-quadruplex/hemin DNAzyme-H₂O₂-mediated oxidation of 3,3',5,5'-tetramethylbenzidine as output. Kanamycin and oxytetracycline, as commonly used antibiotics, have been employed as the models and successfully measured.

Influence of Protamine Functionalization on the Colloidal Stability of 1D and 2D Titanium Oxide Nanostructures

The colloidal stability of titanium oxide nanosheets (TNS) and nanowires (TiONW) was studied in the presence of protamine (natural polyelectrolyte) in aqueous dispersions, where the nanostructures possessed negative net charge, and the protamine was positively charged. Regardless of their shape, similar charging and aggregation behaviors were observed for both TNS and TiONW. Electrophoretic experiments performed at different protamine loadings revealed that the adsorption of protamine led to charge neutralization and charge inversion depending on the polyelectrolyte dose applied. Light scattering measurements indicated unstable dispersions once the surface charge was close to zero or slow aggregation below and above the charge neutralization point with negatively or positively charged nanostructures, respectively. These stability regimes were confirmed by the electron microscopy images taken at different polyelectrolyte loadings. The protamine dose and salt-dependent colloidal stability confirmed the presence of DLVO-type interparticle forces, and no experimental evidence was found for additional interactions (e.g., patch-charge, hydrophobic, or steric forces), which are usually present in similar polyelectrolyte-particle systems. These findings indicate that the polyelectrolyte adsorbs on the TNS and TiONW surfaces in a flat and extended conformation giving rise to the absence of surface heterogeneities. Therefore, protamine is an excellent biocompatible candidate to form smooth surfaces, for instance in multilayers composed of polyelectrolytes and particles to be used in biomedical applications.

Synthesis and formulation of functional bionanomaterials with superoxide dismutase activity

Layered double hydroxide (LDH) nanoparticles were prepared and used as solid support for superoxide dismutase (SOD) enzymes. Structural features were studied by XRD, spectroscopic methods (IR, UV-Vis and fluorescence) and TEM, while colloidal stability of the obtained materials was investigated by electrophoresis and light scattering in aqueous dispersions. The SOD quantitatively adsorbed on the LDH by electrostatic and hydrophobic interactions and kept its structural integrity upon immobilization. The composite material showed moderate resistance against salt-induced aggregation in dispersions, therefore, heparin polyelectrolyte was used to improve the colloidal stability of the system. Heparin of highly negative line charge density strongly adsorbed on the oppositely charged hybrid particles leading to charge neutralization and overcharging at appropriate polyelectrolyte loading. Full coverage of the composite platelets with heparin resulted in highly stable dispersions, which contained only primary particles even at elevated ionic strengths. Our results indicate that the developed bionanocomposite of considerable enzymatic function is a suitable candidate for applications, wherever stable dispersions of antioxidant activity are required for instance in biomedical treatments or in chemical manufacturing processes.

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.

Fluorescence sensor for detecting protamines based on competitive interactions of polyacrylic acid modified with sodium 4-amino-1-naphthalenesulfonate with protamines and aminated graphene oxide

An easy-to-use fluorescent probe for detecting protamines was developed.

Modulating luminescence of Tb(3+) with biomolecules for sensing heparin and its contaminant OSCS

The detection of heparin (Hep) and its contaminant oversulfated chondroitin sulfate (OSCS) is of great importance in clinics but remains challenging. Here, we report a sensitive and selective time-resolved luminescence (TRL) biosensing system for Hep by modulating the photoluminescence of Tb(3+) with guanine-rich ssDNA and Hep-specific AG73 peptide (RKRLQVQLSIRT). With the developed system, Hep including both unfractionated Hep (UFH) and the low molecular weight Hep (LMWH) has been successfully detected with a satisfactory detection limit. Owing to the highly specific interaction between Hep and AG73 peptide, major interfering substances in Hep detection, such as Hep analogs of chondrotin sulfate (Chs) and hyaluronic acid (HA), did not interfere with Hep detection. The established TRL sensing system was then successfully used for monitoring Hep metabolism in living rats by microdialysis. Moreover, the proposed TRL sensing system was further applied to analyze OSCS contaminant in Hep with heparinases treatment by exploring the inhibition effects of OSCS on the activity of heparinases. As low as 0.002% of OSCS in Hep was identified.

Label-free polymerization amplified potentiometric sensing platform for radical reactions using polyion sensitive membrane electrodes as transducers

Based on the cascade amplification abilities of radical polymerization reactions, an amplified potentiometric sensing platform for radical reactions was developed.

MnO2 nanosheet-based heparin and OSCS fluorescent biosensor with lowered background and amplified hybridization chain reaction

A “turn-on” ultrasensitive detection of heparin or OSCS was reported through MnO₂ nanosheet quenched-ultralow background and HCR amplification strategy.

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.

A polyadenosine-coralyne complex as a novel fluorescent probe for the sensitive and selective detection of heparin in plasma

This study presents the development of a simple, label-free, sensitive, and selective detection system for heparin based on the use of a complex of 20-repeat adenosine (A20) and coralyne. Coralyne emits relatively weak fluorescence in an aqueous solution. In the presence of A20, coralyne molecules complexed with A20 through A2-coralyne-A2 coordination. An increase in the fluorescence of coralyne was observed because coralyne remained separate from water in the hydrophobic environment of the folded A20. The presence of heparin and the formation of the coralyne-heparin complex caused coralyne to be removed from the A20-corlayne complex. Because heparin promoted coralyne dimerization, the fluorescence of coralyne decreased as a function of the concentration of added heparin. This detection method is effective because the electrostatic attraction between heparin and coralyne is substantially stronger than the coordination between A20 and coralyne in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer at pH 7.0. Under optimal conditions (5 μM coralyne, 1 μM poly A20, and 10mM HEPES), this probe exhibited high selectivity (>90-fold) toward heparin over hyaluronic acid and chondroitin sulfate. The probe׳s detection limit for heparin was determined to be 4 nM (75 ng/mL) at a signal-to-noise ratio of 3. This study validates the practicality of using the A20-corlayne complex to determine the concentration of heparin in plasma.

Thin layer coulometry based on ion-exchanger membranes for heparin detection in undiluted human blood

We explore here for the first time a potentially calibration-free methodology for the detection of protamine (and, by titration, heparin) in undiluted human blood in the therapeutic concentration range from 20 to 120 mg L(-1). The use of a thin layer sample (5.8 μL) confined between a tubular protamine selective membrane (inner diameter, 600 μm) and a Ag/AgCl wire (diameter 400 μm) achieves an exhaustive depletion from the sample. Coulometry detection was chosen for the interrogation of the thin layer, employing a double pulse technique with 120 s for each pulse. Protamine calibration curves were recorded at physiological concentrations and in undiluted human blood. A linear relationship was obtained in both cases, but a diminished sensitivity was observed in contact with blood, which is explained with a partial passivation of the inner Ag/AgCl element. Heparin-protamine titrations were performed in undiluted human blood samples, mimicking the final application with patients undergoing critical care. The observed values correlate satisfactorily with those of an alternative technique, so-called flash-chronopotentiometry on planar membranes.

Pulsed galvanostatic control of a polymeric membrane ion-selective electrode for potentiometric immunoassays

Pulsed galvanostatic control of ion fluxes across polymeric membrane ion-selective electrodes (ISEs) is an emerging field for potentiometric sensing. Herein we report a novel potentiometric enzyme immunoassay based on current-controlled release of an enzyme substrate, which eliminates the addition of marker ions in the sample solution. In this method, the carboxylated poly(vinyl chloride) matrix at the outer layer of the ISE membrane is employed to attach a primary antibody. A sandwich immunoassay with an alkaline phosphatase labeled antibody (ALP-Ab) as the reporter is used for the determination of human IgG (as a model protein). The large difference between the lipophilicity of the substrate ion and that of the product ion allows p-nitrophenyl phosphate to be used as the enzyme substrate for potentiometric immunosensors. After the immunoreactions, the captured ALP-Ab catalyzes the hydrolysis of the substrate ions released at the sample-membrane interface by using the pulsed galvanostatic technique. This process can be potentiometrically determined by measuring the open circuit potential of the ISE. Under optimal conditions, the potential response of the proposed immunosensor is proportional to the concentration of human IgG in the range of 50-1000 ng/mL with a detection limit of 30 ng/mL (3σ). Owing to simplicity and independence of sample volume and sample turbidity, the proposed potentiometric immunoassay offers a viable alternative to those based on optical absorbance.