Anion-Exchange-Based Amperometric Assay for Heparin Using Polyimidazolium as Synthetic Receptor

Immunosensing of neuron-specific enolase based on signal amplification strategies via catalysis of ascorbic acid by heteropolysate COF

In view of the importance of quantification of neuron-specific enolase (NSE), an electrochemical NSE immunosensor was developed. The sandwich voltammetric immunosensor utilized vinyl-functionalized crystalline covalent organic framework (COFTAPT-Dva) modified electrode to load lots of Ab1 via thiol-ene "click" reaction as matrix. A crystalline cationic EB-COF:Br was used to load Au nanoparticles (AuNPs) and H3[PMo12O40] (PMo12) as immunoprobe. The AuNPs with the size of about 30 nm were firstly grown on EB-COF:Br and then a large number of electroactive PMo12 were uniformly assembled on AuNPs/EB-COF:Br via ion exchanging reaction. The AuNPs not only facilitated the bonding of Ab2 based on Au-S bond, but also improved performance of Ab2/AuNPs/EB-COF:PMo12 immunoprobe. The sensitivity of sandwich electrochemical immunosensor could be primarily amplified based on loaded abundant PMo12. Secondary sensitivity amplification of immunosensor could be achieved by using PMo12 to catalyze ascorbic acid. The linear range of sandwich voltammetric immunosensor based on current change of differential pulse voltammetry is 500 ± 36 fg mL-1 - 100 ± 8 ng mL-1. Thanks to the dual sensitivity amplification strategy, the sensitivity is as high as 54.06 ± 3.2 μA cm-2/lg(cNSE/ng mL-1), and the detection limit is as low as 166 ± 10.8 fg mL-1. It proves that it is completely feasible to amplify sensitivity of sandwich voltammetric immunosensors using polyoxometalate-COF and its catalytic substrate.

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 .

Flower-like ZIF-8 enhance the peroxidase-like activity of nanoenzymes at neutral pH for detection of heparin and protamine

The peroxide-like catalytic activity of gold nanoclusters (Au-NCs) is very low under physiological conditions (pH 7.4), which greatly limits its biological detection applications. A new nanoenzyme platform was constructed by self-assembly of Au-NCs and ZIF-8/CQDs. It was found that heparin can significantly promote the peroxidase-like activity of Au-NCs on the nanoenzyme platform at pH 7.4. In the presence of H₂O₂, the catalytic activity of Au-NCs on the nanoenzyme platform for TMB increased nearly 50 times. Based on this phenomenon, a colorimetric method was developed to determine heparin in the range of 0.0185-9.25 U/mL, with a detection limit of 0.0027 U/mL. When protamine is introduced, heparin and protamine take the lead in specific binding due to antagonism, which makes heparin unable to adsorb on the surface of ZIF-8/CQDS, thus inhibiting the enhancement of the catalytic activity of Au-NCs. Based on this phenomenon, a colorimetric method was developed to determine protamine in the range of 0.01-0.5 μg/mL, with a detection limit of 0.003 μg/mL. Therefore, this method provides a new idea for the visual detection of heparin and protamine under physiological conditions.

The heparinase-linked differential time method allows detection of heparin potency in whole blood with high sensitivity and dynamic range

Anticoagulation therapy with heparin is an effective treatment against thrombosis. Heparin tends to cause spontaneous bleeding and requires regular monitoring during therapy. Most high-sensitivity heparin sensors have focused on the concentration detection in clarified buffer solution. However, the pharmacodynamics of heparin vary depending on individual patient or disease, while potency detection with high sensitivity and dynamic range outperforms concentration detection in clinical diagnosis. In this study, a novel heparinase-linked differential time (HLDT) method was established with a two-zone of Graphene modified Carbon (GR-C) sensor, which was utilized to evaluate heparin potency in whole blood. It was based on electrochemical measurement of clotting time shifting associated with presence or absence of heparinase. Heparinase inhibits the anticoagulant ability of heparin by forming a heparin-antithrombin-thrombin complex during coagulation. And the intensity and peak time of electrochemical current were associated with thrombin activity and clotting on the electrode. The results demonstrated that the sensor had high selectivity for heparin potency in 10 μL of whole blood with a detection limit of 0.1 U/mL, and the linear detection range was 0.1-5 U/mL. The coefficient of variation (CV) of the peak time was less than 5%, and linear correlation between the GR-C sensor and the TEG-5000 instrument was 0.987. Thus, the HLDT method has better clinical application due to its good repeatability, high sensitivity and wide range in heparin potency evaluation.

A fiber optic photoacoustic sensor for real-time heparin monitoring

Heparin is a common anticoagulant, but heparin overdose is a common intensive care unit (ICU) medication error due to the narrow therapeutic window of heparin. Conventional methods to monitoring heparin suffer from long turnaround time, the need for skilled personnel, and low frequency of sampling. To overcome these issues, we describe here a fiber optic photoacoustic (PA) sensor for real-time heparin monitoring. The proposed sensor was validated with in vitro testing and in a simulated in vivo model using the following samples: (1) phosphate-buffered saline (PBS), (2) spiked human plasma, (3) spiked whole human blood, and (4) clinical samples from patients treated with heparin. Samples were validated by comparing the PA signal to the activated partial thromboplastin time (aPTT) as well as the activated clotting time (ACT). Importantly, the proposed sensor has a short turnaround time (3 min) and a limit of detection of 0.18 U/ml in whole human blood. The PA signal is linear with heparin dose and correlates with the aPTT value (Pearson's r = 0.99). The PA signal from 32 clinical samples collected from eight patients linearly correlated with ACT values (Pearson's r = 0.89, in vitro; Pearson's r = 0.93, simulated in vivo). The PA signal was also validated against the cumulative heparin dose (Pearson's r = 0.94, in vitro; Pearson's r = 0.96, simulated in vivo). This approach could have applications in both in vitro and real-time in vivo heparin monitoring.

Label-free bioassay with graphene oxide-based fluorescent aptasensors: A review

Bioassays using a fluorophore and DNA aptamer have been extensively developed due to the ultrasensitivity of fluorophores and recognition ability of DNA aptamers. Conventional fluorescent aptamer-based sensors (aptasensors) require chemical labeling between the fluorophore and aptamer and is technologically impracical for various sensing and assay applications. A simple "mix and go" strategy has been introduced that uses label-free technology as a platform for sensor development. The biosensors comprise a fluorophore, a ssDNA aptamer, and eco-friendly graphene oxide (GO). In the absence of the sensor target, GO quenches the fluorescence of the fluorophore and single-strand DNA aptamer complex. When the target is added, the DNA aptamer conformationally turns into a duplex, G-quadruplexe, or other secondary structure. This structure change leads to release of GO by the fluorophore-aptamer-target complex, generating dramatic fluorescence recovery and amplification. With this sensing method, the DNA aptamer does not need to be chemically labeled. Therefore, flexible fluorophore indicators and ssDNA aptamers can be used in this label-free aptasensing strategy. In this review, we discuss various unlabeled fluorophores, including synthetic small molecular fluorophores and genetically encoded fluorescent proteins, as indicators for generating GO-based fluorescent DNA aptasensors for label-free bioassay.

A rolling circle amplification based platform for ultrasensitive detection of heparin

Heparin has a variety of pharmacological uses, including applications for anti-tumor metastasis, anti-inflammatory and anti-viral activities and is widely used as a clinical anticoagulant. Due to its widespread applications in the clinical procedures, monitoring heparin levels is critically important to ensure the safe use of heparin and to prevent overdose and complications, such as hemorrhage and thrombocytopenia. However, traditional heparin detection relies on the measurements of the activated clotting time or activated partial thromboplastin time, which are not sufficiently reliable or accurate measurements for certain clinical settings. In this work, we describe a dumbbell probe-aided strategy for ultrasensitive and isothermal detection of heparin based on a uniquely strong protamine-heparin interaction and rolling circle amplification driven signal amplification. The detection limit for heparin is 12.5 ng mL-1 (0.83 nM), which is much lower than the therapeutic level of heparin in cardiovascular surgery (17-67 μM) and in postoperative and long-term treatment (1.7-10 μM). Additionally, the proposed sensing platform works well for heparin monitoring in human plasma samples. This simple and ultrasensitive heparin biosensor has potential application in diagnostics, therapeutics, and in biological research.

Revisiting imidazolium receptors for the recognition of anions: highlighted research during 2010-2019

Imidazolium based receptors selectively recognize anions, and have received more and more attention. In 2006 and 2010, we reviewed the mechanism and progress of imidazolium salt recognition of anions, respectively. In the past ten years, new developments have emerged in this area, including some new imidazolium motifs and the identification of a wider variety of biological anions. In this review, we discuss the progress of imidazolium receptors for the recognition of anions in the period of 2010-2019 and highlight the trends in this area. We first classify receptors based on motifs, including some newly emerging receptors, as well as new advances in existing receptor types at this stage. Then we discuss separately according to the types of anions, including ATP, GTP, DNA and RNA.

Au nanoparticles as label-free competitive reporters for sensitivity enhanced fiber-optic SPR heparin sensor

A label-free Au NPs-enhanced surface plasmon resonance (SPR) sensor was developed for the ultrasensitive detection of heparin based on competitive adsorption behavior of heparin and Au NPs on the poly (dimethyl-diallylammonium chloride) (PDDA)-modified optical fiber surface and the corresponding change in the resonance wavelength of SPR. Due to the high affinity between heparin and PDDA, the present senor shows good analytical performance with respect to heparin detection. Two obvious advantages of the proposed heparin sensor over other reported methods are: its much wider linear concentration range (10^-6-10^-10 g/mL) and lower limit of detection (0.0257 ng/mL). The analysis of heparin in serum demonstrated that the present sensor exhibited high sensitivity and selectivity. It should be noted that the sensing strategy takes advantage of a portable fiber-optic SPR sensing system and avoids the need for complex processes for labeled-Au NPs, and thus the present sensor promises to be a practical tool for the point-of-care monitoring of heparin.

Aggregation-Induced Emission Enhancement of CdSe QDs by Protamine and its Application to Sensitively and Selectively Detect Heparin

Background:

Heparin, it is commercially used as an anticoagulant in surgical procedures for the prevention of blood clotting. However, overdose and prolonged use of heparin often induce potentially fatal bleeding complication. So, it is of crucial importance to monitor closely heparin levels for the sake of health. In this work, a sensitive fluorescence sensing platform to detect heparin was set up based on MPA-CdSe QDs (quantum dots) and protamine enhanced fluorescent system.

Methods:

The image of CdSe QDs was taken on a JEM-2100 transmission electron microscope (JEOL Ltd.). The fluorescence spectrum was recorded on a FluoroMax-4 fluorescence spectrophotometer (Horiba, USA). UV–vis absorption spectrum was recorded using a Shimadzu UV-2450 Spectrophotometer (Tokyo, Japan). A vortex mixer IKA MS3 digital was selected to mix the solution.

Results:

Under optimized conditions, the linear response to detect heparin ranges from 0.06 to 14 µg mL-1 with a detection limit of 8 ng mL-1. The approach showed a highly selective response to heparin in the presence of 16 interfered substances.

Conclusion:

A simple method for the detection of heparin was developed based on MPA-CdSe QDs and protamine enhanced fluorescent system. The electrostatic effect between MPA-CdSe QDs and protamine resulted in strong fluorescence enhancement from the MPA-CdSe QDs. Moreover, the addition of heparin could cause a significant fluorescence decrease due to the strong affinity of protamine and heparin. Under optimal conditions, this method displayed a low detection limit and good selectivity over other substances.

A facile chemiluminescence sensing for ultrasensitive detection of heparin using charge effect of positively-charged AuNPs

Heparin is a glycosaminoglycan with the highest negative charge density of any known biological molecule. Herein, this highly negative charge structure of heparin and the charge effect from positively-charged AuNPs for luminol chemiluminescence (CL) reaction were combined to build a facile and sensitive CL strategy for detection of heparin. The highly negative charge structure of heparin molecules (four negatively-charged side groups per repeat unit) and the effective signal amplification of charge effect from positively-charged AuNPs make this analysis to display high sensitivity for heparin detection, and the detection limit is as low as 0.06 ng/mL. It is about two orders of magnitude lower than the previously reported colorimetric assay and far lower than the current analysis methods. The established CL strategy is to use the electrostatic interaction between heparin and signal probe (positively-charged AuNPs). Since polyanionic heparin has the highest negative charge in biological system, this CL sensing shows high selectivity for the detection of heparin, and hyaluronic acid (HA), an analogue of heparin, cannot cause interference. This CL sensing succeeded in detecting heparin in human serum samples. Besides, polycationic protamine, heparin antidote, can respond to the system's CL signals through its strong interactions with heparin, thus indirectly detecting protamine. For protamine in serum samples, the detection result was basically consistent with Coomassie brilliant blue assay.

A protamine-conjugated gold decorated graphene oxide composite as an electrochemical platform for heparin detection

In this study, an effective electrochemical sensor was developed for heparin detection using a protamine-conjugated graphene oxide/gold (GO/Au) composite. Protamine is an antidote that can act as an affinity ligand for heparin. The GO was used as support for signal amplification, and Au nanoparticles (NPs) were employed to immobilize the protamine. This Au NPs also increasing the electron transfer rate and enhancing the signal response during protamine-heparin integration. The proposed affinity sensor had a simple fabrication process, a low detection limit (0.9 nM), a wide linear range (1.9 × 10^-7 M to 1.5 × 10^-9 M), high stability, and high selectivity in the detection of heparin.

Facile synthesis of near-infrared emitting dBSA-templated Cu nanoclusters for sensitive detection of heparin

The near-infrared emitting dBSA-Cu NCs were synthesized through a facile synthesis route and were applied for ultra-sensitive detection of heparin in human plasma.

Sensitive fluorescence detection of heparin based on self-assembly of mesoporous silica nanoparticle–gold nanoclusters with emission enhancement characteristics

Sensitive fluorescence detection of heparin based on self-assembly of mesoporous silica nanoparticle–gold nanoclusters with emission enhancement characteristics was reported.

Fluorescent Strips of Electrospun Fibers for Ratiometric Sensing of Serum Heparin and Urine Trypsin

"Turn-on" or "turn-off" probes remain challenges in the establishment of sensitive, easily operated, and reliable methods for in situ monitoring bioactive substances. In the current study, electrospun fibrous strips are designed to provide straightforward observations of ratiometric color changes with the naked eye in the presence of serum heparin or urine trypsin. A tetraphenylethene (TPE) derivative is constructed and along with phloxine B is grafted on fibers, followed by protamine adsorption to induce static quenching of phloxine B and aggregation-induced emission of the TPE derivative. The presence of heparin or trypsin removes protamine to restore the fluorescence of phloxine B at 574 nm (I₅₇₄) and relieve the emission of the TPE derivative at 472 nm (I₄₇₂). The grafting densities of phloxine B and the TPE derivative are essential to achieve the optimal fluorescence-intensity ratio of I₅₇₄/I₄₇₂ for the ratiometric detection of heparin and trypsin. Under illumination by an ultraviolet lamp, the fibrous mats turn from cyan to green in the presence of heparin at 0.4 U/mL and to a bright yellow at 0.8 U/mL, which is feasible in sensing serum heparin levels during postoperative and long-term care of patients after cardiovascular surgery. The protamine digestion results in similar color transitions with increasing trypsin levels up to 8 μg/mL, indicating the potential for monitoring urine trypsin levels of pancreas transplant patients. The color strips based on the ratiometric fluorescent response indicate advantages in lowering the detection limit and improving the accuracy and reproducibility, bearing great potential for a real-time and naked-eye detection of bioactive substances as self-test devices.

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.

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.

Tuning interionic interaction for highly selective in vivo analysis

The development of highly selective methodologies to enable in vivo recording of chemical signals is of great importance for studying brain functions and brain activity mapping. However, the complexity of cerebral systems presents a great challenge in the development of chem/(bio)sensors that are capable of directly and selectively recording bioactive molecules involved in brain functions. As one of the most important and popular interactions in nature, interionic interaction constitutes the chemical essence of high specificity in natural systems, which inspires us to develop highly selective chem/(bio)sensors for in vivo analysis by precisely engineering interionic interaction in the in vivo sensing system. In this tutorial review, we focus on the recent progress in the tuning of interionic interaction to improve the selectivity of biosensors for in vivo analysis. The type and property of the interionic interaction is first introduced and several strategies to improve the selectivity of the biosensors, including enzyme-based electrochemical biosensors, aptamer-based electrochemical biosensors, and the strategies to recruit recognition molecules are reviewed. We also present an overview of the potential applications of the biosensors for in vivo analysis and thereby for physiological investigations. Finally, we present the major challenges and opportunities regarding the high selectivity of in vivo analysis based on tuning interionic interaction. We believe that this tutorial review provides critical insights for highly selective in vivo analysis and offers new concepts and strategies to understand brain chemistry.

Ultrasound response of aqueous poly(ionic liquid) solution

Ultrasound (US) effects on aqueous poly(ionic liquid) (PIL) solution were investigated using viscosity and FT-IR spectroscopy after exposure to US of 23, 43, and 96 kHz frequencies at 50 W. The viscosity of the poly(1-vinyl-3-butyl-imidazolium chloride) (PIL) aqueous solution decreased during exposure to US. It then increased gradually within about 10 min as US stopped. The aqueous PIL behavior was then observed using FT-IR spectroscopy. The US exposure enhanced the FT-IR band intensity of the OH stretching. The band intensity returned to its original value after the US stopped. These results responded cyclically to the US on/off. Analysis of the FT-IR spectra revealed that US influenced the breakage and reformation of hydrogen bonds in the PIL and water. Two-dimensional correlation and deconvolution were used to analyze the change of components in the region of 3000-3700 cm(-1) for US exposure. Results of these analyses suggest that US exposure might break hydrogen bonds between PIL segments and water. In the absence of US, hydrogen bonds reformation was also observed between the PIL and water.

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.

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.

Dual recognition unit strategy improves the specificity of the adenosine triphosphate (ATP) aptamer biosensor for cerebral ATP assay

Adenosine triphosphate (ATP) aptamer has been widely used as a recognition unit for biosensor development; however, its relatively poor specificity toward ATP against adenosine-5'-diphosphate (ADP) and adenosine-5'-monophosphate (AMP) essentially limits the application of the biosensors in real systems, especially in the complex cerebral system. In this study, for the first time, we demonstrate a dual recognition unit strategy (DRUS) to construct a highly selective and sensitive ATP biosensor by combining the recognition ability of aptamer toward A nucleobase and of polyimidazolium toward phosphate. The biosensors are constructed by first confining the polyimidazolium onto a gold surface by surface-initiated atom transfer radical polymerization (SI-ATRP), and then the aptamer onto electrode surface by electrostatic self-assembly to form dual-recognition-unit-functionalized electrodes. The constructed biosensor based on DRUS not only shows an ultrahigh sensitivity toward ATP with a detection limit down to the subattomole level but also an ultrahigh selectivity toward ATP without interference from ADP and AMP. The constructed biosensor is used for selective and sensitive sensing of the extracellular ATP in the cerebral system by combining in vivo microdialysis and can be used as a promising neurotechnology to probing cerebral ATP concentration.