Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO₃NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO₃NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL^-1. In addition, the in situ formed TPE-2Py-SO₃Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL^-1.

Functional nucleic acids in glycobiology: A versatile tool in the analysis of disease-related carbohydrates and glycoconjugates

As significant components of the organism, carbohydrates and glycoconjugates play indispensable roles in energy supply, cell signaling, immune modulation, and tumor cell invasion, and function as biomarkers since aberrance of them has been proved to be associated with the emergence and development of certain diseases. Functional nucleic acids (FNAs) have properties including easy-to-synthesize, good stability, good biocompatibility, low cost, and high programmability, they have attracted significant research attention and been incorporated into biosensors for detecting disease-related carbohydrates and glycoconjugates. This review summarizes the construction strategies and biosensing applications of FNAs-based biosensors in glycobiology in terms of target recognition and signal transduction. By illustrating the mechanisms and comparing the performances, the challenges and development opportunities in this area have been critically elaborated. We believe that this review will provide a better understanding of the role of FNAs in the analysis of disease-related carbohydrates and glycoconjugates, and inspire further discovery in fields that include glycobiology, chemical biology, clinical diagnosis, and drug development.

A novel near-infrared fluorescent probe based on triphenylamine derivatives for the rapid and sensitive detection of heparin

In this study, a positively charged near-infrared fluorescent probe (TPA-P+) was constructed by connecting a pyridine cation with triphenylamine and successfully used for the detection of heparin.

Nucleotide-Bearing Benzylidene-Tetrahydroxanthylium Near-IR Fluorophore for Sensing DNA Replication, Secondary Structures and Interactions

Thymidine triphosphate bearing benzylidene‐tetrahydroxanthylium near‐IR fluorophore linked to the 5‐methyl group via triazole was synthesized through the CuAAC reaction and was used for polymerase synthesis of labelled DNA probes. The fluorophore lights up upon incorporation to DNA (up to 348‐times) presumably due to interactions in major groove and the fluorescence further increases in the single‐stranded oligonucleotide. The labelled dsDNA senses binding of small molecules and proteins by a strong decrease of fluorescence. The nucleotide was used as a light‐up building block in real‐time PCR for detection of SARS‐CoV‐2 virus.

Fluorescence detection of protamine, heparin and heparinase II based on a novel AIE molecule with four carboxyl

In this research, a new DSA (Distyryl-anthracene) derivative with four carboxyl groups was designed and synthesized. This molecule exhibits aggregation-induced emission property (AIE). With the AIE character, a convenient and sensitive fluorescent probe for the detection of protamine, heparin and heparinase has been developed. The protamine can directly induce the aggregation of probe, which caused by electrostatic attraction. In this way, the turn-on detection of protamine is achieved, and the detection limit is as low as 30 ng mL^-1. When heparin appears, the probes will be redisperse in solution, which causes a decrease in fluorescence intensity. Besides, this method also shows good selectivity and sensitivity, and the linear range of heparin is from 0.08 to 8 μg mL^-1 with detection limit of 37 ng mL^-1. After hydrolyzing heparin by heparinase, the probes rebind with protamine and the fluorescence enhance. The fluorescence enhancement was linearly related to the concentration of heparinase in the range of 0.02-2.0 μg mL^-1 and detection limit as low as 143.7 ng mL^-1. In addition, the results exhibited that the recovery percentage of heparinase in bovine samples reached to 96-101%.

An anionic polyelectrolyte induced aggregate assembly of Thioflavin-T: A prospective platform for Protamine sensing

Protamine, a polycation, is biologically and medically relevant protein. Protamine exhibits a wide array of functions in biological processes like gene transfer, tissue and organogenesis, cell reproduction, etc. Medically, Protamine is the only clinically approved antidote for Heparin and is routinely used in various surgical interventions, and hence controlling Protamine dosing in patients is very crucial. Taking into account the medical significance of Protamine, designing simple, reliable and sensitive fluorescence sensors is highly desirable. In this work, we propose one such sensitive and reliable fluorescent sensor which is based on a template of dye-polyelectrolyte assembly constituting a molecular rotor dye, Thioflavin-T and an anionic synthetic polyelectrolyte, polystyrene sulfonate. The addition of Protamine, prompts drastic modulations in spectral features of dye-polyelectrolyte assembly which enables sensitive detection of Protamine in aqueous solution. Apart from sensitive detection, our sensing platform aids in highly selective sensing of Protamine compared to other proteins. Moreover, our sensor system is constructed on label-free, inexpensive, commercially available molecules posing as an advantage over other sensor systems which involve laborious synthesis protocols. Most importantly, our sensor template is able to sense Protamine in diluted serum sample, indicating the potential practical utility of our sensor system.

A heparin-modified palladium nanozyme for photometric determination of protamine

Heparin was employed as the stabilizing agent in the synthesis of peroxidase-mimicking Pd nanoparticles. The heparin-capped Pd nanozyme can act as both the signal amplifier and the selective binder of protamine. The most efficient nanozyme with the mean size of 3.5 nm consists of 70.8% metallic Pd⁰ and 29.2% Pd²⁺ species. Enzyme kinetic studies show that the K_m values are 0.036 mM for 3,3',5,5'-tetramethylbenzidine and 78 mM for H₂O₂. Protamine shows strong affinity to the heparin-capped Pd nanozyme, and induces an apparent aggregation of the nanoparticles. This results in a significant inhibition of the peroxidase-mimicking activities. Hence, the oxidation of TMB by H₂O₂ to a blue product with a maximum absorption at 652 nm is suppressed. Based on this finding, a photometric assay is developed for the determination of protamine. The linear response is in the concentration range 0.02 ~ 0.8 μg mL^-1, and the limit of detection is 0.014 μg mL^-1. This assay presents high selectivity toward other biological substances. Graphical abstract Highly active and selective Pd nanozyme was synthesized through adopting heparin as the capping agent for quantitative determination of protamine.

Protamine-Induced Supramolecular Self-Assembly of Red-Emissive Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complex for Selective Label-Free Sensing of Heparin and Real-Time Monitoring of Trypsin Activity

A label-free detection assay is developed based on the design and synthesis of a new anionic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine complex with water-soluble pendants. With the aid of electrostatic interaction and noncovalent metal-metal and π-π stacking interactions, protamine is shown to induce supramolecular self-assembly of platinum(II) complexes with drastic UV-vis absorption and red emission changes. On the basis of the strong binding affinity of protamine and heparin, the ensemble has been further employed to probe heparin by monitoring the spectroscopic changes. Other than heparin, this ensemble can also detect the activity of trypsin, which can hydrolyze protamine into fragments, leading to the deaggregation of platinum(II) complexes. By modulation of the self-assembly properties of platinum(II) complexes via real-time UV-vis absorption and emission studies, the reported assay has been demonstrated to be a sensitive and selective detection method for trypsin, as well as trypsin inhibitor screening, which is essential for drug discovery.

A colorimetric sensor for protamine detection based on the self-assembly of gold nanorods on graphene oxide

Here, we report a simple colorimetric detection method for the determination of protamine based on the self-assembly of gold nanorods (AuNRs) on graphene oxide (GO).

Paranemic Crossover DNA: There and Back Again

Over the past 35 years, DNA has been used to produce various nanometer-scale constructs, nanomechanical devices, and walkers. Construction of complex DNA nanostructures relies on the creation of rigid DNA motifs. Paranemic crossover (PX) DNA is one such motif that has played many roles in DNA nanotechnology. Specifically, PX cohesion has been used to connect topologically closed molecules, to assemble a three-dimensional object, and to create two-dimensional DNA crystals. Additionally, a sequence-dependent nanodevice based on conformational change between PX and its topoisomer, JX₂, has been used in robust nanoscale assembly lines, as a key component in a DNA transducer, and to dictate polymer assembly. Furthermore, the PX motif has recently found a new role directly in basic biology, by possibly serving as the molecular structure for double-stranded DNA homology recognition, a prominent feature of molecular biology and essential for many crucial biological processes. This review discusses the many attributes and usages of PX-DNA-its design, characteristics, applications, and potential biological relevance-and aims to accelerate the understanding of PX-DNA motif in its many roles and manifestations.

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.

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.

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.

Adsorption of Antibiotics on Graphene and Biochar in Aqueous Solutions Induced by π-π Interactions

The use of carbon based materials on the removal of antibiotics with high concentrations has been well studied, however the effect of this removal method is not clear on the actual concentration of environments, such as the hospital wastewater, sewage treatment plants and aquaculture wastewater. In this study, experimental studies on the adsorption of 7 antibiotics in environmental concentration of aqueous solutions by carbon based materials have been observed. Three kinds of carbon materials have shown very fast adsorption to antibiotics by liquid chromatography-tandem mass spectrometry (LC-MS-MS) detection, and the highest removal efficiency of antibiotics could reach to 100% within the range of detection limit. Surprisedly, the adsorption rate of graphene with small specific surface area was stronger than other two biochar, and adsorption rate of the two biochar which have approximate specific surface and different carbonization degree, was significantly different. The key point to the present observation were the π-π interactions between aromatic rings on adsorbed substance and carbon based materials by confocal laser scanning microscope observation. Moreover, adsorption energy markedly increased with increasing number of the π rings by using the density functional theory (DFT), showing the particular importance of π-π interactions in the adsorption process.

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.

A simple fluorescent probe based on a pyrene derivative for rapid detection of protamine and monitoring of trypsin activity

We report the synthesis of a simple pyrene derivative and its application in protamine detection and monitoring of trypsin activity. This assay can be conducted in aqueous solution and features rapid response, visual detection, high sensitivity and selectivity. The limit of detection of protamine was 0.5 μg mL(-1). The IC50 value of a soybean trypsin inhibitor was estimated to be 0.51 U mL(-1).

A simple and rapid label-free fluorimetric biosensor for protamine detection based on glutathione-capped CdTe quantum dots aggregation

A novel fluorescent biosensor is developed, based on glutathione-capped CdTe quantum dots aggregation, for the determination of trace amount of an important drug, protamine. In this method with increasing the protamine concentration, the fluorescence of the quantum dots was quenched due to their aggregation. Different parameters affect the sensitivity, such as pH and the amount of the quantum dots, were optimized. Using the new optical biosensor, under the optimized conditions, protamine could be measured in the range of 2.0-200 ng mL(-1) with a detection limit of 1.0 ng mL(-)(1). The relative standard deviation for five replicates determination of 30.0 ng mL(-)(1) protamine was 1.26%. The influence of common interfering species on the protamine detection was studied. The results showed that the biosensor is highly selective and sensitive for the detection of protamine. The optical biosensor was successfully used for the determination of protamine in real samples.