Efficient immobilization of aptamers on the layered double hydroxide nanohybrids for the electrochemical proteins detection

Despite the use of layered double hydroxides (LDH) in different electrochemical (bio)sensors, the construction of aptasensors using LDH-based surfaces was not reported to the best of our knowledge. This may be due to the lack of a suitable linker to attach aptamers to the LDH-modified surface. LDH-based aptasensors are established here as very sensitive and reliable devices in serum and cerebrospinal fluid (CSF) analysis. 5'-NH₂ DNA aptamer probes were immobilized on the LDH-based surfaces in a vertical conformation without any linker materials. Due to the low electron conductivity of the LDH, carbon nanotubes (CNT) with high electronic conductivity and high surface area were combined with LDH. Thrombin was used as a model protein for aptasensing. The sensor shows a linear range of 0.005-12,000 pmol L^-1 and a limit of detection of 0.1 fmol L^-1. Moreover, the aptasensor was used for the sensing of thrombin in CSF and serum samples acquired from both healthy and patients with different disease.

Effect of a Recombinant Human Soluble Thrombomodulin on Baseline Coagulation Biomarker Levels and Mortality Outcome in Patients With Sepsis-Associated Coagulopathy

OBJECTIVES

To assess the effects of recombinant human soluble thrombomodulin treatment on 28-day all-cause mortality in subgroups categorized by baseline coagulation biomarker levels (prothrombin fragment 1.2, thrombin-antithrombin complex, D-dimer) in patients with sepsis-associated coagulopathy in the Sepsis Coagulopathy Asahi Recombinant LE Thrombomodulin trial (SCARLET) (NCT01598831).

DESIGN

Post hoc, subgroup analysis of a randomized, double-blind, placebo-controlled, multinational, multicenter phase 3 study.

SETTING

ICUs at 159 sites in 26 countries.

PATIENTS

Eight-hundred adults with sepsis-associated coagulopathy defined as international normalized ratio greater than 1.40 and platelet count between 30 × 10/L and 150 × 10/L or greater than 30% decrease within 24 hours with concomitant cardiovascular and/or respiratory failure.

INTERVENTIONS

Patients randomized and treated with recombinant human soluble thrombomodulin (0.06 mg/kg/d; n = 395) or equivalent placebo (n = 405) for 6 days.

MEASUREMENTS AND MAIN RESULTS

Recombinant human soluble thrombomodulin did not significantly reduce 28-day all-cause mortality in the Sepsis Coagulopathy Asahi Recombinant LE Thrombomodulin trial: absolute risk reduction was 2.55% (p = 0.32) in patients with sepsis-associated coagulopathy. In this post hoc analysis, mortality steadily increased with increasing baseline prothrombin fragment 1.2 and thrombin-antithrombin complex levels in the placebo group; for those values exceeding the upper limit of normal, the mortality increases in the recombinant human soluble thrombomodulin group were lower or negligible with increasing baseline prothrombin fragment 1.2 and thrombin-antithrombin complex. Consequently, absolute risk reductions were greater in subgroups with higher baseline prothrombin fragment 1.2 or thrombin-antithrombin complex. Absolute risk reductions were also greater in subgroups with baseline coagulation biomarker levels at or above median of the entire study population, ranging from 4.2% (95% CI, -5.0% to 13.4%) to 5.5% (95% CI, -4.0% to 14.9%).

CONCLUSIONS

Compared with patients receiving placebo, patients treated with recombinant human soluble thrombomodulin having higher baseline thrombin generation biomarker levels had lower mortality. Further research regarding the predictive role of coagulation biomarkers for recombinant human soluble thrombomodulin treatment response in sepsis-associated coagulopathy is warranted to evaluate clinical relevance.

Calcium-cation-doped polydopamine-modified 2D black phosphorus nanosheets as a robust platform for sensitive and specific biomolecule sensing

Many polymer decorated/modified 2D nanomaterials have been developed as enhanced drug delivery systems and photothermal theranostic nanoagents. However, few reports describe the use of these novel nanomaterials as nanoplatforms for biomolecule sensing. Herein, we used calcium-cation-doped polydopamine-modified (PDA-modified) 2D black phosphorus (BP) nanosheets (BP@PDA) as a sensing nanoplatform for the detection of nucleic acids and proteins in complex biological samples. Fluorescent-dye-labeled single-strand DNA aptamer/probes are adsorbed by the Ca²⁺-doped BP@PDA mediated by calcium-cation coordination. The PDA coating enhances the stability of the inner BP, provides binding sites to DNA nucleobases, and quenches fluorescence. Without any chemical conjugation, this sensing nanoplatform selectively and specifically detects protein (human thrombin, linear range: 10-25 nM, detection limit: 0.02 nM), single-strand DNA (linear range: 1-10 nM, detection limit: 0.52 nM) in 1% serum diluted samples, and senses intracellular mRNAs (C-myc, and actin) in living cells. The nanoplatform exhibits the advantages of both the 2D nanomaterial (BP) and the coating polymer (PDA), naturally enters living cells unaided by transfection agents, resists enzymatic lysis and shows high biocompatibility. This nanoplatform design contributes towards future biomolecule analytical method development based on polymer decorated/modified 2D nanomaterials.

An integrated microfluidic platform for selective and real-time detection of thrombin biomarkers using a graphene FET

Lab-on-a-chip technology offers an ideal platform for low-cost, reliable, and easy-to-use diagnostics of key biomarkers needed for early screening of diseases and other health concerns. In this work, a graphene field-effect transistor (GFET) functionalized with target-binding aptamers is used as a biosensor for the detection of thrombin protein biomarker. Furthermore, this GFET is integrated with a microfluidic device for enhanced sensing performances in terms of detection limit, sensitivity, and continuous monitoring. Under this platform, a picomolar limit of detection was achieved for measuring thrombin; in our experiment measured as low as 2.6 pM. FTIR, Raman and UV-Vis spectroscopy measurements were performed to confirm the device functionalization steps. Based on the concentration-dependent calibration curve, a dissociation constant of KD = 375.8 pM was obtained. Continuous real-time measurements were also conducted under a constant gate voltage (VGS) to observe the transient response of the sensor when analyte was introduced to the device. The target selectivity of the sensor platform was evaluated and confirmed by challenging the GFET biosensor with various concentrations of lysozyme protein. The results suggest that this device technology has the potential to be used as a general diagnostic platform for measuring clinically relevant biomarkers for point-of-care applications.

Global Coagulation Assays in Transgender Women on Oral and Transdermal Estradiol Therapy

CONTEXT

The thrombotic effects of estradiol therapy in transgender women are unclear. Global coagulation assays (GCA) may be better measures of hemostatic function compared with standard coagulation tests.

OBJECTIVE

To assess the GCA profiles of transgender women in comparison to cisgender controls and to compare how GCA differ between routes of estradiol therapy in transgender women.

DESIGN

Cross-sectional case-control study.

SETTING

General community.

PARTICIPANTS

Transgender women, cisgender male and cisgender female controls.

MAIN OUTCOME MEASURES

Citrated blood samples were analyzed for (i) whole blood thromboelastography (TEG®5000), (ii) platelet-poor plasma thrombin generation (calibrated automated thrombogram); and (iii) platelet-poor plasma fibrin generation (overall hemostatic potential assay). Mean difference (95% confidence intervals) between groups are presented.

RESULTS

Twenty-six transgender women (16 oral estradiol, 10 transdermal estradiol) were compared with 98 cisgender women and 55 cisgender men. There were no differences in serum estradiol concentration (P = 0.929) and duration of therapy (P = 0.496) between formulations. Transgender women demonstrated hypercoagulable parameters on both thromboelastography (maximum amplitude + 6.94 mm (3.55, 10.33); P < 0.001) and thrombin generation (endogenous thrombin potential + 192.62 nM.min (38.33, 326.91); P = 0.009; peak thrombin + 38.10 nM (2.27, 73.94); P = 0.034) but had increased overall fibrinolytic potential (+4.89% (0.52, 9.25); P = 0.024) compared with cisgender men. No significant changes were observed relative to cisgender women. Route of estradiol delivery or duration of use did not influence the GCA parameters.

CONCLUSION

Transgender women on estradiol therapy demonstrated hypercoagulable GCA parameters compared with cisgender men with a shift towards cisgender female parameters. Route of estradiol delivery did not influence the GCA parameters.

Thrombin Generation in Fresh and Frozen-Thawed Platelet Poor Plasma - Is there a Difference?

BACKGROUND

Applicability of thrombin generation tests to clinical routine has been sought for many years. The aim of this study was to compare thrombin generation measured in fresh platelet poor plasma (f-PPP) and frozen-thawed platelet poor plasma (ft-PPP) to prove the consistency of results.

METHODS

In this prospective study, thrombin generation was measured in twenty-fold repetitions in 3.2% citrate PPP obtained from male healthy blood donors aged 19 - 39 years (n = 54 donations). The tests were performed with fresh PPP and repeated after storing the PPP at -60°C. In two subgroup analyses, the effect of higher and lower normal baseline platelet counts on the Calibrated Automated Thrombogram (CAT) assay and the influence of ABO blood groups on thrombin generation were analyzed.

RESULTS

Referring to the parameters of thrombin generation most frequently used in studies, peak thrombin of f-PPP and ft-PPP agreed in about 50% of the samples. Endogenous thrombin potential (ETP) of f-PPP and ft-PPP agreed in nearly two-thirds of the samples. A slightly but significantly slower kinetic was found in the thrombin generation of ft-PPP compared with f-PPP. At least in f-PPP, ETP correlates with baseline platelet counts of the whole blood sample. Peak thrombin was significantly higher in non-O blood groups compared to O blood group.

CONCLUSIONS

A low level of agreement between the results of f-PPP and ft-PPP is shown. In terms of practicability of sample collection using semi-automated thrombin-generation assays ft-PPP should be preferred over f-PPP. We therefore recommend using ft-PPP in clinical studies.

Thrombin Generation and other hemostatic parameters in patients with atrial fibrillation in use of warfarin or rivaroxaban

Patients with atrial fibrillation (AF) present hyperactivation of both platelets and coagulation leading to a hypercoagulable state which contributes to an increased risk of thromboembolism. Therefore, one of the main strategies for treatment of AF is prevention of these events through the use of oral anticoagulants (OAC). The aim of this study was to evaluate hemostasis as a whole in patients with non-valvular AF undergoing warfarin or rivaroxaban by thrombin generation test (TGT), in addition to monocyte-platelet aggregates (MPA), glycoprotein IIb/IIIa (GPIIb/IIIa), and platelet (PMP) and endothelium (EMP) microparticles, compared to age and sex matched controls. PT/INR for OAC use was also determined. In patients taking OAC, compared to control group, a decrease in TGT (p = 0.000 for all parameters) were observed. Patients taking warfarin showed to be more hypocoagulable, presenting lower levels of ETP (p = 0.000) and peak (p = 0.002) than patients using rivaroxaban. Patients on warfarin use with INR > 3 had also lower levels of ETP (p = 0.01) and peak (p = 0.006). A decrease in ETP (p = 0.03) and peak (p = 0.02) values was also observed in patients using rivaroxaban with PT > 21.4 s. Patients using warfarin (p = 0.000) and rivaroxaban (p = 0.000) presented lower levels of MPA in relation to control group. It was also observed in patients using warfarin, lower GPIIb/IIIa levels in relation to control group (p = 0.011). Patients taking rivaroxaban (p = 0.003) and warfarin (p = 0.001) had higher PMP levels compared to control group. There was no difference in levels of EMP between the groups (p = 0.0536). The present study reinforces the usefulness of OAC in AF, which decisively contribute to a better management of the disease preventing possible complications.

Novel Chemiluminescence Sensor for Thrombin Detection Based on Dual-Aptamer Biorecognition and Mesoporous Silica Encapsulated with Iron Porphyrin

Thrombin is a marker of blood-related diseases, and its detection is of great significance in the fields of medical and biological research. Herein, a novel chemiluminescence (CL) sensor for thrombin detection was prepared based on dual-aptamer biorecognition and mesoporous silica encapsulated with iron porphyrin. Mesoporous silica encapsulated with hematin by aptamer1 (Apt1/hematin/M-SiO₂) and magnetic microspheres modified with aptamer2 (Apt2/NH₂-MS) were successfully prepared, and the two materials were used to construct a CL sensor to detect thrombin. Primarily, Apt2/NH₂-MS is used for pretreatment separation of thrombin samples by the biorecognition effect between the aptamer (Apt2) and target (thrombin). Then, thrombin/Apt2/NH₂-MS is again recognized with Apt1 on the surface of Apt1/hematin/M-SiO₂ and Apt1/thrombin/Apt2/NH₂-MS is formed, so dual-aptamer biorecognition is realized. Meanwhile, the generated Apt1/thrombin/Apt2/NH₂-MS makes Apt1 shed off the surface of M-SiO₂ and release hematin. The released hematin can catalyze the luminol-H₂O₂ CL reaction. Therefore, a sandwich-type CL sensor was constructed based on dual-aptamer biorecognition and hematin catalysis for the detection of thrombin. The sensor has a linear range of 7.5 × 10^-15 to 2.5 × 10^-10 mol·L^-1 and a detection limit of 2.2 × 10^-15 mol·L^-1 and also exhibits excellent selectivity, reproducibility, and stability. The sensor was successfully used for the detection of thrombin in serum samples, which makes it possible to apply the sensor in the detection of thrombin in actual samples.

Lattice-Like DNA Tetrahedron Nanostructure as Scaffold to Locate GOx and HRP Enzymes for Highly Efficient Enzyme Cascade Reaction

In this work, the array arrangement of cascade enzymes was implemented by alternately and equidistantly anchoring two model enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) to the vertexes of rigid DNA tetrahedron units in lattice-like nucleic acid scaffold, in which the distance between any adjacent cascade enzymes had been regulated to the optimum for obtaining high enzyme cascade catalytic efficiency. Compared to the enzyme cascade system with no-array arrangement of cascade enzymes, the proposed enzyme cascade system allowed the intermediate H₂O₂ produced by GOx catalyzing substrate glucose to concurrently and equidistantly diffuse toward the four adjacent HRP enzyme surfaces. In this case, the invalid diffusion effect of intermediate H₂O₂ between cascade enzymes could be effectively avoided, thereby promoting the enzyme cascade reaction with high catalytic efficiency. The specific catalytic efficiency (k_cat/K_m) of the cascade enzyme system with array arrangement had been evaluated, which exhibited catalytic efficiency about 3.6 times higher than that of the randomly arranged cascade enzyme system. As a result, this strategy provided a new avenue for constructing a highly efficient enzyme cascade system with ultimate applications in biosynthesis, bioanalysis, and biodiagnostics.

Electrochemiluminescence methods using CdS quantum dots in aptamer-based thrombin biosensors: a comparative study

The detection of thrombin by using CdS nanocrystals (CdS NCs), gold nanoparticles (AuNPs) and luminol is investigated in this work. Thrombin is detected by three methods. One is called the quenching method. It is based on the quenching effect of AuNPs on the yellow fluorescence of CdS NCs (with excitation/emission wavelengths of 355/550 nm) when placed adjacent to CdS NCs. The second method (called amplification method) is based on an amplification mechanism in which the plasmonics on the AuNPs enhance the emission of CdS NCs through distance related Förster resonance energy transfer (FRET). The third method is ratiometric and based on the emission by two luminophores, viz. CdS NCs and luminol. In this method, by increasing the concentration of thrombin, the intensity of CdS NCs decreases, while that of luminol increases. The results showed that ratiometric method was most sensitive (with an LOD of 500 fg.mL^-1), followed by the amplification method (6.5 pg.mL^-1) and the quenching method (92 pg.mL^-1). Hence, the latter is less useful. Graphical abstract Schematic representation of three different methods (quenching, amplification and ratiometric) were applied for detection of thrombin via aptasensor. The CdS nanocrystals, streptavidin (Str) coated AuNPs and also Str-luminol coated AuNPs were used for the construction steps of the electrochemiluminescence (ECL)-based biosensor.

A "signal-on" electrochemical biosensor based on DNAzyme-driven bipedal DNA walkers and TdT-mediated cascade signal amplification strategy

In this work, a dual amplified signal enhancement approach based on coupling deoxyribozyme (DNAzyme)-driven bipedal DNA walkers (BDW) and terminal deoxynucleotidyl transferase (TdT)-mediated DNA elongation signal amplifications has been developed for highly sensitive and label-free electrochemical detection of thrombin in human serums. In presence of thrombin, the BDW complex, which is comprised from the target thrombin and two DNAzyme-containing probes, can exhibit autonomous cleavage behavior on the surface of the substrate DNA (SD) modified electrode, and remove the cleaved DNA fragment from the electrode surface. Subsequently, the TdT can catalyze the elongation of the SD with free 3'-OH termini and formation of many G-quadruplex sequence replicates with the presence of 2'-deoxyaguanosine-5'-triphosphate (dGTP) and adenosine 5'-triphosphate (dATP) at a molar ratio of 6:4. These G-quadruplex sequences bind hemin and generate drastically amplified current response for sensitive detection of thrombin in a "signal-on" and completely label-free fashion. Under optimized conditions, the response peak current was linear with the concentration of thrombin in the range from 0.5 pM to 100000 pM with detection limit of 0.31 pM. This research provides us a sustainable idea for the hyphenated multiple amplification strategies and a stable and effective method for the detection of protein biomarkers.

A novel RNA aptamer-modified riboswitch as chemical sensor

In this study, a novel label- and immobilization-free RNA aptamer-modified riboswitch-based biosensor was developed by using RNA aptamer modified secondary-structural scaffolds to control the identity of the ribosomal binding sequence (RBS). In the developed sensor, the duplex RNA aptamers-modified cis-repressor sequence is introduced upstream to the RBS of the indicating gene (gfp gene), leading to formatting an RNA bubble due to the none-complementary state of the RNA aptamers in the hairpin structure of the cis-repressor sequence. Without the presence of the target molecule, the ribosome cannot identify the RBS of the indicating gene as the RBS is hidden by the introduced cis-repressor, consequently, the indicating gene in the sensor would not be expressed, demonstrating the absence of the target. On the contrary, with the presence of the target molecule, the binding of aptamer with the target would induce the enlargement of the RNA bubble, leading to the separation of the cis-repressor sequence and RBS. Hence, the indicating gene would be expressed, manifesting the existence of the target. In addition, the developed sensor can quantitatively report the target concentrations by measuring the gfp gene-encoded GFP (green fluorescent protein) concentration. The approach proposed in this study can be used to construct sensors for detecting various chemicals by introducing the corresponding aptamers, therefore, this strategy can potentially provide a new set of analytical tools in the field of analytical chemistry.

The synergistic effect of Au-COF nanosheets and artificial peroxidase Au@ZIF-8(NiPd) rhombic dodecahedra for signal amplification for biomarker detection

Here, a new type of signal amplification strategy is proposed employing Au nanoparticle (AuNP)-functionalized covalent organic framework (Au-COF) nanosheets and AuNP functionalized ZIF-8(NiPd) (Au@ZIF-8(NiPd)) rhombic dodecahedra nanocomposites for sandwich electrochemical sensor construction. The peroxidase mimics Au@ZIF-8(NiPd) took the place of natural enzymes in enzyme-assisted amplification strategies, both acting as catalysts for H₂O₂ reduction for signal amplification, and serving as ideal nanocarriers for signal probe anchoring. The cancer biomarker thrombin (TB) was selected as the target. Thrombin binding aptamers (TBA 2) were fixed on Au@ZIF-8(NiPd), and the obtained TBA 2-Au@ZIF-8(NiPd) bioconjugates were employed as tracer labels, and TB was sandwiched between the tracer labels and capture probe TBA 1 which were immobilized on the Au-COF nanosheet modified electrode. Au-COFs with a high specific area, super electroconductivity, and uniformly distributed AuNPs were utilized as the electrode substrate to fix TBA 1. Exploiting the sandwich method, the proposed TB aptasensor exhibited a wide linear range of 0.1 pM to 20 nM with a low detection limit of 15 fM (S/N = 3). The ingenious sensing strategy enriched the application diversity of the artificial enzyme and showed promise in research and development of point-of-care diagnostics.

C60@C3N4 nanocomposites as quencher for signal-off photoelectrochemical aptasensor with Au nanoparticle decorated perylene tetracarboxylic acid as platform

Herein, a novel signal-off photoelectrochemical (PEC) aptasensor was proposed for sensitive detection of thrombin on the basis of C₆₀@C₃N₄ nanocomposites as quencher and Au nanoparticles (depAu) decorated perylene tetracarboxylic acid (PTCA) as sensing platform. Owing to the excellent membrane-forming of PTCA and superior conductivity of depAu, the PTCA between two depAu layers can simply and effectively produce an extremely high initial photocurrent to afford a precondition for sensitive biodetection. Thereafter, the assembly of C₆₀@C₃N₄ nanocomposites on electrode via typical sandwich reaction enabled the generation of a significantly decreased photocurrent. Here, the C₃N₄ with high surface area not only provided massive binding sites for C₆₀ immobilization, but also partly competed with PTCA in light absorption for producing a significantly smaller photocurrent in the presence of electron donor ascorbic acid (AA). Additionally, both the C₃N₄ and C₆₀ have the poor conductivity, which could inhibit the electron transfer to achieve a further decreased photocurrent, effectively improving the sensitivity of proposed biosensor. As a result, the PEC biosensor in a "signal-off" mode showed an extremely low detection limit down to 1.5 fM, providing a sensitive and universal strategy for protein detection.

Inhibition of catalytic activity of fibrinogen-stabilized gold nanoparticles via thrombin-induced inclusion of nanoparticle into fibrin: Application for thrombin sensing with more than 104-fold selectivity

Citrate-capped gold nanoparticles (AuNPs) modified with thrombin-binding aptamer are often implemented for colorimetric, fluorescent, and electrochemical detection of thrombin in an aqueous solution. However, researchers have rarely explored the application of fibrinogen-modified AuNPs (F-AuNPs) for thrombin sensing. We present a simple, inexpensive, sensitive, and selective probe for colorimetric assay of thrombin through combining thrombin-induced inclusion of F-AuNPs into Fibrin and F-AuNPs-catalyzed reduction of 4-nitrophenol with an excess amount of NaBH₄. Considering that fibrinogen stabilized citrate-capped AuNPs against a high-ionic-strength buffer, F-AuNPs efficiently catalyzed the NaBH₄-mediated decrease of yellow 4-nitrophenol to colorless 4-aminophenol. The presence of thrombin converted fibrinogen into fibrin on the nanoparticle surface, leading to the inclusion of nanoparticles into fibrin. The formation of fibrin inhibited that the AuNPs catalyzed the NaBH₄-mediated reduction of 4-nitrophenol. Consequently, the color of the solution gradually varied from colorless to yellow with increasing thrombin concentration. The proposed system was shown to be accurate in the quantification of small differences in the concentration of human thrombin over the range of 4-60 pM. The lowest detectable concentration of human thrombin by the naked eye was as low as 16 pM. We demonstrated the practical application of the proposed system in quantifying 1-15 nM human thrombin in human plasma.

Quenched sandwich-type photoelectrochemical aptasensor for protein detection based on exciton energy transfer

This work proposes a quenched photoelectrochemical sensing method for highly selective and sensitive detection of protein via Energy Transfer (ET) effect between the AuNPs and CdS:Mn quantum dots. This detection was performed on a sandwich-type aptamer sensing interface. Chitosan modified CdS:Mn/TiO₂/ITO electrode was used to immobilize capture DNA (S1) via -CONH- bond. In the presence of target protein, AuNPs labeled DNA (AuNPs-S2) was further bonded to the protein to fabricate sandwich sensing platform, which forced the AuNPs away from the electrode surface. In this state, the photocurrent was greatly depressed, mainly due to two factors: (a) the ET effect produced by interparticle distance between CdS:Mn and AuNPs; (b) the steric hindrance of AuNPs-S2 partly obstructs the diffusion of the electron donor. The photocurrent decreased with the increasing concentration of the target protein. Using thrombin as a target, this sensitized method showed a detectable range of 0.1 pM to 8 nM and a detection limit of 30 fM. It possessed high selectivity and good stability for detection of thrombin. This method is extremely flexible and can be extended to varieties of protein targets.

Label free thrombin detection in presence of high concentration of albumin using an aptamer-functionalized nanoporous membrane

Nanoporous alumina membranes have become a ubiquitous biosensing platform for a variety of applications and aptamers are being increasingly utilized as recognition elements in protein sensing devices. Combining the advantages of the two, we report label-free sensitive detection of human α-thrombin by an aptamer-functionalized nanoporous alumina membrane using a four-electrode electrochemical cell. The sensor response to α-thrombin was determined in the presence of a high concentration (500 μM) of human serum albumin (HSA) as an interfering protein in the background. The sensor sensitivity was also characterized against γ-thrombin, which is a modified α-thrombin lacking the aptamer binding epitope. The detection limit, within an appreciable signal/noise ratio, was 10 pM of α-thrombin in presence of 500 μM HSA. The proposed scheme involves the use of minimum reagents/sample preparation steps, has appreciable response in presence of high concentrations of interfering molecules and is readily amenable to miniaturization by association with existing-chip based electrical systems for application in point-of-care diagnostic devices.

Proximity ligation assay induced and DNAzyme powered DNA motor for fluorescent detection of thrombin

A novel DNA motor for thrombin detection was described here based on proximity ligation assay (PLA) induced DNAzyme recycling cleavage. Fluorophore labeled DNA is modified on gold nanoparticles (AuNPs) and the fluorescent signal is quenched by AuNPs. The PLA between target thrombin and two aptamers induces the forming of Mg²⁺-dependent DNAzyme. The fluorophore labeled DNA is cleaved circularly by the DNAzyme, releasing the fluorescent fragment from AuNPs surface. The cleavage and rebinding process create a processive walking along AuNPs surface track. As a result, the fluorescent intensity recovers significantly. A good linear relationship is obtained between the ratio of fluorescence intensity and thrombin concentration in the range from 10 pM to 10 nM. The limit of detection is calculated to be 4 pM. These results are comparable or even better than other amplification based methods.

Colorimetric and electrochemical (dual) thrombin assay based on the use of a platinum nanoparticle modified metal-organic framework (type Fe-MIL-88) acting as a peroxidase mimic

An electrochemical and colorimetric dual-readout method is described for the determination of thrombin. A platinum nanoparticle (Pt NP) modified metal organic framework (MOF) acts as a peroxidase (POx) mimic that causes the formation of a blue product from 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide, with an absorption maximum at 650 nm. In addition, gold nanoparticles enrich initiators that trigger the hybridization chain reaction for dual signal amplification to generate an electrochemical current typically measured at 0.31 V (from -0.5 to -0.1 V) and allow quantitation of thrombin with high sensitivity and over a wide detection range. The colorimetric and electrochemical (dual) thrombin assay produces two kinds of signals which warrants accuracy, diversity, and an option for visual inspection. The dual-channel sensor allows for the quantitative determination of thrombin with a low detection limit (0.33 fM) for the electrochemical method and 0.17 pM for the colorimetric method) and over a wide detection range (1 fM to 10 nM for electrochemical method and 0.5 pM to 1 nM for colorimetric method). The electrochemical detection limit is lower than that of colorimetry, and the linear range is wider, which is more suitable for further quantitative analysis of the target. Graphical abstract Schematic representation of a colorimetric and electrochemical (dual) thrombin assay based on the use of a platinum nanoparticle modified metal-organic framework for color development and hybridization chain reaction for electrochemical signal. C-TBA: complementary sequences of thrombin aptamer, TBA: thrombin aptamer, I-Au NPs: initiators enriched by gold nanoparticles, S-AuE: sensing gold electrode, RS-AuE: reacted sensing gold electrode, TB: thrombin, MB: Methylene Blue, HCR: hybridization chain reaction.

A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects

A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode-solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered "ice-like" phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.

Host-Derived Molecules as Novel Chagas Disease Biomarkers: Hypercoagulability Markers in Plasma

The most severe clinical symptomatology of Chagas disease affects ~30% of those chronically infected with the Trypanosoma cruzi parasite. The pathogenic mechanisms that lead to life-threatening heart and gut tissue disruptions occur "silently" for a longtime in a majority of cases. As a result, despite there are several serological and molecular methods available to diagnose the infection in its acute and chronic stages, diagnosis is often achieved only after the onset of clinical symptoms in the chronic phase of the disease. Furthermore, although there are two drugs to treat it, the assessment of their performance is impractical with current parasite-derived diagnostics, and therapeutic efficacy cannot be acknowledged in a timely manner.In this chapter we present two procedures to measure host-derived molecules as surrogates of therapeutic response against chronic T. cruzi infection. Their outputs relate to the generation and activity of thrombin, a major component of the blood coagulation cascade. This is due to the fact that a hypercoagulability state has been described to occur in chronic Chagas disease patients and revert after treatment with benznidazole.

Hierarchical Porous Fluorinated Graphene Oxide@Metal-Organic Gel Composite: Label-Free Electrochemical Aptasensor for Selective Detection of Thrombin

Current research effort aims at developing and designing new sensing platform architectures for effectively assaying biological targets that are significantly important for human healthcare and medical diagnosis. Here, we proposed a novel nanostructured sensor based on the combination of fluorinated graphene oxide and iron-based metal-organic gel (FGO@Fe-MOG). The unique properties including hierarchical porosity along with excellent electron transfer behavior make it an ideal candidate for electrochemical sensing of thrombin with superior detection limits compared to other (electrochemical, fluorescence, and colorimetric) strategies. Specifically, thrombin-binding aptamer was immobilized onto FGO@Fe-MOG through strong electrostatic interaction without any special modification or labeling, and the electrochemical impedance spectroscopy was used as the analyzing tool. The introduced aptasensor revealed high selectivity and reproducibility toward thrombin with the detection limit of 58 pM. The effectiveness, reliability, and real applicability of the proposed FGO@Fe-MOG nanohybrid were also confirmed by the determination of thrombin in a complex biological matrix represented by human serum. Taking into account the superior detection limit, high selectivity, reproducibility, and precision, the developed scalable and label-free aptasensor meets the essential requirements for clinical diagnosis of thrombin.

An Ethanol-Free Autologous Thrombin System

Thrombin is a coagulation protein of central importance to hemostasis and wound healing that can be sourced from human blood, bovine blood, and engineered cell lines. Only autologous thrombin lacks the risks of transmitting emergent pathogens or eliciting an immunogenic response. Previous commercial autologous thrombin devices require the use of high concentrations of ethanol to achieve thrombin stability, introducing cytotoxicity risks. A new point of care device for preparing an ethanol-free autologous thrombin serum was investigated. The ethanol-free autologous serum (AS) was prepared using the Thrombinator^™ System (Arthrex, Inc., Naples, FL). A total of 120 devices were tested with the blood of 30 healthy donors to determine the reliability and flexibility of the procedure. AS was prepared from both whole blood (WB) and platelet-poor plasma (PPP). Study endpoints were thrombin activity determined using a coagulation analyzer and formation of cohesive bone graft composites objectively measured using a durometer. The average thrombin activity produced by this system from 24 donors was 20.6 ± 2.7 IU/mL for WB and 13.4 ± 3.8 IU/mL for PPP which correlated to clot times of 3.9 and 5.9 seconds, respectively. The device tolerated use of varying volumes of blood to prepare AS. In addition, the system was able to generate four successive and comparable AS productions. When combined with platelet-rich plasma and bone graft material, cohesive scaffolds were always formed. A new device and method for preparing single donor, ethanol-free, AS with thrombin activity was demonstrated.

Elevated coagulation factor levels affect the tissue factor-threshold in thrombin generation

INTRODUCTION

Altered levels of factor (F)VIII, prothrombin, or antithrombin have been associated with an increased risk for venous thromboembolism (VTE). However, the exact molecular mechanism by which these altered factor levels modulate the risk is incompletely understood. Here we hypothesize that elevated factor levels affect the pro- and anticoagulant balance in coagulation such that even minute amounts of tissue factor (TF) will initiate thrombin formation, thereby contributing to the VTE risk.

MATERIALS AND METHODS

To test this so-called TF-threshold hypothesis, we monitored thrombin generation initiated by very low TF concentrations in FXII-deficient plasma, to avoid any contact pathway-mediated thrombin formation. Furthermore, similar experiments were performed in the presence of increasing concentrations of pro- and anticoagulant proteins.

RESULTS

A TF-threshold was established in the FXII-deficient plasma, which is subject to inter-individual variation. Elevated plasma levels of procoagulant factors, such as FVIII or prothrombin, enhanced thrombin generation and reduced the amount of TF required for the initiation of thrombin formation. Conversely, elevated levels of the coagulation inhibitor antithrombin increased the TF-threshold.

CONCLUSIONS

Our findings support a mediating role for the TF-threshold in the association between high procoagulant factor levels and the risk for VTE. Furthermore, elevated levels of anticoagulants may have a protective effect on the development of VTE.

Ultrasensitive determination of thrombin by using an electrode modified with WSe2 and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase

A sensitive aptamer/protein binding-triggered sandwich assay for thrombin is described. It is based on electrochemical-chemical-chemical redox cycling using a glassy carbon electrode (GCE) that was modified with WSe₂ and gold nanoparticles (AuNPs). The AuNPs are linked to thrombin aptamer 1 via Au-S bonds. Thrombin is first captured by aptamer 1 and then sandwiched through the simultaneous interaction with AuNPs modified with thrombin-specific aptamer 2 and signalling probe. Subsequently, the DNA-linked AuNP hybrids result in the capture of streptavidin-conjugated alkaline phosphatase onto the modified GCE through the specific affinity reaction for further signal enhancement. As a result, a linear range of 0-1 ng mL^-1 and a detection limit as low as 190 fg mL^-1 are accomplished. The specificity for thrombin is excellent. Conceivably, this strategy can be easily expanded to other proteins by using the appropriate aptamer. Graphical abstract Schematic presentation of an electrochemical biosensor for thrombin based on WSe₂ and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase.