Development of a Paper-based Hematocrit Test and a Lateral Flow Assay to Detect Critical Fibrinogen Concentrations Using a Bottom-Up Pyramid Workflow Approach

Fibrinogen is a coagulation factor in human blood and the first one to reach critical levels in major bleeding. Hypofibrinogenemia (a too low fibrinogen concentration in blood) poses great challenges to first responders, clinicians, and healthcare providers since it represents a risk factor for exsanguination and massive transfusion requirements. Thus, the rapid assessment of the fibrinogen concentration at the point of care has gained considerable importance in preventing and managing major blood loss. However, in whole blood measurements, hematocrit variations affect the amount (volume fraction) of plasma that passes the detection zone. In an attempt to accurately determine realistic critical levels of fibrinogen (<1.5 mg/mL) in patients needing immediate treatment and medical interventions, we have developed novel diagnostic systems capable of estimating hematocrit and critical fibrinogen concentrations. A lateral flow assay (LFA) for the detection of fibrinogen has been developed by establishing a workflow employing rapid characterization methods to streamline LFA development. The integration of two detection lines enables (i) the identification of fibrinogen (first line) present in the sample and (ii) the determination of the clinically critical fibrinogen concentrations below 1.5 mg/mL (second line). Furthermore, the paper-based separation of blood cells from plasma provides a semiquantitative estimate of the hematocrit by analyzing the fractions. Initial validation of the point-of-care (PoC) hematocrit test revealed good comparability to a standard laboratory method. The developed diagnostic systems have the ability to accelerate decision-making in cases with major bleeding.

Fungi Fibrinolytic Compound 1 Plays a Core Role in Modulating Fibrinolysis, Altering Plasma Clot Structure, and Promoting Susceptibility to Lysis

Fibrin clot structure and function are major determinants of venous and arterial thromboembolic diseases, as well as the key determinants of the efficiency of clot lysis. Studies have revealed that fungi fibrinolytic compound 1 (FGFC1) is a novel marine pyranisoindolone natural product with fibrinolytic activity. Here, we explore the impacts of FGFC1 on clot structure, lysis, and plasminogen activation in vitro using turbidimetric, enzyme-linked immunosorbent assay, confocal and electron microscopy, urokinase, or plasmin chromogenic substrate. Clots formed in the presence of FGFC1 expressed reduced fibrin polymerization rate and maximum turbidity; however, they did not influence the lag phase of fibrin polymerization. In the absence of scu-PA (single-chain urokinase plasminogen activator), microscopy revealed that FGFC1 increased the number of protofibrils within fibrin fiber and the pore diameter between protofibrils, inducing clots to form a region of thinner and looser networks separated by large pores. The effects of FGFC1 on scu-PA-mediated plasma clot structure were similar to those in the absence of scu-PA. In addition, FGFC1 promoted the lysis of clots and increased the D-dimer concentration in lysate. FGFC1 increased the generation rate of p-nitroaniline in plasma. These results show that FGFC1 has fibrinolytic activity in plasma, leading to interference with the release of fibrinopeptide B to affect lateral aggregation of protofibrils and increase clot susceptibility to fibrinolysis by altering its structure.

Development of Novel Paper-Based Assay for Direct Serum Separation

Background: Many conventional laboratory tests require serum separation using a clot activator/gel tube, followed by centrifugation in an equipped laboratory. The aim of this study is development of novel, equipment-free, paper-based assay for direct and efficient serum separation. Methods: Fresh blood was directly applied to wax-channeled filter paper treated with clotting activator/s and then observed for serum separation. The purity, efficiency, recovery, reproducibility, and applicability of the assay were validated after optimization. Results: Serum was successfully separated using activated partial thromboplastin time (APTT) reagent and calcium chloride-treated wax-channeled filter paper within 2 min. The assay was optimized using different coagulation activators, paper types, blood collection methods, and incubation conditions. Confirmation of serum separation from cellular components was achieved by direct visualization of the yellow serum band, microscopic imaging of the pure serum band, and absence of blood cells in recovered serum samples. Successful clotting was evaluated by the absence of clotting of recovered serum by prolonged prothrombin time and APTT, absence of fibrin degradation products, and absence of Staphylococcus aureus-induced coagulation. Absence of hemolysis was confirmed by undetectable hemoglobin from recovered serum bands. The applicability of serum separated in paper was tested directly by positive color change on paper using bicinchoninic acid protein reagent, on recovered serum samples treated with Biuret and Bradford reagents in tubes, or measurement of thyroid-stimulating hormone and urea compared to standard serum samples. Serum was separated using the paper-based assay from 40 voluntary donors and from the same donor for 15 days to confirm reproducibility. Dryness of coagulants in paper prevents serum separation that can be re-stored by a re-wetting step. Conclusions: Paper-based serum separation allows for development of sample-to-answer paper-based point-of-care tests or simple and direct blood sampling for routine diagnostic tests.

Engineered polymer nanoparticles incorporating l-amino acid groups as affinity reagents for fibrinogen

Synthetic polymer hydrogel nanoparticles (NPs) were developed to function as abiotic affinity reagents for fibrinogen. These NPs were made using both temperature-sensitive N-isopropyl acrylamide (NIPAm) and l-amino acid monomers. Five kinds of l-amino acids were acryloylated to obtain functional monomers: l-phenylalanine (Phe) and l-leucine (Leu) with hydrophobic side chains, l-glutamic acid (Glu) with negative charges, and l-lysine (Lys) and l-arginine (Arg) with positive charges. After incubating the NPs with fibrinogen, γ-globulin, and human serum albumin (HSA) respectively, the NPs that incorporated N-acryloyl-Arg monomers (AArg@NPs) showed the strongest and most specific binding affinity to fibrinogen, when compared with γ-globulin and HSA. Additionally, the fibrinogen-AArg binding model had the best docking scores, and this may be due to the interaction of positively charged AArg@NPs and the negatively charged fibrinogen D domain and the hydrophobic interaction between them. The specific adsorption of AArg@NPs to fibrinogen was also confirmed by the immunoprecipitation assay, as the AArg@NPs selectively trapped the fibrinogen from a human plasma protein mixture. AArg@NPs had a strong selectivity for, and specificity to, fibrinogen and may be developed as a potential human fibrinogen-specific affinity reagent.

Paper-Based Lateral Flow Device for the Sustainable Measurement of Human Plasma Fibrinogen in Low-Resource Settings

Fibrinogen concentration is a major determinant of both clotting and bleeding risk. Clotting and bleeding disorders cause extensive morbidity and mortality, particularly in resource-poor and emergency settings. This is exacerbated by a lack of timely intervention informed by measurement of fibrinogen levels under conditions such as thrombosis or postpartum haemorrhage. There is an absence of simple, rapid, low-cost, and sustainable diagnostic devices for fibrinogen measurement that can be deployed in such environments. Paper-based analytical devices are of significant interest due to their potential for low-cost production, ease of use, and environmental sustainability. In this work, a device for measuring blood plasma fibrinogen using chromatography paper was developed. Wax printing was used to create hydrophobic structures to define the test channel and sample application zone. Test strips were modified with bovine thrombin. Plasma samples (22 μL) were applied, and the flow rate was monitored over 5 min. As the sample traversed the strip, clotting was induced by the conversion of soluble fibrinogen to insoluble fibrin. The flow rate and distance travelled by the sample were dependent on fibrinogen concentration. The device was able to measure fibrinogen concentration in the range of 0.5–7.0 ± 0.3 mg/mL (p < 0.05, n = 24) and had excellent correlation with laboratory coagulometry in artificial samples (r² = 0.9582, n = 60). Devices were also stable at 4–6 °C for up to 3 weeks.

Paper Diagnostic for Direct Measurement of Fibrinogen Concentration in Whole Blood

The ability to diagnose and treat critically bleeding patients can save more than 2 million lives a year. Diagnosing hypofibrinogenemia is essential in these patients. Recently, with the development of new handheld diagnostics, fibrinogen concentration can be measured rapidly at the point of care. However, these diagnostics can only work with plasma and hence need blood cells to be separated before use. In this study, we demonstrate a handheld fibrinogen diagnostic that works with whole blood. The test works by (1) forming a premixed droplet of a whole blood sample and thrombin solution on a solid surface, (2) allowing it to clot, and (3) dropping a paper strip on top. The further that blood moves down the strip, the lower the fibrinogen concentration. The diagnostic can easily measure plasma fibrinogen concentrations below 1.6 g/L for blood samples with hematocrits between 40 and 50%. Furthermore, diluting blood samples not only increases the test's sensitivity but also eliminates the effect of hematocrit and thrombin inhibitors. The test can be completed in 3-4 min, making it suitable for diagnosing early hypofibrinogenemia and allowing for fibrinogen replacement therapy in critically bleeding patients.

An integrated platform for fibrinogen quantification on a microfluidic paper-based analytical device

Fibrinogen (FIB) plays a key role in blood coagulation and thrombosis and its concentration in blood can directly reflect health conditions, thus efficient detection of FIB would benefit the treatments of certain diseases such as liver and heart diseases. However, there is a lack of sensitive, simple, rapid and cheap FIB detection device currently, in lieu of expensive and sophisticated approaches in laboratories. Here, we propose a novel plasma separation and FIB detection platform based on a microfluidic paper-based analytical device (μPAD). It is the first time that dielectrophoretic (DEP) force is combined with capillary force on paper for plasma separation, and the separation efficiency of plasma reaches about 95%, ensuring reliable downstream FIB detection, for which we also propose a new method called the resistance-fibrinogen detection (RFD) method. It not only avoids the use of large-scale instruments for detection, but also possesses high precision and simplicity. The method is found to be reliable in FIB detection for various concentrations ranging from 127.0 to 508.0 mg dL^-1. Moreover, the results obtained from the proposed μPAD show an excellent agreement (R² = 0.9985) with those obtained from an automatic coagulation analyzer with natural human blood samples. Overall, the proposed platform provides a low-cost and reliable approach for FIB detection, especially for clinical use in resource-limited areas.

Fibrinogen Diagnostics in Major Hemorrhage

Fibrinogen is one of the first factors to fall to critically low levels in the blood in many coagulopathic events. Patients with hypofibrinogenemia are at a significantly greater risk of major hemorrhage and death. The rapid replacement of fibrinogen early on in hypofibrinogenemia may significantly improve outcomes for patients. Fibrinogen is present at concentrations between 2 and 4 g/L in the plasma of healthy people. However, hypofibrinogenemia is diagnosed when the fibrinogen level drops below 1.5-2 g/L. This review analyses different types of fibrinogen assays that can be used for diagnosing hypofibrinogenemia. The scientific mechanisms and limitations behind these tests are then presented. Additionally, the current state of clinical major hemorrhage protocols (MHPs) is presented and the structure, function and physiological role of fibrinogen is summarized.

Fibrinogen Increases Resveratrol Solubility and Prevents it from Oxidation

The French paradox describes a lower incidence of cardiovascular problems despite a high intake of saturated fats. This phenomenon was associated with higher consumption of red wine, as it was later discovered that the presence of antioxidants, including resveratrol, have beneficial effects. We hypothesized that resveratrol may have a more direct role in protection from harmful oxidation, presumably through binding to important proteins of the blood coagulation process. Spectrofluorimetry demonstrated that resveratrol is capable of binding to fibrinogen, the main protein in the coagulation process, which is also important as a food additive. Various spectroscopic methods determined that binding does not cause fibrinogen unfolding or destabilization since protein melting temperature remains unchanged. A mutually protective effect against the free radical-induced oxidation of polyphenol and fibrinogen was found. The presence of fibrinogen caused only a negligible masking effect of the antioxidative abilities of resveratrol, measured by a reduction of hexacyanoferrate (III), while greatly increasing its solubility in an aqueous environment, thus increasing its potential bioavailability. Due to its interaction with fibrinogen, resveratrol may serve as an antioxidant at the site of injury. The antioxidative effect of resveratrol may also protect and thus keep the desired characteristics of fibrinogen during the application of this protein as a food additive.

Rapid, hand-held paper diagnostic for measuring Fibrinogen Concentration in blood

Critical bleeding causes over 2 million deaths a year. Early hypofibrinogenemia is a strong predictor of mortality in critically bleeding patients. The early replenishment of fibrinogen can significantly improve outcomes. However, over replenishment can also be dangerous. Furthermore, there is no rapid, cheap, hand-held diagnostic that can aid critically bleeding patients in fibrinogen replacement therapy. In this study, we have developed a hand-held paper diagnostic that measures plasma fibrinogen concentrations. The diagnostic has the potential to be used as a point of care device both inside and outside of hospital settings. It can vastly reduce the time to treatment for fibrinogen replacement therapy. The diagnostic is a two-step process. First, thrombin and plasma are added onto horizontially-orientated paper strips where the fibrinogen is converted into fibrin, drastically increasing the plasma's hydrophobicity. Second, an aqueous blue dye is pipetted onto the strips and allowed to wick through the fibrin. The distance the blue dye wicks through the strip correlates precisely to the fibrinogen concentration. The diagnostic can provide results within a minute. It can distinguish low fibrinogen concentrations (ie. <2 g/L) from normal fibrinogen concentrations. It shows remarkable reproducibility between healthy individuals. It is unaffected by common blood conditions such as acidosis, blood alcohol, severe hypertriglyceridemia, severe haemolysis and warfarin administration. Finally, it is unaffected by humidity and can withstand cold temperatures.