Kinetic analysis of immunointeractions with covalently immobilized fatty acid-binding protein using a grating coupler sensor

Heart type fatty acid binding protein: structure, function and biosensing applications for early detection of myocardial infarction

Heart type fatty acid binding protein (HFABP) as an early marker of cardiac injury holds a promising future with studies indicating surpassing performance as compared to myoglobin. As a plasma marker, this cytoplasmic protein owing to its small size (∼15kDa) and water solubility, appears readily in the blood-stream following cardiomyocyte damage, reaching peak levels within 6h of symptom onset. Low plasma levels of HFABP as compared to tissue levels indicate that minute amounts of the protein when released during myocardial infarction leads to a greater proportional rise. These parameters of kinetic release make it an ideal candidate for rapid assessment of acute myocardial infarction (AMI). The need for development of rapid immunoassays and immunotests so as to use HFABP as an early marker for AMI exclusion is tremendous. In the present review, we outline the various immunoassays and immunosensors developed so far for the detection of HFABP in buffer, plasma or whole blood. The principles behind the detection techniques along with their performance parameters compared to standard ELISA techniques are elucidated.

Quantitative measurement of binding kinetics in sandwich assay using a fluorescence detection fiber-optic biosensor

Fiber-optic biosensors have been studied intensively because they are very useful and important tools for monitoring biomolecular interactions. Here we describe a fluorescence detection fiber-optic biosensor (FD-FOB) using a sandwich assay to detect antibody-antigen interaction. In addition, the quantitative measurement of binding kinetics, including the association and dissociation rate constants for immunoglobulin G (IgG)/anti-mouse IgG, is achieved, indicating 0.38 x 10(6) M(-1) s(-1) for k(a) and 3.15 x 10(-3) s(-1) for k(d). These constants are calculated from the fluorescence signals detected on fiber surface only where the excited evanescent wave can be generated. Thus, a confined fluorescence-detecting region is achieved to specifically determine the binding kinetics at the vicinity of the interface between sensing materials and uncladded fiber surface. With this FD-FOB, the mathematical deduction and experimental verification of the binding kinetics in a sandwich immunoassay provide a theoretical basis for measuring rate constants and equilibrium dissociation constants. A further measurement to study the interaction between human heart-type fatty acid-binding protein and its antibody gave the calculated kinetic constants k(a), k(d), and K(D) as 8.48 x 10(5) M(-1) s(-1), 1.7 x 10(-3) s(-1), and 2.0 nM, respectively. Our study is the first attempt to establish a theoretical basis for the florescence-sensitive immunoassay using a sandwich format. Moreover, we demonstrate that the FD-FOB as a high-throughput biosensor can provide an alternative to the chip-based biosensors to study real-time biomolecular interaction.

Rapid analysis of fatty acid-binding proteins with immunosensors and immunotests for early monitoring of tissue injury

Fatty acid-binding protein (FABP) holds promise for early detection of tissue injury. This small protein (15kD) appears earlier in the blood than large proteins after cell damage. Combined its characteristics of high concentration tissue contents and low normal plasma values provide the possibility of a rapid rise above the respective reference values, and thus an early indication of the appearance of tissue injury. A general review was presented on the current status of different types of FABP for the detection of tissue injury in patients with myocardial injury, brain injury and also in athletes or horses with skeletal muscle injury. To take full advantage of the characteristics of the early marker FABP, rapid analysis is a crucial parameter. In this review, an overview of the development of immunoassay for the quantification of FABP in buffer, plasma or whole blood was outlined. The characteristics of different FABP immunosensors and immunotests were described. The feasibility of these immunoassays to be used in routine clinical practice and in emergency case was also discussed. Nowadays, the improved automated immunoassays (e.g. a microparticle-enhanced turbidimetric immunoassay), less time-consuming bedside immunosensors and immunotests (e.g. a one-step FABP lateral flow immunotest), are the main advance technology in point-of-care testing. With these point-of-care tests, the application of FABP as an early tissue injury marker has a great potential for many clinical purposes.