Low Density Lipoprotein Detection Based on Antibody Immobilized Self-Assembled Monolayer: Investigations of Kinetic and Thermodynamic Properties

Abstract

Human plasma low density lipoprotein (LDL) immunosensor based on surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) was fabricated by immobilizing antiapolipoprotein B (AAB) onto self-assembled monolayer (SAM) of 4-aminothiophenol (ATP). The AAB/ATP/Au immunosensor can detect LDL up to 0.252 microM (84 mg/dL) and 0.360 microM (120 mg/dL) with QCM and SPR, respectively. The SPR and QCM measurements were further utilized to study the reaction kinetics of the AAB-LDL interaction. The adsorption process involved was explored using Langmuir adsorption isotherm and Freundlich adsorption models. The thermodynamic parameters such as change in Gibb's free energy (DeltaG(ads)), change in enthalpy (DeltaH(ads)), and change in entropy (DeltaS(ads)) determined at 283, 298, and 308 K revealed that the AAB-LDL interaction is endothermic in nature and is governed by entropy. Kinetic, thermodynamic, and sticking probability studies disclosed that desorption of the water molecules from the active sites of AAB and LDL plays a key role in the interaction process and increase in temperature favors binding of LDL with the AAB/ATP/Au immunosensor. Thus, the studies were utilized to unravel the most important subprocess involved in the adsorption of LDL onto AAB-modified ATP/Au surface that may help in the fabrication of LDL immunosensors with better efficiency.

Adsorption kinetics of low-density lipoproteins with Langmuir monolayer

“…4. Similar values have been found by Matharu et al [29] based on surface plasmon resonance and quartz crystal microbalance fabricated by immobilizing antiapolipoprotein B into a self-assembled monolayer of 4-aminothiophenol. These interesting results showed that the adsorption of oxLDL was slightly different than that of nLDL on the lipid monolayer as discussed below.…”

Biosensors for detection of Low-Density Lipoprotein and its modified forms

“…In addition, the use of biosensors offer several benefits over conventional diagnostic tools as simplicity, specificity, speed, low-cost, portable instrumentation and capability for continuous monitoring in real-time (Freire et al, 2002;Malhotra et al, 2006;Zhao & Ju, 2006). LDL sensors (lipoprotein sensors) are a new promising group or bioreceptors, because of their outstanding selectivity and stability in responses that provides an evaluation about biomedical diagnosis in plasma LDL levels (Matharu et al, 2009a(Matharu et al, , 2009b(Matharu et al, , 2010. New methods for diagnosis of LDL employing biosensors are the current demand to evaluate the risk factors for atherosclerosis.…”

“…The general working principle of the immunosensors is based on the fact that the specific immunochemical recognition of antibodies (antigens) immobilized on a transducer to antigens (antibodies) in the sample media can produce analytical signals dynamically varying with the concentrations of analytes of interest. Matharu et al (2009a) obtained an accurate and specific human plasma LDL immunosensor based on SPR and QCM by immobilizing anti-apolipoprotein B (AapoB) onto self-assembled monolayer of 4-aminothiophenol (AT). The AapoB/AT/Au immunosensor detected LDL up to 0.252 μM (84 mg/dl) and 0.360 μM (120 mg/dl) with sensitivity of 475.39 Hz/μM and 977.96 m°/μM by QCM and SPR techniques, respectively.…”

“…Due to the introduction of sensitive bench top instruments and the expansion in the range of strategies for studying biological or biochemical systems (Green et al, 2000;Oliveira et al, 2011) in more recent times, SPR based techniques have found expanded use and recently they have been introduced in clinical studies (Matharu et al, 2009a(Matharu et al, , 2009b. The competitive advantages of such techniques include the fact that SPR can be applied to a wide range of biomedically relevant interfaces and allows both real-time qualitative and quantitative assessments of the prevailing biomolecular interactions while eliminating the need of labeling reagents and without any complex sample preparation.…”

“…At the same time to explore monoclonal LDL antibodies (MAbs) in the interaction with the main protein constituent of human low density lipoprotein (apoB-100) a surface plasmon resonance (SPR)-based biosensor has been employed. Using this technique it is possible to measure the multimolecular complex between MAbs and epitopes of the apoB-100 in real time (Matharu et al, 2009a). The SPR detects and measures changes in refractive index due to the binding and dissociation of interacting molecules at or in proximity to the gold surface.…”