E. M. I. Mala Ekanayake

Low density lipoprotein detection based on antibody immobilized self-assembled monolayer: investigations of kinetic and thermodynamic properties.

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 Gibbs 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.

Effect of Glucose Oxidase Immobilizing Techniques on Performances of Nano Scale Polypyrrole Glucose Biosensors

Characteristic dependency of nano scale polypyrrole (PPy) glucose biosensors, achieved by three different immobilizing techniques namely, coentrapment, physical adsorption and a two step method of coentrapment superimposed with physical adsorption is reported. Different enzyme loading and material properties resulted in varied immobilizing methods lead to dissimilarities in characteristics. In this study, Pt coated AnodiscTMs (0.2 µm) were used as electrodes to polymerize PPy at 0.3 mA cm-2 using a solution containing 0.05 M Pyrrole and 0.1 M NaPF6. The polymerization time was optimized to 90 s. In the coentrapment method, glucose oxidase (GOx) (1 mg ml-1) was added to the monomer solution while an aliquot of GOx (5 µl) was placed on the pre-polymerized electrode for physical adsorption. A combined procedure of these two techniques was used as the last immobilization technique. Physical adsorption method gave a sensitivity of 3 mA cm-2 M-1 and a linear range of 0.5–13 mM with a response time of a 3 s. Sensitivity in the case of coentrapment was 3.75 mA cm-2 M-1 while it showed a value of 4.45 mA cm-2 M-1 in two step immobilization thus giving 25 and 48% increases respectively. Response times of 9 and 8 s in latter cases reveal the possible repercussion taking place at enzyme immobilization in three dimensional (3-D) PPy matrix and the delay occur in glucose to reach the enzyme. Linear range of the two step method was extended up to 16 mM due to the reinforced enzyme loading.

Nano-Biosensor Development for Biomedical and Environmental Measurements

Nano biosensor development for biomedical and environmental measurements has been tried by research groups all over the world. Identifying and fabricating suitable nano-materials as enzyme immobilizing matrices to enhance characteristics of the sensor is the most important and difficult task of it. In this chapter we discuss about polypyrrole(PPy) nano-tube array grown on Alumina AnodiscTM to serve this purpose successfully.

Enhanced Adsorption of Glucose Oxidase by Introducing Artificial Porosity into Polypyrrole Based Glucose Biosensors

A polypyrrole (PPy) based biosensor fabricated on a Pt plated nano-porous alumina electrode has been described. By selecting nano-porous electrodes, the enzyme adsorption has been increased and the usage of a cross linking agent has enhanced the performances of the sensor remarkably. A thin film of PPy/PF6 - was synthesized with 0.05 M Pyrrole, 0.1 M NaPF6 at a current density of 0.3 mA/cm2 for 90 s. The immobilization was done by physically adsorbing 5 muL of glucose oxidase (GOx) on PPy thin film. Glutaraldehyde (0.1 wt.%, 5 muL)was used for cross-linking. The synthesized films were characterized by using amperometric electrochemical technique and scanning electron microscopy (SEM). Amperometric responses were measured as a function of different concentrations of glucose. Nanoporous electrodes lead to high enzyme loading. Stability, sensitivity, reproducibility and repeatability have been increased with the usage of cross-linking.

Enhanced glucose nano-biosensor by pulsed deposion of conducting polymer on ITO/Pt

This paper presents the effect of polypyrrole electro-deposition under pulsed electric field. The effect of pulsed electrochemical deposition can clearly be seen from the improved results of sensitivity and the linear range. The main reason behind this effect is the growth of different polypyrrole islands on the Pt/ITO substrate. Sensor performance were further enhanced by introducing glutaraldihyde as a cross-linking agent.

Performance Enhancement of Polypyrrole Based Nano-Biosensors by Different Enzyme Deposition Techniques

This chapter presents a comparison of results from a range of experiments carried out to investigate the performance dependency of polypyrrole based nano-biosensors on fabrication and enzyme immobilization techniques. The methods compared are drop casting, co-entrapment, and electrophoretic enzyme deposition techniques. Templated polypyrrole nanotube array sensors provided high sensitivities and quick response times. The size of the template pore diameter plays a vital role in enzyme immobilizing in terms of loading capacity. Application of a polymer cross linking agent provided enhanced sensitivities. However, the response time of the crosslinked sensor was little longer than that of the physical adsorption type enzyme loading. The templated nanostructures have recorded a glucose measurement sensitivity of 62.5 mAM−1 cm−2 with a response time of 6 s. In contrast to the templated method nano-corrugated polypyrrole structures were fabricated on Indium Tin Oxide planar surface using pulse deposition method. The electrochemically developed nano-corrugated polypyrrole sensors with enzyme loaded under high electric field of 1 kV/m have displayed an extremely high sensitivity of 325 mAM−1 cm−2. The study shows the enzyme immobilizing techniques play a great role in the conducting polymer based nano-biosensor performance.

Functional design of electrolytic biosensor

A novel amperometric biosensbased on conjugated polypyrrole (PPy) deposited on a Pt modified ITO (indium tin oxide) conductive glass substrate and their performances are described. We have presented a method of developing a highly sensitive and low-cost nano-biosensor for blood glucose measurements. The fabrication method proposed decreases the cost of production significantly as the amount of noble metals used is minimized. A nano-corrugated PPy substrate was developed through pulsed electrochemical deposition. The sensitivity achieved was 325 mA/(Mcm2) and the linear range of the developed sensor was 50-60 mmol/l. Then the application of the electrophoresis helps the glucose oxidase (GOx) on the PPy substrate. The main reason behind this high enzyme loading is the high electric field applied across the sensor surface (working electrode) and the counter electrode where that pushes the nano-scale enzyme particles floating in the phosphate buffer solution towards the substrate. The novel technique used has provided an extremely high sensitivities and very high linear ranges for enzyme (GOx) and therefore can be concluded that this is a very good technique to load enzyme onto the conducting polymer substrates.

Characteristics of glucose biosensors with glucose oxidase deposited under high electric field

This paper discuss the characteristics of newly developed glucose biosensors with glucose oxidase deposited under high electric field electrophoresis. Enzyme deposition has been verified using electrochemical impedance spectroscopy. The response time of the fabricated sensor has been found to be within 10s to 20s. the developed sensor shows a sensitivity of 0.13μA/cm2/mM and a linear range of 0-12mM.