Biomedical subjects

E Gizeli

Publications and source records attributed to E Gizeli.

6 recordsLinked to original sources

PubMed2003

Sensitivity of the acoustic waveguide biosensor to protein binding as a function of the waveguide properties.

The aim of this work is to study the effect of operating frequency, piezoelectric substrate and waveguide layer thickness on the sensitivity of the acoustic waveguide sensor during the specific binding of an antibody by a protein. Shear horizontal (SH) wave devices consisting of (a) a LiTaO3 substrate operating at 104 MHz, (b) a quartz substrate operating at 108 MHz and (c) a quartz substrate operating at 155 MHz were coated with a photoresist polymer layer in order to produce acoustic waveguide devices supporting a Love wave. The effect of the thickness of the polymer layer on the Love wave was assessed by measuring the amplitude and phase of the wave before and after coating. The sensitivity of the above three biosensors was compared during the detection of the specific binding of different concentrations of Immunoglobulin G in the range of 0.7-667 nM to a protein A modified surface. Results indicate that the thickness of the polymer guiding layer is critical for obtaining the maximum sensitivity for a given geometry but a trade-off has to be made between the theoretically determined optimum thickness for waveguiding and the device insertion loss. It was also found that increasing the frequency of operation results in a further increase in the device sensitivity to protein detection.

Acoustics↗

PubMed2003

Comparative study of IgG binding to proteins G and A: nonequilibrium kinetic and binding constant determination with the acoustic waveguide device.

The aim of this work was to measure and compare the binding constants of antibody immunoglobulin G (IgG) to bacterial cell wall proteins, streptococcal protein G and Staphylococcus aureus protein A, using an acoustic wave sensor. Devices, which used shear-horizontal acoustic waves propagating in a waveguide configuration at 108 and 155 MHz, were employed in the detection of apparent IgG binding constants at the solid-liquid interface in the range of 6.7-667 nM IgG. Real-time data during IgG-protein G and IgG-protein A binding yielded apparent association constants of 3.29 x 10(4) and 8.02 x 10(3) M(-1) s(-1) leading to equilibrium constants of 1.13 x 10(8) and 2.90 x 10(7) M(-1), respectively. The measured apparent rate constants are consistent with literature reports of higher affinity of protein G for IgG. Furthermore, protein binding through the Fc region of IgG is suggested to occur below 333 nM, while different mechanisms are suggested to occur above 333 nM. For the first time, nonequilibrium studies of IgG-protein G and A binding at a solid-liquid interface has yielded valuable quantitative kinetic information about binding mechanisms. The promise of this detection method is shown by providing quick determination of binding constants with low sample volumes.

Acoustics↗

PubMed2001

Pulse mode operation of Love wave devices for biosensing applications.

In this work we present a novel pulse mode Love wave biosensor that monitors both changes in amplitude and phase. A series of concentrations of 3350 molecular weight poly(ethylene glycol) (PEG) solutions are used as a calibration sequence for the pulse mode system using a network analyzer and high frequency oscilloscope. The operation of the pulse mode system is then compared to the continuous wave network analyzer by showing a sequence of deposition and removal of a model mass layer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC) vesicles. This experimental apparatus has the potential for making many hundreds of measurements a minute and so allowing the dynamics of fast interactions to be observed.

Journal Article↗

PubMed2000

Study of the sensitivity of the acoustic waveguide sensor.

The sensitivity of the acoustic waveguide sensor to mass deposition in the presence of liquid was optimized as a function of the over-layer thickness. The waveguide geometry consisted of a 0.2-2.2-microm poly(methyl)methacrylate (PMMA) over-layer deposited on the surface of a shear acoustic wave device and supported a Love wave. The response of each polymer-coated waveguide was initially assessed by monitoring the frequency and insertion loss of the device in the presence of air. Sensitivity to viscous and mass loading was studied by recording the amplitude and phase of the wave during the application of water and of a supported lipid bilayer, respectively, on the device surface. Supported bilayers are a versatile system for mass calibration in the presence of liquid because they can be formed spontaneously on a hydrophilic surface, resulting in a layer of reproducible mass density. Results clearly showed that the response of both amplitude and phase depends on the over-layer thickness and increases with the thickness of the polymer layer. Phase was generally found to be more sensitive than amplitude to both viscous water and mass loading. The maximum sensitivity to vesicles deposition was measured at 250 cm2 g(-1) and was detected when 1.3 microm of PMMA was used as a waveguide layer. Results showed that the sensitivity of the acoustic wave sensor can be improved by simply increasing the thickness of the PMMA and that supported phospholipid layers can form an ideal system for both mass calibration and interfacial modification.

Journal Article↗

PubMed1997

Antibody binding to a functionalized supported lipid layer: a direct acoustic immunosensor.

A direct immunosensor has been developed using an acoustic wave device as a transducer. The device is based on an acoustic waveguide geometry that supports a Love wave. The biorecognition surface, formed on a gold layer, consisted of a biotinylated supported lipid layer which specifically bound streptavidin and, subsequently, biotinylated goat IgG. The modified surface was used as a model immunosensor and successfully detected rabbit anti-goat IgG in the concentration range 3 x 10(-8) - 10(-6) M. Using the anti-goat IgG binding isotherm and the time-resolved measurements of antibody binding, both the binding and rate constants of the reaction were determined. The specificity of each binding step was studied with the acoustic wave device, and it was concluded that the phospholipid bilayer showed a good suppression of nonspecific binding. Comparative measurements using surface plasmon resonance allowed the response of the immunosensor to be quantitatively correlated with mass binding to the surface.

Acoustic Stimulation↗

PubMed1996

Immunosensors.

Immunosensors are important analytical tools for monitoring antibody-antigen reactions in real time. Recent developments in immunosensors have produced systems that allow rapid and continuous analysis of the binding event without the requirement for added reagents or separation/washing steps. As a result, great interest has focused on commercializing immunosensors for applications in areas such as clinical, environmental and food analysis.

Animals↗