Characterization of biomembranes by spectral ellipsometry, surface plasmon resonance and interferometry with regard to biosensor application

doi:10.1016/0956-5663(94)80105-3

Biosensors and Bioelectronics

Volume 9, Issue 2, 1994, Pages 139-146

https://doi.org/10.1016/0956-5663(94)80105-3 Get rights and content

Abstract

Phospholipid bilayers with transport proteins and antigen/antibody interfaces are considered to be suitable biosensor systems. The quality of such membranes or interfaces depends on the properties of the layers. Optical methods have proved to be an appropriate tool for characterizing those layers in situ and in a non-destructive manner. Two systems with potential for biosensor applications are characterized by some of these methods: phospholipid bilayer membranes spread from vesicle solution and protein-antigens both adsorbed on planar solid support.

The results of spectral ellipsometry, surface plasmon resonance (SPR) and spectral interferometry are compared with respect to quality of characterization, expenditure of sample preparation and measurement, and time resolution.

The phospholipid membranes adsorbed show a relatively low refractive index and a relatively high thickness. Bruggeman effective medium approximation is used to calculate the effective layer thickness. This result is compared to SPR measurements. A correlation between thickness and vesicle concentration may be detected.

Further, the test protocol of an immunoassay is examined by spectral interferometry and SPR. Thicknesses determined are compared to results obtained by applying spectral ellipsometry. The data measured by ellipsometry are in agreement with the molecular dimensions of the immunoglobulins. Differences between details can be explained by physical considerations.

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Ellipsometry is an optical technique for the characterization of thin films, generally used in optic/physics researches. In principle, measurement is performed by intensity measurement of polarized light reflecting off a sample surface. Since the linearly polarized light is often converted into elliptically polarized light after reflecting from the sample surface, this technique is called ellipsometry. On the other hand, after its unique advantages have been combined with the technological development in electronics and computing, using ellipsometry as a sensor is in focus in the last 3 decades. Nowadays, various ellipsometric techniques have been developed and reported as biomedical tools, particularly in sensor applications. As a sensitive tool, optical property changes of the sensor surface due to biomolecular interactions can be used in sub-nanomolar analyte detection. In this chapter, principles and history of ellipsometry, some milestones in the development of ellipsometric techniques, the place of ellipsometric techniques in biological research, benchmarking against other optical methods, and finally, future expectations in ellipsometry-based research are discussed. In addition, some review articles published with ellipsometry content since 2010 have been listed and summarized for the readers to access more detailed information.
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Among which, SE has been mostly employed in semiconductor material research as a quantitative method to determine the properties of thin films [26–29]. It is also used to study the interfacial dynamics of biological matter, particularly to characterize the self-assemblies of biomolecules such as lipid bilayers and lipid-protein complexes [30–35]. For example, E. Finot et al [33].
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The derived refractive index values are consistent with previous observations that smaller molecules, e.g. the hemin and thiol, form a more compact layer with a higher density and refractive index than large proteins, such as HSA and IgC [25]. The derived spectra are also consistent with literature data where the refractive index of the IgC antibody is from 1.39 to 1.45, while values of the refractive index of the albumin are in the range 1.32–1.4 [26–28]. For porphyrins, the refractive index is reported in the range 1.2–1.7 [29], and the extinction coefficient spectrum shows the Soret and broad Q-bands [30].
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Herein, we describe a real-time, label-free biosensing strategy for thrombin detection that uses the orientational properties of nematic liquid crystals (LCs) and the interactions between a polyelectrolyte and a phospholipid monolayer. The imaging principle is based on the disruption of the orientation of 4-cyano-4′-pentylbiphenyl by reorganized 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG) at the aqueous/LC interface. Positively charged, multiple arginine peptides (poly-l-arginine hydrochloride) interacted with negatively charged DOPG at the aqueous/LC interface, which caused reorganization of the phospholipid layer and induced an orientational transition of LCs from a homeotropic to a planar state. As a result, a dark to bright shift in the optical response was observed. Thrombin cleaves poly-l-arginine hydrochloride into peptides. Thus, when thrombin was added, the optical signals generated by the LCs reverted from bright to dark because of the weakened ability of the fragments to induce electrostatic interactions. The limit of detection of the LC-based sensor was 0.25 ng/mL (6.7 pM) thrombin, and the sensor was fully reusable. The detection limit of our LC-based interface sensor is 600 times lower than that of a previously reported enzyme-linked aptamer assay for the detection of thrombin. Thus, we have established a new, simple thrombin biosensor with high sensitivity and low interference.
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Characterization of biomembranes by spectral ellipsometry, surface plasmon resonance and interferometry with regard to biosensor application

Abstract

Thin Solid Films

Sensors and Actuators B

Bios. & Bioelectr.

Sensors and Actuators B

Sensors and Actuators

Biochim. Biophys. Acta