Spectroscopic Ellipsometry and Quartz Crystal Microbalance with Dissipation for the Assessment of Polymer Layers and for the Application in Biosensing

Abstract

Polymers represent materials that are applied in almost all areas of modern life, therefore, the characterization of polymer layers using different methods is of great importance. In this review, the main attention is dedicated to the non-invasive and label-free optical and acoustic methods, namely spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D). The specific advantages of these techniques applied for in situ monitoring of polymer layer formation and characterization, biomolecule immobilization, and registration of specific interactions were summarized and discussed. In addition, the exceptional benefits and future perspectives of combined spectroscopic ellipsometry and QCM-D (SE/QCM-D) in one measurement are overviewed. Recent advances in the discussed area allow us to conclude that especially significant breakthroughs are foreseen in the complementary application of both QCM-D and SE techniques for the investigation of polymer structure and assessment of the interaction between biomolecules such as antigens and antibodies, receptors and ligands, and complementary DNA strands.

Keywords: application for biosensing; biosensors; characterization of polymer layers; conducting polymers; immunosensors; molecularly imprinted polymers (MIPs); quartz crystal microbalance with dissipation (QCM-D); spectroscopic ellipsometry.

Figure 1

Operation principle of spectroscopic ellipsometry.

Figure 2

Schematic representation of ellipsometric measurements. E–electric field vector, E_s–component of electric field vector perpendicular to the plane of incidence E_p–component of electric field vector parallel to the plane of incidence, n–refractive index of the sample, k–extinction coefficient of the sample, E_rs, E_rp–perpendicular and parallel reflected field amplitudes. Ψ–ellipsometric parameter that corresponds to amplitudes ratio upon reflection, Δ–ellipsometric parameter that corresponds to phase difference between p- and s- polarizations, α- angle of incident light.

Figure 3

Schematic representation of QCM-D measurement and operating principle. Δf–time depended change in frequency, ΔD–time depended change in energy dissipation.

Figure 4

Preparation and working principle of molecularly imprinted polymer (MIP) on a QCM-D sensor disk.

Figure 5

Schematic representation of combined SE/QCM-D technique used for the measurements. Ψ–ellipsometric parameter that corresponds to the light amplitude ratio upon reflection, Δ–ellipsometric parameter that corresponds to light wave phase shift, Δf–time depended change in frequency, ΔD–time depended change in energy dissipation.