In Situ Characterization of Biomaterials at Solid‐Liquid Interfaces Using Ellipsometry in the UV‐Visible‐NIR Wavelength Range

Abstract

Understanding interface processes has been gaining crucial importance in many applications of biology, chemistry, and physics. The boundaries of those disciplines had been quickly vanishing in the last decade, as metrologies and the knowledge gained based on their use improved and increased rapidly. Optical techniques such as microscopy, waveguide sensing, or ellipsometry are significant and widely used means of studying solid‐liquid interfaces because the applicability of ions, electrons, or X‐ray radiation is strongly limited for this purpose due to the high absorption in aqueous ambient. Light does not only provide access to the interface making the measurement possible, but utilizing the phase information and the large amount of spectroscopic data, the ellipsometric characterization is also highly sensitive and robust. This article focuses on ellipsometry of biomaterials in the visible wavelength range. The authors discuss the main challenges of measuring thickness and optical properties of ultra‐thin films such as biomolecules. The authors give an overview on different kinds of flow cells from conventional through internal reflection to combined methods. They emphasize that surface nanostructures and evaluation strategies are also crucial parts of in situ bioellipsometry and summarize some of the recent trends showing examples mainly from their research.

Sensing Layer for Ni Detection in Water Created by Immobilization of Bioengineered Flagellar Nanotubes on Gold Surfaces

“…In this study, a Woollam M2000 rotating compensator spectroscopic ellipsometer was used with a homemade Kretschmann–Raether flow cell (Figure ) for internal reflection surface plasmon-enhanced ellipsometry (SPR-SE) , that utilizes the surface plasmon resonance (SPR) effect . SPR is one of the most sensitive optical methods in the field of biorelated research, and its combination with SE provides further advantages, such as the possibility of constructing a complex optical model and utilizing the phase information.…”

“…Efforts for constructing and manufacturing portable heavy metal sensors have been increasing in the past years, applying a wide range of concepts, including optical- (e.g., colorimetric, fluorescent, , Raman, or plasmon-enhanced methods), electrochemical-, , and nanomaterial-based realizations . Each method has advantages and disadvantages depending on the requirements and target elements.…”

Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy

“…Such methods are established in electrocatalysis, battery, and bioelectrochemistry research, and they describe the spectroscopic or microscopic monitoring of electrochemical processes under operational conditions. − Among them, spectroelectrochemistry relies on the optical transparency of the working electrode, and with the implementation of ITO electrodes, this method was commenced to study redox-active proteins about 60 years ago . Up to now, the operando combination of electrochemistry and spectroscopic ellipsometry is rather rarely applied, possibly due to the challenges of optical modeling and the limitations of continuous and reasonably smooth layers. − Nonetheless, ellipsometry is a powerful tool to obtain both the dielectric optical response function (i.e., complex refractive index) of thin films as well as the electric properties for Drude-like behavior, which apply well to ITO thin films. − Furthermore, ellipsometry is a sensitive probe to monitor the adsorption of ultrathin layers at solid–liquid interfaces such as self-assembled monolayers and biomolecules. − Even specific immobilization of biomolecules and cells at functionalized hybrid interfaces for biosensing purposes can be traced. − More specifically, operando ellipsometry allows to study reversible ion intercalation processes upon electrochemical cycling in battery-related research. − For spatially resolved investigation, operando imaging ellipsometry is an emerging probe for battery electrodes, and it provides insights by monitoring the local change of ellipsometric parameters at selected wavelengths. , …”

Mapping and Imaging of Thin Films on Large Surfaces

“…Methods of thin‐film and interface characterization can be classified by numerous different aspects such as the way depth profiling is achieved, [ 1 ] according to illumination and detection, [ 3 ] or based on in‐line capabilities. [ 2 ] In Section 2, we briefly summarize the many opportunities and in the rest of the paper focus on those potentially applicable to large‐area mapping.…”