The construction of a rapid-scan mid-infrared Mueller matrix ellipsometer for the study of protein adsorption at the solid-liquid interface
The proposed project involves the design and construction of a real-time broadband infrared Mueller-matrix ellipsometer for the study of protein adsorption at the solid-liquid interface. By preparing an incident light field in a well-defined polarization state, and then characterizing the change in polarization that occurs upon interacting with a sample (for example, in a reflection geometry), it is possible to learn about many structural details of the molecules that interacted with the beam. This field in general is called polarimetry or ellipsometry. A recently-published technique from our group is capable of measuring all elements of the polarization transfer matrix, in the mid-infrared from 400-4000 wavenumbers. This is especially interesting since this region of the spectrum corresponds to molecular vibrations. As a result, analysis of the polarization fingerprints we observe can be directly related to sub-molecular features. If results corresponding to the vibration of a particular chemical functional group are analyzed quantitatively, it is possible to construct a distribution for the molecular bond orientation. If this is performed for multiple vibrational modes, we learn about the shape of molecules at the solid-liquid interface. Applications include investigating the biocompatibility of polymeric medical implants, thereby studying the propensity for protein denaturation upon adsorption at the polymer-aqueous interface. Although our existing experiment is powerful, and has demonstrated the proof-of-principle, it is slow, thereby limiting its applications to many scientific problems. The MITACS student working on this project would develop an instrument with the same capability, but of an entirely different design. Four photoelastic modulators (piezoelectric crystals) would be employed in order to modulate the light at various frequencies. Demodulation of the signals would then be performed in order to extract the optical, physical, and ultimately chemical properties of interest.