Chapter 3 - Infrared spectroscopy for characterization of biomolecular interfaces

Abstract

Infrared spectroscopy can provide unique insights into the chemistry of surfaces for biological studies. Because the conformations of biological molecules impact their vibrational frequencies, infrared spectroscopy has long been used to characterize surfaces for use in biological studies. While many studies have used infrared spectroscopy to characterize the adsorption of proteins and other biological molecules to surfaces, there is increasing interest in the intentional functionalization of surfaces with molecular/biomolecular layers that provides selectivity, binding only to specific targets in solution. One of the biggest challenges to the use of infrared spectroscopy in biological research is the relatively low sensitivity and the fact that surfaces of practical interest many have strong absorption features that obscure the useful information. As a consequence, the successful use of infrared for biological research demands paying close attention to the detailed optical properties of the relevant interfaces and understanding how to optimize the sensitivity. In a practical sense, optimizing conditions for infrared are largely controlled by the reproducibility of the reference sample that is typically used to calculate the effective absorbance. The ability of infrared spectroscopy to identify the types and number of different chemical functional groups present at a surface in a nondestructive manner has contributed to its widespread application in chemistry and biology. Fourier transform InfraRed (FTIR) spectroscopy is a powerful tool for characterizing molecular and biomolecular layers on surfaces. The single-bounce external reflection geometry is extremely versatile because it can be applied to both transparent and absorbing materials.