Development of Terahertz Time-Domain Spectroscopy for Properties Analysis of Highly Diluted Antibodies

This work represents the development of a three-band (Debye relaxation, intermolecular bending, and stretching vibrational bands) approach to the terahertz time-domain spectroscopy (THz-TDS) for the analysis of aqueous solutions of lactose saturated with highly diluted (HD) antibodies to interferon-gamma. Since THz-TDS is sensitive to a very slight changes in water properties, we aimed to assess its applicability for the analysis of HD antibodies. To evaluate water features in tested samples we also used Fourier transform infrared spectroscopy, considering the first overtone of intramolecular stretching vibrations of water molecules. We showed a broadening of the energy distribution of intermolecular bonds in the solution of HD substances in comparison to the control solution. This broadening corresponded to the presence of an active component even in HD samples. The results of both methods were similar; however, with the THz-TDS it was possible to analyze the changes in energy distribution of intermolecular (hydrogen) bonds in the solutions. Therefore, our approach to THz-TDS method is applicable for analyzing structural properties of the solutions containing HD antibodies and for the indirect investigation of altered aqueous properties in water solutions when direct measurements of a substance concentration are not available.