Terahertz Applications to Biomolecular Sensing

THz time domain spectroscopy of biomolecules was performed to determine applicability of the technique for chemical and conformational identification of biomolecules. Measurements were performed on samples of DNA, bovine serum albumin, collagen, hen egg white lysozyme, myoglobin, and bacteriorhodopsin as a function of temperature, hydration and photoexcitation. The results are compared to normal mode calculations. We demonstrate a clear resemblance of the observed broad and near featureless THz absorbance spectrum to the calculated density of normal modes. While the magnitude of the absorbance and the center of the broad response depends on biomolecular species, unique chemical identification would appear challenging. The observed dependence on hydration is in agreement with mass and dielectric loading, and the dependence on temperature is in agreement with decreasing conformational flexibility with reduced temperature. Finally THz absorbance dependence on the biomolecular conformation and mutation is demonstrated for bacteriorhodopsin.