Probing the existence of non-thermal Terahertz radiation induced changes of the protein solution structure

Abstract

During the last decades discussions were taking place on the existence of global, non-thermal structural changes in biological macromolecules induced by Terahertz (THz) radiation. Despite numerous studies, a clear experimental proof of this effect for biological particles in solution is still missing. We developed a setup combining THz-irradiation with small angle X-ray scattering (SAXS), which is a sensitive method for detecting the expected structural changes. We investigated in detail protein systems with different shape morphologies (bovine serum albumin, microtubules), which have been proposed to be susceptible to THz-radiation, under variable parameters (THz wavelength, THz power densities up to 6.8 mW/cm2, protein concentrations). None of the studied systems and conditions revealed structural changes detectable by SAXS suggesting that the expected non-thermal THz-induced effects do not lead to alterations of the overall structures, which are revealed by scattering from dissolved macromolecules. This leaves us with the conclusion that, if such effects are present, these are either local or outside of the spectrum and power range covered by the present study.

Perspective on Terahertz Applications in Bioscience and Biotechnology

“…For long-wavelength radiation, where the photon energy is far below that needed to induce chemical reactions (e.g., bond energies), and even below that of thermal photons at ambient temperature, one might wonder if any nonthermal mechanisms exist that can induce any biologically relevant changes. This question has been the topic of extensive studies for many years at lower frequencies and also, more recently, in the THz regime. − In most of the cases when the data have been interpreted to show a nonthermal effect arising from exposure to THz light, the experiments did not employ the needed controls and statistics to rule out a more prosaic interpretation, such as heating. − These are exceedingly challenging experiments, as (for example) it is almost impossible to rule out the possibility of spatially nonuniform transient heating with significant temperature variations on a subcellular length scale. Most notably, none of the purported nonthermal effects have ever been verified by a second independent research laboratory, and no plausible underlying mechanism has been proposed for how such effects could be induced by photons with only a few millivolts of energy.…”