Terahertz Absorption Properties of Two Solid Amino Acids and Their Aqueous Solutions

Abstract

A new type of embedded cyclic olefin copolymer microfluidic chip was designed and combined with terahertz (THz) technology to study the effects of glycine and arginine on the THz wave absorption characteristics. This study aims to understand the interactions between solid amino acid molecules and between amino acid and water molecules and to determine the changes in their microstructure. By observing the intensity of the time domain spectra in the range of 0.2–2.6 THz, we found that, as the concentration of glycine and arginine increased, the THz transmission gradually decreased. It can be inferred that the molecular structure and quantity of different amino acids have different influence on the hydrogen bond, which affects the absorption coefficient in solution. It was also found that the terahertz technique is able to identify the solid amino acid species better, and it can also perform some species identification for liquid amino acids. These results provide a reference for future studies on the terahertz absorption properties of amino acid samples. Moreover, Gaussian16 software was used to calculate the terahertz spectra using the density functional theory, B3LYP functional, and 6-31G basis set. Additionally, Gaussian View6 video software provided the frequency values, molecular vibration modes of the theoretical absorption peaks of glycine, arginine, and its aqueous solutions in the frequency range of 0.2–2.6 THz, which offers theoretical support for future studies.

Perspective on Terahertz Applications in Bioscience and Biotechnology

“…However, with a thin (∼100 μm) sample path, the attenuation due to the absorption by liquid water is manageable, and changes in the attenuation due to the introduction of solvated biomolecules, cells, or other biological structures into the microfluidic chamber can therefore be observed . As noted above, these signatures are never in the form of narrow resonant absorption peaks, despite some recent (highly implausible) claims to the contrary . Even in a microfluidic channel, solvated molecules cannot manifest resonant absorption peaks at frequencies below 5 THz (and neither can liquid water).…”

“…95 As noted above, these signatures are never in the form of narrow resonant absorption peaks, despite some recent (highly implausible) claims to the contrary. 96 Even in a microfluidic channel, solvated molecules cannot manifest resonant absorption peaks at frequencies below 5 THz (and neither can liquid water). Rather, the observed changes are broadband and largely uniform across the frequency spectrum, representing a shift in the overall average dielectric constant of the liquid.…”

Terahertz spectroscopic detection of amino acid molecules under magnetic field

“…Finally, a computer is used for data acquisition and processing. The optical path diagram of the experiment is shown in our previous article [ 14 ].…”

“…In our previous article [ 14 ], we focused on the THz spectra of amino acid solutions in the absence of external conditions. In recent years, however, there has been an increasing interest in magnetic field-guided targeted therapy [ 15 ].…”

Experimental Detection and Simulation of Terahertz Spectra of Aqueous L-Arginine

“…In this paper, we investigated the absorption characteristics of L-arginine aqueous solution in THz band through simulation and experimental detection, because it is a semi-essential amino acid in the body, and its main physiological functions are lowering blood pressure [ 38 , 39 , 40 ], regulating blood glucose [ 41 ], protecting the liver [ 42 ], enhancing immunity and limiting tumor growth [ 43 , 44 , 45 , 46 , 47 ], benefit embryo survival and foetal development [ 48 , 49 , 50 , 51 ], accelerating wound healing [ 52 , 53 ]. At present, the THz properties of L-arginine are mainly tested with solid samples [ 54 , 55 ], and the computational accuracy in simulating the THz spectra of solid L-arginine still needs to be improved, and the research on microstructure and intramolecular interactions of L-arginine using THz spectroscopy needs to be deepened, and there is no simulation research on its aqueous solution. In the study of the THz characteristics of water-containing samples, some exploratory studies have been carried out to overcome the strong absorption of THz waves by water and thus achieve their THz spectra [ 56 , 57 , 58 ].…”