The latest achievements in the area of terahertz spectrometers based on transient effects are presented. The potential to use these spectrometers in various applications demanding the composition analysis of multicomponent gas mixtures simultaneously with a high sensitivity (at the ppb level) and resolving power is considered. The results obtained with the use of transient terahertz spectroscopy for medical diagnostics, security systems, etc. are shown.

Diabetes mellitus is a disease caused by the deficit or reduced efficiency of endogenous insulin resulting in blood sugar imbalance.¹ The development of diabetes is associated with impairments in the carbohydrate, protein, and lipid metabolism. It is almost always accompanied by a significant increase of the blood concentrations of glucose, corticosteroid hormones, and some other metabolites.¹ Protein glycation is a non-enzymatic reaction between the carbonyl groups of monosaccharides (e.g., glucose and fructose) and amino groups of proteins (e.g., albumin). Glycation initiates a cascade of protein modifications resulting in the loss of both secondary and tertiary protein structures.² Currently, the following tests are used in clinical practice to diagnose diabetes mellitus and monitor patients, for example, determining the level of glucose in venous blood plasma by the enzyme method or in capillary blood by an electrochemical method, as well as determining the level of glycated hemoglobin in whole venous blood by liquid chromatography.^3,4 All these methods require not only expensive equipment, but also reagents for their implementation. In addition, some studies can only be performed with fresh blood that cannot be stored for a long time. However, to determine some parameters, blood can be stored for a long time, but bulky freezers are required to store it. The development of methods for determining blood parameters and for storing biological samples will reduce the cost of performing diagnostic tests.^3,4

Nowadays, the problem of diagnostics of socially important diseases (diabetes, cancer diseases, etc.), including the early stage, attracts the great attention of scientific groups in the world. One of the new approaches opening new possibilities in diagnostics and treatment of various diseases is metabolomics. Metabolomics is a field of science that investigates the final and intermediate metabolic products of a biological system (cell, organs, or whole organism). The metabolomics can reveal the metabolites which can be the specific features of disease and can play a large role in diagnosis and prognosis for a disease. The media, containing the final and intermediate metabolic products in the human organism and useful for revealing the metabolites associated with diseases and pathologies, are exhaled breath, blood, urine, saliva etc.

Development of high-sensitivity and high resolution analytical spectroscopy is an area of active research interest currently. In the paper a method of two-frequency THz spectroscopy is presented. A laboratory model of spectrometer using two independent radiation sources of 118-178 GHz and 330-390 GHz ranges and a single detector with 500-2500 V/W sensitivity is presented. Test measurements allowed detecting two gases simultaneously with the minimal registration period of 4 μs and the hardware resolution of 1 kHz. These experiments proved this new trend in analytical spectroscopy to have wide application prospects for a variety of fundamental and applied scientific problems. In the first place, it is laboratory modeling of the processes of atmospheric and space chemistry, studying of their dynamics as well as transformations and changes of mixture composition. Besides, the proposed method can be applied to investigations of fast processes, detection of intermediate and short-lived products of chemical reactions.