Study of sorption and the possibility of identifying highly volatile biomolecules in a mixture by e-nose piezo-sensor signals on microsorbents

Abstract

Prompt diagnosis is crucial for the effective treatment of any disease. Biological markers are widely used to diagnose various infectious and non-infectious diseases. Electronic nose sensor systems have recently become common for the detection of many biomarkers. Such systems are based on simultaneously measuring the analytical signal of several chemical sensors when they interact with the vapours of highly volatile substances. The aim of the study was to evaluate the possibility of identifying some volatile biomolecules, disease markers, in a mixture without prior separation using an array of 8 piezo-sensors, after sorption of the molecules on microsorbents.

The main technique for studying the adsorption of organic substances and water in the gas phase on the surface of microphases of nanomaterials of different nature is piezoquartz microweighing. Solid and polymeric sorbents of different weight (2-6 µg) deposited from suspensions in different solvents were used as sensitive layers: nanostructured biohydroxyapatite Ca₅(PO₄)₃OH (HA), carboxylated multi-wall carbon nanotubes (MWCNT_COOH), zirconium oxynitrate ZrO(NO₃)₂•∙2H₂O (ZR), AR grade. The adsorption of highly volatile organic compound vapours was studied under conditions of frontal inlet of the vapours into the open detection cell of the device. The objects of the study were some important biomolecules, condition markers emitted by the skin: butyric acid, water, benzaldehyde, and their mixtures of two types with different volume fractions of components.

It was determined that the lower the mass of the HA phase on the sensor, the greater its sensitivity to water vapour. Therefore, it is recommended to use sensors with a higher HA mass (greater than 2-3 µg) in order to compensate for the influence of the natural human biomolecule. The change in mass has no effect on the sensitivity of the microweighing of organic negative biomolecules.

According to the results of correlation analysis, there is a direct and very reliable relationship between the qualitative identification parameters (A_i/j) and Henry’s thermodynamic coefficient ratios (G_i/j) for the studied substances. The relationship is quantitative for almost all the parameters. This confirms the validity of the previously proposed parameters for identifying substances by single sensor responses in an array (∆F_max).

We confirmed that it was possible to carry out a qualitative analysis of a gas mixture without prior separation using signals from an array of 8 piezo-sensors with different modifiers based on the parameters A_i/j. The parameters are directly proportional to the thermodynamic ratios of Henry’s coefficients (G_i/j) obtained under steady-state conditions.

This greatly simplifies electronic nose learning, sorbent deposition, and justification of sensitivity and selectivity in the analysis of mixtures of biomolecules. The sensitivity of butyric acid and benzaldehyde vapour microweighing with the proposed array was estimated to be at least 0.2371 Hz·s·dm³ /g and 0.03010 Hz·s·dm³ /g, with 5-10 times the excess of water vapour permitted. This supports the solution of some diagnostic issues by scanning the mixture of gases emitted by human/animal skin in 60-80s.