Development of Multiple Analytical Labels for Volatile Organic Compounds Based on the Results of Sorption on CdS Quantum Dots in Chitosan without and with Modification by Rhodamine 6G

Abstract

Analytical solutions with luminescent labels for the analysis of gaseous media and the detection of volatile organic compounds are discussed. Such solutions can potentially be applied to the development of optical and sorption gas sensors, smart label fillers, and test systems with various carriers for the detection of chemical biomarkers in living systems. To solve the problem, it was proposed to develop and study the properties of modifiers based on cadmium sulfide quantum dots. The aim of the work was to study the sorption properties of CdS quantum dots obtained by a method improved along the line of “green chemistry”, with stabilizing pure and modified chitosan shells modified by rhodamine 6G. Sorption properties of various phases based on quantum dots were studied at a temperature of 22 ± 1°C by a highly sensitive direct piezoelectric quartz microweighing method with a resolution of up to 10^–9 g by the sorbent mass in vapors of volatile compounds. The selectivity of the phases based on cadmium sulfide quantum dots in low-mass chitosan (5–10 μg) with respect to volatile organic compounds of different classes was estimated. The relative selectivity and sensitivity of weighing vapor on different phases were evaluated by parameters A(i/j), showing how many times the sorption properties of CdS phases in chitosan differ without and with additions of rhodamine 6G. The method of direct weighing allows us to estimate the rates of sorption and desorption and the capacity of the sorbent phases. It has been found that the substances belonging to one selectivity group in terms of A(i/j), for example, water and ethanol, are characterized by different sorption rates. This feature can be applied to solve problems of the separate detection of vapors; they can be identified at different moments of the exposure of piezobalances with phases based on CdS quantum dots in chitosan without and with additions of rhodamine 6G. The use of cadmium sulfide quantum dots in chitosan as a sorbent of vapors of organic compounds significantly affects sorption kinetics and efficiency. The modification of chitosan with rhodamine 6G changes the sorption properties of quantum dots in chitosan, which can be used for the design of new sorbents for sensor systems. Simple algorithms are proposed for solving problems of the recognition of vapor of volatile compounds according to calculated parameters, even for non-selective sorption systems. Programming the approach can significantly increase the speed of decision-making in integrated analytical systems, for example, “electronic noses” based on sensors, including those with the studied phases. It was found that the mass of the phase based on cadmium sulfide quantum dots in chitosan does not affect sorption properties in the micromass range, which is traditional for nanostructures. Changes in the luminescent properties of phases based on cadmium sulfide, as a possible visually detected analytical response, will be discussed in the next paper.