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Zbigniew. Brzózka, Michal Chudy, Artur Dybko, Kamil Zukowski

Department of Microbioanalytics, Faculty of Chemistry, Warsaw University of Technology; Noakowskiego 3, 00-664 Warsaw, Poland

Determination of the biological important compounds concentration such as carbohydrates (D-glucose, D-fructose, D-galactose, and others) is of great significance in medicine and industry. The possibility of determination of such substances is important because of their connection with various diseases (diabetes, renal glycosuria, cystic fibrosis, phenylketonuria, Parkinson's disease). However, the current methods used to determination of their concentration are imperfect and limited in quite a few ways. These are mostly indirect methods, which determine the concentration of the product resulting from the conversion of such substances as sugar by means of a specific chemical reaction. Therefore, research is conducted in order to create a method for direct determination of sugars concentration. Such possibilities are offered by boronic acids, which as a result of reaction with monosaccharides, form a five- or six-membered cyclic esters. In addition, considering the great easiness in modifying the structure of the compounds, they can be easily combined with the spectrofluorimetric detection, which is one of the most sensitive instrumental methods of analysis. In this case it is of great importance, because of the opportunity to register even the smallest changes in the concentration of the analyte. Another challenge is to conduct dermination of this type of analytes in a fast and cheap manner. For this reason, in recent times there has been a rapid development of systems such as Lab-on-a-chip, which minimize the amount of reagents used, and thus shorten time and reduce costs of the analysis.
The aim of this paper was to develope a fully integrated, automated microsystem for non-enzymatic determination of monosaccharides concetration in aqueous solutions. This microsystem consists of several basic elements including: a turning multi-channel microvalve, piezoelectric micropumps, micromixer and flow cuvette, in which fluorimetric detection takes place. A turning micro-valve controls the order of the introduction of calibration solutions to the micromixer. A boronic acid solution (quinoline-8-boronic acid) enters the micromixer through a separate microchannel. In the presented microsystem a passive, fully 3D micromixer was used, in which the reaction of boronic acid with sugar takes place. As a result of this reaction a cyclic ester is formed, whose solution shows a higher fluorescence intensity than the stock solutions. Most of the components of the presented microsystem have been performed in poly(methyl methacrylate) (PMMA). PMMA is a readily available material and relatively inexpensive. Its additional advantage is a variety of methods of the formation and processing. In this case, all the structures were made by using a micromilling method by means of a micromilling machine controlled numerically.

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