A comprehensive study of the resistance to biofouling of different polymers for optical oxygen sensors. The advantage of the novel fluorinated composite based on core-dye-shell structure

Abstract

The control of the biotechnological reactors for the wastewater processing and for multiple biotechnological syntheses often requires the in situ monitoring of the current concentration of dissolved molecular oxygen (DO) within the reactor. The method of determining of DO based on the quenching of the indicator dye phosphorescence is becoming readily used due to be unaffected by sulfur-containing compounds and relatively insensitive to hydrodynamic conditions as compared with the traditional electrochemical sensors (the Clark electrodes).Any types of sensors inserted into the biotechnological reactor however are objected to biofouling, that is the adsorption of the alive and dead cells of the microorganisms and also the formation of the attached polysaccharide matrix (the biofilm) on the surface of the sensor. Thus any DO sensor inserted into the bioreactor is subjected to two effects, that is 1) the actual change of the bulk DO concentration and 2) the deviation of the sensor readings due to the hindering of the oxygen diffusion to the indicator dye caused by the biofouling. In order to distinguish of these two phenomena we made two series of experiments in the present study. In the first series we subjected optical DO sensors with the sensitive layers manufactured of three different polymers that are polystyrene (PS), polybuthylmetacrylate (PBMA) and fluoroplast 42 (F42) to biofouling and tested the change of their response time in the pure model solutions with the known concentration of DO (in vitro experiments). In the second series we subjected optical DO sensors made of the same materials to the biofouling in the model biotechnological reactors and imitated the technological process of the aeration by purging for a while air throw the biological media (in situ experiments). The comparison of the sensors response in the first and in the second series can account for the contribution of the biofouling and the one of the bulk DO consumption processes.In order to facilitate the dispersion of the indicator dye (Pt(II) 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin, PtTFPP) in the fluorinated matrix and to improve the quality of the sensor we applied an original core-dye-shell technology, where the indicator dye is first absorbed onto the surface of SiO2 particles and then covered by the shell made of the salt of two fluorinated surfactants, that is trimethyl-1-propanaminium iodide (FC-135) and tetraethylammonium perfluorooctanesulfonate (FT-248).For the both in vitro and in situ experiments we used separately Saccharomyces cerevisiae yeast and Pseudomonas putida k12 bacteria.All polymeric sensor films were observed to be vulnerable to the cell absorption and biofilm formation. The sensor with the membrane made of the F42 filled with core-dye-shell particles, was the only to provide the possibility to determine the actual concentration of DO after two weeks of the incubation in the bioreactor, the damage of the film due to biofouling being not critical.