Bacterial hypoxia-responsive liquid-solid phase transition of conductive hydrogel

A hypoxia-responsive hydrogel is synthesized using polyvinyl alcohol (PVA), gelatin, pyrogallol (PG), and silica-integrated polymer dots (si-PD), which undergoes phase transitions between liquid and solid states, with corresponding changes in conductivity and fluorescence depending on the oxygen concentration in the environment. Hydrogel formation in the presence of O₂ occurs via the oxidation of PG, forming a polyphenolic compound that interacts with the amine functional groups of gelatin, thereby resulting in crosslinking. The storage modulus of si-PD/PG@Gel-PVA hydrogel, aerated with O₂ for 24 h, exhibit a higher value of 289.4 Pa, compared with 1.2 Pa for those aerated with N₂. Similarly, the viscosity of N₂-aerated hydrogel solution after 24 h was 45.36 Pas, which was lower than that of the O₂-aerated hydrogel (289.63 Pas) after 24 h. In vitro studies demonstrated that si-PD/PG@Gel-PVA exhibits lower electrical resistance at bacterial concentration of 10⁸ CFU/mL than without bacteria, with a resistance of 40.55 kΩ (S. aureus) and 41.56 kΩ (E. coli). Furthermore, water samples exhibited a resistance of 68.3 kΩ (river water) and 51.5 kΩ (wastewater), which are lower than that of clean water at 105.5 kΩ, indicating no hydrogel formation and contamination of the sample. Additionally, confocal microscopy images of bacteria-containing water treated with the si-PD/PG@Gel-PVA system retained bright blue fluorescence, in contrast with the untreated samples. The si-PD/PG@Gel-PVA system is capable of distinguishing bacterial contamination in water by modulating its electrical, mechanical, and optical properties via phase transitions from liquid to solid.