Gelatin-based photonic hydrogels for visual detection of pathogenic Pseudomonas aeruginosa

Identification or detection of pathogenic microbes is one of the most important aspects to prevent and/or treat bacterial infection. In this study, we report a facile yet versatile strategy for preparation of gelatin-based photonic hydrogel sensors for visual detection of Pseudomonas aeruginosa (P. aeruginosa). The photonic hydrogels are generated by in-situ photopolymerization of acrylamide (AM), N, N’-methylenebis-(acrylamide) (BIS), and gelatin methacrylate (GelMA) with the self-assembled one-dimensional (1D) chain-like structures of carbon-encapsulated Fe3O4 nanoparticles (Fe3O4@C NPs). In the presence of P. aeruginosa, the hydrolysis of gelatin triggered by gelatinase reduces the crosslinking density of photonic hydrogel, expands the hydrogel in volume, increases the lattice spacing of the colloidal particles, and red-shifts the reflection spectra of the photonic hydrogel. The optical appearance variation of the photonic hydrogel, resulting from the reflection peak shift, can be observed by naked eyes. Besides, we show that the photonic hydrogels exhibit negligible appearance changes with the presence of Escherichia coli (E. coli), indicating their potential for distinguishing various bacteria by a simple structural color variation. This finding provides a proof-of-concept for a colorimetric sensor for visual detection of P. aeruginosa and demonstrates the great potential of the photonic hydrogels in visual detection of pathogens.