Glycated albumin based photonic crystal sensors for detection of lipopolysaccharides and discrimination of Gram-negative bacteria.

We present two types of two-dimensional (2D) photonic crystals (PC) hydrogel sensors based on glycated albumin (G-alb) as a proof-of-concept for utilizing recognition between G-alb and bacterial cell surface lipopolysaccharides (LPS) to detect and discriminate Gram-negative bacteria. The G-alb functionalized PC-G-alb hydrogel provides recognition of different LPS via hydrogen bonding and can discriminate different Gram-negative bacteria based on their LPS types. The hydrogel delivered LOD of 0.87 ng mL-1 for E.coli LPS, 153 CFU mL-1 for E.coli, 1.22 ng mL-1 for P.aeruginosa LPS and 225 CFU mL-1 for P.aeruginosa. On the other hand, LPS bioimprinted hydrogel (PC-G-alb-LPSimp) provides selective recognition of E.coli LPS with LOD 0.76 ng mL-1 and for E.coli 58 CFU mL-1, via generation of flexible specific cavities for E.coli and its LPS. The two hydrogels showed remarkable recoveries for both LPS and Gram-negative bacteria in the relevant samples of milk, orange juice, river water, and serum with a short response time of 6-12 min. In the binding process, the hydrogels shrink, and 2D PC particle spacing decreases with diffraction shift from green to blue. The diffraction shifts can be visually observed, measured through Debye's diffraction ring diameter by a laser pointer or determined from a spectrometer.