The sensitive and selective detection of microbial pathogens is often hindered by time-consuming and complex methods. Sanford Asher, Xinyu Liu, and a team at the University of Pittsburgh, PA, USA, set out to create a simple sensor that relies on the combination of two-dimensional photonic crystals (2D PCs) with hydrogels formed from carbohydrate-binding proteins.
The researchers took the lectin Concanavalin A (Con A), which binds to mannans on cell surfaces, and crosslinked it to form Con A hydrogels. 2D photonic crystals were then embedded on the hydrogel surface. The resulting sensor is selective to the microbe Candida albicans.
When Concanavalin A binds to the surface mannans of C. albicans, the particle spacing of the PCs decreases and there is a blue-shift in the refracted light. This change can either be detected by the naked eye or measured spectroscopically. The Con A–mannan interaction is key to the specificity: the sensor showed negligible response with bacteria that lack surface mannans, such as E. coli, and a BSA protein hydrogel sensor control did not respond to the presence of C. albicans.
This combination of a 2D photonic crystal array with protein hydrogels leads to specific sensors with a shorter response time compared to filtration culture methods. The team is working towards hydrogels with a lower degree of crosslinking to increase the sensitivity and decrease the detection times.
- A Photonic Crystal Protein Hydrogel Sensor for Candida albicans,
Zhongyu Cai, Daniel H. Kwak, David Punihaole, Zhenmin Hong, Sachin S. Velankar, Xinyu Liu, Sanford A. Asher,
Angew. Chem. Int. Ed. 2015.