# Plastic biosensor grating
Bragg gratings are structures which involve a periodic variation in the refractive index or geometry of waveguide, so that certain frequencies of light are reflected off the grating while others are transmitted.
Since gratings can be designed to be extremely sentitive to a narrow band of frequencies, one possible application is to detect the presence of foreign molecules. If particles such as biomolecules are deposited on the device, it will no longer have the same reflective properties in the narrow band of frequencies for which it was designed. Therefore, carefully-designed Bragg gratings can be used as biosensors.
In this example, an optical biosensor grating is modeled to detect the presence of biomolecules. The grating is designed to be reflective over a narrow band around its resonant frequency which is modified by the presence of a biomolecule.
The design is inspired by Brian Cunningham, Bo Lin, Jean Qiu, Peter Li, Jane Pepper, Brenda Hugh, “A plastic colorimetric resonant optical biosensor for multiparallel detection of label-free biochemical interactions,” Sensors and Actuators B 85 (2002) (opens new window).
To view the full example in Python, please click here (opens new window).