199Photonic Crystal Biosensors
offering label-free detection. These changes are usually observed as red or blue shifts that
are directly related to the local density of the adsorbed molecules, and are very sensitive to
the target type and quantity. A variety of PhC-sensors have been developed based on this
active detection modality.
8.3.2 Active Photonic Crystal Devices
Polymerized crystalline colloidal arrays (PCCAs) are self-assembled 3D PhC lattices that
result from the electrostatic repulsion between highly charged spheres (Lee and Asher
2000). The repulsion allows the spheres to align in either a face-centered cubic (FCC) or a
body-centered cubic (BCC) array and can signicantly Bragg-diffract visible wavelengths.
The unique characterist ...