Optical readout
Two types of photonic transducer arrays are being developed: photonic wire based sensors and photonic crystal based sensors. Both are fabricated using the same deep UV technology that is used for electronic chip fabrication, which opens the route towards cheap, disposable devices.
The photonic wire sensors are based on ring resonators, typically 10 micrometer across. The photonic crystal sensors are even smaller, but as sensitive, and are based on single-mode defects, waveguides, consisting of one missing row of holes in a planar photonic bandgap. When light is coupled into the sensors, they resonate at a certain wavelengths. Each sensing site has a specific capture zone where the PCR product hybridises with attached genetic probes.
The resonance frequency changes as the biomaterial attaches to the surface, providing the identification of the DNA sequences. Due to the small size, many sensors can be put next to each other on a single photonic chip. The sensitivity of the sensors, especially of the photonic crystals, may come close to the single-molecule limit. Technology is also being developed to couple in and read out light from the entire biosensor array at once.
