A system for determining whether interaction occurs between a trial substance and a target substance. The system includes a photonic crystal sensor having a photonic crystal structure and a defect member disposed adjacent the photonic crystal structure. The defect member defines an operative surface able to receive the target substance and the trial substance. The system further includes a light source that inputs a light signal to the photonic crystal structure and the defect member. The light signal is internally reflected, and a resultant output signal is outputted. The output signal relates to whether the trial substance interacts with the target substance at the operative surface. Furthermore, the system includes an identity detector that identifies the trial substance that interacts with the target substance.