In this work, we theoretically investigated a unique and sensitive optical biosensor for detecting and
sensing blood plasma using a structurally chiral medium. The proposed biosensor is a defective onedimensional structure made from a structurally chiral material with 42¯ m point group symmetry
where the defect layer is considered as a channel for the blood plasma. The transmission and reflection
of the structure are investigated utilizing the transfer matrix method for the circularly polarized waves.
It is shown that a defect mode is created in the middle of the circular Bragg photonic band gap for the
right-handed circularly polarized waves and experiences a red shift by increasing the blood plasma
concentration. Also, it is observed that the sensitivity of the sensor can be increased by increasing the
thickness of the defect layer. In addition, we reveal that the increase of the tilt angle of the structurally
chiral medium results in the decrease of photonic band gap width and causes to blue-shift of the defect
mode. As a result, the performance of the sensor decreases by increasing the tilt angle. The proposed
structure has an easy and efficient manufacturing process, high stability and cost-effectiveness and can
provide real-time blood plasma biosensors.