Designing Real-Time Biosensors and Chemical Sensors Based on Defective 1-D Photonic Crystals

In this letter, we have designed a new biosensing and chemical sensing structure based on 1-D photonic crystals. The proposed structure is a 1-D photonic crystal with a gradient refractive index (GRIN) defect layer in the middle of the structure and two microfluidic channels around the central defect layer. As a result of the introduced GRIN defect layer, which has a spatial refractive index distribution function, spatial defect modes will appear in the first bandgap. By irradiating a beam of light in a chosen frequency of defect modes to the structure, a ring-shaped intensity distribution appears on the output plane of the structure. The radius of this ring is highly sensitive to the refractive index of the fluid that is in two microfluidic channels. By variation of the refractive index, the radius of the ring-shaped intensity profile will change that can be detected by scanning slit beam profilers. The refractive index resolution of Δn = 0.0001 RIU that causes 3.6 μm change in the radius of the ring-shaped intensity can be detected by the introduced structure. One of the key advantages of the proposed sensor is the possibility of real-time monitoring of the variation of refractive indices due to its fast reply to the refractive index changes. As an important example in medical sciences, aggregation of some proteins can cause the variation of the effective refractive index of the solution, which can be monitored in real time by the highly sensitive designed sensor.