Planar Optical Waveguide Evanescent Wave ${\rm CO}_{2}$ Sensor Based on a Clad of Alstonia Scholaris Leaf Extract

An evanescent wave biosensor is designed and developed using a single mode planar optical waveguide based on a spin coated clad of leaf extract of Alstonia Scholaris. The fabricated sensor showed CO₂ concentration dependent response. The specialty of this sensor is that it can be used when stored at room temperature (25degC) up to a maximum of 25-30 days with 90% retention of original sensitivity. These CO₂ sensing biochips showed good operational efficiency for 10 cycles. The planar optical waveguide is versatile, easy to fabricate and can be used for ppm level CO₂ measurement with good sensitivity. Cross sensitivity with respect to humidity is studied. The sensor exhibited a short response time of 4-5 s and recovery time of 25 s with good repeatability and reproducibility.