Fiber Optic Humidity Sensor Based On Spider Dragline Silk

Optical fiber sensors use optical signals as transmission carriers and are commonly used to sense physical parameters such as temperature,mechanical strain,vibration,pressure acceleration,and rotation,but they are not sensitive to chemical or biological compounds.Conventional fiber optic humidity sensors mostly use a method of applying a polymer moisture sensitive material to the surface of the fiber for moisture sensing.However,common fiber optic sensors do not exhibit biocompatibility and thus limit their development of in vivo biosensing.In recent years,many biomaterials have demonstrated superior structure and better performance than synthetic materials,which makes natural biomaterial a new choice in future research and development of humidity sensors.As a natural biomaterial,spider silk has good biocompatibility,bioabsorbability,biodegradability,flexibility and tensile properties,and has a lower ecological footprint than synthetic polymers.Silk fibres are held together by reversible hydrogen bonding that can be changed by polar solvents,which makes silk an ideal for detecting modifying agents such as water molecules,acids,bases,etc.This paper proposes a humidity sensing device that based on spider dragline silk and SMS(Single mode-Multimode-single mode)fiber structure.The sensing device uses spider dragline silk as a moisture sensitive material and spirally winds it on the surface of the fiber at a fixed period.Based on the light-guiding characteristics of the spider dragline silk,some of the light mode transmitted in the fiber core will be coupled into the spider cladding,and lost in the external environment.In this way,we construct a characteristic trough which can present the loss characteristic of the output spectrum of the designed device.When the relative humidity(RH)changes,the combination of spider silk proteins with water molecules results in the change of silk diameter and effective refractive index,which ultimately leads to a change in the characteristic trough.The experimental results show that the sensitivity of the proposed sensing structure to humidity is 1.117 nm/%RH when the relative humidity changes from 33%to 95%.Based on spider dragline silk,this humidity sensor is simple in structure,easy to manufacture,fast in response,high in sensitivity and environmentally friendly.The method can be used to measure ambient humidity and apply spider silk as a moisture sensitive material in the field of fiber sensing.This task has an important driving significance for the practical application of fiber optic humidity sensors combined with natural biomaterials.Compared with the traditional fiber optic humidity sensing structure,the sensing structure based on spider dragline silk as a moisture sensitive material has development potential ang many significant advantages.This structure breaks the limit of traditional moisture sensitive materials,and can also simplify the fiber sensing structure.Using spider dragline silk as a moisture sensitive material can not only easily solve the problem of non-biocompatibility of traditional materials,but also make the fiber moisture sensor combines the advantages of high sensitivity and high response speed,with the characteristics of the sensors based on SMS structure,such as small in size,widely use,good anti-interference ability,high resolution and so on.