Investigation On Fiber-optic Biochemical Sensors Based On Intermodal Interference

Owing to light weight, small size, low power operation, good resistance tocorrosion and electromagnetic interference, high measurement sensitivity and goodcompatibility with optical communication system, etc., fiber-optic sensors are widelyused in chemical analysis, biomedical and food processing and so on. This workstudied and implemented several fiber-optic biochemical sensors based on fiber-opticintermodal interference and biochemical-sensitive film coating technologies:1. Two label-free, Cs/PSS composite film-based fiber-optic interferometricimmunesensors with electrostatic self assembly film [Cs/PSS]10are proposed anddemonstrated. Mach-Zehnder and Michelson immunesensors are fabricated bywaist-enlarged fusion splicing, coating with [Cs/PSS]10film by self electrostaticassembly, and functionalized with goat anti-bovine IgG. When the sensors areimmersed in Anti-IgG antigen solutions, a shift of the interference fringe owing toAnti-IgG-IgG binding will be found, and thus immunesensing is realized. Theachieved sensitivities and detection limits are27.37nm/(ng/mm~2),5.91nm/(ng/mm~2) and0.181nM,4.941nM respectively, which are morecompetitive than those of most fiber-optic immunesensors.2. A fiber-optic highly sensitive humidity sensor by using a chitosan-coated,waist-enlarged bitaper-based Michelson interferometer is proposed and demonstrated.The humidity sensor is made by coating chitosan film onto the surface of theinterferometer by soi-gel technology. When the surrounding humidity varies, thecontent of water of the film will be changed, leading to the change of the intensityand refractive index of the film, and thus the interference fringe is modulated. HFetching of fiber cladding and film oxidization are ultilized to enhance the sensor’shumidity sensitivity. Experimental results show the measurement sensitivity issuccessfully improved by5-fold, reaching135pm/%RH, and the response andrecovery times are~5s and2s, respectively. It also demonstrates none obviousinterference of minim alkaline gases on the sensor.3. A polyvinyl alcohol/polyacrylic alcohol (PVA/PAA) coated fiber pH sensoris proposed and demonstrated. It’s formed by splicing one section of PCF with asingle mode fiber and making the air holes of the photonic crystal fiber (PCF) collapsed at two ends of the PCF, then coating PVA/PAA onto surface of the PCF.When the sensor is immersed in pH solution, changes of the pH value will causeswelling and deswelling of the film, thus leading to variations of the film’s refractiveindex and the interference pattern of the sensor. Experimental results show that thepH sensor coated with11%PVA/PAA hydrogel possess the highest pH sensitivityand detection limit of0.9nm/pH unit and0.022pH unit respectively, and theresponse and recovery times are15s and20s respectivey; what’s more, thesensor can be applicable for measurement of pH value of acid solutions withspecific ionic strength and small temperature fluctuations.