Optical Fiber Biochemical Sensor Based On Fluorescence And Surface Enhanced Raman Spectra

Serious environmental pollution, epidemics and food safety issues made increasingdemands on equipments for detecting toxic and hazardous biochemical molecules.Existing biochemical detection equipments, such as mass spectrometer, flow cytometryand real-time fluorescent quantitative PCR, are often bulky and expensive. The existingexperiments could not realize fast detections as well as in situ testing, which limit theirpotentials in environmental monitoring, medical diagnostics, etc. Point of care testing(POCT) has attracted more attentions since its small structure, intelligent operation, fastand accurate detection adaptability. In order to obtain more stable and compact POCTsystem, we design and implement fiber biochemical sensors based on fluorescence andsurface enhanced Raman scattering (SERS), respectively. Based on their spectralfeatures, the applications of these fiber biochemical sensors are introduced in details.With the strong fluorescent signal intensity, optical fiber biochemical sensor basedon fluorescence enables the detection on low concentrations of labeled samples. Tobuild a compact fiber fluorescent sensor, standard optical fiber devices are used toconstruct the optical section and it is connected by fiber adapters to generate a morestable and compact structure. Combined taper-and-cylinder optical fiber probesdesigned and optimized by finite difference beam propagation method and ray tracingmethod are fabricated by tube-etching approach. Besides, using a series ofconcentrations of propidium iodide solutions, performance of the system is proved witha detecting limit better than1ng/mL. Finally, the fiber fluorescent sensor is used forspecific identification of dead bacteria. Using Escherchia coli (E. coli) O157:H7assample, the method for detecting dead bacteria has been estabilished and the testingprocedures have also been optimized. The results reveal the detecting limit of dead E.coli O157:H7could reach104cells/mL without the interference from live E. coliO157:H7and six other E. coli serotypes. The quantitation could be achieved from104to107cells/mL.SERS provides a trace detection of non-labeled samples for its spectral specificity.To achieve probes with simple preparation and good performance, fiber facet SERSprobes based on gold nanoparticles (AuNP) and gold-silver nanoalloys (Au-AgNA) are prepared by laser-induced deposition method. Via studying the performance of eachprobe, it is found AuNP based fiber probe owns good stability and dispersion whilepoor remote sensing, Au-AgNA based fiber probe has better remote sensing capacityand is also with good controllability. Moreover, to further improve the detectingsensitivity of the probe, combined taper-and-cylinder optical fiber SERS probe isdesigned and prepared which successfully achieves the detection of10-13M Rhodamine6G (R6G) samples. Furthermore, a compact fiber SERS sensor is constructed withintegrated optical fiber devices. With facet fiber SERS probe, the sensor realizedetection of10-3M R6G and10-4M methylene blue (MB) samples. While, withcombined taper-and-cylinder optical fiber SERS probe, the sensor realize detection of10-5M R6G and10-7M MB samples.