Biomedical Optic Fiber Sensing Characteristics Based On Liquid Crystal Media

The relation between liquid crystal and living organism has been the hot spot in biomedicalengineering since the day liquid crystal was found. Because liquid crystal is sensitive to theexternal environment, liquid crystal has been as the sensitive media material and applied tobiomedical sensing fields. To explore a novel, label-free biomedical optical fiber sensor, thebiomedical optical fiber sensing characteristics based on liquid crystal media have been proposedand studied. The biomedical optical fiber sensing technology based on liquid crystal not only hasthe advantages of side-polished fiber (SPF) including low cost, immunity to electromagneticinterference, multiplexing, and small size, but also possesses the sensing characteristics of liquidcrystal, leading to the new breakthroughs in biomedical sensing fields.To verify the feasibility of the biomedical optical fiber sensor based on liquid crystal media,the sensing characteristics of SPF for determination of nematic liquid crystal (NLC) orientationand the helical structure change of cholesteric liquid crystal (CLC) have been studied, and theresponse characteristics of the orientation and helical structure changes of mixing cholestericliquid crystal for the phosphatidylcholine concentration have been investigated.Firstly, the sensing characteristics of SPF for determination of NLC orientation have beenstudied. The mechanical rotating method and voltage modulation method are designedrespectively to change the orientation of NLC on the polished surface. Our experimental resultsshowed that the orientation change of NLC can indeed be sensed by monitoring the outputoptical power transmitted through the SPF. With mechanical rotation, when the rotation angleincreased from0°to90°, the output optical power increased by28.10dB. Within the angle range from0°to30°, the response is almost linear. The average response slope is about0.359dB/°,which indicates relatively high sensitivity. With voltage modulation, when the applied ACvoltage increased more than50V, the output optical power jumped up1.4dB. These experimentalresults indicate that SPF can be used to determine the orientation change of NLC. In particular,there exists a possibility that a SPF overlaid with NLC on its polished surface can potentially bemade into a small transducer of a biosensor.Secondly, the response characteristics of SPF for CLC helical structure changes caused bytemperature have been studied. The temperature sensing characteristics of SPF coated with CLChave been obtained. Our experimental results showed that the helical structure change of CLCcaused by temperature can be sensed by monitoring the transmission spectrum of SPF. In therange of20℃to50℃, with the temperature increased, the loss peak of the transmissionspectrum averagely shifted by about12.98nm/10℃. The experiment results indicate a SPFcoated with the CLC can realize the temperature sensing with high sensitivity.Finally, the response characteristics of the orientation and structure changes of the mixingcholesteric liquid crystal for phosphatidylcholine concentration have been studied. A noveloptical measurement method of phosphatidylcholine concentration based on the mixingcholesteric liquid crystal compounded by CLC and NLC has been proposed and demonstrated.Our experimental results showed that the phosphatidylcholine concentration change can besensed by monitoring the reflection spectrum of the mixing cholesteric liquid crystal. With thephosphatidylcholine concentration increased from0mM to0.1mM, the reflection spectrumred-shifted206.79nm. The experiment results verify the feasibility of the phosphatidylcholineconcentration optical measurement method based on the mixing cholesteric liquid crystal and indicate the mixing cholesteric liquid crystal can realize the phosphatidylcholine concentrationsensing.The innovations of this research are as follows: A novel optical measurement method ofphosphatidylcholine concentration based on the mixing cholesteric liquid crystal has beenproposed and demonstrated for the first time. The sensing characteristics of side-polished fiber(SPF) for determination of nematic liquid crystal (NLC) orientation and the helical structurechange of cholesteric liquid crystal (CLC) have been obtained for the first time. The temperaturesensing characteristics of SPF coated with cholesteric liquid crystal have been obtained.