Liquid Crystal Based Label-Free Optical Sensors forBiochemical Application

Biochemical sensors have important applications in biology,chemistry,and medicine.Nevertheless,many biochemical sensors are hampered by intricate techniques,cumbersome procedures,and the need for labeling.In the past two decades,it has been discovered that liquid crystals can be used to achieve the optical amplification of biological interactions.By modifying recognition molecules,a variety of label-free biochemical sensors can be created.Consequently,biochemical sensors based on the amplification of liquid crystals have become one of the most promising sensors.This paper describes in detail the optical sensing principle of liquid crystals,sensing devices,and optical detection technologies.Meanwhile,the latest research findings are elucidated.Finally,the challenges and future research directions are discussed.

High-sensitivity and fast-response fiber optic temperature sensor using an anti-resonant reflecting optical waveguide mechanism

Temperature sensing is essential for human health monitoring.High-sensitivity(>1 nm∕℃)fiber sensors always require long interference paths and temperature-sensitive materials,leading to a long sensor and thus slow response(6–14 s).To date,it is still challenging for a fiber optic temperature sensor to have an ultrafast(~ms)response simultaneously with high sensitivity.Here,a side-polished single-mode/hollow/single-mode fiber(SPSHSF)structure is proposed to meet the challenge by using the length-independent sensitivity of an anti-resonant reflecting optical waveguide mechanism.With a polydimethylsiloxane filled sub-nanoliter volume cavity in the SP-SHSF,the SP-SHSF exhibits a high temperature sensitivity of 4.223 nm/℃ with a compact length of 1.6 mm,allowing an ultrafast response(16 ms)and fast recovery time(176 ms).The figure of merit(FOM),defined as the absolute ratio of sensitivity to response time,is proposed to assess the comprehensive performance of the sensor.The FOM of the proposed sensor reaches up to 263.94(nm/℃)∕s,which is more than two to three orders of magnitude higher than those of other temperature fiber optic sensors reported previously.Additionally,a threemonth cycle test shows that the sensor is highly robust,with excellent reversibility and accuracy,allowing it to be incorporated with a wearable face mask for detecting temperature changes during human breathing.The high FOM and high stability of the proposed sensing fiber structure provide an excellent opportunity to develop both ultrafast and highly sensitive fiber optic sensors for wearable respiratory monitoring and contactless in vitro detection.