Rapid Response Fiber Optic Humidity Tracing Based on L-Lysine-Modified MXene for Finger Motion Detection

Robotic sensors should possess sub-second response times to ensure imperceptible latency in human-robot interactions considering the transmission speed of neural signals. Therefore, rapid-response sensors are crucial for human-robot interaction intelligent sensing applications. In this work, a fast-response fiber-optic humidity sensor for human finger motion detection was proposed based on the deposition of an L-lysine modified MXene (MXene-Lys) composite film on TFBG. The fabricated sensor demonstrated ultra-fast response kinetics, with equilibrium response and recovery times of 0.54 s and 0.48 s, respectively, in rapid cycling tests (50%-70% RH, 4 s/cycle). A linear transmittance response of 0.056 dB per %RH was observed as the ambient humidity varied, attributed to changes in the dielectric properties of the film. During a week-long humidity response stability test, the sensor exhibited excellent operational stability. Most significantly, experimental results confirmed that the sensor could accurately distinguish approach, dwell and retreat motions of a human finger at distances of 3 mm, 7 mm and 13 mm. In addition, basic hand gestures including one-, two- and three-finger movements across its surface were reliably identified.