Diamond NV ^– -Centered Fiber Cantilever for Adaptive Contact and Noncontact Sensing

Temperature monitoring systems are now essential across a wide range of industries, where they play a vital role in upholding safety, enhancing efficiency, and meeting regulatory standards. Whether in healthcare or manufacturing, these systems are key to optimizing the conditions of the various processes of living organisms or inanimate objects that are required for optimal and efficient output. Herein, a simple and miniaturized fluorescence-based reusable and stable optical fiber cantilever probe is developed for precise and real-time temperature detection and application in monitoring the human respiration rate. The probe is fabricated by integrating negatively charged nitrogen vacancy (NV^-) centers-embedded polydimethylsiloxane (PDMS)-graphene composite (PGC) onto a tapered multimode fiber tip. The developed point probe can work either in wavelength or intensity interrogation and exhibits sensitivity as high as ∼53 pm/°C and 1.45%/°C, respectively, by taking the leverage of intrinsic fluorescence emission of NV^- centers and PGC absorption. The probe exhibits a response time of ∼1.2 s (corresponding to a temperature difference of ∼43.5 °C) for temperature monitoring of various target objects in contact (solid microwire, hot/cold liquid) as well as in noncontact (hot air) mode. Moreover, the fabricated miniaturized probe has successfully demonstrated the capability to analyze human respiration patterns across various conditions (workout, sitting, and meditation). This highlights its unique advantage of enabling noninvasive, noncontact diagnostics through ratiometric sensing, thereby paving the way for transformative applications in healthcare and diverse industrial sectors.