A noninvasive, painless, and sensitive approach to precise glucose monitoring for ever-increasing diabetics worldwide is critical to reduce the long-term severe complications of diabetes. Recently, wireless sensing in the sub-terahertz and terahertz (THz) bands between 100 GHz and 10 THz opens the door to biosensing and bioimaging for innovative medical applications beyond radar and localization. Here, we report the fingertip blood-free non-invasive glucose monitoring using three-dimensional (3D) eye diagram analysis of THz wireless data to replace current blood finger-stick glucose strips and further realize remote healthcare of THz joint communication and sensing. We demonstrate the accurate estimation of blood glucose concentrations by transmitting a 10 Gbps on-off keying-modulated THz wireless data to a fingertip and measuring a 3D eye diagram of the THz wireless signal reflected from the fingertip. In particular, the method addresses personal variation and sensing accuracy through multivariate analysis of eye parameters including eye height, eye width, Q factor, and probability difference. The experimental results clearly demonstrate that the data waveform is distorted and the probability difference between the logic one and zero levels in the histogram increases in proportion to the glucose concentration. The clinical trial results for THz glucose monitoring clearly show a strong linear correlation between the eye parameters of fingertip and blood glucose concentrations and the consistency between glucose dynamics in blood and fingertip in the oral glucose tolerance test. This approach provides an innovative and effective route for developing daily diabetes management and THz joint sensing and communication.
We report a fiber-optic plasmonic probe with nanogap-rich gold nanoislands for on-site surface-enhanced Raman spectroscopy (SERS). The plasmonic probe features nanogap-rich Au nanoislands on the top surface of a single multimode fiber. Au nanoislands were monolithically fabricated using repeated solid-state dewetting of thermally evaporated Au thin film. The plasmonic probe shows 7.8 × 106 in SERS enhancement factor and 100 nM in limit-of-detection for crystal violet under both the excitation of laser light and the collection of SERS signals through the optical fiber. The fiber-through measurement also demonstrates the label-free SERS detection of folic acid at micromolar level. The plasmonic probe can provide a tool for on-site and in vivo SERS applications.
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