“…14,16 Meanwhile, new detection equipment such as quantum cascade laser and high signal-to-noise ratio (SNR) detectors also offer strong hardware support. 17,18 With the development of new technologies, good in vivo test results under strict experimental conditions have been obtained using mid-infrared absorption spectroscopy, 19 photoacoustic spectroscopy, [9][10][11][12] near-infrared (NIR) spectroscopy, 20 Raman spectroscopy, 8 etc., which have verified the feasibility of in vivo situation with these methods. For glucose measurement, each method has advantages and encounters challenges, for example, (i) Raman spectroscopy has good spectral specificity but needs high-power excitation light to irradiate skin; (ii) the glucose absorption at the mid-infrared band is strong, but the light can only propagate in a shallow depth due to the strong absorption of water in skin; (iii) photoacoustic spectroscopy, needs high-power excitation light to generate the acoustic signal; and (iv) the detection depth of NIR light (about several millimeters for 1000-1600 nm) is deeper than mid-infrared light and the influence of scattering caused by glucose becomes stronger.…”