Theoretical design of a second harmonic mode biosensor based on layered metastructures for blood tissue detection and temperature sensing

Second harmonic generation (SHG) is a process of doubling the frequency of the incident light, allowing for non-invasive detection. However, temperature factors often interfere with the detection of the refractive index of the sample, reducing measurement accuracy. Therefore, based on the transfer matrix method, a layered metastructure (LMS) is theoretically proposed to realize SHG, measuring the changes in refractive index (RI) and temperature simultaneously. The proposed LMS is based on a layered structure composed of LiNbO 3 1, LiNbO 3 2, air, SiO 2 , and one detection cavity, where detected samples like blood tissues can be injected into the detection cavity, causing the RI changes of the detection cavity. A sensing matrix is utilized to demonstrate the feasibility of simultaneous measurement, addressing cross-sensitivity issues. By tracking frequency shifts in the measured values, the dual sensitivity of the fundamental waves (FW) and second harmonic waves (SHW) allows for precise detection. The FW and SHW exhibit sensitivities of −10.29909 THz/RIU and -20.61429 THz/RIU to refractive index, and −1.13 GHz/K and −2.26 GHz/K to temperature, respectively. Considering that the RI range detected by the LMS covers the RIs of some blood components, the LMS not only has excellent potential in biological tissue analysis but also supports further research of multi-parameter simultaneous measurement technology.