Qualitative and quantitative detection of sex-targeted hormones in chicken embryo based on terahertz spectroscopy and metamaterial technology

Gender identification of chick embryos at the early stages of incubation is of significant importance to poultry industry. Existing studies showed reproductive hormone concentrations are associated with gender of chick embryos. Accurate detection of reproductive hormone concentration can assist in gender identification. This paper explores the feasibility of terahertz time-domain spectroscopy (THz-TDS) and metamaterial techniques for qualitative and quantitative detection of reproductive hormones of chick embryos. First, the absorption characteristics of four key reproductive hormones-estrone (E₁), estradiol (E₂), estriol (E₃), and testosterone (T)-were investigated within the terahertz band. E₃ and T were selected as the sex-targeted hormones for their absorption features. Next, a novel metamaterial structure coupled with the absorption properties of E₃ and T was designed, and simulations were conducted to analyze the sensing mechanism and performance. Results showed that the proposed structure deliver a high refractive index sensitivity reaching 196 GHz/RIU. The Q-factor and figure of merit (FoM) can reach 3.927 and 0.877, respectively. Finally, E₃ and T solutions were prepared at six concentrations (10-2000 μg/mL), and transmission spectra of hormone films of different concentrations on the metamaterial surface were measured. Based on that, frequency shifts-concentration fitting models of E₃ and T were established. Results showed that there is no intersection area in 2D intensity-frequency diagram of E₃ and T, and the correlation coefficient can reach 0.9744 and 0.9527, respectively. The limit of detection (LoD) is 100 μg/mL. This study provides a theoretical and experimental basis for early-stage gender identification of chicken embryos.