Quantitative detection modeling of lysine and histidine in animal feed based on terahertz metamaterial sensing...

This study develops a method for rapid lysine (Lys) and histidine (His) detection using pure standards. A terahertz time-domain spectroscopy (THz-TDS) system was employed to measure the absorption characteristics of Lys and His standards within the 0.1-1.5 THz frequency range. Molecular vibrational modes associated with the characteristic absorption peaks were identified based on density functional theory (DFT) analysis. A novel double-ring gold metamaterial sensor was designed, and its surface electric field, current distribution, and terahertz absorption responses to samples with different refractive indices on the metamaterial surface were simulated. Standard solutions of Lys and His were prepared at concentrations of 1, 5, 10, 15, 20, and 25 mg/mL, along with 9 mixed solutions at equal gradient ratios (n = 21). Quantitative detection experimental results demonstrated that the terahertz absorption measurements of the two amino acids were in good agreement with the DFT theoretical calculations. Under simulation conditions, the proposed metamaterial exhibited optimal sensing performance at 0.881 THz, with a sensitivity of 198 GHz/RIU, a Q-factor of 7.436, and a FOM of 1.678. Quantitative calibration models for Lys (R² = 0.964, RMSEC = 8.933 GHz), His (R² = 0.960, RMSEC = 6.251 GHz), and their binary mixture (R² = 0.975, RMSEC = 6.830 GHz) exhibited linear correlation. These metrics were derived from calibration data without independent validation. The practical detection of concentration in this study ranges from 1 mg/mL to 25 mg/mL. This is a preliminary study based on pure amino-acid standards, with potential application to real feed matrices envisaged as future work.