Fig. 1. The geometric diagram of the proposed metamaterial sensor based on SRR structure

Fig. 2. The surface current and electric field profiles of SRR structure (a) with and (b) without tip ends, the red colored y-axis signifies the polarization direction of the incident electric field

Fig. 3. The optical microscopy images of the fabricated metamaterial sensor (a) array structure of SRR, (b) single structure of SRR

Fig. 4. (a) Sensor assembled with fixture, (b) measurement platform of the THz-TDS system

Fig. 5. (a) Simulated transmission spectra of metamaterial sensor for different refractive index analyte with the thickness of 0.4 μm, (b) simulated transmission spectra of metamaterial sensor for different thickness analyte with the refractive index of 1.2

Fig. 6. (a) and (b) represent the relationship between frequency shift and refractive index and the relationship between frequency shift and the thickness of sample film, respectively

Fig. 7. (a), (b) and (c) represent the measured transmission spectra of inositol (IS), leucine (LC), and taurine (TR) with different concentrations, respectively

Fig. 8. (a) and (b) represent the relationship between frequency shift and concentration of inositol (IS) and leucine (LC) solution changing from 0.2 to 4 mg/ml, respectively

Fig. 9. The measured transmission spectra of inositol（IS），leucine（LC），and taurine（TR）with the solution concentration of 4 mg/ml