Terahertz meta-biosensor for bovine serum albumin sensing based on electromagnetic-induced transparency-like effect

Bovine serum albumin (BSA) sensing plays an important role in the diagnosis of various diseases, yet, there is still a lack of a cost-effective terahertz solution. Terahertz metamaterials based on electromagnetically induced transparency (EIT)-like effects show significant potential for biosensing due to their narrow transparent peak. This study aims to fabricate terahertz metamaterials based on EIT effect for non-destructive, trace-level detection of BSA.

We demonstrate a multiband EIT-like metasurface that merges C-, toroidal, and D-shaped resonators to generate two transparency windows at 0.973 and 1.118 THz via strong bright-bright near-field coupling between adjacent resonators. Finite-element modelling was used to optimise the bright-bright near-field coupling before fabricating the 200-nm-contact-lithography device on a quartz substrate. A 100 µL aliquot of 0 to 6 mg/mL BSA solution was pipetted onto the metasurface. After drying at 50 ℃ for 20 min in an oven, the sample was measured with a terahertz time-domain spectrometer. The resonance shift was used to determine the sensitivity of the fabricated terahertz metamaterial for BSA detection and to calculate the limit of detection.

Simulated frequency sensitivity reached 222.6 GHz/RIU (refractive index unit) and 257.8 GHz/RIU at 0.973 and 1.118 THz, respectively. For BSA in water, the lower-frequency peak gave an experimental sensitivity of 14.43 GHz/(mg/mL) and 18.98 GHz/(mg/mL). The limit of detection was as low as 26.33 µg/mL and 20.02 µg/mL for the two transparency peaks, respectively.

The chip-scale sensor merges foundry-compatible fabrication, dual-band operation and sub-picogram BSA resolution, offering an immediate upgrade path for point-of-care albumin assays and bioreactor monitoring.