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

Abstract

Background: 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. Methods: 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. Results: 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. Conclusions: 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.