Five-Segment THz Refractive Index Metamaterial Biosensor With Perfect Absorption for Carcinoembryonic Antigen Measurement

Carcinoembryonic antigen (CEA) is an essential biomarker used to diagnose and track various types of cancers, including colorectal, gastric, breast, and lung cancer. However, the accurate quantification of CEA remains a key challenge limiting early cancer detection and treatment monitoring. This work reports the design of a highly sensitive metamaterial biosensor based on surface plasmon resonance (SPR) for the detection of CEA cancer biomarkers down to clinically significant ng/mL concentrations in terahertz (THz) band. The proposed biosensor consists of three horizontal arms placed between two vertical arms (five-segment). A Teflon dielectric spacer is sandwiched between the metamaterial biosensor and a gold reflector. The formed metal-insulator–metal (MIM) structure excites localized surface plasmons (LSPs), which enhance the absorbance characteristic of the sensor. The sensor exhibits a perfect absorption of 99.99% at the resonance frequency
$f_{{0}}=7.56$
THz. A high sensitivity of
${S} \; =1.44$
THz/RIU, figure of merit (FoM) of 26.6 RIU
$^{-{1}}$
, and a quality factor of 132.2 is achieved. Moreover, the sensor exhibits a red shift of 51.4 GHz/
$\mu $
m and 14.06 GHz/RIU with the increase of analyte thickness layer and refractive index (RI), respectively. Evaluating the biosensor’s performance using CEA concentrations ranging from 1 to 5 ng/mL in human serum demonstrates its consistent ability to detect extremely low levels, emphasizing its capacity for early disease detection.