Graphene-based LSPR sensors enable polarization-independent detection of CEA antigens

This study presents a biosensor based on cleaved graphene, compared with a graphene-gold nanoparticle structure, for detecting carcinoembryonic antigen (CEA), leveraging graphene's tunable resonance frequency and the structure's polarization-independent performance. This sensor consists of three layers: a gold substrate with a conductivity of 4.7 × 10⁷, a silicon dioxide (SiO₂) dielectric layer with a permeability of 3.9, and a graphene layer with strategic cuts to increase absorption. The performance of the proposed structure has been measured by measuring its absorption around the 8.9 terahertz frequency band, which has reached absorption values ​​above 99.4-99.9% for the first structure and absorption above 99.6-100% for the second structure, which includes graphene plus gold nanoparticles, respectively. These high absorption rates make the sensor an excellent candidate for biosensing applications, especially for the detection of CEA in clinical samples. By testing the sensor with analytes containing CEA in concentrations of 1, 2, 3, 4, and 5 ng/ml, the refractive index values ​​were 1.3337, 1.33374, 1.3448, and 1.3485, respectively. When the analyte layer is placed on the three-band absorber structure, the peak shift is absorbed and allows the detection of the desired analyte. The second proposed structure showed significant sensitivity and achieved 4.3 THz / RIU at 1.3411 refractive index and 8.8483 THz frequency, LOD = 0.001 and FOM = 26. This high sensitivity is especially useful for detecting low concentrations of analyte. Such a sensor has a high potential to increase the detection of biomarkers. These findings highlight the potential of the sensor for CEA detection with high sensitivity.