Sensitive plasmonic biosensor for CEA detection using asymmetric crescent nanostructures

Early detection and screening of colorectal cancer are challenging due to the low sensitivity of conventional diagnostic methods in detecting trace levels of carcinoembryonic antigen (CEA), as the main clinically validated biomarker for colorectal cancer. In this study, we developed an advanced plasmonic biosensor that utilizes a regularly patterned arrangement of asymmetric crescent-shaped gold nanoparticles constructed on a quartz foundation. Its sensing mechanism is based on the localized surface plasmon resonance (LSPR), allowing for direct, marker-free detection of CEA in real-time measurements. Using detailed Finite-Difference Time-Domain (FDTD) computational analysis, we established strong localized electromagnetic field enhancement around the crescent nanostructures, producing a clear extinction peak near 900 nm. Parameter optimization studies revealed that maximum sensitivity and figure of merit (FoM) are obtained with a crescent configuration angle of roughly 100° and particle separation of 40 nm. The biosensor shows predictable linear wavelength shifts when exposed to refractive index variations in the detection medium, confirming its ability to identify minute CEA concentrations. These results demonstrate the considerable potential of this plasmonic technology as a high-performance, marker-free sensing solution for early cancer detection. This optimized nanostructure design, combined with advanced plasmonic properties, provides a powerful tool that overcomes existing limitations in current cancer screening approaches, potentially enabling more precise and earlier identification of colorectal cancers through enhanced biomarker detection capabilities.