Miniature fiber end-integrated reflective surface plasmon resonance biosensor with chimney-like structure for ultra-sensitive alpha-fetoprotein detection

As an indispensable biomarker in hepatocellular carcinoma (HCC) screening, the highly sensitive detection of trace alpha-fetoprotein (AFP) provides a crucial auxiliary approach for the early screening and differential diagnosis of this malignant tumor. This paper presents a functionally integrated chimney-like microstructure for surface plasmon resonance (SPR) sensing. The proposed sensor is fabricated on the end-face of a single mode fiber (SMF) with an ultra-compact footprint of 10μm× 10μm× 16μm, achieving the advantages of miniaturization and trace liquid detection capability. The feasibility of the structure to excite SPR was verified through systematic simulations, and the critical geometric parameters were optimized. The structure features a facile fabrication process utilizing two-photon polymerization (2PP) technology combined with direct current (DC) diode sputtering. The proposed sensor demonstrated an AFP sensitivity of 0.684 nm/(ng/mL) with an ultra-low limit of detection (LOD) of 0.029 ng/mL, and exhibited excellent selectivity. Overall, this novel chimney-like SPR sensor achieves significant size reduction while maintaining exceptional AFP sensitivity compared to traditional sensors. These advances position the sensor as a promising platform for early-stage HCC screening and low-abundance biomarker analysis.