3D fiber-probe surface plasmon resonance microsensor towards small volume sensing

Integrating surface plasmon resonance (SPR) structures on fiber end facets enables the sensing system to be miniature, label-free, real-time, and remote detection. Yet, the wave vector matching condition for SPR excitation is hard to be satisfied by regulating the wave vector of light emitted from fiber ends. Here, we demonstrate a novel SPR microsensor realized by integrating a 3D micro waveguide onto the fiber tip. The mechanism of SPR excitation is illustrated by wave vector matching between the in-plane component of waveguide mode and surface plasmon polaritons. Using two-photon polymerization (2PP) and metallization process, the designed 3D waveguide probe with a length of 10 mu m is fabricated on the fiber tip. Then, the microsensor was applied for the immune-sensing of anti-human IgG and human IgG interactions, and a LOD of 1.11 nM was achieved. The ultracompact structure endows with the capability for high-performance detection in the micrometre scale through a convenient "dip-and-read" manner. As a proof-of-concept for this "dip-and-read" small volume sensing, immunoassay detection in a small sample volume of 5 mu L was also successfully demonstrated. The obtained results indicated that our 3D fiber-probe SPR microsensor may provide a powerful tool for small-volume biosensing applications.