Gold Nanoparticle-Functionalized Surface Plasmon Resonance Optical Fiber Biosensor: In Situ Detection of Thrombin With 1 n·M Detection Limit

We present an optical fiber biosensor that employs both long-range and localized surface plasmon resonances (SPRs) to sensitively detect very small changes in the resonances due to the surrounding refractive index. A tilted optical fiber Bragg grating inscribed in standard single-mode fiber couples light into the fiber's cladding, where it induces micrometer-scale SPRs in a 50-nm-thick gold coating. The limit of detection of the targeted protein, thrombin, is enhanced by resonance between the long-range SPRs and localized SPRs induced in 13-nm-diameter gold nanoparticles bonded via aptamers to the protein molecules. The sensor demonstrates stable and reproducible response to thrombin concentration down to a limit of detection of 1 n·M, which is three orders of magnitude more sensitive than previous optical fiber protein sensors. Meanwhile, it does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices (core mode). The high sensitivity, simplicity, compact size, and remote monitoring capability of the sensor open many new opportunities for environmental, biological, and medical sensing.