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A highly sensitive optical fiber surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) and staphylococcal protein A (SPA) co-modified tilted fiber Bragg grating (TFBG) is proposed and demonstrated for the detection of human immunoglobulin G (IgG) for the first time. The gold film on the surface of the sensor was first fixed with GO and then modified with an SPA to improve the sensitivity of the sensor. Large specific surface area and abundant functional groups of GO can adsorb more antibodies. The combination of SPA and the antibody molecule Fc region makes the Fab area with antigen-binding sites extend outward, resulting in highly oriented antibody immobilization on the sensor surface and high antigen–antibody binding efficiency. The experimental results show that the sensitivity as well as the limit of detection of GO-SPA-modified TFBG-SPR biosensor is around 0.096 dB/($\mu \text{g}$ /mL) and $0.5~\mu \text{g}$ /mL, showing better responses to human IgG solutions with a concentration range of 30– $100~\mu \text{g}$ /mL compared with the TFBG-SPR biosensors modified singly with GO or SPA. The biosensor exhibits the advantages of small size, ease of fabrication, high sensitivity, label-free, and rapid response, and provides a new solution for detecting low concentration of biological solution, presenting great application potential in the biochemistry field. [ABSTRACT FROM AUTHOR]

An optical fiber biosensor based on gold nanoparticles and protein A co-modified Au film coated photonic crystal fiber (Au-PCF) is proposed and demonstrated for human IgG detection. For the electric field coupling effect between surface plasmon resonance (SPR) of Au film and localized surface plasmon resonance (LSPR) of gold nanoparticles, the refractive index sensitivity can be enhanced significantly. Besides, goat anti-human IgG is immobilized by protein A modified on the gold nanoparticles surface to interact with human IgG. Protein A can specifically bind the Fc region of the antibodies and has a high degree of orientation for capturing antibodies. Experimental results indicate that the refractive index sensitivity of Au-PCF sensor modified gold nanoparticles reaches 3915 nm/RIU, which is about 1.6 times higher than the Au-PCF sensor without gold nanoparticles modified. The lowest detection limit of human IgG based on gold nanoparticles and protein A co-modified Au-PCF sensor is 37 ng/mL, which is about 2.4 times and 6.3 times lower than gold nanoparticles-Au-PCF sensor and Au-PCF sensor, respectively. Such a sensitivity enhanced optical fiber biosensor based on SPR-LSPR coupling effect has potential application in clinical disease diagnosis and immunoassays. [ABSTRACT FROM AUTHOR]

In this paper, a high sensitivity of splicing regions tapered photonic crystal fiber (PCF) Mach–Zehnder interfero- metric refractive index (RI) sensor is described and experimentally demonstrated. Compared with cascaded bi-tapered single-mode fiber (SMF) Mach–Zehnder interferometer (MZI), the splicing regions tapered PCF MZI have higher sensitivity for the reason that it can better control and excite higher order modes, and has lower energy loss than cascaded bi-tapered PCF in the process of light transmission. Experimental results indicate that the RI sensitivity of splicing regions tapered PCF MZI could be up to 240.16 nm/RIU which is almost four times of cascaded bi-tapered SMF in the RI range of 1.3333–1.3792. Meanwhile, this splicing region tapered PCF Mach–Zehnder interferometric RI sensor has the advantages of higher RI sensitivity, good linearity, simple in making, and more potential practical value in the measurement of external RI. [ABSTRACT FROM PUBLISHER]