A novel design of grooved fibers for fiber-optic localized plasmon resonance biosensors

Abstract

Bio-molecular recognition is detected by the unique optical properties of self-assembled gold nanoparticles on the unclad portions of an optical fiber whose surfaces have been modified with a receptor. To enhance the performance of the sensing platform, the sensing element is integrated with a microfluidic chip to reduce sample and reagent volume, to shorten response time and analysis time, as well as to increase sensitivity. The main purpose of the present study is to design grooves on the optical fiber for the FO-LPR microfluidic chip and investigate the effect of the groove geometry on the biochemical binding kinetics through simulations. The optical fiber is designed and termed as U-type or D-type based on the shape of the grooves. The numerical results indicate that the design of the D-type fiber exhibits efficient performance on biochemical binding. The grooves designed on the optical fiber also induce chaotic advection to enhance the mixing in the microchannel. The mixing patterns indicate that D-type grooves enhance the mixing more effectively than U-type grooves. D-type fiber with six grooves is the optimum design according to the numerical results. The experimental results show that the D-type fiber could sustain larger elongation than the U-type fiber. Furthermore, this study successfully demonstrates the feasibility of fabricating the grooved optical fibers by the femtosecond laser, and making a transmission-based FO-LPR probe for chemical sensing. The sensor resolution of the sensor implementing the D-type fiber modified by gold nanoparticles was 4.1 × 10(-7) RIU, which is much more sensitive than that of U-type optical fiber (1.8 × 10(-3) RIU).

Keywords: biosensor; fiber-optic localized plasmon resonance; microfluidic.

Figure 1.

Schematic illustration of the FO-LPR microfluidic chip: (a) detecting principle of the FO-LPR and (b) structure of the chip and illustration of fluidic operation.

Figure 2.

Dimensions and design of the grooved fibers. (a) U-type fiber. (b) D-type fiber.

Figure 3.

Schematic diagram of the tensile test machine.

Figure 4.

Schematic diagram of the modification of Au nanoparticles on the surface of the grooved optical fiber (D-type fiber was taken as an example).

Figure 5.

Simulated time histories for the average concentration of bound analyte on (a) the U-type and (b) D type fibers. (a) U-type fiber. (b) D-type fiber.

Figure 6.

Contours of the flow field in the FO-LPR microfluidic chip with (left) the U-type and (right) the D-type fiber.

Figure 7.

Mixing patterns in the FO-LPR microfluidic chip for (a) the U-type and (b) D-type fiber for numbers of grooves.

Figure 8.

Simulated time histories for the average concentration of bound analyte on the U-type and D-type optical fibers (N_g = 6) with different injected flow-rates when the injected volume was fixed at 100 μL.

Figure 9.

The load-elongation curve diagrams for optical fibers with different types of grooves.

Figure 10.

SEM images of (left) the optical fiber fabricated by the femtosecond laser and (right) its exposed surface after modification by gold nanoparticles for (a) U-type and (b) D-type fibers.