Fabrication of long range surface plasmon waveguide biosensors in a low-index fluoropolymer

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The authors report the fabrication of long-range surface plasmon polariton biosensors consisting of thin narrow Au stripes embedded in a low refractive index fluoropolymer with etched fluidic channels. The fabrication process incorporates a sacrificial SiO2 channel etch stop layer to avoid waveguide damage and prevent channel over-etching, and an Al etch mask to minimize thermal cracking of the fluoropolymer during channel etching. Process details are reported along with fabrication results, and the optical and biosensing performance of the fabricated devices are demonstrated. The biosensors were tested for bulk sensitivity and bovine serum albumin (BSA) protein adsorption producing notable changes for solutions with different refractive indices (increment of 2 × 10−3) and a change in insertion loss of 0.1 dB as a monolayer of BSA forms on the device.