Low detection limits using sandwich and inhibition assays on long-range surface plasmon waveguide biosensors

Abstract

A long-range surface plasmon polariton waveguide composed of a gold stripe embedded in CYTOP with an etched microfluidic channel has been used as a label-free real-time biosensor to demonstrate enhanced assay formats capable of very low detection limits. Specifically, sandwich and inhibition (competitive) assays were developed and demonstrated using Bovine Serum Albumin (BSA) and anti-BSA produced in rabbit as a model bio-specific pair. Carbodiimide coupling to a self-assembled COOH-terminated alkanethiol monolayer on the gold stripe was used to immobilize biomaterial to its surface. The optical output power from the biosensor was measured continuously over time and converted into surface mass density. Titration curves were extracted for both immunoassays. We demonstrate that protein concentrations in solution of 10 pg/ml can be detected with a signal-to-noise ratio of 20 using this new optical biosensor technology.