Conjugation of aptamers and their corresponding analytes onto plasmonic nanoparticles mediates the formation of nanoparticle assemblies: molecularly bound nanoclusters that cause a measurable change in the colloid's optical properties. The optimization of a surface-enhanced Raman spectroscopy (SERS) competitive binding assay utilizing plasmonic "target" and magnetic "probe" nanoparticles for the detection of the toxin bisphenol-A (BPA) is presented. These assay nanoclusters were housed inside three types of optofluidic chips patterned with magnetically activated nickel pads, in either a straight or array pattern. Both Fe2O3 and Fe2CoO4 were compared as potential magnetic cores for the silver-coated probe nanoparticles. We found that the Ag@Fe2O3 particles were, on average, more uniform in size and more stable than Ag@Fe2CoO4, whereas the addition of cobalt significantly improved the collection time of particles. Using Raman mapping of the assay housed within the magnetofluidic chips, it was determined that a 1×5 array of 50 μm square nickel pads provided the most uniform SERS enhancement of the assay (coefficient of variation ∼25%) within the magnetofluidic chip. Additionally, the packaged assay demonstrated the desired response to BPA, verifying the technology's potential to translate magnetic nanoparticle assays into a user-free optical analysis platform.
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