Ferric plasmonic nanoparticles, aptamers, and magneto-fluidic chips: towards the development of diagnostic SERS assays

Conjugation of aptamers and their corresponding analytes onto plasmonic nanoparticles mediates the formation of nanoparticle assemblies: molecularly bound nanoclusters which cause a measurable change in the colloid’s optical properties. In this paper the optimization of a surface enhanced Raman spectroscopy (SERS) competitive binding assay is presented utilizing plasmonic ‘target’ and magnetic ‘probe’ nanoparticles for the detection of the toxin bisphenol-A (BPA). 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 magneto-fluidic chips, it was determined that a 1 x 5 array of 50 µm square nickel pads provided the most uniform SERS enhancement of the assay (coefficient of variation ~25%) within the magneto-fluidic 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.