chips: towards the development of diagnostic SERS assays

Conjugation of aptamers and their corresponding analytes onto plasmonic nanoparticles mediates the 13 formation of nanoparticle assemblies: molecularly bound nanoclusters which cause a measurable change in the 14 colloid’s optical properties. In this paper the optimization of a surface enhanced Raman spectroscopy (SERS) 15 competitive binding assay is presented utilizing plasmonic ‘target’ and magnetic ‘probe’ nanoparticles for the 16 detection of the toxin bisphenol-A (BPA). These assay nanoclusters were housed inside three types of optofluidic 17 chips patterned with magnetically-activated nickel pads, in either a straight or array pattern. Both Fe2O3 and 18 Fe2CoO4 were compared as potential magnetic cores for the silver coated probe nanoparticles. We found that the 19 Ag@ Fe2O3 particles were, on average, more uniform in size and more stable than Ag@ Fe2CoO4, whereas the 20 addition of cobalt significantly improved the collection time of particles. Using Raman mapping of the assay housed 21 within the magneto-fluidic chips, it was determined that a 1 x 5 array of 50 μm square nickel pads provided the most 22 uniform SERS enhancement of the assay (coefficient of variation ~25%) within the magneto-fluidic chip. 23 Additionally, the packaged assay demonstrated the desired response to BPA, verifying the technology’s potential to 24 translate magnetic nanoparticle assays into a user-free optical analysis platform. 25 26