Dynabeads are superparamagnetic particles widely used for magnetic purification of biomolecules without the need for columns or centrifugation; their uniform size distribution and tunable surface functionality provides immense versatility. Post-capture, identification of targets still relies on tedious culturing, fluorescence staining and/or amplification-based techniques. Raman spectroscopy presents a promising, rapid and simple alternative, but Raman signals from small targets can be weak, typically requiring plasmonic enhancement using metallic nanoparticles. While Dynabeads have been used with plasmonic nanoparticles for Raman detection, these substrates require sophisticated synthesis protocols, limiting their reproducibility. Here, we show the Raman reporter property of antibody-coated Dynabeads, serving as both a capture and detection agent. We deploy Dynabeads coated with antibodies against Salmonella enterica, a widely known foodborne pathogen, to magnetically concentrate and detect bacteria. In dry and liquid samples, single and clustered beads provide a 30- and 65-fold increase respectively in intensity from cells alone using a 785 nm incident laser at 10 mW laser power. Using TEM and EDX imaging, we attribute the spectral signature of Dynabeads to the polystyrene coating (1000 & 1600 cm^-1 from aliphatic and aromatic C-C stretching respectively) with the iron oxide core providing plasmonic enhancement. Our findings shed light on the dual function of Dynabeads for isolation and detection without additional sample preparation, staining, or unique plasmonic substrate engineering, advancing their field deployable applications in heterogeneous samples like food, water, and blood.

Marissa McDonald

Graduate Research Assistant, MIT

Appearances