More than magnetic isolation: Dynabeads as strong Raman reporters toward simultaneous capture and identification of targets

Dynabeads are superparamagnetic particles used for the immunomagneticpurification of cells and biomolecules. Post-capture, however, target identifica-tion relies on tedious culturing, fluorescence staining, and/or target amplifica-tion. Raman spectroscopy presents a rapid detection alternative, but currentimplementations target cells themselves with weak Raman signals. We presentantibody-coated Dynabeads as strong Raman reporter labels whose effect canbe considered a Raman parallel of immunofluorescent probes. Recent develop-ments in techniques for separating target-bound Dynabeads from unboundDynabeads make such an implementation feasible with high specificity. Wedeploy Dynabeads anti-Salmonella to bind and identify Salmonella enterica, amajor foodborne pathogen. Dynabeads present major peaks around 1000 and1600 cm1 from aliphatic and aromatic C-C stretching of the polystyrene coat-ing and near 1350 cm1 from the ɣ-Fe 2 O 3 and Fe 3 O 4 core, confirmed withelectron dispersive X-ray (EDX) imaging. Minor to no contributions are madefrom the surface antibodies themselves as confirmed by Raman analysis ofsurface-activated, antibody-free beads. Dynabeads’ Raman signature can bemeasured in dry and liquid samples even at single shot 30 30 μm areaimaging using 0.5 s, 7-mW laser acquisition with single and clustered beadsproviding a 44- and 68-fold larger Raman intensity compared with the signa-ture from cells. Higher polystyrene and iron oxide content in clusters yieldslarger signal intensity, and conjugation to bacteria strengthens clustering as abacterium can bind to more than one bead as observed via transmission elec-tron microscopy (TEM). Our findings shed light on the intrinsic Ramanreporter nature of Dynabeads. When combined with emerging techniquesfor the separation of target-bound Dynabeads from unbound Dynabeadssuch as using centrifugation through a density media bilayer, they have the otential to demonstrate their dual function for target isolation anddetection without tedious staining steps or unique plasmonic substrateengineering, advancing their applications in heterogeneous samples like food,water, and blood.