Supraparticle Assemblies of Magnetic Nanoparticles and Quantum Dots for Selective Cell Isolation and Counting on a Smartphone-Based Imaging Platform

There are numerous diagnostic and therapeutic applications for the detection and enumeration of specific cell types. Flow cytometry is the gold standard technique for this purpose but is poorly suited to point-of-need assays. The ideal platform for these assays would combine the immunocytochemical capabilities of flow cytometry with low-cost, portable instrumentation, and a simple and rapid assay workflow. Here, we present a smartphone-based imaging platform (SIP) in tandem with magnetic-fluorescent suprananoparticle assemblies as a step toward these ideal criteria. The assemblies (MNP@QD) are magnetic iron oxide nanoparticles surrounded by a dense corona of many brightly luminescent semiconductor quantum dots (QDs), where both the assemblies and their immunoconjugates are prepared by self-assembly. As proof of concept, we show that the MNP@QD and SIP pairing is able to selectively isolate, fluorescently immunolabel, and count breast cancer cells that are positive for human epidermal growth factor receptor 2 (HER2). These results are an important foundation for future point-of-need diagnostics capable of multiplexed isolation, counting, and immunoprofiling of cells on a smartphone, enabled by the highly advantageous optical properties of QDs.