Figure 4. Evaluating the clinical utility of the μHD using tumor cells in vitro.

(A) The μHD was insensitive to the background of unprocessed biological material. The tumor cell line MDA-MB-453 was profiled for EpCAM in human whole blood and in the presence of excess, free MNPs. Cells were measured in PBS (blue), whole blood (red), and PBS+excess MNPs (grey) with both μHD and flow cytometry. (B) The μHD was used to count rare cells in unprocessed whole blood samples. Flow cytometry was used to count cells in RBC-lysed blood samples. These values were compared to the expected cell counts. Data is displayed as mean ± SEM from triplicate measurements. (C) To simultaneously detect multiple biomarkers, cells were labeled with different types of MNPs, each targeting a different biomarker. The magnetic moments of the labeled cells were then measured by placing microfabricated Hall sensors in a spatially varying field (B₁, B₂, B₃). (D) The measured magnetic moments m versus the applied field for MnFe₂O₄ MNPs with three different diameters (10, 12, and 16 nm). (E) The Hall voltages of cells labeled for all three cancer biomarkers were measured at varying applied field strengths. The magnetization curve (dotted line) is a fit using the magnetization curves of three different types of MnFe₂O₄ MNPs. Data are means ± SEM from 1000 V_H values, SEM is insignificant compared to data. (F) Based on the magnetic moments measured at different fields as well as the known magnetic properties of each MNP, the number of each particle type could be calculated. MDA-MB-468 human cancer cells were labeled for three biomarkers: HER2/neu, EGFR, and EpCAM. The heat map compares the relative expression levels measured using flow cytometry (FCM), as well as separate and multiplexed measurements using the μHD.