Microfluidic Magnetic Spatial Confinement Strategy for the Enrichment and Ultrasensitive Detection of MCF-7 and Escherichia coli O157:H7

A microfluidic magnetic spatial confinement strategy was developed and employed to realize an ultrasensitive cell immunoassay. The straight confined channels in poly(dimethylsiloxane)-glass hybrid microchips were used as the enrichment and detection chambers for the proposed microfluidic magnetic cell immunoassays (μMCI). To accomplish the μMCI, prepared magnetic cell immunocomplexes were introduced into microchannels and preconcentrated in the detection zone under a permanent magnet. The magnetic cell immunocomplexes were constructed from aptamer-/antibody-coated magnetic beads and antibody-linked horseradish peroxidase-labeled target cells to guarantee the specificity and enhance the detection signal generated from the enzyme reaction. The sensitivity enhancement of μMCI was confirmed in a one-dimensional space confined microchamber, especially in the analysis of cells having more enzyme conjugating sites on their surface. This spatial confinement strategy based μMCI was then applied for model cell detection in the microchannel, the limits of detection (LODs) were 2 cells/mL for MCF-7 and 34 colony-forming unit/mL for Escherichia coli O157:H7 (E. coli O157:H7), which corresponded to up to 1202-fold LOD sensitivity improvement compared to the results of the similar immunoassays in microwell plates. The satisfactory selectivity and reproducibility of the strategy were also obtained. Moreover, it enabled rare MCF-7 detection in whole blood and E. coli O157:H7 detection in milk after time-shortened incubation. Constructing an appropriate confined space, this strategy can be extended to detect various cells with higher sensitivity, which provides a valuable approach for rare cell detection in practical applications.