Rapid isolation of Escherichia coli from water samples using magnetic microdiscs

This work introduces a method for rapid isolation of target bacterial cells using “bacteria-sized,” gold-coated magnetic microdiscs (1.5 μm in diameter, 80 nm in thickness). These microdiscs are functionalized with DNA aptamers for selectively isolating Escherichia coli cells from lab-prepared and environmental water samples at concentrations as low as 10² CFU/100 mL with no enrichment. This microdisc platform enables viability assay on the magnetically captured discs using fluorescent markers such as SYTO9, propidium iodide, and carbon quantum dots, providing both a detection and viability step in a single analysis. The significance of this gravity-driven separation technique is the ability to rapidly isolate target cells from relatively large sample volumes (up to 100 mL) with simple field-deployable apparatus in one step, without the use of complicated equipment or energy. This technique has immediate application for rapid (< 45 min) isolation and detection of fecal indicators (E. coli) in agricultural water and can be used for drinking water analysis if an enrichment step is added. In addition to targeting E. coli, the platform can be used for targeting other cells based on functionalization of the microdiscs with other bioreceptors such as aptamers, lectins, phages, or peptides.