A semi-automated monodispersity-tunable magnetic platform for on-chip detection of bacteria

Microfluidic chips enable precise manipulation of small fluid volumes, thereby enhancing antibody binding to magnetic particles and improving the sensitivity of immunomagnetic separation (IMS)-based detection. Herein, we report a new approach with the integration of rotational magnetophoresis (rotaphoresis) and an X-displacement principle for on-chip IMS, enabling semi-automated control of magnetic particle (MP) monodispersity for viable bacterial detection.

Our semi-automated monodispersity-tunable magnetic platform (MTMP) consists of:

1. A chip holder allowing simultaneous operation of four chips.
2. Magnet-holding step motors for controllable rotaphoresis to collect MPs at the center of the microfluidic channel.
3. An X-displacement stage that breaks down particle clusters and controls the X-Y displacement of MPs to facilitate image analysis.

For proof-of-concept testing, Escherichia coli (E. coli) expressing green fluorescent protein (GFP) and anti-E. coli antibody-modified MPs were used as model bacteria and magnetic particles, respectively. The optimum nearest-neighbor distance of MPs was found to be 25 ± 10 µm to facilitate microscopy-based enumeration of MPs and MP-captured bacteria.

Our platform enables detection of 2–2000 viable bacteria within 50 minutes, while a mini-incubator setup supports viability testing after 3–12 hours of incubation. The developed MTMP, combined with a portable incubator, may be useful for future on-site bacterial detection.