Cascaded spiral channel microfluidic for high purity and throughput medical sample pre-processing for direct S. aureus sensors

Staphylococcus aureus (S. aureus) is a leading bacterial cause of death worldwide and can be found in a wide range of bodily fluids, including blood, urine, respiratory secretions, and synovial fluid. The development of culture-free, point-of-care (POC) diagnostics is critical for minimizing antibiotic resistance, reducing treatment side effects, and lowering healthcare costs. However, this remains challenging due to the variation in medical sample viscosity and fluid properties, low bacterial concentrations in uncultured samples, and the need to miniaturize laboratory processes for portability and cost-effectiveness. This work presents a novel, 2-stage, spiral-channel microfluidic bacteria filtration device that is compatible with viscoelastic and shear-thinning media and features simple fabrication and compact footprint. The chip uses a two-stage design. The first stage is a sheathed spiral channel that employs Dean Flow Fractionation (DFF) and inertial forces to remove ≥10 μm debris from the flow while passing the target bacteria onto the second stage. The second stage is a sheathless spiral channel that acts as a secondary filter, capturing any residual debris and enabling a narrow target outlet to reduce dilution effects from the sheath flow. The combination of a sheathed and unsheathed spiral channel is novel and enables high flow rate and high-purity separation with minimal pressure loss and dilution. The device achieves 100% purity and 60% recovery of 1μm polystyrene beads separated from 10μm beads in water, with a sample flow rate of ~300μL/min. DFF and inertial focusing were observed using 1 μm and 10 μm polystyrene beads in bovine synovial fluid. The device can recover 40% of S. aureus from Fetal Bovine Serum (FBS). This work contributes to the development of direct, POC diagnostics of S. aureus from viscoelastic and shear-thinning biological media.