Inertial–Immunomagnetic Synergistic Microfluidic Chip for Continuously Separating Bacteria with High Flow Velocity

Inertial microfluidic chips have been widely accepted to efficiently separate large bioparticles from body fluids with a simple chip structure and a high processing speed. However, the inertial microfluidic chips can hardly be considered as efficient tools for separating small bioparticles from body fluids due to the lack of a stable inertial focusing position. In fact, completely separating bioparticles smaller than human cells, such as pathogenic bacteria, from body fluids is often crucial for saving lives from, for instance, severe bacterial infection. This study presents a novel concept of simultaneously applying inertial and immunomagnetic separations in a simple microfluidic chip to realize the complete separation of large and small bioparticles with high flow velocity. By complementing a simple spiral microfluidic channel for inertially separating large bioparticles with a magnetic field for separating small bioparticles, we developed a synergistic inertial-immunomagnetic microfluidic chip (SIM-Chip). The inertial, hydrodynamic, and magnetic forces applied to bioparticles were carefully analyzed to define the motion trajectory of the bioparticles in SIM-Chip. Experiments show that the efficiency of separating <i>Escherichia coli</i> (<i>E. coli</i>) from human bronchoalveolar lavage fluid (BALF) reaches 86.09% in SIM-Chip. The <i>E. coli</i> colony concentration in the BALF culture assay was also enhanced by 44.92%. Meanwhile, it took only 5 min to process 2 mL of BALF. The results demonstrate that the concept of combining active (immunomagnetic) and passive (inertial) separation in a single device is technically feasible and can realize a complete separation of large and small bioparticles from body fluids, with high processing speed.