A fast and label-free DC-iDEP microfluidic device detects bacterial motility and andrographolide efficacy in motility...

Bacteria motility is one of the critical bacterial behavior to exploit available resources and environments due to their biological movement toward resources supporting proliferation. Commonly used techniques investigating bacterial motility include cell staining, DNA sequencing, and fluorescent labeling, which are time consuming and challenged by limited markers and subsequent native bacterial cell high information collections. Distinguishing bacteria with high/low motility potential with simple and fast techniques are in demand. Here, a label-free DC-iDEP (Direct-current insulator based dielectrophoresis) based microfluidic device is introduced to detect the motility behavior of Bacillus subtilis. Bacillus subtilis incubated at pH 5, 7, 9 culture medium showed different high/low motility in agar stabbed tests. These bacteria samples with different motilities were used as controls to explore the motility influences on the biophysical characterizations in DC-iDEP. Results indicate the new approach is capable of distinguishing motility changes based on biophysical properties of Bacillus subtilis even before days of bacterial agar tests. The characterization biophysical factor (ratio of electrokinetic to dielectrophoretic mobility, EKMr) of Bacillus subtilis were found to increase as motility increases. Furthermore, andrographolide, a herbal medicine, was found to inhibit the motility behavior and this could be detected by DEP as the characterized biophysical property of andrographolide treated bacteria (5.3 × 10⁹ V/m²) shows significant smaller EKMr than control (9.8 × 10⁹ V/m²). Anti-cBir1-IgG, an anti-bacterial flagellin antibody, was found level increase after andrographolide treatment by the enzyme-linked immunosorbent assay (ELISA). The results indicated that the new approach enables motility detection without the need of time-consuming agar culturing and exhibited possible causes of the convergent movement of bacteria. The microfluidic approach is promising in screening medicines that induce bacteria motility changes contributing to environmental and microbiology studies.