Asynchronous Magnetic Bead Rotation (AMBR) Microfluidic Biosensor Platform for Rapid Microbial Growth and Susceptibility Studies.

Abstract

The emergence and spread of antimicrobial resistance is one of the world’s most pressing health problems. The methicillin-resistant S. aureus (MRSA) kills more Americans (approximately 19,000 persons) annually than emphysema, HIV/AID, Parkinson’s and homicide combined. To address this concern, antimicrobial susceptibility tests (AST) that can more rapidly determine the antibiotic susceptibility of infectious organisms are being developed, enabling prompt and most appropriate therapies. In this dissertation, we present an asynchronous magnetic bead rotation (AMBR) droplet microfluidic platform that can measure the growth of a single or small population of bacteria and rapidly determine the minimum inhibitory concentration (MIC) of antibiotics.

By compartmentalizing individual 2–20 µm magnetic beads in 1 nL aqueous droplets, we enhance the sensitivity and parallelization capabilities of the AMBR system. When placed within a rotating magnetic field, at driving field frequencies above the critical frequency (20–800 Hz), the AMBR sensor rotates asynchronously. The rotational rate of the sensor provides insight into the system’s physical (e.g. shape and volume) and environmental (e.g. viscosity) properties. With this platform, we monitored the growth of individual bacteria by measuring the elongation (e.g. 80 + 38 nm length change) of E. coli, corresponding to the sensor volumetric change of 0.1 µm3.

By increasing the bead size and modifying its surface functionalization, we measured the growth of a small population of E. coli within an order of magnitude of a single division time. For AST applications, we applied three approaches: (1) volumetric single bacterium approach, (2) volumetric small population approach, and (3) viscosity based small population approach. Bacteria were treated with ampicillin or gentamicin, at concentrations above and below the reported MIC values, and we were able to differentiate between growing and non-growing E. coli within 100 minutes. We envision that this platform may reduce the turnaround time for AST by 80 % when compared to commercial systems, which take an average of 6 hours for E. coli. Development of more rapid AST system can improve patient lives, reduce the use of wide-spectrum antibiotics and slow the spread of antimicrobial resistance.