Asynchronous Magnetic Bead Rotation (AMBR) for Biosensors.

Abstract

As antibiotic resistance of pathogenic bacteria is now a declared global threat, dubbed by the US Centers for Disease Control (CDC) as one of the most pressing public health problems worldwide, faster, growth-based methods are needed to be able to treat infections more effectively. Here we present the latest developments in the Asynchronous Magnetic Bead Rotation (AMBR) biosensor toward this goal. Asynchronous rotation of a magnetic bead in a fluid occurs when a rotating magnetic field exceeds a critical driving frequency. The frequency of the asynchronously rotating magnetic bead is a linear function of its volume, as well as of the fluid’s viscosity, and can therefore be used as a volumetric sensor. These sensors, called here Asynchronous Magnetic Bead Rotation (AMBR) sensors, were first used for bio-applications in 2007. This dissertation shows the development of various aspects of the AMBR biosensor: (1) the effect of the sensor’s frequency on its sensitivity of detection is investigated, (2) an AMBR sensor is optimized for measuring the growth of individual bacterial (E. coli) cells, achieving an 80 nm sensitivity to the cell length, (3) an off-the-microscope method for the observation of AMBR sensor signals is demonstrated, and (4) self-assembled AMBR sensors are developed for potentially rapid and scalable antibiotic susceptibility testing of bacteria. AMBR offers a simple and robust method for translating nanoscale volumetric changes into easily measurable frequency changes. It is a platform technology applicable to a multitude of high resolution volumetric and viscosity measurements, one of the primary applications being in healthcare: bacterial growth can be measured even on the single cell level. Due to AMBR biosensors high sensitivity, the bacterial resistance to antimicrobials can be rapidly determined. The resistance was determined within one hour for a clinical E. coli isolate, potentially leading to faster information on what would be the appropriate therapy for the specific case/patient.