  Developing rapid methods for pathogen detection and growth monitoring at low
cell and analyte concentrations is an important goal, which numerous
technologies are working towards solving. Rapid biosensors have already made a
dramatic impact on improving patient outcomes and with continued development,
these technologies may also help limit the emergence of antimicrobial
resistance and reduce the ever expanding risk of foodborne illnesses. One
technology that is being developed with these goals in mind is asynchronous
magnetic bead rotation (AMBR) biosensors. Self-assembled AMBR biosensors have
been demonstrated at water/air and water/oil interfaces, and here, for the
first time, we report on self-assembled AMBR biosensors used at a solid
interface. The solid interface configuration was used to measure the growth of
Escherichia coli with two distinct phenomena at low cell concentrations:
firstly, the AMBR rotational period decreased and secondly, the rotational
period increased after several division times. Taking advantage of this low
cell concentration behavior, a 20% signal change from the growth of E. coli
O157:H7 was detected in 91 \pm 4 minutes, with a starting concentration of 5 x
103 CFU/mL. Such a rapid cell growth sensor could dramatically improve the
detection time and sensitivity in applications requiring phenotypic testing of
target cells.
