## 3 Experimental Methods  
### Experimental Process  
In order to demonstrate the increase in elution from the swab due to impingement of the magnetic particles, experiments were performed in settings with and without magnetic agitation, using swabs that were dipped in artificial sputum samples containing polystyrene beads. In these experiments, dry swabs were immersed in the artificial sputum samples with 10% v/v (\(\sim\)10\({}^{9}\) particles/mL) polystyrene bead concentrations. Next, the swabs were air dried for 30 s and dipped into the vial containing DI water. The experiments were repeated (\(n=5\)) for various elution times (30 s-180 s) at 30 s intervals. In another set of experiments (\(n=5\)), swabs dipped in the same samples were dipped into the vial with DI water and were agitated using mechanical impingement caused by magnetic particles under the influence of the external magnet rotating at 300 RPM for various elution times (30 s-180 s). Recovery efficiencies were obtained by measuring the number of beads eluted into the DI water solution using techniques described in the methods section.  
Rotational speed of the magnetic particles is an important parameter for elution, which determines the number of impacts to the swab fibres and therefore is related to the amount of material scrubbed per minute. In order to characterize its effect of rotational speed of the magnets on the number of eluted particles and recovery efficiency, dry swabs were immersed in artificial sputum solutions of 10% v/v (\(\sim\)10\({}^{9}\) polystyrene particles/mL), air dried for 30 s, immersed inside the vial with elution fluid, and exposed to various rotational speeds (0-500 RPM), for 30 s. The number of eluted particles and recovery efficiencies were both recorded for five experiments at each rotational speed. The duration of elution procedure also has a significant effect on the recovery efficiency, since it determines the number of impingements that are caused over the entire period of time. To predict the nature of elution rate with changes in time, experiments were done with 10% polystyrene in artificial sputum samples. Dry swabs were dipped in artificial sputum samples concentrated with 10% v/v (\(\sim\)10\({}^{9}\) particles/mL concentration) polystyrene beads, air dried for 30 s and immersed in the vial with elution fluid. The motor was set to a specific rotational speed and the number of eluted particles was noted with the change of time (30 s-120 s).  
Experiments were also done with a specific elution time and rotational speed to determine the effects of concentration on recovery efficiency. The concentration of the sample also influences the recovery and is a vital parameter when body fluids with varying microbial concentrations are under consideration. Since it had already been established that higher rotational speeds (400-500 RPM) and elution times (120 s) produce a better recovery of beads, experiments were performed only with those specific parameters. Dry swabs were dipped in artificial sputum solutions of different concentrations (\(\sim\)10\({}^{9}\)-10\({}^{6}\) particles/mL), air dried for 30 s and immersed in DI water in a vial for elution. The rotational speed of the magnet was set at 400 or 500 RPM and the elution of materials from the swab was measured. Similar experiments were repeated with bacterial samples to show the respective changes in recovery efficiency with changes in rotational speed, time and concentration.