## 4 Results  
### Effect of Magnetic Impingement on Elution  
Several experiments were done with the artificial samples containing polystyrene beads, as described in Section 3.1, and the resulting recovery efficiencies were recorded. The recovery efficiencies, as shown in Figure 3, increases with elution time, till 120 s, and then remain steady. In the case of elution without agitation, the recovery efficiency increases from 33.68 to 41.8% when dipped in the DI water between 30 and 120 s. Similarly, in the case of elution with magnetic agitation at 300 RPM, the recovery efficiency increases from 51% to 63.2% over 30-120 s of agitation. The difference in elution efficiency between agitated and non-agitated case was found to be statistically significant (\(p\)-value \(<\) 10\({}^{-5}\)).  
The capture and release of polystyrene beads has been demonstrated through scanning electron microscope images in Figure 4a,b. The structural details of the fibres and the entrapment of polystyrene beads have been clarified with figures at 5000\(\times\) magnifications (Figure 4a,b). Figure 4a shows the polystyrene beads retained in the swab fibres, when eluted without agitation, in close detail. The polystyrene beads are entrapped in the fibre matrix, and some beads also penetrate the inner matrix, when the swab was dipped in the sample. After elution without agitation, the artificial sputum on the top fibres dissolve and most of the particles on the top matrix are eluted. But, some of the fibres in the inner matrices are retained. Figure 4b shows the swab fibres after elution by magnetic actuation. This figure shows that less number of beads are retained in the inner matrix of the swab as compared to the elution without agitation. Beads trapped in the small cracks and crevices are hard to remove, although the ones on the surface of fibres get eluted easily. Finally, these photographs also show the sources of the entrapment of beads, which cannot be removed, even with an active mechanism and higher impact force, thereby causing a deviation from 100% recovery.  
For better understanding, microscopic images were taken post elution at different concentrations (Figure 4c-f). 10 \(\upmu\)L of the post-eluted sample was taken on a microscopic plate, covered with a microscopic slide, and imaged under the fluorescent microscope. Higher number of particles are eluted when the initial concentration of the sample is higher. This is visible from the pictures, which were taken with different pre-elution concentrations from 1 \(\times\) 10\({}^{6}\) to 1 \(\times\) 10\({}^{9}\) particles/mL.  
Figure 4: Distribution of polystyrene beads on swab fibres (**a**) post elution (no agitation); (**b**) post elution (magnetic beads agitation)-5000\(\times\). Fluorescent microscopic images of post elution at different bead concentration: (**c**) 10\({}^{6}\) particles/ML; (**d**) 10\({}^{7}\) particles/mL; (**e**) 10\({}^{8}\) particles/mL; and, (**f**) 10\({}^{9}\) particles/mL.  
Figure 3: Comparison of recovery efficiencies for elution without agitation and with magnetic impingement (300 RPM) of swabs dipped in 10% v/v (\(\sim\)10\({}^{9}\) particles/mL) concentrated samples (* signifies \(p\) > 0.001, ** signifies \(p\) < 0.001).