## 3 Results and Discussion  
Figure 3 shows the images of the gold chips after the streptavidin coated magnetic beads self-assembled on the micro contact printed BBSA. Optical micrographs of the certain lines were \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Formula** & **Calculated Values** \\ \hline Magnification & \(MAG=(5\times 10^{5}\ \upmu\)m) \(\frac{2(n-1)}{nD}\) & 97.1 \\ Effective Focal Length & \(EFL=\frac{nD}{4(n-1)}\) & 2575 \\ Back Focal Length & \(BFL=EFL-\frac{D}{nD}\) & 820 \\ Numerical Aperture & \(NA=\frac{2n(n-1)}{nD}\) & 0.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Spherical ball lens parameters (all distances are in units of \(\upmu\)m) [19]. both recorded by both the optical microscope (Nikon) and cell phone microscope (97\(\times\) magnification). The images, acquired using the ultra-low-cost spherical ball lens, were noisy and the quality of the images was low compared to the images acquired by the reference microscope. In order to analyze the immunomagnetic bead amount on the chips, images were processed using the developed algorithm and converted into binary images. As an indication of the image quality, the variation of pixel intensities along the reference line was plotted. The original image acquired by the cell phone microscope is blurry and not clear thus the intensity difference between the magnetic bead lines and the background is 35 (range is of 0-255); however for the original image acquired by the reference microscope this difference is 150. After the image processing steps the intensity difference between the magnetic bead lines and the background is increased and thus enhanced. Figure 3 reveals that it is possible to detect single beads using the reference microscope however the cell phone microscope is not able to detect single beads. Instead it can be used to measure groupS of beads which form lines in this case. The white pixels represent the magnetic beads on micro-contact printed lines. The next step is to vary the concentration of the magnetic beads and test the cell phone microscope response. Figure 4 shows the optical micrographs and processed images for various concentrations (0.0335 mg/mL, 0.067 mg/mL, 0.67 mg/mL and 6.7 mg/mL) of streptavidin coated magnetic beads. Figure 3: Images of certain micro-contact printed lines acquired by reference microscope and cell phone microscope, pixel intensity variations along the profile line below each image. Top row images acquired by cell phone microscope, bottom row images acquired by reference microscope: (**a,e**) original image; (**b,f**) greyscale image; (**c,g**) after the dilation and adjustment steps; (**d,h**) binary image. Magnetic bead concentration was 0.67 mg/mL. After the cell phone microscope images were processed and the binary images were obtained, the black and white pixel areas were calculated. Images acquired by the Nikon microscope were also analyzed as a reference. The calculated pixel areas of the magnetic beads from the images acquired by the Nikon microscope were approximately 20 times of the calculated pixel areas of the magnetic beads from the images acquired by the cell phone microscope (Figure 5). Figure 4: Images of the self-assembled gratings by varying concentrations of streptavidin-coated beads on micro contact printed BBSA. Top and middle rows: Optical micrographs recorded by Nikon microscope and cell phone microscopy respectively; Bottom Row: Processed images acquired by cell phone microscopy. Figure 5: Calculated pixel area of gratings corresponding to magnetic bead amounts. (**a**) Pixel areas from the images acquired by Nikon microscope; (**b**) Pixel areas from the images acquired by cell phone microscope. There are mainly two reasons for the 20 fold difference in pixel areas; (1) In the field of view of the spherical ball lens, optical aberrations significantly lower the image quality away from the middle point [16] for that reason a sub image was cropped from the center area of the acquired image and then the sub-image was processed.