## 3 Results and Discussion
However images acquired by the Nikon microscope did not have optical aberrations and the whole images were processed without cropping; (2) The resolution of the Nikon microscope is higher than the resolution of the cell phone microscope resulting in a higher number of pixels in the images. The difference in pixel areas between the microscopes is not important because the width of the micro contact printed lines is 20 \(\upmu\)m and this width can be used as a reference to convert pixel calculations to units of micrometers. A conversion ratio for a microscope type, which is the corresponding pixel length for the line width, needs to be determined. Once the conversion ratios are determined by using the processed images, any real length and area of lines can be calculated. The trends of pixel areas changing with respect to the magnetic bead concentration are similar for both microscopes. To compare the variation of the pixel area with respect to the concentration for both microscopes, pixel areas were normalized by dividing each pixel area by the pixel area corresponding to the lowest concentration (0.0335 mg/mL) of magnetic beads (2805505 for the Nikon microscope and 148036 for the cell phone microscope). Figure 6 shows the normalized pixel area of the magnetic beads for various concentrations. The resolution of the cell phone microscope was not high enough to detect a single bead, however the aim of this study was to show that the cell phone microscope with the help of image processing can be used to quantify the group of magnetic beads on the micro contact printed lines. Figure 6 reveals that the cell phone microscope incorporated with the image-processing algorithm is able to detect concentration variations of magnetic beads on micro contact printed lines. Biosensors based on micro-contact printed probes and immunomagnetic beads were used to detect biologically significant target molecules such as cancer related folate receptor [9], and platelet-derived growth factor (PDGF) [8], and cardiovascular disease related s-adenosyl homocysteine [7]. In these biosensing applications the number of beads on the surface is proportional to the target concentration. The introduced method in this manuscript can be used to detect and quantify the magnetic bead amount thus a portable, low cost system would be available for the measurements of biologically significant targets. In order to further test the system's versatility we used the optical micrograph presented in [9] for detecting 700 fM folate receptor and calculated the normalized pixel area of the corresponding immunomagnetic beads for 1000 \(\upmu\)m\({}^{2}\). Figure 6: Normalized pixel area from the binary images acquired by both microscopes. We converted the RGB image to a binary image using ImageJ software [21] and measured the pixel area of the magnetic beads. In an area of 1000 \(\upmu\)m\({}^{2}\), 5057 pixel area represents the amount of magnetic beads that captured 700 fM of folate receptor. The binary images presented in Figure 4 for 0.067 mg/mL of streptavidin coupled magnetic beads correspond to a white pixel area of 1032 in an area of 1000 \(\upmu\)m\({}^{2}\) for the images acquired by the cell phone microscope. Table 2 shows that the cell phone microscope is capable of detecting biologically significant target molecules and further tests can be conducted to verify the calculations. The capture and binding efficiency of immunomagnetic beads are important parameters that directly affect the sensitivity of the cell phone microscope. The spherical ball lens used in this study costs less than 10 US cents and the cell phone microscope can be assembled easily in less than a couple of minutes. However the ultra-low-cost spherical ball lens has significant aberrations and creates low quality images. With the help of image processing, the low quality images of immunomagnetic beads captured on micro contact gratings can be analyzed and meaningful data can be extracted.