# A Low-Cost and Portable Smart Instrumentation for Detecting Colorectal Cancer Cells
## 3 Results and Discussion  
Figure 4a illustrates the experimental setup of our developed prototype, while Figure 4b is an image of the commercial system (Li-Cor Odyssey) used to visualize the cancer cells with and without conjugating fluorophore. The resulting device is portable, which uses less power, costs less, is small in size as well as lightweight and provides an alternative to the conventional fluorescent microscope. The photodiode is kept inside the custom-built sample chamber and the flashlight is held on top of the cultured sample. When the light from the excitation source excites the cultured sample of HCT116 cells expressing IRFP702, a fluorescent signal is produced. At the receiving end, the light is collected by the photodiode and is converted to the current, which is linearly proportional to the collected light [24]. The photodiode is reverse biased with the help of Arduino Uno's 5 V pin, and the anode is connected to the ground via a resistor. The Arduino Uno has 5 analog pins (A0-A5). The photodiode is connected to the Arduino Uno through a A0 pin. When the light strikes the photodiode, it causes the current to flow through the resistor, which causes the voltage across it. The sensitivity of photodiode was adjusted by utilizing this principle. In order to test the minimum confluency required for the proposed device to work successfully, we cultured the cells of different confluency on the coverslips. The confluency of the cells varied from 10% to 90% in 10 percent increments. The samples were distributed evenly throughout the coverslip. Four samples of each confluency were cultured on different glass slides in order to test the performance of the proposed device. A confluency of 100% was mapped to 0.3 million cells per coverslip. The other confluency level was set accordingly. It was concluded that a minimum of 60% confluency is required for the proposed device to work successfully. It is to be noted that the developed device was able to get readings from the samples that were less than 60% confluent. However, the obtained readings from these samples were not conclusive as the readings were variable. Since the readings were not  
Figure 4: Experimental setup: (**a**) an overall setup of the proposed system (ruler is added in the picture to show the relative size) and (**b**) a commercial system: Li-Cor Odyssey. consistent, the remaining experiments were performed by keeping the samples at a minimum of 60% confluent. Moreover, the distance between the sample and the flashlight was fixed at 2 cm with the help of a holder. Figure 5a shows the cultured HCT116 cells expressing IRFP702, and Figure 5b is the control cells when viewed under a commercial imaging system (Odyssey CLx, LI-COR Biosciences, Lincoln, NE, USA). The same cell line that was used with the commercial system [25] was then used with our prototype to validate the reading. The proposed prototype was able to detect the emitted fluorescent signal from the HCT116 colorectal cancer cells expressing IRFP702 and hence was able to distinguish between control cells and the fluorescent cells. The excitation and emission maximum of IRFP702 fluorophore is 673 nm and 702 nm respectively, as shown in Figure 5d. The optical filter and light source as well as the photodiode were chosen cautiously so that they cover the excitation and emission region of this IRFP702 fluorophore. The longpass filter was selected so that it matches the emission wavelength of the IRFP702 fluorophore, thus ensuring that the emitted fluorescent wavelength passes down to the photodiode. This is to ensure that the light that is detected by the photodiode is from the cell line and not from the excitation source. Although a dichroic mirror/excitation filter is usually used in combination with the excitation light source [7; 26], this work shows that extra components can be removed if the experimental set-up is performed cautiously as it was also shown in [27]. The complete system is powered and controlled by the help of a microcontroller (Arduino Uno).