Equipment Design
Our optical detection hardware mainly consists of two parts: testing equipment and the smartphone. The testing equipment mainly includes a light source, an excitation filter, and an emission filter. The main function of the smartphone is to collect and process our images. The picture of our equipment is shown in Fig.1.
We continued to use the fluorescence detection equipment of iGEM-BIT 2019. We take the flash of a smartphone as the light source of our detection equipment. According to the target light (The excitation wavelength is 492nm and the emission wavelength is 522nm.) that we need to detect, we selected the appropriate emission filter and excitation filter. The optical structure of our testing equipment is shown in Fig.2.In the process of detection, the light from the flash of our smartphone shines on our paper-based chip at a certain angle after passing through the optical filter and fiber, then the fluorophore on the chip is excited to emit fluorescence signals. After that, the fluorescence signal enters the camera of the smartphone and we use the phone to take pictures and collect them for the next step. Additionally, we designed a small device to place and fix our paper-based chip during the detection process. The picture of the support equipment is shown in Fig.3.
Test Result
In order to use this equipment to correctly detect and reflect the fluorescence signal of our biological samples, we designed an experiment to detect the fluorescence produced by a series of sodium fluorescein solutions with different concentration gradients on a 4mm diameter glass fiber disc through this device.
We prepared sodium fluorescein solutions with concentrations of 0, 2, 4, 6, 8, and 10μmol/L respectively, and added 10μL of each to the 4mm diameter glass fiber. After waiting for a certain amount of time, we put the same disc into the device to take three pictures and ensured the position of every disc and camera parameters were as consistent as possible. Finally, we cut the picture of discs to the same size, spliced them according to the concentration gradient, and used ImageJ to analyze the total grayscale of the pictures by image method. The real picture of this experiment is shown in Fig.4 below and the data processing results are shown in Fig.5.
This experiment proved that the linearity of our device can reach 0.9712 when detecting 0-10μmol/L fluorescein sodium solution, which showed that our equipment can produce linear detection results.