In recent years, breast cancer has become one of the highest incidental cancer. But the mortality rate of breast cancer is relatively lower. It means that if you can predict that you have breast cancer with early diagnosis and get effective treatment measures, you will largely reduce the mortality of breast cancer. However, due to a series of cost factors such as time, money and energy as well as the contradictions existing in the system of contemporary medical that restricts people to get periodically breast cancer detection. Many patients missed the best diagnosis and treatment time and then made patients lost their lives. Studies have shown that when we have breast cancer, the expression degree of microRNA-21 and microRNA-155 in the human body will be significantly higher than the normal human body. Based on the above background, this project applies the artificial designed biological system to realize the detection of expression levels of microRNA (associated with breast cancer) in the serum environment, the concrete realization method is: Detect microRNA expression level in the serum samples through the engineering bacteria (directional transformed) , the higher microRNA expression degree can produce green fluorescent protein,  then using miniaturized signal hardware to detect fluorescence, and through the mathematical modeling of the model to calculate microRNA expression level. Finally deduce the theoretical diagnosis to user. The value can be presented to the user directly by the hardware device. Also, it can transmit data to a mobile phone, the mobile phone software client presented to the user. This project is a real-time inspection system for breast cancer detection, which can make that process more convenient and quickly though without the professional operation. It can be finished the detection in a short time, and provide patients with reference significance testing data, and the testing costs can be drastically reduced, alleviate the contradiction of medical treatment system.