Our project is based on the study for the quorum-sensing of <li>Escherichia coli</i> K12 and aim to amplify the lactic acid signal so as to facilitate the sensitive and convenient real-time detection of lactic acid content. We planned to try it in fermenter firstly because lactic acid is one of the main by-products of alcohol fermentation and real-time quantitative detection of lactic acid can ensure the quality of fermentation broth. In addition, lactic acid also has a wide range of effects in many other areas, such as food safety, medicine and hygiene, and cosmetics. As our technology matures and improves, we can consider further exploring these areas. Generally, acid-base titration is used to detect lactic acid content in fermentation industry. This method is difficult to detect or accurately determine lactic acid content in a certain range of low lactic acid concentration, and it usually takes time to extract the liquid and test the lactate concentration outside the fermenter. The accuracy and timeliness of the method are poor. Therefore, our goal is to construct a more sensitive lactic acid sensor using the group sensitivity of <i>E. coli</i> K12. Once lactic acid exists, the integrated green fluorescent protein will be expressed in the bacteria and we can use optical fiber to detect green fluorescence, and estimate the concentration of lactic acid according to signal intensity. What’s more, the fluorescence intensity data will be fed back to the external lactic acid concentration meter and the circuit can be switched on in real time by photoelectric conversion. In addition, we will examine the appropriate concentration of lactic acid in different fermentation industries to set up a grading alarm device. In order to monitor the concentration of lactic acid in fermenter in real time, the fermentation time and degree can be controlled more accurately.