As the global industrialization has been developed, heavy metal ions became assignable factors of water pollution, which may cause serious damage to human health. However, the measurements for the concentration of heavy metals are complex and expensive. In our project, we have applied several transcription factors which are sensitive to the concentration of copper ions and chromium ions to regulate the expression of protein ribB. The existence of ribB will enhance the production of riboflavin. Moreover, riboflavin, as the electron carrier, could improve the electricity producing performance of the Microbial Fuel Cells (MFCs). So in this way, we successfully correlated the concentration of heavy metal ions together with the output voltage of the MFC. What’s more, we further created a convenient device—Micro Holmes (a combination of MFC and electronic components), to monitor heavy metal ions of water sample any place any time.