Initially, we fitted the data of zinc ion concentration to the priming intensity of the zinc-sensitive promoter pcutR, allowing us to use the equation to understand the priming of the zinc-sensitive promoter by zinc ion concentration.

By curve fitting, the relationship between zinc ion concentration and PzntR initiation intensity was y=0.7922x+6.1. By substituting zinc ion concentration into x value, the initiation intensity of the promoter can be obtained.

In our operating system, zinc ion concentration is converted into voltage. And we stimulated the expression of riboflavin with zinc ions, so we modeled the relationship between riboflavin concentration and maximum voltage. The zinc concentration is linear with the riboflavin concentration, so in our model, x is the zinc concentration.

By curve fitting, the relationship between riboflavin concentration and voltage was y=0.2156x+32.941. The maximum voltage can be obtained by substituting the zinc ion concentration with the x value.

And finally, we added the amplification system, which is our overall biosensor system.

We test our total system and curve fit the obtained data, and finally get the equation: y =0.5465x+148.6

We can take the maximum voltage we measured, plug in y, and we get x, which is the concentration of zinc ions in the water, and that's how we work.

We transferred the recombinant plasmid to e. coli BL21 and then set up a two-compartment MFC-operated reactor (each compartment volume was 240mL) with the anode and cathode of the cell connected to an external resistor through a titanium wire. In the MFC system, different concentrations of zinc ions make our sensor generate different voltages. The maximum voltage value is denoted as y value and substituted into the square y =0.5465x+148.6 to obtain the zinc ion concentration x, and zinc contamination is detected according to the data.