Zinc contamination refers to the contamination of the environment by zinc and its compounds. In zinc mining, smelting and processing, machine manufacturing and zinc plating, instrumentation, organic synthesis, and paper industry emissions. Both contain high levels of zinc compounds. Zinc metals or their compounds can pollute the atmosphere in soot and dust produced by smelting zinc mines, waste incineration, automobile tire wear, and coal combustion. The zinc hydroxyl complex is common in industrial wastewater.

Zinc is many times more toxic to fish and aquatic animals than to humans and warm-blooded animals. Zinc, which is enriched in the soil, will also be enriched in the plant, causing harm to people and animals who eat the plant. Irrigating farmland with zinc-containing sewage has a great influence on crops, especially wheat, resulting in uneven emergence of wheat, fewer tillers, short plants, and yellow leaves. Excess zinc can also inactivate the soil, reduce the number of bacteria and weaken the role of microorganisms in the soil. Zinc is insoluble in water, but zinc salts such as zinc chloride, zinc sulfate, zinc nitrate, etc., are easily soluble in water. Zinc carbonate and zinc oxide are insoluble in water. Worldwide, about 3.93 million tons of zinc enter the oceans through rivers each year. Industrial effluents discharged from mining sites, concentrators, alloy plants, metallurgical complexes, machine factories, galvanizing plants, instrument and instrument factories, organic synthesis plants, and paper mills contain large amounts of zinc compounds.

Zinc in the soil can be divided into water-soluble zinc, substitution zinc, insoluble zinc (zinc in minerals), and organic zinc. Zinc in soil comes from various soil-forming minerals. The weathered zinc enters the soil solution in the form of Zn2+, and may also become the monovalent complex ions Zn(OH)+, ZnCl+, Zn(NO3)+, etc., sometimes forming the precipitation of hydroxide, carbonate, phosphate, sulfate, and sulfide. Zinc ions and zinc-containing complex ions participate in the substitution reaction in soil, often adsorbed and fixed. The enrichment of zinc in the soil inevitably leads to the enrichment in the plant, which is not only harmful to the plant, but also to the people and animals who eat the plant. Zinc-containing sewage irrigated farmland has a great influence on the growth of crops, especially wheat, resulting in uneven emergence of wheat, fewer tillers, short plants, and yellowing of leaves. The zinc acting on plants is mainly in the substitutional form. Excessive zinc can also inactivate soil enzymes, reduce the number of bacteria and weaken the role of microorganisms in the soil.

Conventional methods for the detection of zinc include anodic stripping voltammetry, UV-VIS spectroscopy, fluorescence spectroscopy, colorimetric method, flame atomic absorption spectrometry (FAAS), X-ray fluorescence spectrometry (XFS) and inductively coupled plasma emission spectrometry (ICP-OES). Among them, anodic stripping voltammetry and UV-VIS spectroscopy are insensitive. XFS is the quantitative analysis of fluorescence intensity emitted by atoms excited by radiative energy. FAAS and ICP-OES measure HM concentration by observing its characteristic peaks formed in the gas phase. These methods can be used for the comprehensive detection of heavy metals with high sensitivity and accuracy. However, they usually require expensive equipment, laborious operation, specialized technicians, and complex preprocessing processes. In addition, due to the large equipment and complex detection process, it is not suitable for real-time measurement and in situ analysis.

Recently, microbial fuel cell-based (MFC-based) biosensors have been widely developed as a novel alternative for contaminant detection, with the advantages of miniaturization, ease of operation, and low cost. However, this technique for substrate-specific monitoring is still underutilized. As a low-power in situ sensing tool, synthetic biology-mediated MFC biosensors show great potential for system design and engineering applications in the electrochemical field. By combining different promoters and voltage output elements to design "and" and "or" circuit logic gates, modular genetic elements can be used to customize biosensors for analysis of various or multiple target contaminants. Therefore, the combination of synthetic biology and engineering will further expand the potential of MFC biosensors to detect specific substrates.

We decided to create a biosensor for zinc ion detection based on microbial fuel cell (MFC), which provides an economical, sensitive and practical technology for zinc ion detection.

E. coli BL21 was genetically engineered to express ribB and OprF with the zn-sensitive promoter PzntR, which can synthesize porin and sense zinc ions to produce riboflavin, which promotes electron transport, and porin increases cell membrane permeability of the engineered strain.

The engineered strains were used in a microbial fuel cell (MFC) -based biosensors.

In the presence of zinc ions, the zinc-sensitive promoter PzntR is activated, and the RibB gene is expressed, which promotes the synthesis of riboflavin, and riboflavin promotes electron transport to generate voltage. With the help of OPRF-encoded porins, electron transport is facilitated and voltage generation in the MFC is increased.

We curve to fit the zinc ion concentration to the maximum voltage generated by MFC, and finally obtain the equation: Y =0.5465x+148.6

According to the measured maximum voltage, we can substitute y to get X, which is the concentration of zinc ions in water. We can test whether the concentration of copper ions in water meets the standard according to X.