For this year's iGEM Competition, our team will be focusing on putting forward a biological approach to detect nickel ions as a heavy metal contaminant in the natural environment. Through our study over this summer, we are expecting to make the expression of green fluorescent protein by nickel ion concentration control. In a certain concentration range, we will try to establish a quantitative relationship between fluorescence intensity and nickel ion concentration in the environment. This may build a nickel ion concentration quantitative detection system.

In order to achieve this goal, we use a nickel-sensitive repressive promoter (pncrA). In the absence of nickel ions, the repressor protein (NcrB) binds to the promoter, preventing the expression of the subsequent gene. The nickel ions in the environment can bind to repressor proteins to alter the domain of the protein, so that the fluorescent protein gene behind the promoter is expressed and produces fluorescence.

Nickel is an important element for humans. Normally, the human body maintains a daily demand of 0.3mg nickel. However, it is also one of the metal elements that easily cause allergy among human beings, with an estimated 20% of people being allergic to it. As is claimed by experts, an intake of more than 0.6mg nickel at a time can cause allergy to almost any person. A chronic excessive intake of nickel can cause a variety of toxic reactions, including dermatitis, respiratory disorders and even respiratory cancer. In addition, nickel is also considered to be one of the relevant factors that cause leukemia, asthma, and urinary stones. Also, it can possibly lead to reduced fertility and teratogenicity.

Nickel pollution generally refers to excessive amounts of nickel existing in the environment that humans are exposed to. Traditionally, major sources of nickel in the environment are the industry of steelmaking and electroplating, with approximately 85% of nickel being used in certain process. However, with the rapid development of science and technology, the manufacturing of electronic products has brought a substantial amount of nickel ions to the environment. Also, with the popularity of new energy vehicles, nickel-metal hydride batteries being its major power source has contributed to an increasing demand of nickel, and unavoidably, an increasing amount of nickel ions to the environment as well. Statistics indicate that the 2016 global raw nickel consumption reached 200 million tons. The future demand for nickel is predicted to continue increasing at an annual 5% growth rate on average. As a consequence, we may have to anticipate a deterioration of nickel pollution. Therefore, the detection of nickel ions in the environment and hence methods to alleviate nickel pollution will be vitally important.

Currently, the most commonly adopted method of nickel ion detection is spectrophotometry, with which an amount of nickel ion within the range from 0.08 to 5.0 mg / L in solid samples and within the range from 0.25 to 10 mg / L in water samples can be detected. However, spectrophotometry has obvious limitations, being very susceptible to interference from other substances throughout its process and thus making itself a relatively less reliable detecting approach. Moreover, the procedures are fairly complicated and costly as well. Therefore, our team is striving to put forward a biological approach of nickel ion detection, which can achieve the same accuracy as spectrophotometry yet is simpler in procedures and probably much lower in cost.