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Toxic ions pollution in water has long plagued people. How to detect the concentration of toxic ions and how to decrease the detection limit as much as possible have become a challenging task.

The most common and sensitive methods of detecting trace toxic ions today are based on instrumental analysis, such as Atomic Absorption Spectrometry(AAS) and Inductive Coupled Plasma Emission Spectrometer(ICP), however, these methods require expensive instruments, and the operation is cumbersome as well. Hence the applications of these methods are limited to professional testing organizations and scientific research institutions. In addition, although there have been test paper, detection kits and other low-cost products which can be used to detect toxic ions, they also face the problems such as low efficiency, poor sensitivity, and tedious process. Thus the existing detection technology is not suitable for the general population to use.

Although there were many iGEM teams trying to design a variety of detecting systems to detect pollutants as the same as us, they might have many defections such as the detection limit is high and that the detection time is long. In order to find a better way of detecting comparably small quantities of toxic ions, methods such as the biological signal-amplifiers, the microfluidic chips and the portable hardware are of great importance and practical significance. .

An interesting method to detect the concentration of ions using Escherichia coli is to select the corresponding ion-sensitive promoters binding with the reporter genes like the fluorescent protein genes. By constructing this kind of recombinant plasmids, the concentration signal can be transferred into a semi-quantitatively detectable signal like electric current and so on. However, the detection limit is extremely low that only high level accumulation of toxic ions in the environment can be detected. To solve this problem, we aimed to construct an amplifier to detect the concentration of the toxic ions including the ions semi-quantitativly with small volume.

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A sensitive detector for harmful ions in water based on a chip

Arsenic contamination in drinking water has long been a serious problem in many countries throughout the world, including China and the US. In this circumstance, XMU-China hopes to provide a sensitive and user-friendly device to detect arsenic in water and a microfluid chip is designed and produced to achieve our goal. The chip is an arsenic detector containing genetically modified E.coli that is able to express green fluorescent protein or lacZ in response to a certain range of arsenic concentration of arsenic. By calibrating the fluorescence intensity or current strength caused by luciferase or lacZ respectively, a whole range of arsenic levels in water can be detected.

We also plan to use this chip model to detect other harmful ions such as iron and mercury. To simplify the process, we will adopt a certain universal approach by constructing a common intermediate which can eliminate the differences among detection of different harmful ions. And T7 induced expression system is used to realize the effect of amplifying the signal in response to these ions. What’s more, we try to explore potential application of iLOV, a kind of small FMN-based fluorescent protein, to detect and recycle these harmful ions because of its inherent, binding properties towards them with high affinity.