In order to acquaint the needs of the target users, we visited an electroplating factory and asked the responsible person what problems they would encounter in the practical testing.
The head of the factory first led us to visit the electroplating process to find out how the polluted water produce. She said “a great number of heavy metals in inorganic form are used in the electroplating and they are usually excessive. So the wastewater contains a lot of heavy metal ions. And wastewater will be treated before discharge and checked the content of heavy metals before and after treatment.”
Then we introduced our testing paper method to her for some suggestions.” The accuracy of indicator papers is not high enough for factories. Besides, judging the heavy metal concentration according to the color depth by workers is prone to deviation. But cheaper testing method is really appealing to the users.” she said.
We finally used application in phone to scan the sample so that the concentration of the heavy meatal can be presented in digital form and the cost of indicator paper can be saved.
Associate professor, school of life science, Sun Yat-sen University; Nature’s ten people who mattered this year (2015)
Prof. Huang said, “for better application in actual environment, you should put the modified E. coli not only in the samples only containing heavy metal ions but also in the samples from the actual environment. You can collect and detect the water samples with heavy metal pollution and then compare the results with those of physical or chemical methods.”
Figure 1. We took the sample in the pool near Jiahewanggang subway station in Guangzhou City, and put some mercury in it to simulate the heavy metal pollution in actual environment. We had strongly proved that our product can be actually used in the reality world.
Associate professor, school of biological science and engineering， South China University of Technology
She told us that we should find out the minimum detectability of each heavy metal ion and compare it with those of physical and chemical methods. More importantly we should make sure that our minimum detectability is lower than China’s national drinking water safety standards.
Associate professor, school of life science, South China Normal University
She said,” The sensibility is relatively high but the specificity is also important because there may be a variety of metal ions in the actual water samples. If the sensor responds in the presence of other metal ions, it will bring deviation to the experimental results. So it is necessary to repeat the specificity experiment of sensors to verify the correctness of the data from papers.”
Figure 2. The growth of the E. coli with lead detecting device after adding different metal ions and ddH2O.
Figure 3. The growth of the E. coli with mercury detecting device after adding different metal ions and ddH2O.
Figure 4. The growth of the E. coli with cadmium detecting device after adding different metal ions and ddH2O.
Our questionnaire also included part of the public acceptance of engineering bacteria.
Laying stress on the drinking water safety, 94% of respondents said they were willing to use convenient testing tools to detect heavy metals concentration in nearby water source.
In “how do you think of genetically modified bacteria (non pathogenicity) used to detect contaminants”, 92% of respondents accepted and supported these applications.
But there were still a few respondents who were not able to accept biological methods, mainly because of the existence of biological safety problems. Therefor we invited Professor Zhaozheng Guo from BGI to come to school and set up a lecture on biological safety ethics, hoping to improve public acceptance of bioassay.
The problems above showed that cheap, fast and portable biological methods for detecting heavy metals in water or soil were of great interest to the public and small and medium-sized factories.
. Integrated wastewater discharge standard (China,GB8978-1996)
. National drinking water standards（China,GB5749-2006）
. 2011 Edition of the Drinking Water Standards and Health Advisories (the USA)