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Nicotine test result of the first generation system
We measured the expression of fluorescent protein of the first version monitoring system in different concentrations of nicotine solutions. The following result showed that the growth of E. coli was not affected in a large scale when the concentration was approximately 0.001 g/L (Figure. 1) and 0.01 g/L (Figure. 2). However, the fluorescence expression intensity of the latter did not increase with the passage of time, and the effect was not obvious compared to the former concentration. In the concentration of 0.1g/L (Figure. 3), the relative expression of fluorescent protein at each time point was negative, from which we inferred that nicotine was harmful for E. coli. As we continued to increase the concentration of nicotine, the expression of fluorescent protein was getting lower and lower, which also confirmed our hypothesis that expression of fluorescent protein would abate with nicotine toxicity in certain range.
E. coli growth
Above-mentioned nicotine gradient shows that the expression of fluorescent protein positively correlated with the concentration of nicotine and the toxicity of nicotine itself to E. coli also cannot be ignored. We have searched for a suitable threshold for the operation of the first generation detection systems. From the following figure, the E. coli in the first version of detection system began to decrease sharply at 4h, at 0.32g/L concentration. In addition, the mathematical modeling prediction showed the same increase rate compared with the rate of decline of E. coli, according with the experimental results.
In summary, according to mathematical modeling (with modeling), the first generation detection system suited to work in environment that the concentration of nicotine was not more than 0.32g/L and the detection time was longer than 4h.
Comparison between the second generation system and the original system
As shown below, we chose a lower concentration of nicotine (0.0001g / L). The next version of detection system could express fluorescent protein, however, only had function of detection. Compared to the first version, the expression of fluorescent protein increased significantly. The fluorescence expression of the second version of detection system was obviously higher than that of the first version. It increased greatly at 1h and reached top at 3h. Then, the fluorescence intensity dropped significantly. Thus, finally we chose the second generation system--with the recommended concentration of nicotine in the bacteria solution, 0.0001g/L, and the results obtained within 1~3h.
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