Study On The Formaldehyde Microbial Biosensor

Formaldehyde content has become an important safety indicator in Pollution Monitoring of living room, food and textiles. Currently the main formaldehyde detection methods are spectrophotometry, electrochemical detection, chromatography and electrochemical sensors. Spectrophotometry is restricted by the water bath, or concentrated sulfuric acid and other operating conditions; electrochemical detection has a high requirement in sample preparation; the equipment of chromatography is more expensive and difficult to use, and its operation and maintenance are relatively cumbersome; electrochemical sensors suffered more interfering substances and have a short life. The interferce of formaldehyde microbial sensor is small because the selected strains has a specificity response to formaldehyde, and microbial sensor has a good application prospects in the realization of a fast, intuitive determination of formaldehyde because of its fast testing speed, high sensitivity and good reproducibility.Bacillus subtilis, Bacillus licheniformis and Escherichia coli strains was selected as biological components, which were immobilized by sandwich on dissolved oxygen electrode. By studying the response of these three kinds of strains to formaldehyde, it was found that Bacillus subtilis was the most sensitive microorganism. And its immobilization effects were studied. We selected diatomite as immobilized carrier to enhance the response performance of immobilized microbial membrane. And further optimize the sandwich immobilization technology by determining the addition of immobilized carrier and the amount of bacteria.The optimum working conditions of Bacillus subtilis microbial sensor were investigated. The results showed that the optimum temperature was (33.5±0.5)℃, the appropriate pH was 6.76 and the appropriate concentration of GGA was 18 mg·L-1 in bottom fluid. The liner relationship between the response signal and the concentration of formaldehyde was obtained in the range of 0.005～0.2 mg·mL-1, corresponding the liner regression equation y=13.534x-0.0177(R2=0.9966). The relative standard deviation of 10 times parallel determination was 1.13%, and the recovery was 107%. Interference tests showed that phenol, methanol and ethanol had smaller interference on the determination results, and when determined 0.1 mg·mL-1 of formaldehyde ,it can co-exist 450 times of phenol, 600 times of methanol, 2370 times of ethanol. Acetaldehyde had some interference on the determination, and when determined 0.05 mg·mL-1 of formaldehyde, it can co-exist 10 times of acetaldehyde. The results also showed that the best membrane film's retention time can surpass 60 d.In order to verify the performance of Bacillus subtilis formaldehyde microbial-sensor, the acetylacetone spectrophotometric method was used for comparison, and the conditions of which were as follows: measurement wavelength 413 nm; boiling water bath time 3 min; reagent dosage 2.00 mL; measured within 5 min after color cooling. The liner regression equation y = 0.0211x-0.0093, correlation coefficient was 0.9996. Determined the unknown concentration of formaldehyde within these two methods, and carried on a t test to the results according to SPSS software, and it was found that P>0.05, which demonstrated that these two methods have a good consistency.