Abstract
Whole cell biosensors always face the challenge of low stability of biological components and short storage life. This paper reports the effects of poly(2-hydroxyethyl methacrylate) (pHEMA) immobilization on a whole cell fluorescence biosensor for the detection of heavy metals (Cu, Pb, Cd), and pesticides (dichlorophenoxyacetic acid (2,4-D), and chlorpyrifos). The biosensor was produced by entrapping the cyanobacterium Anabaena torulosa on a cellulose membrane, followed by applying a layer of pHEMA, and attaching it to a well. The well was then fixed to an optical probe which was connected to a fluorescence spectrophotometer and an electronic reader. The optimization of the biosensor using several factors such as amount of HEMA and drying temperature were undertaken. The detection limits of biosensor without pHEMA for Cu, Cd, Pb, 2,4-D and chlorpyrifos were 1.195, 0.027, 0.0100, 0.025 and 0.025 μg/L respectively. The presence of pHEMA increased the limits of detection to 1.410, 0.250, 0.500, 0.235 and 0.117 μg/L respectively. pHEMA is known to enhance the reproducibility of the biosensor with average relative standard deviation (RSD) of ±1.76% for all the pollutants tested, 48% better than the biosensor without pHEMA (RSD = ±3.73%). In storability test with Cu 5 μg/L, the biosensor with pHEMA performed 11.5% better than the test without pHEMA on day-10 and 5.2% better on day-25. pHEMA is therefore a good candidate to be used in whole cell biosensors as it increases reproducibility and enhances biosensor storability.
Highlights
Heavy metals and pesticides are amongst the most significant environment pollutants today [1,2,3].These pollutants are chemically different and require different methods of detection
We report the effect of poly(2-hydroxyethyl methacrylate) (pHEMA) as the immobilizing agent in a cyanobacteria-based fluorometric biosensor for heavy metal and pesticide detection
Bold Basal Medium was modified from the Bristol Medium, which contained all macronutrients and micronutrients necessary for the optimum growth of cyanobacteria and for long term cultivation of algae and cyanobacteria [26,27]
Summary
Heavy metals and pesticides are amongst the most significant environment pollutants today [1,2,3] These pollutants are chemically different and require different methods of detection. Many lab-based techniques for measuring heavy metals and pesticides are based on spectroscopic and chromatographic methods These instruments require skillful operators and are time consuming, when rapid screening of environmental samples is required [4,5,6,7]. Gelation of polysaccharides and proteins generally requires slightly elevated temperatures or non-neutral pH conditions These requirements are less desirable compared to pHEMA, which can form an immobilization matrix for cells under room temperature and neutral pH conditions. We report the effect of pHEMA as the immobilizing agent in a cyanobacteria-based fluorometric biosensor for heavy metal and pesticide detection. Experiments on the effects of pHEMA were conducted by coating a layer of pHEMA on top of the immobilized cyanobacteria
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