Development of biosensor for heavy metal detection

Abstract

In the present study bacteria were isolated from soil on the basis of urease and alkaline phosphatase activities. Enzyme activities of the bacterial isolates were monitored in free and immobilized state and effect of three metal ions Cu, Zn and Cd was observed to determine the threshold concentrations of the metal ions. Two transducer systems potentiometric and amperometric were used to assemble the whole cell and electrode system to monitor the enzyme reactions and inhibition by metal ions electrochemically in order to develop a biosensor for heavy metal detection.Two urease producing strains were isolated from soil and identified as Bacillus sp. MD028 (FJ005050) and Bacillus subtilis strain MD008 (EU780733) using 16S rDNA sequencing. Bacillus sp. MD028 (FJ005050) showed good urease activity(12 U/mg (Dry cell weight)) as compared to Bacillus subtilis strain MD008(EU780733) [9 U/mg (Dry cell weight)].The effect of three heavy metals viz., Cu, Cd and Zn on the alkaline phosphatase activity of free and immobilized P. striata cells showed an inhibition trend ofZngtCdgtCu. The inhibitory response of heavy metals was linear in the concentration range of 0.01-1 mgl-1 for Zn, 0.1-4 mgl-1 for Cd and 1-30 mgl-1 for Cu.This work presented a novel and efficient strategy for immobilization of lyophilizedcell mass of P. striata in poly vinyl chloride matrix which upon immobilization retained more than 85 % of the alkaline phosphatase activity which indicated thatthe protein structure was not damaged after immobilization. An equally efficient and novel strategy of immobilization was used for the immobilization of lyophilized biomass of Bacillus sp. MD028 (FJ005050) by covalently attaching the bacteria cells on the conducting polymer matrix of PPy-PVS/ITO electrodes. The Bacillus sp. MD028 cells retained approximately 98 % of the urease activity after immobilization. Both these immobilization techniques are novel and are being reported for the first time for the immobilization of bacterial cells.