Biosensors for in Field Measurements: Optimisation of Parameters to Control Phosphororganic Pesticides in Water and Vegetables

Abstract

Enzymatic sensors based on the ion sensitive field effect transistor (ISFET) and semiconductor structures for detection of phosphororganic pesticides were developed. Their characteristics were optimised to control these pollutants in field. Acetyl-(AChE), butyril- (BChE) cholinesterase’s (ChE) and crude substances contained both forms of ChE were used as chemically sensitive substances to the phosphororganic pesticides. Detectable phosphororganic components were o,o-diethyl o-3,5,6-trichloro-2 pyridil phosphortionate, 2,2-dichlorovinyl dimethyl phosphate and phasolone. They are irreversible inhibitors for above mentioned ChE’s. It is shown that the usage of replaceable enzymatic membrane is more preferable for repeated analysis than its reactivating. Alginate gel and nitrocellulose (NC) strips are very suitable for creation of replaceable enzymatic membrane. The standard deviation of sensor responses for series measurements and for different membrane castings did not exceed 10%. The working characteristics of enzymatic sensors based on the ISFETs depend on medium condition of samples to be analysed. Vegetable sap influences on the value of sensor response. To prevent dependence of sensor signal on medium of analysed samples, the measurements should be performed in standard solution (3–5 mmo1/1, pH 7.3 tris-HCL buffer, contained 140 mmo1/1 sodium chloride). The sensitivities of enzymatic sensors based on the ISFETs to above mentioned pesticides were within the range 10⁻⁵ – 10⁻⁷ mol/l. ChE’s are reversible inhibited by heavy metal ions. The activity of ChE’s is significantly reduced at their concentration 10⁻³mo1/l and higher. To diminish nonspecific signal which is generated by ChE’s in the presence of heavy metal ions, it is necessary to have information from urease sensor. The usage of urease and any ChE as well as transducer in form of Si-SiO₂-Si₃N₄-Ta₂O₅-electrolyte metal allows to get multichannel sensor for pesticide analysis. The detectable concentration of phasolone by multi-enzymatic sensor was about 10⁻⁷ mol/1. The sensitivity of analysis by both developed sensors is significantly higher than permissible limit of pesticide concentration in water and in vegetable food.