A composite modified electrode with biomembrane was prepared for amperometric detection of herbicide, which was based on the photosynthesis-inhibiting effect of certain herbicides on photosystem Ⅱ of chloroplast thylakoid.The thylakoid membrane isolated from spinach leaves was entrapped in polyvinylalcohol bearing styrylpyridinium groups (PVA-SbQ).The membrane was then fixed on the head of the Prussian blue-modified carbon paste electrode.Reductive catalytic current of hydrogen peroxide was detected at 0.05 V in pH 6.8 phosphate buffer solution containing 1.5×10^-3 mol/L NaCl and 5×10^-3 mol/L MgCl₂.In the presence of herbicides, the concentration changes of hydrogen peroxide produced by photosynthesis-inhibiting were observed, and the corresponding current changes were in proportion to their inhibitory effects.The electrode allowed to detect the herbicides in the concentration ranges of 1×10^-8～1×10^-6 mol/L for diuron, 2×10^-8～1×10^-6 mol/L for atrazine and 5×10^-8～1×10^-6 mol/L for propanil with detection limits of 3.6×10^-9, 6.1×10^-9 and 8.7×10^-9 mol/L, respectively.The sensitivity of the electrode was improved remarkably due to the incorporation of the electron-mediate of Prussian blue.

Key words: herbicide, composite modified electrode, thylakoid membrane, Prussian blue, photosystem Ⅱ