Novel Nano-Biosensor For Rapid Detection Of Environmental Hormones

Organophosphate pesticides (OPs) are a kind of toxitic agent of nervous system, which have been widly used in agriculture. When OPs are uptaken by human over a long term, they would irreversibly inhibit the activity of acetylcholinesterases (AChE) and subsequent prevent the nerve transmission by blocking breakdown of the transmitter acetylcholine. The rapid and accurate quantification of these toxic agents in the environment is of great significance for food security and human health. The electrochemical acetylcholinesterase biosensors have been extensively investigated for organophosphate pesticide detection based on the inhibition effect of OPs towards AChE in the past decades, due to their high sensitivity, low cost and ease of miniaturization. However, the relatively high working potentials (⁷00mV) of the biosensors required for thiocholine oxidation could lead to interferences from co-existed electroactive species and high background currents. Herein, a novel AChE biosensor is fabricated based on the composites forming by Nafion and multiwall carbon nanotube (MWNTs). The working potential is reduced from 700mV to 300mV, which would result in the promoting of selsctivity of the biosensor, due to the excellent electro-catalytic property and immobilization of enzyme. The biosensor is simply constructed by two steps coating, with good sensitivity, stability and detection limit.Multiwall carbon nanotubes (MWNTs) are well dispersed by Nafion to form the MWNTs-Nafion nanocomposite, which are subsequently coated onto a glass carbon electrode (GCE). Then, AChE is immobilized on the electrode by the Nafion matrix, obtaining the biosensor: AChE/nafion-MWNTs/GCE. The fabrication methods and detection conditions are optimized. It is found that the electron-transfer resistance dereased greatly. It is confirmed by cylic voltammograms that Nafion-MWNTs composites modified electrode could efficiently catalyze oxidation of thiocholine at ³00mV with ten times higher current than that of bare electrode. The biosensor showes excellent amperometric response to ATCl in a wide linear concentration range from 0.02mM to 1.1mM, with a sensitivity of 10.303 nA·μM^-1. The Michaelis constant (Km) of immobilized AChE is calculated to be 0.57mM. The as-constructed biosensor is used for OPs detection using paraoxon as a model compound. The inhibition rate of paraoxon towards AChE is proporational to the pesticide concentration from 10^-11g/mL to 10^-8g/mL, with a detection limit of 3×10^-12g/mL. The relative recovery rate of paraoxon is calculated to be 95%¹07% by adding certain concentration of paraoxon to pipe water.