This invention relates to a multiwalled carbon nanotube (MWNT) biosensor for the detection of paraoxon contained in organ phosphorous (OP) nerve agents, Acetylthiocholine esterase (AChE) is an enzyme which is necessary for the transmission of nerve impulses in the body. For the normal functioning of the nervous system AChE is a critical enzyme. However, OP compounds result in acute tcmcity by inhibiting the normal functioning of the enzyme leading to cholinergic dysfunction and death.
It is therefore an object of this invention to propose a simple, sensitive and rapid acting biosensor for the monitoring and detection of these harmful compounds.
It is another object of this invention to propose a biosensor which is useful for the detection of very low quantities, such as, 0.1 nM of highly toxic paraoxon.
We therefore propose such a biosensor which, according to this invention, is based on multiwalled

carbon nanotubes (MWNTs) for the detection of paraoxon contained in organ phosphorous (OP) nerve agents, and comprises functionalized MWNTs with their surface decorated with metal Nan particles, said MWNTs being modified to glassy carbon (GC) electrodes.
Purified MWNTs are functionalized using oxidative functional groups and decorated with metal Nan particles. These functionalized MWNT based Nan composites are employed for the modification to GC electrode which have been tested for the sensing of OP compound.
Paraoxon was used as standard pesticide for the AChE inhibition measurement. For these measurements enzyme AChE functionalized metal coated carbon nanotubes modified GC electrode was employed as the working electrode. Substrate acetylthiocholine iodide was used in the electrolyte. By measuring the reduction in current due to addition of paraoxon, using

the following equation, the percentage of inhibition is measured:

The biosensor employed for the detection of paraoxon analyte and the inhibition curve was obtained by plotting inhibition percentage (1%) vs. Paraoxon concentration This inhibition plot shown in Fig.l of AChE shows high linearity in the range measured from 7 riM to 0.1 nM. Limit of detection is 0.1 nM.
This invention disperses the AChE enzyme on metal (gold) Nan particles decorated MWNTS. Metal nanopaiticles on the surface of MWNTS create favorable surface for the enzyme immobilization and enhance the enzyme electrode interaction due to increased electron transfer rate of the MWNTs

We Claim:
1. A multiwalled carbon nanotube (MWNT) biosensor for the detection of paraoxon contained in organophosphorous (OP) nerve agents, comprising functionalised MWNTs with their surface decorated with metal nanoparticles, said MWNTs being modified to glassy carbon (GC) electrodes.
2. A biosensor as claimed in claim 1 wherein the nanoparticles are of gold.
3. A multiwalled carbon nanotube (MWNT) biosensor for the detection of paraoxon contained in organophosphorous (OP) nerve agents substantially as herein described.
4.An apparatus for the detection of paraoxon contained in organophosphorous (OP) nerve agents as claimed in any one of the preceding Claims wherein the said biosensor is the electrode and substrate acetylthiocholine is in the electrolyte for measurement

of reduction in current on addition of paraoxon and thus for obtaining the percentage inhibition of AChE.