New "ON-OFF"-type nanobiodetector

A new type of nanobiodetector based on a limited number of polyaniline nanofibrils has been designed and tested against bacteria Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Enterococcus faecalis. The cells attaching conducting nanofibrils modify locally the electrical conductivity making the polymer nanowires electrically inhomogeneous. The "defects" accumulate in nanofibrils changing suddenly their electrical conductivity above a threshold density (the percolation limit), enabling an easy flow of the charge carriers. The results are unique: the device works like an "ON-OFF" switch with nearly linear response above a threshold number of cells in the suspension examined, which is of an order of 10(5) to 10(6) CFU per 1 ml. Such a behaviour is important for bio-alarm systems, environmental monitoring and medical applications.