Nanotech bacteria detector

A group of

researchers have developed a novel technique called SEnsing of Phage-Triggered Ion Cascade, or SEPTIC, to rapidly detect and identify bacteria.

Using a nanowell device with two antenna-like electrodes, the scientists can detect the electric-field fluctuations that result when a type of virus called a bacteriophage infects a specific bacterium, and then identify the bacterium present. The researchers tested their technology on strains of E. coli and experienced a 100% success rate in detecting and identifying the bacteria quickly and accurately.

Dr. Laszlo Kish and Dr. Mosong Cheng, both in the Department of Electrical Engineering, collaborated on the work with Dr. Ryland Young and Dr. Maria Dobozi-King, both in the Department of Biochemistry and Biophysics.

The scheme works because only a specific phage can infect a specific bacterium. When a bacteriophage infects a bacterium, the phage injects its DNA into the bacterium and "reprograms" it to produce multiple copies of the phage, called virons. During the infection process, about 100 million ions escape from the host cell. This ion leakage causes fluctuations in the electric field around the bacterium, and the nanowell developed by Cheng detects these fluctuations.

Kish said that the observed electrical field fluctuations have very different dynamics than the background noise.

"Due to this reason and due to the selectivity of phages - phages never infect a wrong bacterium - the method is virtually free of false alarm," Kish said.

SEPTIC identifies bacteria within minutes, with no false alarms and very low probability of missed detection. The method is also relatively cheap. Other detection methods such as PCR (polymerase chain reaction) culturing require hours or days of processing and more expensive instrumentation, and also don't distinguish very well between living and dead bacteria. In addition, other methods require trained personnel, whereas SEPTIC only needs minimal personnel involvement.

"Rapid and sensitive identification of bacteria is extremely important in clinical, veterinary and agricultural practice, as well as in applications to microbiological threat detection and reduction," Cheng said.

"But given its fast response, high specificity and relatively low cost, SEPTIC could be invaluable in clinical, veterinary and agricultural practice, as well as in the current fight against bioterrorism. Eventually, every nurse or soldier may be equipped with a cell phone-like, wireless SEPTIC biolab."

"Our ultimate aim is to have a biochip where hundreds of nanowells and their preamplifiers are integrated. Each nanowell covers a different phage, and if a relevant bacterium is present, the corresponding nanowell will signal and identify the bacterium. This would be a pen-size biolab that would be able to identify hundreds of bacteria in five minutes," added Kish.

The researchers are now working also with Dr. Cheng Kao in the Department of Biochemistry and Biophysics on implanting their nanowell device in plants. Plant cells die after a virus attack, and the device can send a signal warning of a viral attack.