Functional magnetic nanoparticles for biodefense and biological threat monitoring and surveillance.

A new methodology toward biodefense and threat surveillance by water-dispersible, bactericidal, paramagnetic nanoparticles is presented. The nanoparticles consist of magnetite clusters (approximately 70 nm) modified by polyethyleneimine (PEI) and poly(hexamethylene biguanide) (PHMBG) and are prepared by a two-step procedure at an acceptable cost. The cationic nanoparticles are colloidally stable in water at pH < or = 10, where they sequester DNA or whole microbes. The nanoparticles and bound DNA are captured by high-gradient magnetic separation. Methods of efficient extraction and quantification of the DNA by real-time PCR are developed. Broad bactericidal activity of the nanoparticles is demonstrated at concentrations far below cytotoxicity levels for mammalian cells. The levels of the DNA detection sensitivity obtained in our experiments allow us to project the applicability of the developed method for the detection of DNA molecules of various germs.