Rapid identification of viable Escherichia coli with a goldnanoparticle biosensor

Many strains of Escherichia coli are known to be dangerous human pathogens that can cause life- threatening conditions including bloody diarrhea, hemorrhagic colitis, renal failure and meningitis [1]. Conventional culture tests for coliforms and faecal coliforms are time-consuming and bacterial identification requires days to weeks to complete. These conventional microbiological methods for identifying bacterial strains employ selective culture as well as biochemical and serological characterization [2]. Several rapid methods for E. coli identification have been developed [3]. Many are based on the measurement of certain enzyme activities such as β-galactosidase and glutamate decarboxylase [4,5] as well as β-glucuronidase, which is generally present only in Enterobacteriaceae [6]. Microorganism identification has also been reported using high-resolution proton magnetic resonance spectroscopy and mass spectrometry. This paper reports a new theoretically ultra-sensitive nanosensor based on color shift, where selectiverecognition is accomplished using gold nanoparticles functionalized with carbohydrates (glyconanoparticles) that recognize and bind to cell-surface lectins. The gold nanoparticles function as concentrators that amplify the bacterial cell lectins recognition by confining several carbohydrates molecules in a nanoscale domain. Bindingof lectins and glyconanoparticles lead to the aggregation of gold nanoparticles and thus the shift of color shows the presence of E. coli in sample.