br Conclusions br Introduction Safety concerns about

Conclusions
Introduction Safety concerns about food, drinking water, health surveillance, and clinical diagnosis related to microbial pathogens have attracted increasing attention worldwide. On the basis of pkm2 structure and stain ability with gram stain (weakly alkaline solution of crystal violet or gentian violet), bacteria are grouped into two categories. The bacteria which retain the color of the stain are gram positive bacteria and which lose the color of the stain are gram negative bacteria. Gram negative bacteria (Escherichia coli 0157:H7) are the leading cause of urinary tract infection, food borne illness, inflammation, bloody diarrhea, etc. [13,21]. National health statistical reports reveals that urinary tract infections (UTI) are the second most common infections in human body accounting for about 8.1 million visits to health care providers each year [24]. UTI may be defined as a condition in which bacteria are established and multiplying within the urinary track [14]. The majority of cases are caused by a limited number of bacterial genera; E. coli strains in particular are responsible for 80% of the UTI cases seen in outpatient clinics [8]. The pathogenic strain E. coli 0157:H7 produces toxins that damage the lining of the intestine, cause anemia, stomach cramps and bloody diarrhea, and serious complications called hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). In addition to UTI infection E. coli is commonly used as an indicator in the field of water purification. Urine culture is deemed positive if it shows a bacterial colony count of greater or equal to 103cells/mL. Early illness detection is crucial for early interventions when treatment is most effective and when prevention of dramatic changes is still possible. Early illness recognition and treatment are not only key to improving health status with rapid recovery after an acute illness or exacerbation of chronic illness, but also key to reducing morbidity and mortality in older adults. Therefore various methods have been developed in the past for the analysis of Gram negative bacteria (E. coli 0157:H7). Conventional techniques used for the detection of pathogenic bacteria include culturing techniques [12,5] polymerase chain reaction (PCR) [9,11,3,20], enzyme linked immunosorbent assay (ELISA) [16,22,10], long range surface plasmon-enhanced fluorescence spectroscopy (LRSP-FS) [7] and inductively coupled plasma mass spectrometry (ICPMS). However all these techniques suffer from limitations such as time consumption, high cost instrumentation and complicated preconcentration. Hence exploring an accurate, rapid and conventional analytical method to detect E. coli in UTI patients still remains a challenge. Sensor technology provides a cost effective way to remotely monitor older adults at home, detect impending illness, and allow for early intervention. Naked eye detection of E. coli in urine using one step functionalization can be a great achievement in the ever developing field of research. Colloidal gold is extensively used for molecular sensing due to the wide opportunities it offers in the design of easy to perform methods [2]. One of the approaches for the design of functional nanomaterials is based on the assembly of AuNPs with specific ligands or biomolecules such as proteins, lipids and nucleic acids [15,4,17,18,19,1]. The modification process or alignment of AuNPs leads to tunable optoelectronic properties which in fact is used in sensing applications. Most of the sensing approaches utilize the nano surface plasmon resonance (SPR) mechanism which is based on binding induced aggregation of spherical particles. In our effort to develop a colorimetric sensor for E. coli we modified AuNPs with cysteine (CAuNPs). The NH2 receptors on the surface of cysteine modified AuNPs bind with E. coli 0157:H7 via electrostatic adhesion between positive charge of cysteine and high negative charge caused by the endotoxin or lipopolysaccharrides found in the outer cell wall of E. coli 0157:H7. The negative charge helps in the overall stabilization of E. coli. Thus CAuNPs can be cross linked in presence of definite amount of bacteria causing a visible color change of the solution from red to blue providing a simple detection by naked eye. The results emerged indicate that this method could hopefully be integrated into clinical labs, as this does not demand either any hazardous and costly chemicals or any complex synthetic routes. Also this method could be used by patients as a self checking method at home in warranting further medical attention.