Cysteine capped gold nanoparticles for naked eye detection of E. coli bacteria in UTI patients

Abstract Nanomedicine is a rapidly growing field and expectations that it will help in improving the treatment of many pathologies are high. Colloidal gold is extensively used for molecular sensing because of the wide flexibilities it offers in terms of modifications of the gold nanoparticles (AuNPs) surface with a variety of functional groups. We present here a sensitive colorimetric method for the detection of Escherichia coli 0157:H7 ( E. coli 0157:H7) in the urine sample of patients suffering from urinary track infections (UTI), where material and reagent costs are minimal. The method involves one step functionalization of AuNPs by cysteine. Cysteine gold nanoparticles (CAuNPs) binds with E. coli 0157:H7 bacteria through electrostatic adhesion between the positive potential of cysteine and the negative potential of E. coli 0157:H7. The red shift in the plasmon absorption spectra of CAuNP with different concentrations of E. coli 0157:H7 followed by the color change of the solution from red to blue is the basic principle applied here for the detection of E. coli 0157:H7. The method was successfully applied for the detection of E. coli 0157:H7 bacteria in patients suffering from UTI. The results correlated well with the conventional method indicating that the method could potentially be used as a self screening method for the patients suspecting UTI, for warranting further medical attention. The method exhibits a linear relationship in the range of 1 × 10 3 –4 × 10 3  cells/mL with a detection limit of 100 cells/mL.