A Label Free Nanobiosensor for the Detection of E.coli Using Cysteine Capped Gold Nanoparticle

This study presents a novel one-pot synthesis method to generate positively charged gold nanoparticles (+) Au NPs, utilizing the thiol-containing amino acid cysteine as a capping agent. The resulting Cys-Au NPs displayed a self-assembled monolayer of uniformly sized gold nanoparticles with the diameter of size 36 nM and demonstrated a distinct color change and absorbance shift from 530 to 512 nm when exposed to E. coli , enabling the development of a colorimetric biosensor for rapid and reliable detection of the bacteria. Cys-Au NPs were characterized using spectroscopy, SEM (Scanning electron microscopy); X-ray diffractometer analysis and the photophysical properties of the particles towards E. coli were investigated through absorption spectroscopy and colorimetric tests. The electrostatic binding between Cys-Au NPs and the negatively charged E. coli cell wall facilitated the sensor’s specificity. The biosensor exhibited a detection limit of 2.2 × 10 2 CFU/mL, with a linear detection range between 2.2 × 10¹ and 2.2 × 10 4 CFU/mL. The sensor’s applicability extends to the detection of E. coli in potable water, presenting significant potential in food safety and clinical diagnostics. This innovative detection method provides a quick and efficient means of identifying E. coli in water samples, offering broad applications in various fields, including rapid bacterial detection, food safety, and clinical diagnostics.