Green synthesized nickel nanoparticles for targeted detection and killing of S. typhimurium

Simple and sensitive colorimetric immunosensor based on peroxidase mimetic activity and photothermal effect of nickel oxide nanoparticle (NiOGs) has been developed to detect and kill food borne pathogen Salmonella typhimurium. NiOGs showed superior peroxidase mimetic activity for oxidation of peroxidase substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB). Oxidation of TMB by NiOGs followed Michaelis-Menten kinetics with K_m and V_max values of 0.25mM and 2.64×10^-8M/s respectively. NiOGs was coated with citric acid (CA-NiOGs) followed by conjugation with antibody (anti-S. typhimurium) (Ab-CA-NiOGs) that effectively captured S. typhimurium. Colorimetric detection of S. typhimurium by Ab-CA-NiOGs showed a linear relationship between pathogen concentration (1×10¹ to 1×10⁶cfu/mL) and color signal (652nm) with limit of detection (LOD) of 10cfu/mL. The proposed method showed no cross reactivity against other pathogens. Recovery of S. typhimurium in milk and juice samples was found to be 95 to 100% and 92 to 99% respectively. NiOGs exposed to laser irradiation showed dose dependent increase in temperature and singlet oxygen within 5min. Bacteria bound to Ab-CA-NiOGs after laser irradiation, induced membrane damage and reduced bacterial viability to 6%. The bifunctional peroxidase-mimetic activity and photothermal effect of NiOGs can be exploited in selective sensing and killing of target pathogens respectively in food products.