Functionalized polymeric magnetic nanoconstructs for selective capturing and sensitive detection of Salmonella typhimurium

Abstract

Rapid detection and enumeration of pathogens is essential for monitoring contamination and spoilage of food products to ensure improved quality control management. Functionalized polymeric magnetic nanoconstructs (FPMNCs) were developed as an effective immunomagnetic separator and sensing platform for the selective capturing of Salmonella typhimurium. Novel FPMNCs were prepared in three stages involving synthesis of iron oxide (IO) dispersion, capping with sodium oleate and encapsulation of preformed IO nanoparticles by in-situ free radical emulsion polymerization of styrene (St), methyl methacrylate (MMA) and acetoacetoxy ethylmethacrylate (AAEM). PMMA improves the stability of FPMNCs by bridging extremely hydrophobic PS and hydrophilic PAAEM. Core-shell morphology of hydrophobic core of IO, PS & PMMA and hydrophilic shell of PAAEM was demonstrated by SEM, TEM and FTIR studies. FPMNCs with surface functionalized acetoacetoxy groups were covalently attached with polyclonal antibodies against Salmonella common structural antigen (CSA-1-Ab) without using any linker and catalyst. Colorimetric readout signal was acquired using CSA-1-Ab-HRP as secondary antibody after formation of sandwich immunocomplex with bacteria where the optical density of the samples were recorded using ELISA plate reader at 450 nm. The developed immunoassay was specific and selective which captures only targeted S. typhimurium with a detection limit of 10 cells/mL lower than infectious dose of salmonellosis infection. Minimal interference of food matrix with high signal to noise ratio was shown by various food samples. In addition, the performance of developed FPMNC based immunoassay was superior to commercially available immunomagnetic microbeads demonstrating undisputed advantage for capturing and detecting specific bacteria without any pre-enrichment of sample.

Keywords: Detection; Immunoassay; Immunomagnetic separation; Magnetic nanoparticles; Polymeric magnetic nanoconstructs; Salmonella typhimurium.