Phycocyanin-conjugated chitosan-coated iron oxide nanoparticles for the separation of Escherichia coli cells

This study proposes a novel method for isolating Escherichia coli bacteria using iron oxide nanoparticles coated with phycocyanin, a fluorescent blue protein pigment found in cyanobacteria that can bind to the genomic area of the cell. This novel technique can be a promising method for the removal of E. coli cells from polluted water samples and also in the downstream processing sector with the separation of E. coli cells using phycocyanin-conjugated chitosan-coated iron oxide nanoparticles with high efficiency. Moreover, the conjugate can also be used for rapid and quick separation and detection of polluted samples. Hence, this study introduces a novel application of phycocyanin as a cell separation method, utilizing its binding affinity to effectively attach to microbial cells for separation purposes. Phycocyanin pigment was extracted from Spirulina platensis, which was later purified using activated charcoal. A yield of 17.6 mg/g of biomass was obtained along with a purity index of 1.2 from the algal biomass. Chitosan-coated magnetic iron oxide nanoparticles were synthesized using the coprecipitation method. The synthesized magnetic nanoparticles were characterized using various techniques such as field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and zeta potential. The results showed that synthesized nanoparticles were 12-15 nm in size. The E. coli cells associated with the phycocyanin-conjugated nanoparticles were separated using a neodymium magnet due to the magnetic property of nanoparticles. The optimum concentration of phycocyanin-conjugated chitosan-coated nanoparticles was found to be 400 mg/L for maximum separation efficiency. The separation effectiveness was found to be 65.7% based on measurements of cell density before and after separation. The attachment of cells to the nanoparticles was observed using fluorescence and transmission electron microscopy. Thus, the coating of phycocyanin over chitosan magnetic nanoparticles allows the adhesion of E. coli cells onto the nanoparticles.