Preparation, characterisation and evaluation of antimicrobial activity of Al³⁺ -modified starch nanoemulsion

An oil-in-water nanoemulsion comprising of aluminium ions encapsulated in a chemically modified starch derivative was prepared, characterised and evaluated for the antimicrobial activity. The nanoemulsion was prepared by emulsion-coacervation method under ultrasonication conditions. Based on the aluminium oxinate chelate of Al³⁺ ions, Al(ox)₃, the encapsulation efficiency (92%) was determined by ultraviolet-visible spectrometry measured at 365 nm, and the subsequent drug loading efficiency was also calculated to be 92%. Fourier transform infrared spectroscopy confirmed the formation of carboxymethyl starch, and the degree of substitution was found to be 0.17 by back-titration, using phenolphthalein as an indicator. Transmission electron microscopy (TEM) micrographs revealed spherical nano-droplets with a minimum particle diameter of 7 nm that had coalesced to form nano aggregates of variable diameters. There was also an indication of the formation a larger nano cluster with a length of approximately 215 nm. Freeze-thaw cycles revealed that the nanoemulsion was stable. Disc diffusion method was used to evaluate the antimicrobial activity of the synthesized aluminum ion nanoemulsion on selected gram-negative bacteria (E. coli and P. aeruginosa) and gram-positive bacteria (B. subtilis and S. aureus).