Mexican researchers have shown that compounds extracted from corn husks may offer a route to low-cost synthesis of antibacterial silver nanoparticles.

Since ancient times, silver has been famed for its antibacterial properties - the Romans added silver coins to their drinking water to keep it clean, and during World War I, soldiers’ wounds were commonly treated with silver leaf to prevent infection. The widespread introduction of antibiotics in the late twentieth century meant that silver’s use in medical applications slowly dwindled, but recent advances in nanosilver has put it firmly back on the research agenda.

This work, published in a recent issue of Materials Letters [DOI: 10.1016/j.matlet.2015.03.097], reports on the production of nanoparticles of silver (Ag) and silver chloride (AgCl) using antioxidants extracted from corn husks. The husk that surrounds a corncob accounts for 40% of its weight, but has historically been viewed as a waste product. In 2012, its phytochemical properties were characterised and the husk was found to contain naturally-occurring compounds that could reduce silver ions. This suggested that they could be used as production agents for silver nanoparticles.

Marco Antonio Flores-González and his team used this idea to design a low-cost method of nanoparticle (NP) production which could be carried out at ambient temperatures – in stark contrast to conditions required for existing NP synthesis methods. This paper demonstrated that the husk’s three phenolic molecules – cellulose, hemicellulose, and lignin – each play a role in the production of nanostructures. The researchers added silver nitrate (AgNO3) to a suspension of ground corn husks in water. By then varying the pH of this mixture, the synthesis of Ag and AgCl nanoparticles could be controlled. At pH 7, pure silver nanoparticles were produced with a diameter of less than 10 nm, while at higher pH levels, both Ag and AgCl were identified (average size 20 nm)

In addition, the antibacterial properties of the nanoparticles were determined by testing them against Escherichia coli and Staphylococcus aureus. Against S. aureus, the husk-based NPs performed similarly to commercially produced NPs. But against E. coli, the AgCl NPs considerably outperformed commercial particles. With the weight of corn produced in Mexico predicted to reach 25 million tonnes by the end of 2015, the team may just have found a simple way to turn a substantial source of waste into a high-value product for use in medical applications.

Materials Letters 152 (2015) 166–169,”Aqueous corn husk extract–mediated green synthesis of AgCl and Ag nanoparticles” DOI: 10.1016/j.matlet.2015.03.097