Habaneros restore shine to silver nanoparticle production

Habanero peppers can do more than burn our mouths and make us sweaty. Their applications extend beyond the culinary world. While their abundance and flavor make them a staple in hot sauces and spicy cuisines, habaneros could also find use for synthesizing silver nanoparticles.

With applications in antibacterial coatings for textiles, keyboards, wound dressings, and biomedical devices, silver nanoparticles also have valuable optical properties. These nanomaterials absorb and scatter light well because their surface-conductive electrons collectively oscillate when excited by light at certain wavelengths. Their properties can be altered by controlling their shape and size, which alters the local refractive index near the particle surface.

While the abundance and flavor of habaneros make them a staple in hot sauces and spicy cuisines, the peppers are also a useful ingredient when ‘whipping up a batch’ of silver nanoparticles.

But there are no silver-bullet solutions in life, not even from silver nanoparticles. These materials are synthetized by chemically reducing silver nitrate (AgNO₃), a salt. Commonly used reagents for this reduction process have been shown to be toxic and environmentally unfriendly.

This drawback prompted researchers at the University of Guadalajara and the University of Colima in Mexico to look for a more sustainable solution. As resourceful scientists, they didn’t have to look beyond their local eatery for a solution — the spicy, orange habanero pepper offered a fiery catalyst for optical discoveries.

A traditional Mexican crop, habaneros are packed with antioxidants that can be used to promote the formation of nanoparticles by decreasing the effects of oxidative stress. The antioxidants stabilize molecules by reducing and scavenging electrons.

With these qualities in mind, the researchers experimented with two habanero-infused solutions that had different molar (M) concentrations of silver nitrate — one with a 0.001 M concentration, the other with 0.005 M. Each produced silver nanoparticles, though the absorption peak of the 0.005 solution was at a longer wavelength, which indicated larger particles.

The researchers subsequently sampled 10, 50, and 100 mL concentrations of habanero infusion — mild, hot, and five alarm — and monitored each solution’s pH and oxidation reduction potentials. The spiciest sample, with the 100-mL concentration, showed the highest absorption peak and the greatest decrease in pH, signaling a higher yield of nanoparticles.

This humble, delicious, and extraordinarily effective method of creating silver nanoparticles offers a more ecological alternative to conventional and more toxic production techniques, and it could restore the shine to the idea of using the materials in many applications. Olé!