From nanoparticles to crystals: one-pot programmable biosynthesis of photothermal gold structures and their use for biomedical applications

Abstract

Inspired by nature, green chemistry uses various biomolecules, such as proteins, as reducing agents to synthesize metallic nanostructures. This methodology provides an alternative route to conventional harsh synthetic processes, which include polluting chemicals. Tuning the resulting nanostructure properties, such as their size and shape, is challenging as the exact mechanism involved in their formation is still not well understood. This work reports a well-controlled method to program gold nanostructures' shape, size, and aggregation state using only one protein type, mucin, as a reduction and capping material in a one-pot bio-assisted reaction. Using mucin as a gold reduction template while varying its tertiary structure via the pH of the synthesis, we demonstrate that spherical, coral-shaped, and hexagonal gold crystals can be obtained and that the size can be tuned over three orders of magnitude. This is achieved by leveraging the protein's intrinsic reducing properties and pH-induced conformational changes. The systematic study of the reaction kinetics and growth steps developed here provides an understanding of the mechanism behind this phenomenon. We further show that the prepared gold nanostructures exhibit tunable photothermal properties that can be optimized for various hyperthermia-induced antibacterial applications.

Selective metal recovery by mucin: turning gold from wastewater into a peroxymonosulfate-activated catalyst

“…It should be noted that the NPs formation kinetics could be expedited (to 2–3 hours) by heating the solution to 70 °C, as was established in a previous paper. 35…”

“…It should be noted that the NPs formation kinetics could be expedited (to 2-3 hours) by heating the solution to 70 °C, as was established in a previous paper. 35 It was observed that the mixed-metal solution, after a few hours from the addition of mucin, changed in color from light yellow to light red, similar to the solution with Au in Environmental Science: Nano Paper isolation. This observation again indicates the formation of Au NPs with mucin's assistance.…”

“…Mucin is also known not only as a reducing agent but also as a stabilizer and a capping one, and it even has a role in determining the shape and size of NPs. 35,37 Overall, it could be assumed that in the mixture, Pd or Fe were responsible for a portion of the Au ions' reduction over time in addition to the ions reduced by mucin. However, mucin is responsible for the NPs formation and growth on top of the existing seeds.…”

“…32,33 Importantly, mucin has also been shown to participate in a bio-assisted synthesis of metal ion-derived NPs within the mucin structure (particularly, with gold, palladium, and silver). 28,34,35 It is assumed that the cysteine amino acid in mucin's molecule can serve as a reduction agent, as its thiol groups can reduce metal ions. 36 Mucin can also serve as the scaffold for NPs formed on the mucin surface, which affects the NP structure and size and stabilizes the NPs from aggregating.…”

One-pot green bio-assisted synthesis of highly active catalytic palladium nanoparticles in porcine gastric mucin for environmental applications

“…Examples include Au, Ag and even complex metal-insulator structures. [32][33][34][35][36][37][38] Mucin glycoproteins belong to a large family of mucus proteins, 39 a complex viscous adherent secretion synthesized by specialized goblet cells in the epithelium for shielding functions. These cell lines are present in organs exposed to the external environment, including the respiratory, gastrointestinal, and reproductive tracts.…”