Triangular nanoparticles made from gold could prove useful photothermal agents in cancer treatment because of their plasmonic properties. But synthesizing these materials typically requires harsh conditions. Now researchers from Tokyo Institute of Technology in Japan, University of Leeds in the UK, and Chung-Ang University in Korea have shown that biological molecules known as peptides can be used to synthesize nanoplates under mild conditions [Tanaka et al., Acta Biomaterialia 131 (2021) 519-531,].

“We have developed a technique for preparing triangular gold nanoplates,” explains Masayoshi Tanaka. “In the one-pot synthetic process, a gold salt, HAuCl4, is mixed with a peptide named B3 at room temperature.”

Gold nanoparticles, especially nanorods, nanoshells and nanoplates, absorb strongly in the near-infrared (NIR) region of the spectrum, generating localized heat. Since NIR light can pass readily through tissue, and gold is both stable and non-toxic, these nanostructures are very promising for cancer photothermal therapy, where localized heating is used to kill tumor cells. However, current synthesis routes for these structures, including nanoplates, rely on highly toxic surfactants to control the morphology, which must be removed before use.

“In this study, we investigated much milder conditions conducive to synthesizing triangular gold nanoplates using our B3 peptide,” says Tanaka. “All reagents are combined in a single reaction vessel in a so-called ‘one-pot’ synthesis.

The researchers screened many potential peptides showing catalytic behavior for the synthesis of gold nanoparticles before settling on the B3 peptide. The resulting simple process, which is carried out in a buffer solution at neutral pH, produces triangular and circular gold nanoplates with different levels of NIR absorption, depending on the peptide concentration.

“This synthesis route is a simpler, safer and more eco-friendly protocol for gold nanoplate synthesis. We believe that this approach could also be used to produce other nanomaterials,” adds Tanaka.

Currently, however, the yield of the process is low and a relatively large size distribution of nanoplates is produced (from around 40 nm to over 90 nm). Although this is problematic for applications, the researchers believe that better understanding of the process will bring improved morphological control.

But the approach can isolate peptide sequences for the synthesis of various other types of functional nanomaterial or particle as well. The team has already isolated some peptides for the synthesis of silver nanoparticles and the magnetic alloy, CoPt [Tanaka et al., Int. J. Mol. Sci. 21 (2020) 2377,; Jarrald et al., Bioconjugate Chem. 31 (2020) 1981,] and are confident that there could be more.

Schematic of the one-pot synthesis of gold nanoplates, for cancer photothermal therapy, using peptides at room temperature.
Schematic of the one-pot synthesis of gold nanoplates, for cancer photothermal therapy, using peptides at room temperature.