Lead sulphide (PbS) is a narrow bandgap semiconductor and is widely used in photovoltaic conversion devices, optical switches and other photoelectric applications. However, the problem is that the unique optical, electronic and photovoltaic properties of nanoscale PbS depend on the shape, structure and distribution of the nanoparticles. And it is very difficult to construct well-organized PbS nanoparticles on most substrates under ambient conditions.

Eggshell membranes
Huilan Su from the State Key Lab of Metal Matrix Composites at Shanghai Jiaotong University and colleagues may now have come up with a solution to this – by using eggshell membranes as the reactive substrates for the formation and assembly of PbS nanocrystallites.

Eggshell membranes are collagen-based matrices found between the egg white and the mineralized shell of an egg. They consist of outer and inner shell membranes, but Su and colleagues chose the former. The researchers isolated this membrane by soaking eggshells in hydrochloric acid for a few minutes, rinsing them with distilled water and then drying them in vacuum.

It was then a matter of growing the ordered PbS arrays onto the membrane. This was done by dipping the membrane into a solution of lead acetate and acetic acid for about 10 hours at room temperature. The membrane was then rinsed under distilled water to remove any unreacted ions and immersed in a solution of sodium sulphide for a further 12 hours. It was finally dried in vacuum for two hours to leave a brown membrane, which contained the PbS nanoclusters orderly arranged in arrays on the membrane fibres.

Excellent biocompatibility
"The as-prepared PbS nanoclusters not only have good quantum size effects and are well distributed, but they also exhibit excellent biocompatibility," Su told nanotechweb.org. "When combined with the reactive biosubstrate, the nanocomposites could be promising for applications in photoelectronics, photonics and electronics." The technique could also be extended to synthesize other functional nanomaterials with pre-designed structures and interrelated properties, she adds.

The team will now investigate other biomaterials, such as silk fibre, butterfly wings and bird's feathers, as the biosubstrates and templates for functional nanostructures.

The work was reported in Smart Materials and Structures.