Growth of gold nanoclusters and nanocrystals induced by lysozyme protein in thin film conformation

- Gold nanoclusters and nanocrystals form on thin film of lysozyme protein.
- Nanocrystals formation is possible from mM concentration of HAuCl4.
- Both nanoclusters and nanocrystals follow Langmuir-like growth on protein surface.
- Growth rate of nanocrystal is slower than nanocluster.
- On protein surface nanocrystals take triangular, hexagonal and disc as shape.

Structures and growth behavior of gold nanoclusters and nanocrystals have been explored on thin films of globular protein lysozyme by using UV-vis and photoluminescence spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). A simple and one-step environment friendly method has been used to grow nanocrystals on protein surface from HAuCl4 solution. It has been found that if different interaction times are provided between lysozyme films and HAuCl4 solution, then initially formed tiny gold nanoclusters on protein surface transform into nanocrystals with the passage of time. XRD analysis shows the formation of faced-centered cubic lattice along (1 1 1) crystalline direction and AFM images confirm the presence of circular, rod-like, triangular and hexagonal crystal structures. Langmuir-like growth behavior has been identified for both the gold nanoclusters and nanocrystals formation induced by the lysozyme films, however, nanocrystal growth is relatively slower than nanocluster.

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