Title
Green synthesis of protein protected fluorescent gold nanoclusters (AuNCs): Reducing the size of the AuNCs by partially occupying the Ca2+ site by La3+ in apo-α-lactalbumin and the utility of AuNCs in sensing Hg2+
Author
Deepthi S. Yarramala, Ananya Baksi, Thalappil Pradeep, Chebrolu Pulla Rao
Year
2017
Journal
ACS Sustainable Chemistry & Engineering
Abstract
In this paper, we report the studies relevant to controlling the size of protein protected gold nanoclusters (AuNCs). In order to demonstrate this, we have chosen lactalbumin (Apo-α-LA), which has specific binding site for Ca2+, and La3+ occupies this position when Apo-α-LA is treated with lanthanum trichloride. The Apo-α-LA when treated with Au3+ it results in the formation of protein coated Au10 nanoclustesr where the protein reduces Au3+ to Au0 and protects the nanoclusters (Apo-α-LA-AuNCs) and these are luminescent. In this protein protected luminescent gold nanoclusters, the protein is involved both in the reduction as well as protection, and thereby supporting the green synthesis. As the La3+ occupies the Ca2+ site in Apo-α-LA, the size of the AuNCs formed is reduced to smaller than the Au10 and the size is dependent on the extent to which La3+ is bound to the protein and accordingly the luminescence of these clusters increased substantially. The Apo-α-LA-AuNCs and the same formed in the presence of different concentrations of La3+ bound protein were all characterized by analytical, spectral and microscopy techniques. The control on the size of gold nanoclusters formed was also studied by using Gd3+ instead of La3+ and found similar results. In particular, the size variation of AuNCs was clearly demonstrated by MALDI-TOF-MS and HRTEM. These clusters exhibit selective sensing of Hg2+ ions among one dozen ions studied based on the fluorescence intensity measurements. Thus the Apo-α-LA protein coated gold nanocluster is a useful green material for mercury sensing.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Chemical stability, Nanostructures, Biochemistry, Material,