Jul 14, 2016 - Yong Yu , Junlong Geng , Edward Yong Xi Ong , Vijila Chellappan , and Yen Nee Tan * .... brown in solution (Figure 1 A, item no. 1 of inset) and ...
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Bovine Serum Albulmin Protein-Templated Silver Nanocluster (BSA-Ag13): An Effective Singlet Oxygen Generator for Photodynamic Cancer Therapy Yong Yu, Junlong Geng, Edward Yong Xi Ong, Vijila Chellappan, and Yen Nee Tan* availability of abundant surface chemistries for conjugation. These desirable features render protein-templated metal NCs extremely suitable for a wide range of biomedical applications. Since the first report of bovine serum albumin (BSA) (BSA denotes the globular bovine serum albumin protein)-templated Au NCs back in 2009,[16] a large variety of proteins, including BSA and human serum albumin (HSA),[17,18] lysozyme,[19] lactoferrin,[20] horseradish peroxidase,[21] insulin,[22] and many more,[23–25] have been demonstrated for the synthesis of luminescent Au NCs; and the resultant protein-templated Au NCs have shown their versatile biological applications like sensing,[26–29] cellular imaging,[30] tumor site targeting,[31,32] intercellular pH indication,[33] and drug screening.[34] In stark contrast to the extensive studies of protein-templated Au NCs reported in literatures, reports on the synthesis and application of its Ag analogue so far are surprisingly rare[35–38] despite the cheapness of Ag in price but richness in resources. One of the potential reasons accounting for less exploration of protein-templated Ag NC is that Ag+ is more difficult than Au3+ to reduce into its metallic state as the redox potential of Ag+/Ag (≈0.8 V) is lower than that of AuCl4−/Au (≈1.0 V). Those conventionally used reducing agents for the synthesis of Au NCs, such as tyrosine[16] and tryptophan[39] residues contained in the selected proteins (e.g., BSA, HSA), are thus not strong enough to reduce Ag+; and extraneous, more potent reducing agents such as NaBH4 are needed, adding up to the complexity of the reaction system. As NaBH4 reacts violently with water to lose its reducing power over time,[40] reaction conditions such as solution temperature, adding mode (e.g., dropwise vs one shot) and adding duration of NaBH4 solution,[35,37] become nontrivial to control the reaction kinetics and more skillfulness is thus required for the successful synthesis of protein-templated, luminescent Ag NCs. What is even worse is that Ag NCs are less stable than Au NCs and are more susceptible to the environment.[41] The oxidative decomposition of Ag NCs induced by atmosphere oxygen during the synthesis may further exaggerate the difficulty in its reproducibility. Development of more robust and reliable synthesis methods for protein-templated Ag NCs is thus in pressing need to investigate their largely unknown properties and unexplored practical applications.
This paper reports a novel synthesis approach of bovine serum albumin (BSA) protein-templated ultrasmall (
