Linear assembly of Au nanorods using biomimetic ligands

The main goal of self-assembly processes is to arrange nanomaterials in specific orientations to produce designer three-dimensional architectures. These structures are produced in response to desired target systems where a specific arrangement of materials is required for structural, electronic, or optical applications. The level of complexity attained using present materials-based processes is relatively low, while highly complex structures are regularly produced in nature through processes developed after millennia of evolution. By modeling biomimetic processes with current materials designs, production of highly structured and three-dimensionally assembled materials is possible. Simple amino acids represent starting biobased systems to study the biomimetic assembly of nanomaterials in solution. Here we present evidence demonstrating that the assembly of Au nanorods into linear structures using the amino acid cysteine is controlled by both thiol and amine attachment to the tips of adjacent nanorods. This structural motif was isolated by studying the assembly process using cysteine and its biomimetic homologues 3-mercaptopropionic acid and cysteamine at a variety of solution pH values and ionic strengths. Understanding the fundamental mechanism of assembly for small biological molecules may prove useful in the development of assemblies based upon larger species such as peptides and proteins.