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Bioassembly of gold nanomaterials

Recent advances in the synthesis procedures has resulted in gold nanoparticle of various shapes, including spheres, rods, wires, and cubes. By varying the shape of the materials, their vibrant optical properties can be discreetly tuned from the visible to the IR region of the spectrum. Particularly the enhanced plasmonic properties make Au nanorods of interest for a variety of sensing and biological applications. For example researchers of University of Chicago have made nanoparticles whose optical properties can be precisely tuned and could be even used as a switch in an optical circuit.

Au nanorods are prepared in a two-step; seed mediate process where the surfactant cetyltrimethylammonium bromide (CTAB) is used as a surface passivant. In this mechanism, Au nanoparticle seeds are introduced to a growth solution containing excess CTAB and HAuCl4 from which the nanorods are grown off the surface of the seeded nucleates. The final rod-like structure possesses a surfactant bilayer on the surface, thus imparting a significant positive charge to the materials, which is the driving force for this solution stability.
Bio synthesis and applications
Bio-based assembly processes will facilitate the nanorods to be soluble in biological media and serve to be precursor architectures for use in biological systems.
Usually, Au nanorods with aspect ratios less than 3.5 are prepared using the standard methods. Here, after synthesis, the materials were centrifuged once at14,000 RPM, to remove the supernatant and the pellet is redispersed in an appropriate solvent.
For the analysis of the Au nanorod stability in buffers, the selected solvent is Tris buffer at pH 7.42 of increasing concentrations. The buffer concentrations can range between 0.0 mM and 400 mM. For the bio-based assembly of Au nanorods, the materials are redissolved in deionized water titrated to a pH value between 1.0 and 7.0. To this solution, a freshly prepared aliquot of cysteine is added to result in a final amino acid reaction concentration of 600 μM.
By this synthesis a complete electronic double layer is produced on the Au nanorod surface resulting in their stabilization which is important for the biological use of these materials where a tightly controlled pH system is required. By changing the reaction conditions selected dimensions and assembly orientations can be realized so as to use in optical, electronic, and sensing applications where the structure controls the final properties.

Bio mimetic synthesis and self-assembly in one step

Literature reports reveal a recent development of a one step synthesis by researchers of Southwest University, China on a simple, controllable and environmentally friendly strategy for bio mimetic synthesis and self-assembly of gold nanoparticles (Au-NPs). They used a kind of polysaccharide derivate both as a reducing agent and a stabilizer. The as-prepared one-dimensional Au-NP exhibits plasmon resonant coupling and excellent biocompatibility, making them great precursors of future optical nanodevices and promising candidates for biological applications.

Biomaterials represent a burgeoning field in which the demonstration and control of bio-compatibility between the inorganic nanomaterials and the biological scaffolding, as well as the maintenance of bioactivity of the biological framework is crucial to the development of the field.
Florida state University researchers have demonstrated that bio-compatibility and bio-activity are maintained for biomaterials composed of duplex DNA appended with 1.4 nm Au particles. They used highly selective proteins that induce sequence-specific structural perturbations on the DNA. These results lay a foundation for interfacing more complex and diverse protein-DNA-nanomaterial systems, and mechanism for the analysis of the resultant conjugate structures.

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