Metallization of Branched DNA Origami Templates

A simple and robust method for creating a wide variety of shapes and patterns, DNA origami can accommodate the increased complexity and flexibility needed for both the design and assembly of useful circuit templates. The next enabling step for circuit fabrication is the selective metallization of DNA origami templates in order to provide the conductive pathways for integrated nanoelectronics. Liu and colleagues provide improved understanding of and possible solutions to several key challenges for the metallization of DNA origami templates for nanoelectronic device fabrication.

Reviewed by Jeff Morse, Ph.D, National Nanomanufacturing Network

• Liu J, Geng Y, Pound E, Gyawali S, Ashton JR, Hickey J, Woolley AT, and Harb JN. 2011. Metallization of Branched DNA Origami for Nanoelectronic Circuit Fabrication. ACS Nano Article ASAP 16 February 2011. DOI: 10.1021/nn1035075.

As integrated circuit fabrication processes face inherent limitations for increased circuit speed and density, transformative approaches combining top-down and bottom-up fabrication techniques are broadly being investigated. Some methods exploit the benefits of self-assembly processes to form controlled nanostructures, such as directed self-assembly, which has been included on the ITRS roadmap and has the potential to impact next generation nanoelectronic circuits.

DNA origami provides another alternative approach to fabricating transistor templates.  A simple and robust method for creating a wide variety of shapes and patterns, DNA origami can accommodate the increased complexity and flexibility needed for both the design and assembly of useful circuit templates. It has been demonstrated that DNA origami can be reproduced in size and shape, as well as positioned and oriented on lithographically patterned substrates. The next enabling step for circuit fabrication is the selective metallization of DNA origami templates in order to provide the conductive pathways for integrated nanoelectronics. While metallization of a range of single-stranded DNA structures has been demonstrated, DNA origami presents numerous challenges in comparison due to the instability of the folded DNA structure that is held together by several short DNA strands and may be prone to unfolding during the metallization process sequence.

Recently, Liu et. al. reported on their investigation of selective metallization of branched DNA origami on a mica surface. The investigation provides improved understanding of and possible solutions to several key challenges for the metallization of DNA origami templates, including the stabilization of the origami in the metallization process, achieving adequate selectivity to metalize small origami structures, the adhesion of small structures to the surface so that they will not be removed when subject to multiple metallization steps, and the influence of excess staple strands on the origami. In Liu’s approach, DNA origami was cross-linked using amine-modified psoralen, and purified by dialysis. The DNA origami was then functionalized by reacting with glutaraldehyde, followed by another dialysis step to remove any excess glutaraldehye. The DNA origami was then seeded with silver, followed by electroless plating of gold on the silver seeds. In studying this process, the authors found that the key variables included the composition of the rinse solution along with the amount of excess staple strands present in the dialysis steps. For example, they determined that the addition of magnesium ions to the rinse solution increased the stability of the origami, preventing it from unfolding on the substrate. The ions possibly balance the repulsive force present between the negatively charged DNA origami and the staple strands. Further adjustments of staple strand ratio and buffer solution used during dialysis optimized the stability of the folded DNA during both the solution seeding and electroless plating process steps as well. In addition, the authors determined that the presence of excess staple strands has a significant impact on the selectivity of metal electrodeposition. Minimization of excess staple strands through dialysis provides an effective approach to selectively metalize DNA origami templates.

The described methods potentially provide the basis for increasingly complex templates for next generation nanoelectronics. The authors have reported a facile, solution-based process to stabilize DNA origami templates on a surface, and selectively metalize the templates. This represents an enabling approach to extend the synthesis of DNA origami towards future nanolectronic and sensor device technology.

Image reproduced with permission from Liu J ACS Nano Article ASAP 16 February 2011. DOI: 10.1021/nn1035075. Copyright 2011 American Chemical Society.