Nanoscale & Nanoscale Advances Blog

DNA origami machine components

DNA origami is an emerging field of nanotechnology that exploits the unique base-pairing capabilities of the DNA bases to produce complex and mechanically stiff self-assembled nanoscale geometries. Recently, DNA origami has found uses in applications such as single molecule sensing, drug delivery and templating molecular components.

This review, by researchers from Ohio State University, sets out to explore the mechanical nature of DNA nanostructures in order to understand how these structures will respond to physical interactions. The review covers three major areas of progress, including measuring and designing mechanical properties of DNA nanostructures, designing complex nanostructures based on imposed mechanical stresses and, finally, designing and controlling structurally dynamic nanostructures.

For researchers interested in the future possibilities of DNA origami, this review should provide an insightful first stop for discussing the mechanical design of DNA nanostructures.

Mechanical design of DNA nanostructures
Carlos E. Castro, Hai-Jun Su, Alexander E. Marras, Lifeng Zhou and Joshua Johnson
Nanoscale, 2015, Advance Article. DOI: 10.1039/C4NR07153K

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS). Follow him on twitter: @L_Bargie

With a limited amount of fossil fuels in the ground, developing alterative strategies for energy production is of the utmost importance.  However, without a way to store that energy, these endeavors could be futile.

From the team of Gyeonghee Lee, Chakrapani V. Varansi, and Jie Liu (an Associate Editor here at Nanoscale), comes one of this month’s HOT papers, “Effects of morphology and chemical doping on electrochemical properties of metal hydroxides in pseudocapacitors.” In this paper, the team’s specific metal hydroxide of interest is Ni(OH)_2.

Schematic illustration of the proposed mechanism for the morphology modification of Ni(OH)2 by glucose in the solvothermal medium.

Lee et al. state “…that both morphology control and chemical doping positively affect the electrochemical performance of Ni(OH)₂ when applied individually.”  In this paper, they set out to determine what happens to the electrochemical performance when morphology and doping are combined instead of applied individually.  In order to investigate the effects of both, they chose a solvothermal synthesis route for metal hydroxide flakes, creating both cobalt-doped (Co_xNi_1-x(OH)₂) and undoped particles (Ni(OH)₂) that have varying amounts of D-glucose added.  For both the doped and undoped particles, four sets of particles are created, where 0, 10, 20, and 50% of the urea normally used in the solvothermal process is replaced by the D-glucose.  All of the particles were characterized with x-ray diffraction (XRD) and scanning electron microscopy (SEM), with the SEM showing that increasing amounts of glucose decreased flake size.  XRD and thermogravimetric analysis also revealed that increasing D-glucose amounts created an increase in the amount of interlayer water, with XRD also indicating degree of crystallinity decreased with increasing D-glucose.

In order to understand how the glucose affects morphology, the authors ran the solvothermal synthesis without the metal precursor. XRD and nuclear magnetic resonanace (NMR) data indicates the presence of ethyl-substituted glucose (formed during the synthesis process) instead of D-glucose.   The authors conclude that “…ethyl glucoside molecules can hinder the precursor diffusion and thus inhibit the metal hydroxide growth during synthesis.”

The electrochemical performance of all of the types of particle is evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS).  Increasing glucose levels on undoped particles increased specific capacitance and cobalt doping is also shown to improve specific capacitance.  Combining the two showed that specific capacitance increased up to 50% of Co doping, but was less effective above 50%.

Lee et al. find that “…the addition of glucose in the ethanol-mediated solvothermal synthesis effectively reduces the particle size of metal hydroxide flakes. The specific capacitance is improved as a result of the increased surface area and reduced particle size.”  In terms of specific capacitance, the higher interlayer water levels found for increasing glucose levels may make ion mobility easier in the materials, enhancing the specific capacitance of the doped-Ni(OH)₂.  In the doped materials, the specific capacitance was increased with low doping and decreased with high doping.

In designing future iterations of Ni(OH)₂ batteries, careful attention will need to be placed on both morphology and doping levels in order to find the best balance for electrochemical performance.

Effects of morphology and chemical doping on electrochemical properties of metal hydroxides in pseudocapacitors
Gyeonghee Lee, Chakrapani V. Varanasi and Jie Liu
Nanoscale, 2015, 7, 3181-3188. DOI: 10.1039/C4NR06997H

Stephanie E. Vasko is currently a Senior Research Assistant at The Rock Ethics Institute at the Pennsylvania State University in State College. Her research focuses on science communication, STEM education, and the intersections between art, craft, and science.  You can follow her on Twitter at @stephanievasko.

The opinions and views expressed in this piece are those of the author and do not represent or reflect the opinion, views, or policy of the Pennsylvania State University, the Rock Ethics Institute, or the National Science Foundation.

SEM images of the polymer submicro-channels and photographs of the fabricated submicro-optofluidic PGMR filter with empty channels and with water filled channels, respectively.

Optical filters are routinely included in devices used for communications, displays and bio-sensing. One such class of optical filters, which have been frequently used, are guided-mode resonance (GMR) filters. Inherent errors with common GMR filters are assigned to fabrication difficulties and as a result, new classes of reconfigurable GMR filters have been created.

In this HOT article, Jin and co-workers have proposed and devised a novel polymer-based GMR (PGMR) which can be incorporated into lab on a chip devices and become tuned by the optical properties of the fluidic mixture present. The simple and low cost PGMR filter was fabricated in three stages, using two-beam interference lithography, floating nanofilm transfer, and finally, thermal bonding technology.

The tunability of this class of PGMR was tested by filling the fluidic channels with a range of liquid mixtures of differing refractive indices. The resulting PGMR exhibited high reflection efficiency in the visible wavelength region, a narrow band tuning range and a high tuning efficiency. The successful incorporation of the PGMR in an optofluidic device operating in the visible wavelength region opens up the possibility of the inclusion of such PGMR devices in future lab on a chip devices.

A tunable submicro-optofluidic polymer filter based on guided-mode resonance
Guohui Xiao, Qiangzhong Zhu, Yang Shen, Kezheng Li, Mingkai Liu, Qiandong Zhuang and Chongjun Jin
Nanoscale, 2015, 7, 3429-3434. DOI: 10.1039/C4NR07233B.