Poster | ACS Fall 2025 | Washington, DC
Low Voltage Electron Microscopy for the Morphological Characterization and Elemental Analysis of Gold Nanoparticle-DNA Origami Hybrids
Emad Shahnam, James Houston, Daniela Vieira, Alexander Marras, Jared Lapkovsky
Delong America, Montreal, QC, Canada | University of Texas at Austin, Austin, TX, USA
At ACS Fall 2025 in Washington, DC, Delong Instruments and collaborators at the University of Texas at Austin showed that low voltage electron microscopy can image gold nanoparticle DNA origami hybrids and confirm where each gold particle sits using EDS, all on one instrument.
DNA origami uses DNA strands as building blocks to self assemble engineered 2D and 3D nanostructures. These structures are finding uses in molecular biology, pharmaceutics, drug delivery and nanomachines, and they can be built as dynamic devices that actuate in response to salt conditions, temperature or pH. Because each strand position is programmable, DNA origami offers nanometer scale control over where substrates such as gold nanoparticles (AuNPs) are placed. Gold attached to origami creates hybrid materials with unique optical and electrical properties and can be used to actuate structures for biosensors and nanoelectronics.
TEM is the gold standard for imaging DNA origami, but conventional high voltage TEM (HV-TEM, above 80 kV) struggles with contrast. DNA is made of carbon, nitrogen, oxygen and phosphorus, all light elements that scatter a high energy beam weakly. HV-TEM is also costly and needs dedicated infrastructure. This poster explores low voltage electron microscopy (LVEM) for both the morphological and the elemental characterization of DNA origami decorated with gold.
Key findings
- EDS in STEM mode at 15 kV detected the Au Mα line (2.122 keV) and mapped individual gold nanoparticles within the origami framework.
- Quantitative EDS on one hybrid sample measured 70.45 mass% gold, with carbon at 80.42 atomic%.
- EDS line scans across two different origami structures showed distinct gold peaks at the positions expected from the structural design.
- TEM images at 5 kV and 25 kV showed higher contrast on DNA origami than images at 100 kV.
Materials and Methods
A three arm DNA origami linkage was fabricated at UT Austin, with each arm covered in single stranded DNA (ssDNA) overhangs designed to be complementary to a second sequence so the linkage can be actuated. The structures were deposited on carbon coated TEM grids. Several Au DNA origami hybrid structures were also provided by UC Berkeley, pre deposited on TEM grids.
Low voltage TEM and STEM were performed on Delong Instruments' LVEM 5 (5 kV) and LVEM 25E (TEM at 25 kV, STEM at 15 kV). Elemental mapping used a Bruker EDS detector coupled to the LVEM 25E in 15 kV STEM mode. HV-TEM images at 100 kV were provided for comparison, and pixel intensities were measured in ImageJ.
LVEM and EDS of Gold DNA Origami Hybrids
Fig A. Gold nanoparticles attached to DNA origami. Left: TEM at 25 kV. Middle: qualitative EDS overlay highlighting Au in STEM mode at 15 kV. Right: Au elemental map (inset: STEM image at 15 kV).
Fig B. A second Au DNA origami hybrid: (a) TEM at 25 kV, (b) STEM at 15 kV, (c) EDS elemental map with gold shown in blue.
Fig C. EDS line scans across gold nanoparticles on two different DNA origami structures. The Au signal peaks at each nanoparticle position.
Fig D. Top: actuation design, where an ssDNA functionalized gold nanoparticle binds both arms of the three arm linkage and closes it. Bottom: LVEM 5 TEM images of the linkages at 5 kV, with a gold nanoparticle highlighted on one structure.
Images acquired with the LVEM 25E (TEM at 25 kV, STEM and EDS at 15 kV) and the LVEM 5 (TEM at 5 kV).
Results and Discussion
Elemental analysis. EDS in STEM mode at 15 kV confirmed both the presence and the location of gold in the hybrid structures. The Au Mα line at 2.122 keV was clearly detected, allowing unambiguous identification of the nanoparticles within the origami framework (Fig A). On a second sample, TEM at 25 kV, STEM at 15 kV and the elemental map all show chains of gold particles following the origami (Fig B). Quantitative EDS of that sample gave 70.45 mass% (12.98 atomic%) gold, 26.61 mass% (80.42 atomic%) carbon and 2.89 mass% (6.56 atomic%) oxygen.
Line scans. Beyond mapping, EDS line scans across gold nanoparticles on two distinct origami structures showed sharp intensity peaks at each nanoparticle, matching the locations expected from the structural design (Fig C).
Actuation mechanism. To actuate the three arm linkage, gold nanoparticles are functionalized with ssDNA complementary to the overhangs on the origami arms. When the AuNPs are introduced, they bind both arms and force the structure to close (Fig D). Pairing the programmability of DNA nanotechnology with gold nanoparticles opens routes toward nanophotonics and nanoelectronics.
Contrast. Pixel intensities measured along 500 nm lines across DNA origami jacks and normalized showed that TEM images at 5 kV and 25 kV have higher contrast than images of the same structures at 100 kV.
Conclusion
LVEM gives enhanced contrast for imaging DNA origami without the need for heavy metal staining, and its EDS mode adds elemental mapping of hybrid DNA origami, so morphology and composition can be checked on the same instrument.
LVEM is accessible and efficient for biotechnology labs, offering TEM, ED, SEM, STEM and EDS imaging modes with minimal infrastructure requirements.
Presented at
ACS Fall 2025
American Chemical Society | August 17 to 21, 2025 | Washington, DC
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