# DNA–Gold Nanoparticle Dumbbells: Synthesis and Nanoscale Characterization

## TL;DR

This paper describes a method to create DNA-linked gold nanoparticle dumbbells and studies how their structure changes when dried on different surfaces.

## Contribution

A novel synthesis method for DNA-gold nanoparticle dumbbells and insights into their structural stability during drying.

## Key findings

- Dumbbell structures remain stable in solution but partially collapse when dried on certain substrates.
- Deposition on polylysine-coated mica preserves the DNA bridge length, while carbon grids cause contraction.
- The study highlights the importance of substrate choice for accurate DNA nanoparticle characterization.

## Abstract

We report an efficient, high-yield method for synthesizing dumbbell-shaped conjugates composed of gold nanoparticles (AuNPs) connected by double-stranded (ds) DNA. The dsDNA, bearing terminal thiol groups, was covalently attached to two AuNPs to form uniform constructs comprising either 15 nm or 25 nm particles bridged by 38 base pairs (bp) or 100 bp dsDNA. The dumbbells were purified by gel electrophoresis and exhibited high stability, remaining intact for several days in pure water or buffers at ambient temperature. Deposition onto solid substrates followed by drying, however, led to their partial structural collapse. TEM imaging showed that deposition on carbon grids typically yielded dumbbell structures with interparticle gaps of only 1–2 nm, suggesting that the dsDNA bridge contracts during deposition and drying. However, deposition on polylysine-coated mica for AFM imaging preserved the native geometry, with the gaps consistent with the expected DNA length. Our results reveal that deposition significantly affects the structure and integrity of dsDNA bridges in dumbbell constructs, highlighting the importance of appropriate substrate and surface coating selection for reliable characterization of DNA properties in dried dumbbells.