Exploring the thermal stability of DNA-linked gold nanoparticles in ionic liquids and molecular solvents

While water is the most commonly used solvent for DNA, many co-solvents have been added for various applications. Ionic liquids (ILs) are molten salts at around room temperature. ILs have been tested as a green solvent for many reactions and many biopolymers can also be dissolved in ILs. In this work, we study DNA-linked gold nanoparticles (AuNPs) in seven types of ILs. DNA-functionalized AuNPs possess a high density of negative charges and thus may generate new physical properties in ILs. We have identified the role of ILs to transit from salts to increase DNA duplex stability to solvents to decrease DNA melting temperature. The onset of this transition depends on the structure of ILs, where more hydrophobic cations destabilize DNA at lower IL concentrations. This trend is opposite to molecular solvents (e.g. ethanol, DMSO, ACN and DMF) that destabilize DNA at low solvent concentration. Specific DNA base pairing is disrupted at high DMSO concentrations, and AuNPs are held together by non-specific interactions. The other tested molecular solvents are able to maintain DNA base pairs, although strong non-specific interactions are also present. Several ILs can release proton and thus drastically change pH, which also changes the melting temperature of DNA. This study also reveals the feasibility of using ILs as solvents for DNA-functionalized nanomaterials.