Spectroscopy of single gold nanoparticles reveals strong heterogeneity in the kinetics of ssDNA functionalization

Plasmonic nanostructures have recently emerged as versatile and programmable nanomaterials for various applications. DNA-conjugated gold nanoparticles have great potential in fields of drug delivery or gene regulation and also... [ view full abstract ]

Plasmonic nanostructures have recently emerged as versatile and programmable nanomaterials for various applications. DNA-conjugated gold nanoparticles have great potential in fields of drug delivery or gene regulation and also constitute sensitive nanosensors for probing biological processes. The functionalization of gold nanoparticles with DNA has been studied extensively in solution, however these ensemble measurements do not reveal particle-to-particle differences. Here we study the functionalization of gold nanorods with single stranded DNA (ssDNA) at the single-particle level and find an unexpected kinetic heterogeneity.

We use single-particle scattering spectroscopy to show that the kinetics of ssDNA functionalization strongly depends on the pH and the ionic strength of the employed buffer, which we attribute to modulations of the effective charge on the ssDNA and on the particle. Surprisingly, we find binding rates that differ from particle-to-particle by an order of magnitude, even though the buffer conditions are identical. We analyse this behaviour in the context of DLVO theory, which indicates that this heterogeneity is caused by a distribution of energy barriers caused by particle-to-particle variations in surface charge.

In the future we plan to use these ssDNA-conjugated nanoparticles to study the conformational changes of single biomolecules using an asymmetric plasmon ruler consisting of a single gold nanorod and a tethered gold nanosphere. Conformational changes of the ssDNA result in modulations of the interparticle distance causing plasmon shifts. The bright and photostable plasmon allows us to probe these conformational changes on microsecond timescales and reveal the folding pathway in real-time.