(461d) Surface Coverage On A Nanoparticle

Here we present electrospray-differential mobility analysis (ES-DMA) as a tool to determine the conformation and surface coverage of long, flexible molecules on engineered nanoparticles. As an initial model system, we examine gold nanoparticles coated with single-stranded DNA (ssDNA), which hold potential for a variety of uses ranging from cancer treatments to DNA sequencing probes. Key to each of these applications is the determination of the coverage and configuration of the strands on the surface of the particle, as they affect the stability, properties, and utility of the suspension. We employ ES-DMA to determine the size distribution of both coated and bare particles, and thus the apparent coating thickness, based on their electrical-to-drag force ratio. We then determine the configuration and surface coverage with a simple analytical model. We find the ssDNA adopts a random coil configuration and the surface coverages determined by this method, 2.5*10¹²-8.7*10¹³ molecules/cm², are in accord with those reported by other techniques. These results indicate the value of ES-DMA within the repertoire of tools for the characterization of engineered nanoparticles.