The zeta potential of surface-functionalized metallic nanorod particles in aqueous solution.

Metallic nanoparticles suspended in aqueous solutions and functionalized with chemical and biological surface coatings are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. We describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. For comparison, we present zeta potential data for typical charge-stabilized polystyrene particles. We compare experimental zeta potential data with theoretically predicted values for SAM-coated and bimetallic particles. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.

Microfabricated templates for the electrodeposition of metallic barcodes for use in multiplexed bioassays.

Lithographically defined polyimide templates were prepared using microfabrication techniques. The templates consist of high aspect ratio pores that were formed by deep plasma etching. Different metals are electrodeposited into the pores, and then the template is removed to allow the metallic rods (particles) to be released into solution. The striping pattern of metals on the particles is used to optically identify the particles. Particles range in size from 0.6 mum in diameter by 7.7 mum in length to 4.2 mum by 27 mum in length. These particles have been evaluated in a multiplexed DNA hybridization assay.