Correlated electrochemical and optical tracking of discrete collision events.

Optical tracking of collisions between insulating microbeads and an ultramicroelectrode surface are correlated to electrochemical measurements and 3D simulations. The experiments are based on partial blocking of the electrode surface by the beads. Results obtained using these three methods provide details regarding the radial distribution of landing locations, the extent of current blockage, collision frequency, motion of beads on the electrode surface following collisions, and aggregation behavior both prior to collisions and afterward on the electrode surface.

Electrochemical detection of individual DNA hybridization events.

We report on real-time electrochemical detection of individual DNA hybridization events at an electrode surface. The experiment is carried out in a microelectrochemical device configured with a working electrode modified with single-stranded DNA probe molecules. When a complementary DNA strand labelled with a catalyst hybridizes to the probe, an easily detectable electrocatalytic current is observed. In the experiments reported here, the catalyst is a platinum nanoparticle and the current arises from electrocatalytic oxidation of hydrazine. Two types of current transients are observed: short bursts and longer-lived steps. At low concentrations of hydrazine, the average size of the current transients is proportional to the amount of hydrazine present, but at higher concentrations the hydrazine oxidation reaction interferes with hybridization.

Synthesis and characterization of NiSn dendrimer-encapsulated nanoparticles.

We report the synthesis and characterization of NiSn dendrimer-encapsulated nanoparticles (DENs) with sizes in the range of approximately 1.2 nm. These types of materials have potential applications in energy storage, and particles in the 1-3 nm size range are particularly attractive for this use. The NiSn DENs described here contain an average of 147 atoms and are encapsulated within hydrophobic, sixth-generation poly(amidoamine) dendrimers. DENs prepared using four different Ni/Sn ratios, along with monometallic Ni and Sn DENs, are described. To prevent oxidation, the synthesis was carried out under dry conditions in toluene. These bimetallic DENs were characterized by UV-vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results indicate that the compositions of the nanoparticles reflect the ratio of Ni(2+) and Sn(2+) used in the first step of the synthesis; the NiSn nanoparticles remain encapsulated within the dendrimers, and when dry they have a degree of stability even after a short exposure to air.