Surface conduction and electroosmotic flow around charged dielectric pillar arrays in microchannels.

Dielectric microstructures have been reported to have a negative influence on permselective ion transportation because ions do not migrate in areas where the structures are located. However, the structure can promote the transportation if the membrane is confined to a microscopic scale. In such a scale where the area to volume ratio is significantly large, the primary driving mechanisms of the ion transportation transition from electro-convective instability (EOI) to surface conduction (SC) and electroosmotic flow (EOF). Here, we provide rigorous evidence on how the SC and EOF around the dielectric microstructures can accelerate the ion transportation by multi-physics simulations and experimental visualizations. The microstructures further polarize the ion distribution by SC and EOF so that ion carriers can travel to the membrane more efficiently. Furthermore, we verified, for the first time, that the arrangements of microstructures have a critical impact on the ion transportation. While convective flows are isolated in the crystal pillar configuration, the flows show an elongated pattern and create an additional path for ion current in the aligned pillar configuration. Therefore, the fundamental findings of the electrokinetic effects on the dielectric microstructures suggest an innovative application in micro/nanofluidic devices with high mass transport efficiency.

Au nanospheres and nanorods for enzyme-free electrochemical biosensor applications.

Au nanocrystals with different morphologies were prepared and used for enzyme-free electrochemical biosensor applications. To investigate the electrocatalytic properties of Au nanocrystals as a function on their morphologies, Au nanocrystals, Au nanospheres (NSs) on silica, Au NSs, and Au nanorods (NRs) with aspect ratios of 1:3 and 1:5, were coated on the screen printed electrodes and further measure the amperometric responses to hydrogen peroxide via three-electrode system. The electrodes modified with Au nanocrystals showed biosensing properties without any enzyme being attached or immobilized at their surface. The hydrogen peroxide detection limits of the biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) were 6.48, 8.65, and 9.38 µM (S/N = 3), respectively. The biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) showed the sensitivities of 11.13, 54.53, and 58.51 µA/mM, respectively. These results indicate that morphologies of Au nanocrystals significantly influence the sensitivity of the biosensors. In addition, the enzyme-free biosensors with Au nanocrystals were stable for 2 months. Au nanocrystal-based enzyme-free system, which is proposed in this study, can be used as a platform for various electrochemical biosensors.