Jos L. Campbell

Electrowetting of superhydrophobic ZnO nanorods.

This paper reports the electrowetting properties of ZnO nanorods. These nanorods were grown on indium tin oxide (ITO) substrates using different liquid-phase deposition techniques and hydrophobized with sputtered Teflon. The surfaces display superhydrophobic properties. When the applied voltages are less than 35 V, the contact angle change is small and exhibits instant reversibility. For higher voltages, larger contact angle changes were observed. However, the surface was not reversible after removing the applied voltage and required mechanical agitation to return to its initial superhydrophobic state.

Quasi-cubic magnetite/silica core-shell nanoparticles as enhanced MRI contrast agents for cancer imaging

Development of magnetic resonance imaging (MRI) contrast agents that can be readily applied for imaging of biological tissues under clinical settings is a challenging task. This is predominantly due to the expectation of an ideal MR agent being able to be synthesized in large quantities, possessing longer shelf life, reasonable biocompatibility, tolerance against its aggregation in biological fluids, and high relaxivity, resulting in better contrast during biological imaging. Although a repertoire of reports address various aforementioned issues, the previously reported results are far from optimal, which necessitates further efforts in this area. In this study, we demonstrate facile large-scale synthesis of sub-100 nm quasi-cubic magnetite and magnetite/silica core-shell (Mag@SiO2) nanoparticles and their applicability as a biocompatible T2 contrast agent for MRI of biological tissues. Our study suggests that silica-coated magnetite nanoparticles reported in this study can potentially act as improved MR contrast agents by addressing a number of aforementioned issues, including longer shelf life and stability in biological fluids. Additionally, our in vitro and in vivo studies clearly demonstrate the importance of silica coating towards improved applicability of T2 contrast agents for cancer imaging.

Cationic Amino Acids Specific Biomimetic Silicification in Ionic Liquid: A Quest to Understand the Formation of 3-D Structures in Diatoms

The intricate, hierarchical, highly reproducible, and exquisite biosilica structures formed by diatoms have generated great interest to understand biosilicification processes in nature. This curiosity is driven by the quest of researchers to understand natures complexity, which might enable reproducing these elegant natural diatomaceous structures in our laboratories via biomimetics, which is currently beyond the capabilities of material scientists. To this end, significant understanding of the biomolecules involved in biosilicification has been gained, wherein cationic peptides and proteins are found to play a key role in the formation of these exquisite structures. Although biochemical factors responsible for silica formation in diatoms have been studied for decades, the challenge to mimic biosilica structures similar to those synthesized by diatoms in their natural habitats has not hitherto been successful. This has led to an increasingly interesting debate that physico-chemical environment surrounding diatoms might play an additional critical role towards the control of diatom morphologies. The current study demonstrates this proof of concept by using cationic amino acids as catalyst/template/scaffold towards attaining diatom-like silica morphologies under biomimetic conditions in ionic liquids.

Novel tuneable optical elements based on nanoparticle suspensions in microfluidics

This work demonstrates the application of dielectrophoretic (DEP) control of silica nanoparticles to form tuneable optical elements within a microfluidic system. The implementation consisted of a microfluidic channel with an array of curved microelectrodes along its base. Various DEP conditions were investigated at alternating current voltage amplitudes, flow rates and frequencies from 5 to 15 V, 2 to 10 μL/min and 0 to 20 MHz, respectively. The fluid channel was filled with deionized water suspending silica particles with diameters of 230 and 450 nm. Experiments were conducted to demonstrate DEP concentration and deflection of the particles and the impact of these particles distributions on the optical transmission through the fluid channel. Both confinement and scattering of the light were observed depending on the particle dimensions and the parameters of the DEP excitation. The results of this investigation illustrate the feasibility of DEP control in an optofluidic system and represent a significant step toward the dynamic formation of electrically controlled liquid optical waveguides.

Superhydrophobic and superhydrophilic surfaces with MoOx sub micron structures

Presented is an investigation of surface morphology of arrayed MoOx structures with increasing aspect ratios, and their resultant superhydrophillic, and their modified superhydrophobic properties. Molybdenum oxide (MoOx) submicron structures were grown on lithium niobate (LiNbO3) substrates via the thermal evaporation of MoO3 nanopowder at 750°C in a horizontal tube furnace. A mixture of 90% argon and 10% oxygen was introduced into the thermal evaporation tube at flow rate of 1L/min. This resulted in the formation of a white film which consisted of submicron tabular structures. Scanning electron micrographs revealed that the tabular molybdenum oxide grew in arrays 80-100° with respect to the plane of the substrate, with tabular structures with a thickness of approx 0.5 - 1.5μm. Initial testing of MoOx structures revealed that they were extremely super hydrophilic. Such MoOx arrays were coated with fluoropolymer Teflon, deposited using the RF sputtering technique. The addition of a semi-conformal Teflon layer effectively converts the superhydrophilic MoOx layer into a superhydrophobic surface. These superhydrophobic surfaces exhibit contact angles with aqueous media in excess of 150°. Such surfaces can be utilized for the selective adsorption and desorption of protein or pharmacokinetic molecules, with applications in drug delivery and biomedical systems.