Gold-implanted plasmonic quartz plate as a launch pad for laser-driven photoacoustic microfluidic pumps.

Enabled initially by the development of microelectromechanical systems, current microfluidic pumps still require advanced microfabrication techniques to create a variety of fluid-driving mechanisms. Here we report a generation of micropumps that involve no moving parts and microstructures. This micropump is based on a principle of photoacoustic laser streaming and is simply made of an Au-implanted plasmonic quartz plate. Under a pulsed laser excitation, any point on the plate can generate a directional long-lasting ultrasound wave which drives the fluid via acoustic streaming. Manipulating and programming laser beams can easily create a single pump, a moving pump, and multiple pumps. The underlying pumping mechanism of photoacoustic streaming is verified by high-speed imaging of the fluid motion after a single laser pulse. As many light-absorbing materials have been identified for efficient photoacoustic generation, photoacoustic micropumps can have diversity in their implementation. These laser-driven fabrication-free micropumps open up a generation of pumping technology and opportunities for easy integration and versatile microfluidic applications.

Photoacoustic laser streaming with non-plasmonic metal ion implantation in transparent substrates.

Photoacoustic laser streaming provides a versatile technique to manipulate liquids and their suspended objects with light. However, only gold was used in the initial demonstrations. In this work, we first demonstrate that laser streaming can be achieved with common non-plasmonic metals such as Fe and W by their ion implantations in transparent substrates. We then investigate the effects of ion dose, substrate material and thickness on the strength and duration of streaming. Finally, we vary laser pulse width, repetition rate and power to understand the observed threshold power for laser streaming. It is found that substrate thickness has a negligible effect on laser streaming down to 0.1 mm, glass and quartz produce much stronger streaming than sapphire because of their smaller thermal conductivity, while quartz exhibits the longest durability than glass and sapphire under the same laser intensity. Compared with Au, Fe and W with higher melting points show a longer lifetime although they require a higher laser intensity to achieve a similar speed of streaming. To generate a continuous laser streaming, the laser must have a minimum pulse repetition rate of 10 Hz and meet the minimum pulse width and energy to generate a transient vapor layer. This vapor layer enhances the generation of ultrasound waves, which are required for observable fluid jets. Principles of laser streaming and temperature simulation are used to explain these observations, and our study paves the way for further materials engineering and device design for strong and durable laser streaming.

Growth Pattern of Magnetic Field-Treated Bacteria.

A study of the induced effect of different types of weak magnetic field exposure on bacterial growth is performed, comparing the relative changes after removal from the magnetic fields. This investigation is relevant to understand the effect of magnetic field exposure on human beings due to electronic devices. For this purpose, we use four species of common bacteria in reference to human health and safety including Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. The choice of these four bacteria also allows us to check for effects which rely upon the Gram-staining properties or shapes of bacterial species. These species were initially exposed to static, non-homogeneous, and alternating weak magnetic fields, and then they were grown in incubators in the same environment at 37 °C simultaneously. Comparative measurements of optical density are then used to track the sustained impact on bacterial growth in the experimental samples. Bacteria were first grown in different weak magnetic fields on a plain glass surface both in liquid and solid media. Magnetic field-treated bacteria were then transferred into similar test tubes to grow in an incubator concurrently. Bacterial cultures in liquid nutrient broth on plain glass proliferated faster in most species. Different magnetic fields affect the growth pattern of bacteria differently, depending on the bacterial strain. The weak magnetic field seems to decelerate the growth rate, even after the magnetic field is removed. With application of this study, we can potentially investigate the effect of weak field exposures on Eukaryotic cells and gene dynamics.

Adhesion of gram-negative rod-shaped bacteria on 1D nano-ripple glass pattern in weak magnetic fields.

This research project has major applications in the healthcare and biomedical industries. Bacteria reside in human bodies and play an integral role in the mechanism of life. However, their excessive growth or the invasion of similar agents can be dangerous and may cause fatal or incurable diseases. On the other hand, increased exposure to electromagnetic radiation and its impact on health and safety is a common concern to medical science. Some nanostructure materials have interesting properties regarding facilitating or impeding cell growth. An understanding of these phenomena can be utilized to establish the optimum benefit of these structures in healthcare and medical research. We focus on the commonly found rod-shaped, gram-negative bacteria and their orientation and community development on the cellular level in the presence of weak magnetic fields on one dimensional nano-ripple glass patterns to investigate the impact of nanostructures on the growth pattern of bacteria. The change in bacterial behavior on nanostructures and the impact of magnetic fields will open up new venues in the utilization of nanostructures. It is noticed that bacterial entrapment in nano-grooves leads to the growth of larger colonies on the nanostructures, whereas magnetic fields reduce the size of colonies and suppress their growth.

Self-Assembled Gold Nano-Ripple Formation by Gas Cluster Ion Beam Bombardment.

In this study, we used a 30 keV argon cluster ion beam bombardment to investigate the dynamic processes during nano-ripple formation on gold surfaces. Atomic force microscope analysis shows that the gold surface has maximum roughness at an incident angle of 60° from the surface normal; moreover, at this angle, and for an applied fluence of 3 × 1016 clusters/cm², the aspect ratio of the nano-ripple pattern is in the range of ~50%. Rutherford backscattering spectrometry analysis reveals a formation of a surface gradient due to prolonged gas cluster ion bombardment, although the surface roughness remains consistent throughout the bombarded surface area. As a result, significant mass redistribution is triggered by gas cluster ion beam bombardment at room temperature. Where mass redistribution is responsible for nano-ripple formation, the surface erosion process refines the formed nano-ripple structures.

Improved cellular response of ion modified poly(lactic acid-co-glycolic acid) substrates for mouse fibroblast cells.

In this report, the effects of argon (Ar) ion irradiation on poly(lactic acid-co-glycolic acid) (PLGA) substrates on biocompatibility were studied. PLGA scaffold substrates were prepared by spin coating glass surfaces with PLGA dissolved in anhydrous chloroform. Previously, we showed that surface modifications of PLGA films using ion irradiation modulate the inherent hydrophobicity of PLGA surface. Here we show that with increasing ion dose (1×10(12) to 1×10(14) ions/cm(2)), hydrophobicity and surface roughness decreased. Biocompatibility for NIH3T3 mouse fibroblast cells was increased by argon irradiation of PLGA substrates. On unirradiated PLGA films, fibroblasts had a longer doubling time and cell densities were 52% lower than controls after 48 h in vitro. Argon irradiated PLGA substrates supported growth rates similar to control. Despite differences in cell cycle kinetics, there was no detectible cytotoxicity observed on any substrate. This demonstrates that argon ion irradiation can be used to tune the surface microstructure and generate substrates that are more compatible for the cell growth and proliferation.

Phosphopeptide separation using radially aligned titania nanotubes on titanium wire.

Phosphoproteomic analysis offers a unique view of cellular function and regulation in biological systems by providing global measures of a key cellular regulator in the form of protein phosphorylation. Understanding the phosphorylation changes between normal and diseased cells or tissues offers a window into the mechanism of disease and thus potential targets for therapeutic intervention. A key step in these studies is the enrichment of phosphorylated peptides that are typically separated and analyzed by using liquid chromatography mass spectrometry. The mesoporous titania beads/particles (e.g., Titansphere TiO2 beads from GL Sciences Inc., Japan) that are widely used for phosphopeptide enrichment are expensive and offer very limited opportunities for further performance improvement. Titiania nanotube arrays have shown promising characteristics for phosphopeptide separation. Here we report a proof-of-concept study to evaluate the efficacy of nanotubes on Ti-wire for phosphoproteomics research. We used titania nanotubes radially grown on titanium wires as well as the commercial beads to separate phosphopeptides generated from mouse liver complex tissue extracts. Our studies revealed that the nanotubes on metal wire provide comparable efficacy for enrichment of phophopeptides and offer an ease of use advantage versus mesoporous beads, thus having the potential to become a low cost and more practical material/methodology for phosphopeptide enrichment in biological studies.