Pei-Yu Chiou

Massively parallel manipulation of single cells and microparticles using optical images

The ability to manipulate biological cells and micrometre-scale particles plays an important role in many biological and colloidal science applications. However, conventional manipulation techniques—including optical tweezers, electrokinetic forces (electrophoresis, dielectrophoresis, travelling-wave dielectrophoresis), magnetic tweezers, acoustic traps and hydrodynamic flows—cannot achieve high resolution and high throughput at the same time. Optical tweezers offer high resolution for trapping single particles, but have a limited manipulation area owing to tight focusing requirements; on the other hand, electrokinetic forces and other mechanisms provide high throughput, but lack the flexibility or the spatial resolution necessary for controlling individual cells. Here we present an optical image-driven dielectrophoresis technique that permits high-resolution patterning of electric fields on a photoconductive surface for manipulating single particles. It requires 100,000 times less optical intensity than optical tweezers. Using an incoherent light source (a light-emitting diode or a halogen lamp) and a digital micromirror spatial light modulator, we have demonstrated parallel manipulation of 15,000 particle traps on a 1.3 × 1.0 mm2 area. With direct optical imaging control, multiple manipulation functions are combined to achieve complex, multi-step manipulation protocols.

Light actuation of liquid by optoelectrowetting

Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.

Photothermal effects of supramolecularly assembled gold nanoparticles for the targeted treatment of cancer cells.

Noble-metal nanostructures with unique photophysical properties have been considered as prime candidate agents for the photothermal treatment of cancer.[1–4] Typically, the photothermal properties of these nanostructures can be controlled by manipulating their sizes and shapes.[4,5] Over the past decade, significant endeavors have been devoted to the production of a variety of gold nanostructures, such as nanoparticles,[6,7] nanoshells,[8–10] nanorods,[11,12] and nanocages,[5,13,14] which are able to overcome limitations of organic-dye-based photothermal agents,[7] such as low light absorption and undesired photobleaching. For sufficient energy to be harvested/generated to damage tumor cells, the size of these nanostructure-based agents are required in the range of tens to hundreds nm.[15] However, the relatively “large” size of the agents often leads to poor bioclearance (i.e., accumulation in the liver, spleen, and kidneys), which is a major obstacle to their in vivo application.[16–18] Alternatively, the photophysical properties of noble-metal nanostructures can be altered systematically by the formation of aggregates through self-assembly.[19–30] The antibody-assisted aggregation of Au nanoparticles on cell membranes or in intracellular environments led to the enhancement of photothermal performance[31] as a result of the collective effects[32,33] associated with the assembled structures. Therefore, the self-assembly of small noble-metal building blocks, that is, noble-metal colloids with diameters of less than 8 nm[16–18] (compatible with renal clearance) would be a promising approach toward a new class of noble-metal photothermal agents.

Dynamic Cell and Microparticle Control via Optoelectronic Tweezers

This paper reports on cell and microparticle manipulation using optically induced dielectrophoresis. Our novel optoelectronic tweezers (OET) device enables optically controlled trapping, transportation, and sorting via dielectrophoretic forces. By integrating a spatial light modulator and using direct imaging, arbitrary dynamic manipulation patterns are obtained. Here, we demonstrate manipulation functions, including particle collectors, single-particle traps, individually addressable single-particle arrays, light-defined particle channels, and size-based particle sorting. OET-induced particle manipulation velocities are analyzed as a function of the applied voltage, optical pattern linewidth, and single-particle trap dimensions.

Optically Controlled Cell Discrimination and Trapping Using Optoelectronic Tweezers

Optoelectronic tweezers (OET) provide a powerful tool for the manipulation of micro- and nanoparticles. The OET device produces an optically controlled dielectrophoretic force, allowing complex dynamic manipulation patterns using light intensities up to 100 000 times lower than that of optical tweezers. Using OET, we demonstrate the separation of live and dead human B cells, and the separation of HeLa and Jurkat cells. We also present, for the first time, a modified single-sided OET device that promises to facilitate the integration of OET and microfluidics. Unlike standard OET, this single-sided OET device produces electric fields that are oriented parallel to the plane of the device. We demonstrate the manipulation of polystyrene beads using this new single-sided OET device, and discuss its capabilities

Dissection of the Burkholderia intracellular life cycle using a photothermal nanoblade

Burkholderia pseudomallei and Burkholderia thailandensis are related pathogens that invade a variety of cell types, replicate in the cytoplasm, and spread to nearby cells. We have investigated temporal and spatial requirements for virulence determinants in the intracellular life cycle, using genetic dissection and photothermal nanoblade delivery, which allows efficient placement of bacterium-sized cargo into the cytoplasm of mammalian cells. The conserved Bsa type III secretion system (T3SSBsa) is dispensable for invasion, but is essential for escape from primary endosomes. By nanoblade delivery of B. thailandensis we demonstrate that all subsequent events in intercellular spread occur independently of T3SSBsa activity. Although intracellular movement was essential for cell–cell spread by B. pseudomallei and B. thailandensis, neither BimA-mediated actin polymerization nor the formation of membrane protrusions containing bacteria was required for B. thailandensis. Surprisingly, the cryptic (fla2) flagellar system encoded on chromosome 2 of B. thailandensis supported rapid intracellular motility and efficient cell–cell spread. Plaque formation by both pathogens was dependent on the activity of a type VI secretion system (T6SS-1) that functions downstream from T3SSBsa-mediated endosome escape. A remarkable feature of Burkholderia is their ability to induce the formation of multinucleate giant cells (MNGCs) in multiple cell types. By infection and nanoblade delivery, we observed complete correspondence between mutant phenotypes in assays for cell fusion and plaque formation, and time-course studies showed that plaque formation represents MNGC death. Our data suggest that the primary means for intercellular spread involves cell fusion, as opposed to pseudopod engulfment and bacterial escape from double-membrane vacuoles.

Light-Actuated AC Electroosmosis for Nanoparticle Manipulation

We present a novel light-actuated ac electroosmosis (LACE) mechanism that allows the concentration and transportation of micro- and nanoscopic particles using light-patterned dynamically reconfigured microfluidic vortices on a photoconductive surface. LACE is realized by sandwiching an aqueous liquid medium between a featureless photoconductive surface and a transparent indium tin oxide electrode. By applying an ac electrical bias with a frequency that is close to the electric double-layer relaxation frequency, a light-patterned virtual electrode can induce ac electroosmotic flow to concentrate and transport nanoscopic particles on the photoconductive surface. By integrating with a spatial light modulator such as a digital micromirror device microdisplay, we can create 31000 microfluidic vortices on a 1.3 times 1-mm2 area for massively parallel trapping of 2- and 1-mum polystyrene beads. We have also demonstrated LACE concentration and transportation of nanoscopic particles including 200- and 50-nm polystyrene beads, lambda-phage DNA molecules, and quantum dots.

Pulsed laser triggered high speed microfluidic fluorescence activated cell sorter

We report a high speed and high purity pulsed laser triggered fluorescence activated cell sorter (PLACS) with a sorting throughput up to 20,000 mammalian cells/s with 37% sorting purity, 90% cell viability in enrichment mode, and >;90% purity in high purity mode at 1,500 cells/s or 3,000 beads/s. Fast switching (30 μs) and a small perturbation volume (~90 pL) is realized by a unique sorting mechanism in which explosive vapor bubbles are generated using focused laser pulses in a single layer microfluidic PDMS channel.

High-speed droplet generation on demand driven by pulse laser-induced cavitation

We report on a pulse laser-driven droplet generation (PLDG) mechanism that enables on-demand droplet generation at rates up to 10,000 droplets per second in a single-layer PDMS-based microfluidic device. Injected droplet volumes can be continuously tuned between 1 pL and 150 pL with less than 1% volume variation.

Optoelectronic tweezers for particle and cell manipulation

Optoelectronic tweezers is a new tool for parallel optical manipulation of colloids and cells. Using a digital projector to pattern dynamic virtual electrodes on a photoconductive surface, we demonstrate parallel trapping, transporting, and sorting of micro/bio-particles