Hsan-Yin Hsu

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

Parallel single-cell light-induced electroporation and dielectrophoretic manipulation

Electroporation is a common technique for the introduction of exogenous molecules across the, otherwise, impermeant cell membrane. Conventional techniques are limited by either low throughput or limited selectivity. Here we present a novel technique whereby we use patterned light to create virtual electrodes which can induce the parallel electroporation of single cells. This technique seamlessly integrates with optoelectronic tweezers to provide a single cell manipulation platform as well. We present evidence of parallel, single cell electroporation using this method through use of fluorescent dyes and dielectrophoretic responses. Additionally, through the use of integrated microfluidic channels, we show that cells remain viable following treatment in the device. Finally, we determine the optimal field dosage to inject propidium iodide into a HeLa cell and maintain cellular viability.

Operational Regimes and Physics Present in Optoelectronic Tweezers

Optoelectronic tweezers (OET) are a powerful light-based technique for the manipulation of micro- and nanoscopic particles. In addition to an optically patterned dielectrophoresis (DEP) force, other light-induced electrokinetic and thermal effects occur in the OET device. In this paper, we present a comprehensive theoretical and experimental investigation of various fluidic, optical, and electrical effects present during OET operation. These effects include DEP, light-induced ac electroosmosis, electrothermal flow, and buoyancy-driven flow. We present finite-element modeling of these effects to establish the dominant mode for a given set of device parameters and bias conditions. These results are confirmed experimentally and present a comprehensive outline of the operational regimes of the OET device.

NanoPen: Dynamic, Low-Power, and Light-Actuated Patterning of Nanoparticles

We introduce NanoPen, a novel technique for low optical power intensity, flexible, real-time reconfigurable, and large-scale light-actuated patterning of single or multiple nanoparticles, such as metallic spherical nanocrystals, and one-dimensional nanostructures, such as carbon nanotubes. NanoPen is capable of dynamically patterning nanoparticles over an area of thousands of square micrometers with light intensities <10 W/cm(2) (using a commercial projector) within seconds. Various arbitrary nanoparticle patterns and arrays (including a 10 x 10 array covering a 0.025 mm(2) area) are demonstrated using this capability. One application of NanoPen is presented through the creation of surface-enhanced Raman spectroscopy hot-spots by patterning gold nanoparticles of 90 nm diameter with enhancement factors exceeding 10(7) and picomolar concentration sensitivities.

Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate

The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.

Motile and non-motile sperm diagnostic manipulation using optoelectronic tweezers

Optoelectronic tweezers was used to manipulate human spermatozoa to determine whether their response to OET predicts sperm viability among non-motile sperm. We review the electro-physical basis for how live and dead human spermatozoa respond to OET. The maximal velocity that non-motile spermatozoa could be induced to move by attraction or repulsion to a moving OET field was measured. Viable sperm are attracted to OET fields and can be induced to move at an average maximal velocity of 8.8 ± 4.2 µm s(-1), while non-viable sperm are repelled to OET, and are induced to move at an average maximal velocity of -0.8 ± 1.0 µm s(-1). Manipulation of the sperm using OET does not appear to result in increased DNA fragmentation, making this a potential method by which to identify viable non-motile sperm for assisted reproductive technologies.

Trap profiles of projector based optoelectronic tweezers (OET) with HeLa cells

In this paper we present trap profile measurements for HeLa cells in Optoelectronic Tweezers (OET) based on a data projector. The data projector is used as a light source to illuminate amorphous Si creating virtual electrodes which are used to trap particles through dielectrophoresis. We show that although the trap stiffness is typically greater at the edges of the optical spot it is possible to create a trap with constant trap stiffness by reducing the traps size until it is similar to the object being trapped. We have successfully created a trap for HeLa cells with a constant trap stiffness of 3 x 10(-6) Nm-1 (capable of moving the cell up to 50 microms-1) with a 12 microm diameter trap. We also calculate the depth of the potential well that the cell will experience due to the trap and find that it to be 1.6 x 10(-16)J (4 x 10(4) kBT).

Light-actuated digital microfluidics for large-scale, parallel manipulation of arbitrarily sized droplets

We report on a new light-actuated digital microfluidics device which is capable of using on demand, ‘virtual’ electrodes formed by a data projector to enable large-scale, parallel manipulation of arbitrarily sized droplets. The device features a thin, high-quality Al2O3 film deposited via atomic layer deposition (ALD) which allows aggressive scaling of the dielectric thickness, while maintaining high device reliability. We demonstrate the splitting, merging and parallel manipulation of droplets at high actuation speeds (2 cm/s). Due to the thin ALD dielectric layer, this high actuation speed is achieved at 85x lower optical power and 5x lower voltage than our previous device.

Phototransistor-Based Optoelectronic Tweezers for Cell Manipulation in Highly Conductive Solution

We report on a novel phototransistor-based optoelectronic tweezers (OET) that, for the first time, enables operation in high-conductivity solutions, such as physiological buffers and cell culture media. This new capability allows the manipulation of cells in biocompatible environments. The controlled transport of HeLa and Jurkat cells at velocities of up to 35 mum/s in phosphate-buffered saline (PBS) solution has been demonstrated.

Trapping and Transport of Silicon Nanowires Using Lateral-Field Optoelectronic Tweezers

We present a new optoelectronic tweezers device that produces electric fields parallel to the plane of the device. This device is capable of trapping and transporting p-type silicon nanowires at velocities of 20 mum/s.