Sun-Uk Hwang

Single-cell optoporation and transfection using femtosecond laser and optical tweezers

In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell.

Immersive modeling system (IMMS) for personal electronic products using a multi-modal interface

In developing new personal electronic products, the development time has shortened to a few months due to high competition in the market. Now it has become very hard to meet the time to market by evaluating products by making physical prototypes. To overcome this problem, we propose an immersive modeling system (IMMS) that enables us to interact with a digital product model in the augmented virtual environment using a multi-modal interface. The IMMS allows the user to evaluate the product model realistically using visual, auditory, and tactile/force senses. The architecture and main modules of the system are described in detail. The integration problems encountered during the development of the test bed are discussed. Application examples to personal electronic products are also included.

Simulation of an oil immersion objective lens: A simplified ray-optics model considering Abbe’s sine condition

In this paper, a simplified mathematical ray-optics model for an oil immersion objective lens, considering Abbes sine condition, is presented. Based on the given parameters of the objective lens, the proposed model utilizes an approach based on a paraxial thin lens formulation. This is done to simplify the complexity of the objective lens by avoiding the consideration of many lens elements inside a single objective lens. To demonstrate the performance of the proposed model, comparisons with exact ray tracing method, based on the specification of real objective lens, are presented in terms of several different criteria including the variation of shape of the light cone, the extent of vignetting and the focus displacement. From the exemplary simulations, it was demonstrated that the proposed model can describe the focusing of light through the objective lens precisely, even when the incident beam rotates.

Traceable assembly of microparts using optical tweezers

Assembly of components with a size in the order of tens of micrometers or less is difficult because the gravitational forces become smaller than weak forces such as capillary, electrostatic and van der Waals forces. As such, the picked-up components commonly adhere to the manipulator, making the release operation troublesome, and the repeatable supply of components cannot be guaranteed because the magazining and bunkering scheme available in conventional scale assembly cannot be extended to these small objects. Moreover, there are also no effective ways known to deliver the finalized assembly externally. In this paper, we present the manipulation and assembly of microparts using optical tweezers, which by nature do not have stiction problems. Techniques allowing bunkering and finalizing the assembly for exporting are also presented. Finally, we demonstrate an exemplary microassembly formed by assembling two microparts: a movable microring and a microrod fixed on a glass substrate. We believe this traceable microassembly to be an important step forward for micro- and nano-manufacturing.

Interactive control of holographic optical traps with fast hologram generation

Holographic optical tweezers (HOTs) make use of computer generated holograms to manipulate multiple optical traps. Uptill now, various algorithms have been proposed to calculate the hologram patterns. However the update rate of such holograms for a spatial light modulator (SLM) is often restricted to around 10Hz due to the slow computation in computer, limiting fast manipulation of optical traps in real-time. In this paper, we present the method and control software for interactive control of holographic optical traps with fast hologram generation by increasing the update rate of holograms. The developed software is written in Visual C++ platform and is capable of computing complex holograms with an update rate of 55 Hz, regardless of the number of traps. For experimental demonstrations, we show three dimensional, real-time manipulations of 5 µm polystyrene beads.

Three-Dimensional Scanning Optical Tweezers

There are several new tools for manipulating microscopic objects. Among them, optical tweezers (OT) has two distinguishing advantages. Firstly, OT can easily release an object without the need of a complicated detaching scheme. Secondly, it is anticipated to manipulate an object with six degrees of freedom. OT is realized by tightly focusing a laser beam on microscopic objects. Grabbing and releasing is easily done by turning a laser beam on and off. For doing a dexterous manipulation on an object, a complicated potential trap must be calculated and applied. We foresee that such calculation method will be developed in the near future. One of the candidates for implementing the calculated trap is scanning optical tweezers (SOT). SOT can be built by using actuators with a scanning frequency in the order of a hundred Hertz. We need fast scanners to stably trap an object. In this study, we present our design of such SOT. The SOT uses piezo-actuated tilt mirror and objective positioner to scan full three-dimensional workspace.

Near-axial rotation of nanorods by focused laser beams using dual-beam method

A dual-beam method for the near-axial rotation of dielectric nanorods was devised. The method uses two laser beams, where a focused Gaussian beam holds the object in the beam axis while a focused Laguerre-Gaussian beam rotates the object. The near-axial rotation of ZnO nanorods usingthismethodwasthenexperimentallydemonstrated, andtheradialoffsetdistance of the rotating nanorod from the beam axis was quantified via a video tracking method. C 2011

Snap-fit assembly of microscopic components by optical tweezers

We investigate that components held in multiple optical traps can be manipulated and assembled together using snap-fit assembly. There are several works on manipulating microscopic objects with optical tweezers and assembling them. However, these techniques cannot sustain the assembled structure after turning off the laser source. In contrast, our technique utilizes snap-fit assembly so that assembled components do not detach. With this approach, components and sub-assemblies can be readily controlled in real-time and assembled into a permanent assembly. Our method can be used for constructing micrometer scale devices.

Measurement of hardness and friction properties of pencil leads for quantification of pencil hardness test

We have investigated the various properties of different types of pencil leads in order to quantify a pencil hardness test for reliability. The chemical composition and mechanical properties for different types of pencils (F, 2H, 4H, 6H and 8H) were measured using X-ray diffraction, nano-indentation and a tribometer. The values for nano-indentation hardness of the pencil leads are in the range of 0.3–0.8 GPa. A higher hardness grade in the pencil lead leads to a wider error range. The clay content of the lead seems to be proportional to the hardness of the pencil lead. Different crystalline phases in clays for each grade of pencil lead result in variations in the degree and distribution of the hardness. Consequently, the content of the crystalline phases in the clay affects deviations in the hardness.

Manipulation and assembly of three-dimensional microparts produced by two-photon photo polymerization

Microassembly has been identified as one of critical techniques in innovating the promising era of micro/nano technology. Several works have been investigated to fabricate various micro-devices such as micro-sensors and microactuators. Assembly plays an important role for fabricating micro-devices. However, there are only few studies in the assembly of microparts. In this paper, we present manipulation and assembly of three-dimensional microparts produced by two-photon polymerization where optical trapping technique was used to manipulate microparts. We show exemplary microassembly formed by assembling two microparts, a movable female part and a male part fixed on a glass substrate.