L. K. Chin

Nuclear deformation during breast cancer cell transmigration.

Metastasis is the main cause of cancer mortality. During this process, cancer cells dislodge from a primary tumor, enter the circulation and form secondary tumors in distal organs. It is poorly understood how these cells manage to cross the tight syncytium of endothelial cells that lines the capillaries. Such capillary transmigration would require a drastic change in cell shape. We have therefore developed a microfluidic platform to study the transmigration of cancer cells. The device consists of an array of microchannels mimicking the confined spaces encountered. A thin glass coverslip bottom allows high resolution imaging of cell dynamics. We show that nuclear deformation is a critical and rate-limiting step for transmigration of highly metastatic human breast cancer cells. Transmigration was significantly reduced following the treatment with a protein methyltransferase inhibitor, suggesting that chromatin condensation might play an important role. Since transmigration is critical for cancer metastasis, this new platform may be useful for developing improved cancer therapies.

Different curvatures of tunable liquid microlens via the control of laminar flow rate

This letter reports the tunable liquid microlens using three laminar flows injected into an expansion chamber. Different lens shapes and curvatures can be achieved and tuned through the control of three flow rates. The expansion chamber is designed to improve the fluidic stability and maintain the ideal lens shape for precise microscale optical measurement. The optical aberration is also eliminated by minimizing the diffusive broadening at the interfaces. The collimation and focusing capabilities of three liquid microlenses are demonstrated. The tunable liquid microlens is promising as a tool to realize different optical components that can be integrated onto a microchip.

A reconfigurable optofluidic Michelson interferometer using tunable droplet grating

This paper presents a novel optofluidic Michelson interferometer based on droplet microfluidics used to create a droplet grating. The droplet grating is formed by a stream of plugs in the microchannel with constant refractive index variation. It has a real-time tunability in the grating period through varying the flow rates of the liquids and index variation via different combinations of liquids. The optofluidic Michelson interferometer is highly sensitive and is suitable for the measurement of biomedical and biochemical buffer solutions. The experimental results show that it has a sensitivity of 66.7 nm per refractive index unit (RIU) and a detection range of 0.086 RIU.

Differential single living cell refractometry using grating resonant cavity with optical trap

This letter reports the measurement of single living cell’s refractive index (RI) using the optical grating resonant cavity with buffer modulation on a biochip. The cell’s RI is a significant cell biophysical property which has potential in cancer and disease diagnoses. The single cell is trapped optically within the cavity, and the transmission spectra shift due to the change of surrounding buffer, without/with cell, are used to determine the cell’s effective RI and effective thickness. The measurement shows that Madin-Darby canine kidney cell has an effective RI of 1.383±0.001. Moreover, the optical trapping technique eliminates uncertainty and avoids cell damage.

Stirring in Suspension: Nanometer‐Sized Magnetic Stir Bars

Rapid mixing is essential for achieving effective chemical and biological reactions. Because passive diffusion is a slow process, it is often necessary to agitate or stir a solution. Generating such disturbance must involve an external input of energy, for example, transduction of magnetic field energy through the use of commercial magnetic stir bars. But such use is impractical for the tiny channels and droplets, which are of great importance for lab-on-chip applications and microliter bioassay. The main challenge lies in the fabrication of low-cost stir bars that are sufficiently small but still able to transduce external energy for the mixing. Moreover, the stir bars should be introduced, operated, and extracted with ease. In microfluidic research, a number of methods have been developed to improve mixing. For a lamellar flow confined in a channel, turbulence can be induced by forcing the solution through a complex winding channel, or by pulsed injection of additional solution/bubbles from the side channels, thermal gradients can be used to induce convection, direct physical agitation can be achieved using ultrasound or piezoelectric transducers, and in-channel stirring was achieved using magnetic turbines that were fabricated by lithographic methods. These mixing schemes were often fabricated together with the channel systems, because it is too difficult to introduce them after the fabrication. In static microdroplets, however, transducing external energy for mixing remains a challenge, particularly in arrays of microdroplets. Ultrasonication and violent stirring can break up the droplets, while thermal gradients across tiny droplets are impractical. To date, magnetic stirring is still the most convenient option. Micro-sized stir bars have been reported, for example, linear chains of polymer beads embedded with magnetic nanoparticles (NPs), star-shaped micro-stirrers made by soft lithography, and cobalt-based magnetic bars cut by laser micromachining. Because of gravitational and magnetic attraction, micro-sized stir bars tend to stir only at the bottom of the vessel, leaving most part of the solution unstirred. While facile and scalable synthesis remains a challenge, the main problem of microsized stir bars is still their size: they are too large to remain suspended, but too small to churn up the whole solution. Herein, we report a simple and scalable method for fabricating magnetic stir bars, which are tunable from 75 nm– 1.4 mm in width and up to around 17 mm in length (Figure 1). They are straight single-line chains assembled from 40 nm

Label-free detection with micro optical fluidic systems (MOFS): a review

AbstractThe paper reviews the state-of-art for micro optical fluidic systems (MOFS), or optofluidics, which employs optics and fluidics in a microsystem environment to perform novel functionalities and in-depth analysis in the biophysical area. Various topics, which include the introduction of MOFS in biomedical engineering, the implementation of near-field optics and also the applications of MOFS to biophysical studies, are discussed. Different optical detection techniques, such as evanescent wave, surface plasmon resonance, surface enhanced Raman scattering, resonators and transistors, have been studied extensively and integrated into MOFS. In addition, MOFS also provides a platform for various studies of cell biophysics, such as cell mass determination and cell Young’s modulus measurement. FigureCell encapsulation and trapping for refractive index measurement in MOFS

An on-chip liquid tunable grating using multiphase droplet microfluidics

This letter reports the realization of liquid tunable long-period grating (LPG) using multiphase droplet microfluidics that is integrated onto a microfluidic chip. A stream of plugs is formed by two immiscible liquids and acted as LPG. It provides the tunability in the grating period by tuning the flow rates of the liquids, the refractive index and the index variation of the core layer by using different combinations of liquids. The experimental results show attenuation strength of 0.14 and attenuation bandwidth of 7.6nm. The chip is promising as a sensor for biochemical applications and a tunable filter for optical measurement.

Transformation optofluidics for large-angle light bending and tuning

Transformation optics is a new art of light bending by designing materials with spatially variable parameters for developing wave-manipulation devices. Here, we introduce a transformation optofluidic Y-branch splitter with large-angle bending and tuning based on the design of a spatially variable index. Differing from traditional splitters, the optofluidic splitter is achieved in an inhomogeneous medium by coordinate transformation. The designed bidirectional gradient index (GRIN) distribution can be achieved practically by the convection-diffusion process of liquid flowing streams. The transformation optofluidic splitter can achieve a much larger split angle with little bend loss than the traditional ones. In the experiments, a large tunable split angle up to 30° is achieved by tuning the flow rates, allowing optical signals to be freely transferred to different channels. Besides the symmetrical branch splitting, asymmetrical Y-branch splitting with approximately equal power splitting is also demonstrated by changing the composition of the liquids. The optofluidic splitter has high potential applications in biological, chemical and biomedical solution measurement and detection.

A Flat Lens with Tunable Phase Gradient by Using Random Access Reconfigurable Metamaterial

The first demonstration of an optofluidic metamaterial is reported where resonant properties of every individual metamolecule can be continuously tuned at will using a microfluidic system. This is called a random-access reconfigurable metamaterial, which is used to provide the first demonstration of a tunable flat lens with wavefront-reshaping capabilities.

Microfluidic droplet grating for reconfigurable optical diffraction.

This Letter presents a reconfigurable optical diffraction grating using multiphase droplets on a microfluidic chip. The uniform and evenly spaced circular droplets are generated by continuously dispersing two immiscible liquids into a T junction to produce plugs, which are then transformed into a circular shape at a sudden expansion of the microchannel. In experiments, the droplet grating shows a detection limit of ~6.3x10(-5) when used as an opto fl uidic refractometer and produces different colors as a color filter. Such a grating has the advantages of high stability and wide tunability in droplet size, grating period, and refractive index, making it promising for biochemical and biomaterial applications.