Md. Zahurul Islam

Rapid and cheap prototyping of a microfluidic cell sorter

Development of a microfluidic device is generally based on fabrication‐design‐fabrication loop, as, unlike the microelectronics design, there is no rigorous simulation‐based verification of the chip before fabrication. This usually results in extremely long, and hence expensive, product development cycle if micro/nano fabrication facilities are used from the beginning of the cycle. Here, we illustrate a novel approach of device prototyping that is fast, cheap, reliable, and most importantly, this technique can be adopted even if no state‐of‐the‐art microfabrication facility is available. A water‐jet machine is used to cut the desired microfluidic channels into a thin steel plate which is then used as a template to cut the channels into a thin sheet of a transparent and cheap polymer material named Surlyn® by using a Hot Knife™. The feature‐inscribed Surlyn sheet is bonded in between two microscope glass slides by utilizing the techniques which has been being used in curing polymer film between dual layer automotive glasses for years. Optical fibers are inserted from the sides of chip and are bonded by UV epoxy. To study the applicability of this prototyping approach, we made a basic microfluidic sorter and tested its functionalities. Sample containing microparticles is injected into the chip. Light from a 532‐nm diode laser is coupled into the optical fiber that delivers light to the interrogation region in the channel. The emitted light from the particle is collected by a photodiode (PD) placed over the detection window. The device sorts the particles into the sorted or waste outlets depending on the level of the PD signal. We used fluorescent latex beads to test the detection and sorting functionalities of the device. We found that the system could detect all the beads that passed through its geometric observation region and could sort almost all the beads it detected.

Light scattering characterization of single biological cells in a microfluidic cytometer

The characterization of single biological cells in a microfluidic flow by using a 2D light scattering microfluidic cytometric technique is described. Laser light is coupled into a microfluidic cytometer via an optical fiber to illuminate a single scatterer in a fluidic flow. The 2D light scattering patterns are obtained by using a charge-coupled device (CCD) detector. The system is tested by using standard polystyrene beads of 4 μm and 9.6 μm in diameter, and the bead experimental results agree well with 1D Mie theory simulation results. Experiments on yeast cells are performed using the microfluidic cytometer. Cell results are studied by finite-difference time-domain (FDTD) method, which can simulate light scattering from non-homogeneous cells. For example, a complex biological cell model with inner mitochondrial distribution is studied by FDTD in this paper. Considering the yeast cell size variations, the yeast cell 2D scatter patterns agree well with the FDTD 2D simulation patterns. The system is capable of obtaining 2D side scatter patterns from a single biological cell which may contain rich information on the biological cell inner structures. The integration of light scattering, microfluidics and fiber optics described here may ultimately allow the development of a lab-on-chip cytometer for label-free detection of diseases at a single cell level.

Development of a Microcontroller-Based AC Voltage Controller with Soft Start Capability

This paper describes the development of a prototype of a microcontroller-based phase angle controlled single-phase AC voltage controller that can efficiently control AC voltage and also accommodates soft start capability for single-phase induction motors. The output voltage of the controller is regulated to maintain a desired fixed RMS value and provide stabilized output by implementing a feedback control system. One microcontroller generates PWM signals in synchronism with the supply voltage to control the firing angle of thyristors while a second microcontroller remains dedicated for measuring the RMS value of the output voltage and sending that to the main microcontroller for the purpose of feedback control. The provision for soft starting of a load is also incorporated into this prototype.

Development of an optomicrofluidic flow cytometer for the sorting of stem cells from blood samples

In this paper, we report the preliminary development of a fiber coupled microfluidic flow cytometer with its potential application of sorting the very small embryonic like (VSEL) stem cells out of a mixture of platelets and VSEL stem cells. The identification of a VSEL stem cell from a platelet is based on the large difference of their abilities to scatter light. A simple cytometer prototype was built by cutting the fluidic and other channels into a polymer sheet and bonding it with epoxy between two standard glass slides. Standard photolithography was used to expose an observation window over the upper coated glass to reduce background scattered light. Liquid sample containing micro-particles (such as cells) is injected into the microfluidic channel. Light from a 532-nm CW diode laser is coupled into the optical fiber that delivers the light to the detection region in the channel to interrogate the flowing-by micro-particles. The scattering light from the interrogated micro-particle is collected by a photodiode placed over the observation window. The device sorts the micro-particle into the sort or waste outlet depending on the level of the photodiode signal. We used fluorescent latex beads to test the detection and sorting functionalities of the device. It was found that the system could only detect about half of the beads but could sort almost all the beads it detected.

Document Removed From IEEE Xplore Development of a microcontroller-based pure sine-wave voltage-source inverter employing bipolar SPWM switching scheme

This paper reports the design, simulation, hardware implementation and testing of a sinusoidal pulse width modulation (SPWM) based single-phase voltage-source sine-wave inverter. SPWM is a promising method of switching for motor drive control and inverter applications. In this development, we implemented the bipolar SPWM voltage modulation scheme as this method, compared to the unipolar scheme, offers the advantage of having output rms voltage being closest to the input DC voltage and effectively requiring the output filter to be smaller, and making it cheaper and easier to implement. The bipolar scheme was implemented by using a microcontroller. A good sinusoidal waveform was obtained at the output and a good agreement between simulation and experimental results was achieved.

Quasi-3D Modeling and Efficient Simulation of Laminar Flows in Microfluidic Devices

A quasi-3D model has been developed to simulate the flow in planar microfluidic systems with low Reynolds numbers. The model was developed by decomposing the flow profile along the height of a microfluidic system into a Fourier series. It was validated against the analytical solution for flow in a straight rectangular channel and the full 3D numerical COMSOL Navier-Stokes solver for flow in a T-channel. Comparable accuracy to the full 3D numerical solution was achieved by using only three Fourier terms with a significant decrease in computation time. The quasi-3D model was used to model flows in a micro-flow cytometer chip on a desktop computer and good agreement between the simulation and the experimental results was found.

Tuning of transmission characteristics of epsilon-near-zero metamaterials by controlling permittivity of embedded defects

In this paper we present the results of analytical and numerical studies on the effect of change of permittivity of embedded defects on the transmission characteristics of epsilon-near-zero (ENZ) metamaterials. We investigated electromagnetic wave transmission in the microwave regime through an isotropic ENZ metamaterial-based waveguide embedded with rectangular defects. We found that by adjusting the permittivity of the defect the transmission coefficient can be adjusted over a wide range, and even total transmission can be achieved. With a single rectangular defect, precise control of its permittivity is necessary to achieve and maintain near-perfect transmission through the waveguide. We found that if two defects are used in the ENZ medium, the range of permittivity for near-perfect transmission can be increased. We have also shown that this increase of permittivity range for total transmission and total reflection is also possible in anisotropic ENZ (AENZ) materials with rectangular defect(s).

Optimization of an optical waveguide biosensor based on hybrid coupler with short-range surface plasmon polariton

The presented study is an analysis of an integrated sensor based on a dielectric waveguide structure with Gold nanolayer. It consists of a short-range surface Plasmon polariton (SRSPP) generating hybrid coupler and a SiNx dielectric waveguide. The output transmission spectra of the sensor is observed to change significantly with the refractive index of the detection liquid, and the sensing region can be adjusted by varying the length and thickness of it. For ultra-thin layer bimolecular detection, the application of the wavelength interrogation method has been shown here. It is also shown that varying the thickness of layers can give rise to spectral changes. A brief analytical formulation of the SPP excitation and the comparison of this with the simulated results, which are accomplished using the finite element method via the COMSOL Multiphysics software have been presented. The scope of the study includes the spectral responses of the sensor configuration in energy domains, with varying analytes and thickness of layers along with the advantages and disadvantages of the different combinations these attributes. This sensor is expected to have significantly high effective sensitivity for detecting a hundred-nanometer-thick layer owing to the highly bounded field of the SRSP mode.

Measurement of fiber optic imaging device parameters

A new method for testing the parameters of fiber optic imaging devices (fiber optic taper, fiber optic faceplate and fiber optic inverter) featuring a single integral sphere and a CCD camera is put forward. Compared with the method of two integral spheres with photoelectric detector, this method features simply structure, wealth information and fast testing operation. It can realize the measurement of many parameters such as total or partial transmittances, center-edge transmittances relative errors, resolution target, and pincushion and barrel distortions by processing the CCD images of those devices. The testing principle is analyzed and proved feasible by the experiment

Effects of phosphorus doping on J-V and C-V characteristics of pulsed laser deposited camphoric carbon/P-silicon heterojunction device

The current density-voltage (J-V) and capacitance voltage (C-V) characteristics of a p-n heterojunction device are studied. The device was fabricated by depositing phosphorus (P) doped carbon (C) thin film on p-type silicon (Si) substrate by pulsed laser deposition (PLD) technique at room temperature. Camphor (C10H16O), a natural source, was used as the starting precursor for the carbon layer of the heterostructure. Carbon layers of the device were obtained using target containing different amount of P. Both the J-V and C-V characteristics reveal that the device behaves as a successful p-n junction device up to a certain P content of the target material for C layer, and this is near about 5% of P by mass. At higher P content of the target, the material properties of the grown C layer on Si change and the device performance deteriorates. The built-in potential of the device with varying P content of the target material for C is also estimated and found them to agree well with the experimentally obtained device characteristics.