Combining microfluidic chip and binary optical element for flow cytometry

This work introduces three rectangular quasi-flat-top spots, which are provided by binary optical elements (BOEs) and utilized for the illumination in a microflow cytometer. The three spots contain, respectively, one, two, and three rectangles (R1, R2, and R3). To test the performance of this mechanism, a microflow cytometer is established by integrating the BOEs and a three-dimensional hydrodynamic focusing chip. Through the experiments of detecting fluorescence microbeads, the three spots present good fluorescence coefficients of variation in comparison with those derived from commercial instruments. Benefiting from a high spatial resolution, when using R1 spot, the micro flow cytometer can perform a throughput as high as 20 000 events per second (eps). Illuminated by R2 or R3 spot, one bead emits fluorescence twice or thrice, thus the velocity can be measured in real time. Besides, the R3 spot provides a long-time exposure, which is conducive to improving fluorescence intensity and the measurement stability. In brief, using the spots shaped and homogenized by BOEs for illumination can increase the performance and the functionality of a micro flow cytometer.

In this article, we demonstrate single-layered, "microfluidic drifting" based three-dimensional (3D) hydrodynamic focusing devices with particle/cell focal positioning approaching submicron precision along both lateral and vertical directions. By systematically optimizing channel geometries and sample/sheath flow rates, a series of "microfluidic drifting" based 3D hydrodynamic focusing devices with different curvature angles are designed and fabricated. Their performances are then evaluated using confocal microscopy, fast camera imaging, and side-view imaging techniques. Using a device with a curvature angle of 180°, we have achieved a standard deviation of ±0.45 μm in particle focal position and a coefficient of variation (CV) of 2.37% in flow cytometric measurements. To the best of our knowledge, this is the best CV that has been achieved using a microfluidic flow cytometry device. Moreover, the device showed the capability to distinguish 8 peaks when subjected to a stringent 8-peak rainbow calibration test, signifying the ability to perform sensitive, accurate tests similar to commercial flow cytometers. We have further tested and validated our device by detection of HEK-293 cells. With its advantages in simple fabrication (i.e., single-layered device), precise 3D hydrodynamic focusing (i.e., submicrometer precision along both lateral and vertical directions), and high detection resolution (i.e., low CV), our method could serve as an important basis for high-performance, mass-producible microfluidic flow cytometry.

This paper presents a micro-machined cytometric device which can achieve a three-dimensional (3D) hydrodynamic focusing only through a novel but simple microfluidic structure, with the uniqueness that the depth of the microchannels is non-uniform. By using a SU-8 soft lithography containing two exposures, the PDMS device prototype is fabricated, and tested for its performance through fluorescent optical experiments. At the same time, a two-fluid model to describe the micro-flow transport and interaction behaviors is also established, based on volume of fluid (VOF) method for multi-phase flow. It is found that the experiment and the simulation results have good consistencies. Based on this, the influences of a few geometry parameters on device 3D focusing performance, which is evaluated by the focused width as well as the corresponding height, are further explored by numerical simulations. The results indicate that good 3D focusing could be obtained at relatively not high sheath-sample velocity ratios, mainly due to the introducing of the unique depth difference. The work of this paper, not only validates the design conception of the proposed novel structure convincingly, but also enhances our understanding of 3D hydrodynamic focusing in the design of cytometers, as well as similar microfluidic devices.

Binary optical elements are finding increased use in a wide range of applications. Fabrication of binary optical elements generally remains a time consuming and expensive process. Even in high volume, costs can be prohibitive, especially for elements larger than a few millimeters in diameter. Replications techniques, such as injection molding, have recently begun to show promise as a means of manufacturing binary optical elements, and doing so at a significant cost reduction over conventional photolithographic means. We report on recent improvements in the application of injection molding techniques to the replication of binary optical elements. Several examples of binary elements fabricated by these techniques, as well as present process capability, will be discussed.

This paper reports a micro flow cytometer fabricated in Polymethylmethacrylate (PMMA) in which a 3d hydrodynamic flow focusing is employed in order to align the particles in a single line along the focused stream. The device has been fabricated by direct micro milling of two parts of PMMA that were finally bonded together. With a suitable choice of the fluidic channel geometry, a circular sample stream located in the center of the channel is obtained. Numerical simulations have been performed in order to investigate the flow characteristic of the structure and find the desiderated geometry. Three dimensional hydrofocusing of the sample fluid was analysed and demonstrated by cross sectional fluorescence imaging in good agreement with numerical simulations. Flow cytometry measurements have been performed by using 10μm particles. From the analysis of the fluorescence signals collected at each transit event we can confirm that the device was capable of creating a single-file particle stream. The results show that the device was capable of discriminating single microparticles with a good signal-to-noise ratio and a high throughput.

The liquid crystal spatial light modulator (SLM) is an effective active beam-shaping device through adjusting each pixel transmittance to improve the spatial beam quality of the output laser, which can also be used as a binary optical element (BOE) with each pixel transmittance 0 or 1 to realize spatial beam shaping for high-power lasers. We present and demonstrate an efficient shaping method of the SLM used as BOE based on diffraction principle. The method can be used to control the output nearfield actively by compensating the spatial nonuniformity of transmission and amplification in the high-power laser system. Results show the output nearfield beam quality improves significantly after shaping by using this method with the fluence contrast changing from 22% to 11.3% within only two shots in the single-shot operation laser.

Binary optical element (BOE) is applied to infrared hyperspectral detector. A new type of infrared hyperspectral detecting image system is designed based on the characteristics of abundant color-dispersion of BOE, and an example of combining refractive-diffractive zoom optical system with Cassegrain system is presented. The system not only has simple structure, long back-working distance and few requirements for material but also can increase the image resolution, abilities of accepting ray energy and registration. Consequently, by adding an appropriate stare array detector to the system, the detecting precision can be raised.

The Application of Microfluidics in Preparing Nano Drug Delivery Systems

We report on the use of femtosecond laser irradiation followed by chemical etching as a microfabrication tool for innovative microfluidic networks that implement hydrodynamic focusing. The capability of our microfabrication technology to interconnect microchannels in three dimensions was exploited to demonstrate 2D hydrodynamic focusing, either in the horizontal or in the vertical plane, and full 3D hydrodynamic focusing. In all cases only two inlets were required, one for the sample and one for the sheath flows. Fluidic characterization of all devices was provided. In addition, taking advantage of the possibility to write optical waveguides using the same technology, a monolithic cell counter based on 3D hydrodynamic focusing and integrated optical detection was validated. Counting rates up to 5000 cells s(-1) were achieved in this very compact device, where focusing and counting operations were implemented in less than 1 mm(3). Integration of this hydrodynamic focusing module into several devices fabricated by the same technology as optical cell stretchers and cell sorters is envisaged.

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.

A method of multiple images produced by binary combined optical element of off-axis type is reported. The element having both functions of splitting and focusing is combined with a 2D Dammann grating and Fresnel zone plate. A imaging lens can be omitted in practical geometry. The setup became more simple and more compact. The arrangement of images is the same as the split arrays. The images are also clear and uniform.

A novel technique to improve the focus depth of a Gaussian beam is presented in this paper. The improvement is based on two-step beam shaping using a cascade of binary phase diffractive optical elements (BPDOEs). The first BPDOE transforms the incident Gaussian beam into a high-order radial Laguerre-Gaussian beam (LGp0). Then the second BPDOE rectifies the obtained LGp0 beam and gives rise to a quasi-Gaussian one in the focal plane of a converging lens. This resulting quasi-Gaussian beam exhibits a lower divergence and larger focus depth compared to the pure Gaussian beam having the same beam waist. These results open new possibilities in laser beam manufacturing and micromachining, and in applications that need an extended focus depth.

The design and fabrication of two binary phase diffractive optical elements are presented. We used iterative design procedures and performed numerical two-dimensional Fourier transforms in order to evaluate the reconstruction pattern. Fraunhofer and Fresnel diffraction patterns for the same intensity distribution are compared, using computer simulations. The elements were fabricated by configuring either thermally grown silicon dioxide on silicon substrate or aluminium layers. The experimental results are shown to be close to the results obtained by simulations.

In this paper we consider the calculation of binary diffraction optical elements (DOEs) for the formation and detection of optical vortices of arbitrary order. The synthesis of binary DOEs is based on a combination of the method of carrier spatial frequencies and binary coding with a variable fill factor. Unlike various methods of multiplication, the method of carrier spatial frequencies is characterized by great flexibility and versatility. It allows us to not only form the given field distributions in arbitrary diffraction orders, but also to give them arbitrary weight ratio (energy distribution in orders). As a rule, such universality leads to the need to form a complex amplitude-phase distribution in the input plane. To avoid this, in this paper it is proposed to use binary coding with a variable level. The effect of such coding is studied in detail both theoretically and numerically. It is shown that the level variation makes it possible to change the set of the observed diffraction orders. The positions and orders of the optical vortices formed are uniquely determined by the values of the carrying spatial frequencies and the topological charges of the vortices in the basic order. The results can be useful in optical communications.

Many optical systems used in the infrared spectrum have, so far, adopted binary optical elements (BOE) to achieve a better performance. Especially, in the middle and long infrared spectrum, binary optical elements are commonly used. Thus, limited by the manufacture technology, the applications of binary optics in the visible spectrum are rare. This tentative research aims at finding the practicability of applying BOEs in the visible spectrum. We attempted to replace the reference lens group in the interferometer with a harmonic diffractive/refractive hybrid lens group, expecting that the wave aberration be well-corrected. In this paper, the main procedure of designing a hybrid optical system is introduced with an example of “F2” lens group. After the analysis on the interference pattern and wave front, the comparison between the tested result and theoretical result can be made. It demonstrates that the hybrid optical system is capable of being applied in the visible spectrum. The analysis also discloses that raising the diffractive efficiency is the next step for us to take.