Optofluidic sensor system with Ge PIN photodetector for CMOS-compatible sensing

Vertical optofluidic biosensors based on refractive index sensing promise highest sensitivities at smallest area footprint. Nevertheless, when it comes to large-scale fabrication and application of such sensors, cheap and robust platforms for sample preparation and supply are needed—not to mention the expected ease of use in application. We present an optofluidic sensor system using a cyclic olefin copolymer microfluidic chip as carrier and feeding supply for a complementary metal–oxide–semiconductor compatibly fabricated Ge PIN photodetector. Whereas typically only passive components of a sensor are located within the microfluidic channel, here the active device is directly exposed to the fluid, enabling top-illumination. The capability for detecting different refractive indices was verified by different fluids with subsequent recording of the optical responsivity. All components excel in their capability to be transferred to large-scale fabrication and further integration of microfluidic and sensing systems. The photodetector itself is intended to serve as a platform for further sophisticated collinear sensing approaches.     

单泵控制聚焦流形态的微流控芯片的研制

研究一种单动力源、聚焦流形态可控的用于细胞排队的微流控芯片。建立了样品沟道与鞘流沟道不同长度比例、不同夹角的模型并进行了不同负压条件下聚焦流形态仿真,运用SPSS软件进行了回归分析并进行了模型优化。在芯片的微加工过程中,利用印刷电路板(PCB)制作了母板,以聚二甲基硅氧烷(PDMS)为芯片主要材料,制作了PDMS—PDMS,PDMS—玻璃及PCB—PDMS三种芯片。制作的芯片能够在单个动力源条件下控制聚焦流宽度,使不同大小的微粒及细胞呈单个排列流动。研究结果为分析不同尺寸的细胞而选择合适的样品流沟道与鞘流沟道长度、夹角等条件提供了依据,所制作的芯片也达到了廉价且实用的目的。     

Optofluidic device for ultra-sensitive detection of proteins using surface-enhanced Raman spectroscopy

An optofluidic device is reported in this paper that can highly improve the robustness of surface-enhanced Raman scattering (SERS) detection and provide fingerprint information of proteins with a concentration in the nanogram per liter range within minutes. Moreover, the conformational change of protein can also be obtained using this device. Fabricated by standard photolithography processes, the optofluidic device has a step microfluidic–nanofluidic structure, which provides robust SERS detection. The sensitivity of the device is investigated using insulin and albumin as target analytes at a concentration of 0.9 ng/L. The ability to detect conformational changes of proteins using this technology is also shown by probing these analytes before and after their denaturation.     

Toward the commercialization of optofluidics

Optofluidics is a marriage between the field of optics and microfluidics. This field aims at providing practical solutions with the integration of optical tools into lab-on-chip systems. Often, this results in opportunities for commercialization due to the advancement offered after the integration. Although numerous novel functions and properties have been demonstrated with the combination of optics and microfluidics, the market has witnessed only few transferals of optofluidic technologies from academic laboratories. This stemmed from a lack of a “killer applications” despite several decades of development. Therefore, it is necessary to have a retrospective review on this topic, particularly on the basic optofluidic components, to analyze what might be the hurdles to stop the market uptake of optofluidic devices. Specifically, this review paper is focused on discussion of optofluidic components in terms of fabrication standardization, device and operational cost and practicability for end users. It is believed that these factors play important roles in the market uptake of a novel technology. We then provide perspectives on how to align the development of optofluidics with the requirements imposed by the industry.     

A massively parallel microfluidic device for long-term visualization of isolated motile cells

Visualizing the natural behavior of motile cells over many hours is a challenge, as cells can leave the field of view of a microscope in a matter of minutes. Many interesting cell behaviors—such as cell division, motility phenotype, cell–cell interactions, and multicellular colony formation—require hours of observation to characterize. We present a microfluidic device that traps hundreds of single motile cells in isolated chambers, thereby allowing observation over several days. This polydimethylsiloxane device features 400 circular chambers, connected to a central serpentine channel. Motile cells are loaded into these chambers through the serpentine channel. The channel is then purged with air, fluidically isolating the chambers from each other and effectively trapping the cells. We applied the device to observe the behavior of the choanoflagellate Salpingoeca rosetta. Because of its ability to live in both solitary and colonial forms, S. rosetta is a useful model organism for the study of the evolutionary origins of multicellularity. In particular, S. rosetta can take on two distinct colonial forms: chain colonies and rosette colonies. With our device, we are able to observe the formation of these colonies from single cells more easily and with higher throughput than ever before. This device has the potential to be a powerful tool for studying the long-term behavior of motile cells.     

Interaction of guided light in rib polymer waveguides with dielectrophoretically controlled nanoparticles

This work demonstrates an optofluidic system, where dielectrophoretically controlled suspended nanoparticles are used to manipulate the properties of an optical waveguide. This optofluidic device is composed of a multimode polymeric rib waveguide and a microfluidic channel as its upper cladding. This channel integrates dielectrophoretic (DEP) microelectrodes and is infiltrated with suspended silica and tungsten trioxide nanoparticles. By applying electrical signals with various intensities and frequencies to the DEP microelectrodes, the nanoparticles can be concentrated close to the waveguide surface significantly altering the optical properties in this region. Depending on the particle refractive indices, concentrations, positions and dimensions, the light remains confined or is scattered into the surrounding media in the microfluidic channel.     

Optimized design and fabrication of a microfluidic platform to study single cells and multicellular aggregates in 3D

A microfluidic platform for cell motility analysis in a three-dimensional environment is presented. The microfluidic device is designed to study migration of both single cells and cell spheroids, in particular under spatially and temporally controlled chemical stimuli. A layout based on a central microchannel confined by micropillars and two lateral reservoirs was selected as the most effective. The microfluidics have an internal height of 350 μm to accommodate cell spheroids of a considerable size. The chip is fabricated using well-established micromachining techniques, by obtaining the polydimethylsiloxane replica from a Si/SU-8 master. The chip is then bonded on a 170-μm-thick microscope glass slide to allow high spatial resolution live microscopy. In order to allow the cost-effective and highly repeatable production of chips with high aspect ratio (5:1) micropillars, specific design and fabrication processes were optimized. This design permits spatial confinement of the gel where cells are grown, the creation of a stable gel–liquid interface and the formation of a diffusive gradient of a chemoattractant (>48 h). The chip accomplishes both the tasks of a microfluidic bioreactor system and a cell analysis platform avoiding critical handling of the sample. The experimental fluidic tests confirm the easy handling of the chip and in particular the effectiveness of the micropillars to separate the Matrigel? from the culture media. Experimental tests of (i) the stability of the gradient, (ii) the biocompatibility and (iii) the suitability for microscopy are presented.     

An integrated microfluidic signal generator using multiphase droplet grating

An integrated and reconfigurable optofluidic signal generator based on multiphase droplet grating is demonstrated in this paper. The chip is fabricated with an inexpensive, optically clear and non-toxic silicone elastomer-polydimethylsiloxane (PDMS) by conventional soft lithography. Droplet grating is formed by a stream of plugs which are generated through a typical microfluidic T-junction. Since the refractive indices of the two immiscible liquids are different, the alternative mobility of the plug results in the periodical change of the reflectivity at the fluid/PDMS interface. The real-time tunability in the frequency and amplitude of the signal can be realized by varying the flow rates of the liquids. In experiments, both rectangle and triangle signals are displayed and the signal frequency ranges from 1 to 525 Hz. This signal generator can be easily integrated into other microfluidic networks to create versatile functionalities. Furthermore, we present coding functions based on the signal generator on a chip. Such a signal generator has great potential as a signal source or a part of functionalities for lab-on-a-chip applications.     

Two optofluidic devices for the refractive index measurement of small volume of fluids

Two simple optofluidic devices based on a microprism and a refraction channel, respectively, are proposed for measuring the refractive index of fluids. The microprism chip consists of an optical waveguide channel and a single triangular chamber filled with the test fluid, while the refraction channel chip consists of a single turning channel which functions as a liquid-core/solid-cladding optical waveguide. In both chips, the refractive index of the test fluid is calculated from a CCD image of the refracted ray in accordance with simple geometrical optics principles. The experimental results show that the refraction channel chip provides a more accurate measurement performance than the microprism chip; particularly for colloidal samples. However, the refraction channel chip is suitable only for the measurement of fluids with a refractive index greater than that of the chip substrate. Overall, the results presented in this study show that both devices provide a simple, low cost and effective means of determining the refractive index of a wide range of common test fluids with nano-liter volume.     

智能避障小车设计

介绍一种基于STC89C52单片机实现的智能避障小车设计。该系统前方采用两个红外反射式光电传感器ST188检测障碍物,底部采用两个红外反射式光电传感器ST188检测悬崖,控制系统通过检测信号识别障碍物及悬崖并发出指令使小车绕行。     

Microfluidic fluorescence-activated cell sorting (μFACS) chip with integrated piezoelectric actuators for low-cost mammalian cell enrichment

A low-cost, microfluidic fluorescence-activated cell sorting (μFACS) microchip integrated with two piezoelectric lead–zirconate–titanate actuators was demonstrated for automated, high-performance mammalian cell analysis and enrichment. In this PDMS–glass device, cells were hydrodynamically focused into a single file line in the lateral direction by two sheath flows, and then interrogated with a forward scattering and confocal fluorescent detection system. The selected cells were displaced transversely into a collection channel by two piezoelectric actuators that worked in a pull–push relay manner with a minimal switching time of ~0.8 ms. High detection throughput (~2500 cells/s), high sorting rate (~1250 cells/s), and high sorting efficiency (~98%) were successfully achieved on the μFACS system. Six cell mixture samples containing 22.87% of GFP-expressing HeLa cells were consecutively analyzed and sorted on the chip, revealing a stable sorting efficiency of 97.7 ± 0.93%. In addition, cell mixtures containing 37.65 and 3.36% GFP HeLa cells were effectively enriched up to 83.82 and 78.51%, respectively, on the microchip, and an enrichment factor of 105 for the low-purity (3.36%) sample was successfully obtained. This fully enclosed, disposable microfluidic chip provides an automated platform for low-cost fluorescence-based cell detection and enrichment, and is attractive to applications where cross-contamination between runs and aerosol hazard are the primary concerns.     

Computational and performance analysis of a continuous magnetophoretic bioseparation chip with alternating magnetic fields

This paper presents the modeling and optimization of a magnetophoretic bioseparation chip for isolating cells, such as circulating tumor cells from the peripheral blood. The chip consists of a continuous-flow microfluidic platform that contains locally engineered magnetic field gradients. The high-gradient magnetic field produced by the magnets is spatially non-uniform and gives rise to an attractive force on magnetic particles flowing through a fluidic channel. Simulations of the particle–fluid transport and the magnetic force are performed to predict the trajectories and capture lengths of the particles within the fluidic channel. The computational model takes into account key forces, such as the magnetic and fluidic forces and their effect on design parameters for an effective separation. The results show that the microfluidic device has the capability of separating various cells from their native environment. An experimental study is also conducted to verify and validate the simulation results. Finally, to improve the performance of the separation device, a parametric study is performed to investigate the effects of the magnetic bead size, cell size, number of beads per cell, and flow rate on the cell separation performance.     

Study of high-throughput cell electrofusion in a microelectrode-array chip

A microfabricated high-throughput cell electrofusion chip with 1,368 pairs of high aspect ratio silicon microelectrodes is presented. These microelectrodes, which were distributed in six individual microscale cell-fusion chambers, were covered with titanium and gold thin film to improve their electric conductivity as well as surface hydrophobility. Six chambers having different electrode distances make the chip highly suitable for fusing cells with different sizes. A microfluidic platform was set up for flowing control, cell manipulation and also experimental observation. Cells for electrofusion were first aligned at the prearranged locations by the dielectrophoretic force between two counter-electrodes, which benefits the traverse of electric pulse through the cell–cell contacting point for electroporation. Several on-chip cell electrofusion experiments have been carried out on different kinds of animal cells and plant protoplasts. Compared with conventional electrofusion methods, higher fusion efficiency was achieved on this device for precisely forming micropores on the proximate membranes of two contacting cells, and high throughput was also obtained due to the use of a large number of microelectrodes for cell manipulation and fusion. Moreover, a much lower power supply was required for the shorter distance between two counter-electrodes.     

Mathematical analysis of oxygen transfer through polydimethylsiloxane membrane between double layers of cell culture channel and gas chamber in microfluidic oxygenator

For successful cell culture in microfluidic devices, precise control of the microenvironment, including gas transfer between the cells and the surrounding medium, is exceptionally important. The work is motivated by a polydimethylsiloxane (PDMS) microfluidic oxygenator chip for mammalian cell culture suggesting that the speed of the oxygen transfer may vary depending on the thickness of a PDMS membrane or the height of a fluid channel. In this paper, a model is presented to describe the oxygen transfer dynamics in the PDMS microfluidic oxygenator chip for mammalian cell culture. Theoretical studies were carried out to evaluate the oxygen profile within the multilayer device, consisting of a gas reservoir, a PDMS membrane, a fluid channel containing growth media, and a cell culture layer. The corresponding semi-analytical solution was derived to evaluate dissolved oxygen concentration within the heterogeneous materials, and was found to be in good agreement with the numerical solution. In addition, a separate analytical solution was obtained to investigate the oxygen pressure drop (OPD) along the cell layer due to oxygen uptake of cells, with experimental validation of the OPD model carried out using human umbilical vein endothelial cells cultured in a PDMS microfluidic oxygenator. Within the theoretical framework, the effects of several microfluidic oxygenator design parameters were studied, including cell type and critical device dimensions.     

Non-destructive on-chip imaging flow cell-sorting system for on-chip cellomics

We have developed a non-destructive imaging flow cell-sorting system using an ultra-high-speed camera (shutter speed of 1/10,000 s) with a real-time image analysis unit and a poly(methyl methacrylate) (PMMA)-based disposable microfluidic chip for single-cell-based on-chip cellomics. It has a 3-D micropipetting device that supports fully automated sorting and collection of samples. The entire fluidic system is implemented in a disposable plastic chip, enabling biological samples to be lined up in a laminar flow using hydrodynamic focusing. Its optical system enables direct observation-based cell identification using specific image indexes and phase-contrast/fluorescence microscopy, real-time image processing. It has a non-destructive, wider dynamic range, sorting procedure using mild electrostatic force in a laminar flow; agarose gel electrodes are used to prevent electrode loss and electrolysis bubble formation. The microreservoir used for recultivating collected target cells is contamination-free. An integrated ultra-high-speed droplet polymerase chain reaction measurement module is used for DNA/mRNA analysis of the collected target cells. This system was used to separate cardiomyocyte cells from a mixture of various cells. All the operations were automated using the 3-D micropipetting device. The results demonstrate that this imaging flow cell-sorting system is practically applicable for biological research and clinical diagnosis.     

Review and analysis of performance metrics of droplet microfluidics systems

Droplet microfluidics has enabled many recent applications in high-throughput screening and diagnostics. Little work has been done, however, to analyze the performance of droplet-based assays. This review aims to apply what is known in the literature to the analysis of the performance metrics of droplet-based assays, with specific relevance to diagnostic and biomedical applications based on two processes: enzymatic reactions and cell culture in droplets. By considering the physical scaling of individual processes—droplet generation, reaction kinetics, cell growth, and droplet interrogation—it is possible to extract a practical relationship between input parameters (e.g., droplet size and droplet polydispersity) and the output characteristics (e.g., throughput, dynamic range, and accuracy) of the assay. This review can serve as a guide to the design of droplet-based assays for achieving desired performance. While the focus is on assays based on enzymatic reactions and cell cultures, a similar analysis can be applied to other assays based on polymerase chain reaction and the detection of nucleic acids.     

On-chip whole blood plasma separator based on microfiltration,sedimentation and wetting contrast

Miniaturized on-chip blood separators have a great value for point-of-care diagnosis. In our work, a combined design strategy—microfiltration, sedimentation in a retarded flow, and wetting contrast—was taken to overcome the known limitations of on-chip blood separators. Our microfluidic chip consists of a polydimethylsiloxane micropillar array and an etched glass with microchannel branches. The red blood cells are significantly slowed and gradually settled down due to micropillars and enlarged dimension of a chamber. An etched glass microchannel allows the extraction of blood plasma exclusively due to the capillary effect. The fabricated microfluidic device can separate blood plasma from a whole blood sample without any external driving force or dilution. The measured plasma separation efficiency was close to 100 % from human whole blood. Autonomous on-chip separation and collection of blood plasma was demonstrated.     

A cell electrofusion microfluidic chip with micro-cavity microelectrode array

A new cell electrofusion microfluidic chip with 19,000 pairs of micro-cavity structures patterned on vertical sidewalls of a serpentine-shaped microchannel has been designed and fabricated. In each micro-cavity structure, the two sidewalls perpendicular to the microchannel are made of SiO₂ insulator, and that parallel to the microchannel is made of silicon as the microelectrode. One purpose of the design with micro-cavity microelectrode array is to obtain high membrane voltage occurring at the contact point of two paired cells, where cell fusion takes place. The device was tested to electrofuse NIH3T3 and myoblast cells under a relatively low voltage (~9 V). Under an AC electric field applied between the pair of microelectrodes positioned in the opposite micro-cavities, about 85–90 % micro-cavities captured cells, and about 60 % micro-cavities are effectively capable of trapping the desired two-cell pairs. DC electric pulses of low voltage (~9 V) were subsequently applied between the micro-cavity microelectrode arrays to induce electrofusion. Due to the concentration of the local electric field near the micro-cavity structure, fusion efficiency reaches about 50 % of total cells loaded into the device. Multi-cell electrofusion and membrane rupture at the end of cell chains are eliminated through the present novel design.     

加速器控制系统中温度采集单元设计

介绍了基于AT89C51单片机的温度采集单元的结构与组成,分析了该单元的测温原理与特点。经现场试验,得到了理想的测量结果,测温准确度达到±0.8℃。该单元具有功能强、电路设计新颖、控制可靠、抗干扰能力强、组网方便等特点,满足了国家重大科学工程———兰州重离子加速器冷却存储环的控制系统要求。     

Isolation and elution of Hep3B circulating tumor cells using a dual-functional herringbone chip

Circulating tumor cells (CTCs), which are derived from primary tumor and circulate to secondary site, are regarded as the cause of metastasis. Many methods have been applied for CTC isolation and enumeration so far. However, it remains a challenge to effectively elute the captured cells from the device for further cellular and biomolecular analyses. In this paper, we fabricate a dual-functional herringbone chip to achieve both CTC capture and elution based on the immunoassay of epithelial cell adhesion molecule antigen expressed on the surface of human liver cancer cell line Hep3B. The results show that the capture limit of Hep3B cells can reach as low as 3 cells per ml with capture efficiency over 50 % on average. On the other hand, the elution rate of more than 50 % of the captured Hep3B cells can be achieved for cell density ranging from 5 to 2 × 10³/ml. It demonstrates that this herringbone chip exhibits excellent dual functions with high capture efficiency and considerable elution rate, indicating its promising capability for clinical assay in cancer diagnosis.