Droplets Array Research Articles

Highly precisive digital polymerase chain reaction based on inkjet printer

BackgroundTo eliminate the indeterminate droplet partitions that highly obfuscate the distinguishment of the positive and the negative partitions in digital polymerase chain reaction (dPCR), the highly precisive droplets array of dPCR was developed via the inkjet printer coupled with the X-Y stage. ResultsThe highly precisive droplets could be generated by the inkjet printer and the droplets array would be arranged by the movable X-Y stage at the same time. The highly precisive droplets array in a volume of at least 20,000 droplets could be obtained with a coefficients of variation (CV) of 1.57 % for the decided droplets in a diameter of 145.16 μm. The CV of the fluorescence intensities of droplets in array could be lowered to 3.17 % for the droplets of 5 μM fluorescein sodium solution, which guaranteed the clear identification of the positive droplets in the absolute quantification of dPCR. In addition, the thermal amplification in dPCR was designed to implement at the same sheet to avoid the delivery of the droplet partitions. The highly precisive dPCR was demonstrated through the wide linear range of more than 103 in the measurement of the model GAPDH gene with a low limitation of detection (LOD) of 0.60 copies/μL. Finally, the practicality of developed dPCR was confirmed by the measurement of the human mammaglobin (hMAM) gene in MCF-7 cell as well. Significance and noveltyThe successful development of the highly precisive droplet array through the inkjet printer coupled with X-Y stage eliminated the indeterminate positive droplet partitions in dPCR. It paved a way to develop the compact and highly sensitive dPCR.

Design and evaluation of a linear nozzle array with double auxiliary electrodes for restraining cross-talk effect in parallel electrohydrodynamic jet printing

It is attractive and challenging to fabricate micro-nano scale patterns in large area by parallel electrohydrodynamic jet printing (E-jet printing) with nozzle array. However, cross-talk effect (i.e. interference phenomenon) between nozzles may probably lead to poor positioning accuracy and cause jet instability. In this paper, design and evaluation of a special linear nozzle array with double auxiliary electrodes at both ends were proposed to restrain the cross-talk effect. Firstly, the numerical simulation model of multi-nozzle E-jet printing was established considering with electro-hydraulic coupling effect. The corresponding multi-nozzle E-jet printing processes in several geometry configurations were successfully simulated based on a commercial multi-physical software ‘COMSOL’. Secondly, the unique design of new type linear nozzle array with double auxiliary electrodes was proposed after accomplishing theoretical analysis and comparison study of simulation results. Thirdly, several experiments were carried out on a constructed multi-nozzle E-jet printing system to verify feasibility and effectiveness of the provided design. The experiments show that the proposed manner has obvious advantages in restraining cross-talk compared with traditional suppressing method ‘with single flat-head auxiliary electrode at both ends’. When nozzle space is 0.5 mm, the jet deflection angle 2.8° and Taylor cone angle 3.3° could be reduced to 0° and 0.05° with two methods respectively. Finally, the printability of fabricated new multi-nozzle was also characterized. Microscale droplets array (mean diameter about 200–240 μm) could be achieved with no deflection and the gap between them is equal with the distance between adjacent nozzles. This study can provide a reference for the design of high integrated printhead and E-jet printing system.

A Rapid Digital PCR System with a Pressurized Thermal Cycler

We designed a silicon-based fast-generated static droplets array (SDA) chip and developed a rapid digital polymerase chain reaction (dPCR) detection platform that is easy to load samples for fluorescence monitoring. By using the direct scraping method for sample loading, a droplet array of 2704 microwells with each volume of about 0.785 nL can be easily realized. It was determined that the sample loading time was less than 10 s with very simple and efficient characteristics. In this platform, a pressurized thermal cycling device was first used to solve the evaporation problem usually encountered for dPCR experiments, which is critical to ensuring the successful amplification of templates at the nanoliter scale. We used a gradient dilution of the hepatitis B virus (HBV) plasmid as the target DNA for a dPCR reaction to test the feasibility of the dPCR chip. Our experimental results demonstrated that the dPCR chip could be used to quantitatively detect DNA molecules. Furthermore, the platform can measure the fluorescence intensity in real-time. To test the accuracy of the digital PCR system, we chose three-channel silicon-based chips to operate real-time fluorescent PCR experiments on this platform.

Self-assembled photocurable polymer biconvex microlens array based on double-faced discontinuous hydrophobic surface

Biconvex microlens arrays (MLAs) are key parts in optical systems. In this work, a facile method was developed for the fabrication of biconvex MLAs on ultrathin glass substrates, in which both sides were modified with microholes patterned hydrophobic layers. The difference of the hydrophobicity inside and outside the microholes pattern were very large. The photocurable polymer formed droplets array on the discontinuous hydrophobic layer self-assembly, and polymeric biconvex MLAs were obtained after UV curing. Each polymeric dome formed on front and back sides was concentric and preserved the same size. The as-obtained biconvex MLAs showed an average diameter of 297 μm, a focal length of 669 μm, a numerical aperture (NA) of 0.21, and a maximum resolution of 45.3 lp/mm. Compared to plano-convex MLAs using the same materials with the same size, which exhibits the maximum resolution of 16 lp/mm, the biconvex MLAs displayed highly improved optical resolution. In sum, the advantages of the proposed method in terms of simple fabrication, good optical performances and high consistency in large areas make it promising for use in 3D displays, image processing, fiber coupling, optical data storage, light extraction, and biomedical processing.

Facile fabrication of microlens array on encapsulation layer for enhancing angular color uniformity of color-mixed light-emitting diodes

In this work, we proposed a concave microlens array (MLA) on an encapsulation layer to enhance the angular color uniformity (ACU) of color-mixed light-emitting diodes (cm-LEDs). The MLAs with continuously adjustable curvature were fabricated by using a low-cost and facile approach based on water droplets condensation. Through initiative cooling, the water vapor was condensed on the surface of a polymer film and then the water droplets array was utilized as a template to obtain the MLA. By controlling the cooling temperature at −15, 0, and 15 °C, the sag height-to-diameter ratios (aspect ratio, AR) of MLAs were obtained at 0.68, 0.63, and 0.53, respectively. Through adjusting the three-phase state of the polymer-water droplets-sacrificial layer system by introducing a second-step cooling temperature of 0 and −15 °C after the first-step cooling temperature of 15 °C, the ARs were further decreased to 0.49, and 0.37, respectively. Haze tests demonstrated the scattering ability of MLAs, and encapsulation layer with MLA was applied in packaging of the cm-LEDs to enhance their ACU and luminous efficacy (LE). Consequently, the maximum correlated color temperature (CCT) deviation of the cm-LEDs was reduced from 853 K to 273 K and the LE of cm-LEDs was increased by 9.1% at 200 mA after applying the fabricated MLAs.

Facile and scalable fabrication of Ni cantilever nanoprobes using silicon template and micro-electroforming techniques for nano-tip focused electrohydrodynamic jet printing

Electrohydrodynamic jet (E-Jet) printing is a powerful technique for micro/nanostructure fabrication with high resolution and efficiency. However, conventional E-Jet printing are still limited in printing accuracy and ink adaptability due to the nozzle clogging effect. In this paper, we develop a nano-tip focused electrohydrodynamic jet (NFEJ) method to print high-resolution structures. The Ni cantilever nanoprobes with nanoscale radius of curvature (ROC) on their tips were manufactured by a facile and scalable method using silicon template and micro-electroforming technique. Scanning electron microscope was used to analyse the micromorphology of the silicon template with inverted pyramid pits, which was obtained from anisotropic wet etching of silicon. Electroforming mold was obtained by photolithography and plasma etching which divide the top side of Ni film into isolated cantilever pits. Ni cantilever nanoprobes with an average tip ROC of about 48 nm were achieved by the subsequent micro electroforming process. High-resolution droplets array with an average diameter of about 890 ± 93 nm were printed by the NFEJ printing head equipped with these Ni nanoprobes, which verified the practicality of the developed Ni nanoprobes for NFEJ printing.

Droplets isolated array: A universal platform of delaying molecule cross-contamination between microdroplets for digital enzyme-based immunoassay

Digital biodetection in picoliter-volume microdroplets has great potential for ultra-sensitivity detection due to the wide development of microfluidic technology and the high throughput of droplets generation. However, the diffusion of enzyme catalytic fluorescent products between droplets makes signal reading confused and inaccurate. Here, a spherical Poly (acrylic acid) Brushes immobilized Alkaline phosphatase (SP-AKP) as signal amplification block was synthesized and introduced into 14 pL droplet, and the SP-AKP digital detection was realized within only 6 min, which significantly improved the catalytic efficiency and shortened the detection time. Furthermore, aimed to decrease the diffusion rate of fluorophore between droplets, we proposed a Droplets Isolated Array (DIA) where droplets were trapped in chambers to keep them isolated. The DIA could trap ∼34,000 droplets once and reach 82.6 % of droplet coverage with high throughput and efficiency. Compared to conventional non-isolated droplets array, the DIA delayed the diffusion of fluorophore, and the reading time of droplet signal could be extended from 1 min to 30 min, which greatly improved the operability of the detection system and ensured the accuracy of the results. Finally, an accurate signal identification makes the limit of detection of SP-AKP achieve 309 aM.

Electric breath figure: mechanism and application

Electric breath figures, EBF, is a novel method for producing ordered porous structure. This work reviewed the EBF process from its design, mechanism, to application. In general, the EBF is developed from the conventional BF by using the electrostatic generator to assist the BF process. Comparing to the normal BF process request of controlling a lot of factors, the EBF showed advances in only using the voltage variety to control the process for fabrication of micro- and nanostructured porous materials. With the help of the electricity, the EBF process was performed under low surface tension condition that leads the moist air blown over a solution stabilized and the formed water droplets array on the liquid surface with opposite charges. In this work, the normal EBF process and two furthermore developed surfactant and nanomaterial-assisted EBF processes were reviewed in relation to the mechanisms and application.

Analyte capture in an array of functionalized droplets for a regenerable biosensor.

We describe in this work an advanced microfluidic chip for the capture of bioanalyte on the surface of droplets arranged in a dense array. We show the procedure for generating, functionalizing, and arranging the droplets inside the device for capturing a specific bioanalyte. Then, we demonstrate the capacity of the array to capture analyte from a cross-flowing liquid, using a biotin/streptavidin model. The paper also proposes to use the droplets array, after integration with acoustic detection, as a regenerable detection interface for bioanalyte sensing. We model the arrangement of droplet in dense array and show that they present a larger effective capture surface and shorter capture distance than standard flat surface biosensor of the same footprint. As the droplets can be easily evacuated and replaced inside the device analysis chamber, the proposed biosensor would allow biointerface regeneration and chain measurement without dismounting the device.

Direct patterning of silver electrodes with 2.4 μm channel length by piezoelectric inkjet printing

The control of channel length is of great significance in the fabrication of thin film transistors (TFTs) with high-speed operation. However, achieving short channel on untreated glass by traditional piezoelectric inkjet printing is problematic due to the impacting and rebounding behaviors of droplet impinging on solid surface. Here a novel method was proposed to obtain short channel length on untreated glass by taking advantage of the difference in the retraction velocities on both sides of an ink droplet. In addition, droplets contact mechanism was first introduced in our work to explain the formation of short channel in the printing process. Through printing droplets array with optimized drop space and adjusting appropriate printing parameters, a 2.4μm of channel length for TFT, to the best of our knowledge, which is the shortest channel on substrate without pre-patterning, was achieved using piezoelectric inkjet printing. This study sheds light on the fabrication of short channel TFT for large size and high-resolution displays using inkjet printing technology.

Versatile microfluidic droplets array for bioanalysis.

We propose a novel method to obtain versatile droplets arrays on a regional hydrophilic chip that is fabricated by PDMS soft lithography and regional plasma treatment. It enables rapid liquid dispensation and droplets array formation just making the chip surface in contact with solution. By combining this chip with a special Christmas Tree structure, the droplets array with concentrations in gradient is generated. It possesses the greatly improved performance of convenience and versatility in bioscreening and biosensing. For example, high throughput condition screening of toxic tests of CdSe quantum dots on HL-60 cells are conducted and cell death rates are successfully counted quickly and efficiently. Furthermore, a rapid biosensing approach for cancer biomarkers carcinoma embryonic antigen (CEA) is developed via magnetic beads (MBs)-based sandwich immunoassay methods.

1305 微小擬似軽油液滴列による輝炎の温度分布計測(GS05-5 熱工学・流体工学)

1305 微小擬似軽油液滴列による輝炎の温度分布計測(GS05-5 熱工学・流体工学)

Ignition of fuel sprays by shock wave mathematical modeling and numerical simulation

The paper presents the results of developing of physical and mathematical model making it possible to take into account the effect of droplets non-uniformity in space and size distribution on ignition conditions for fuel sprays. The influence of condensed phase volume fraction on ignition and combustion of sprays was studied, physical and mathematical models for multi-phase flows, mixture formation and combustion of liquid fuels based on solving Navier–Stokes equations for gas phase accounting for thermal and mechanical interaction with poly-dispersed droplets array. The problems of particulate phase dynamics are regarded accounting for the interaction with gas phase atomization, evaporation and combustion.It was shown that depending on droplet size distribution and aerosol cloud density different flow scenarios were possible.Several ignition zones could be formed behind incident shock wave depending on mixture properties and initiation parameters. The possibility of numerical simulation permitting variation of definite parameters only made it possible to explain this fact.

Highly Sensitive Method for Assay of Drug-Induced Apoptosis Using Fluorescence Correlation Spectroscopy

Apoptosis plays a crucial role in many biological processes and pathogenesis of various malignancies and diseases of the immune system. In this paper, we described a novel method for sensitive detection of drug-induced apoptosis by using fluorescence correlation spectroscopy (FCS). The principle of this method is based on the assay of DNA fragmentation in the process of the drug-induced apoptosis. FCS is a single molecule method, and it can be used for sensitive and selective assay of DNA fragmentation without separation. We first developed a highly sensitive method for characterization of DNA fragments using a home-built FCS system and SYBR Green I as fluorescent DNA-intercalating dye, and then established a model of drug-induced apoptosis using human pancreatic cancer cells and a drug lidamycin. Furthermore, FCS method established was used to directly detect the fragmentation of DNA extracted from apoptotic cells or in the apoptotic cell lysate. In FCS assay, the single-component model and the multiple-components model were used to fit raw FCS data. The characteristic diffusion time of DNA fragments was used as an important parameter to distinguish the apoptotic status of cells. The obtained data documented that the characteristic diffusion time of DNA fragments from apoptotic cells significantly decreased with an increase of lidamycin concentration, which implied that DNA fragmentation occurred in lidamycin-induced apoptosis. The FCS results are well in line with the data obtained from flow cytometer and gel electrophoresis. Compared to current methods, the method described here is sensitive and simple, and more importantly, our detection volume is less than 1 fL, and the sample requirement can easily be reduced to nL level using a droplets array technology. Therefore, our method probably becomes a high throughput detection platform for early detection of cell apoptosis and screening of apoptosis-based anticancer drugs.

Two-dimensional electrostatic actuation of droplets using a single electrode panel and development of disposable plastic film card

In order to form large micro-droplet-arrays, we have developed a device that can merge and transport microdroplets in two directions. Transportation of droplets is performed by electrostatic actuation technique. The speciality of this method is that it uses only one electrode panel, based on standard printed circuit board (PCB), and in it, only 18 independent controls are needed. We have also developed disposable plastic films cards, which can substantialy reduce the development cost because the actuation chip has been separated into two parts: a fixed electrode panel and a less costly removable card. The droplets array is formed and analyzed in the card.

313 非定常流中での 2 液滴列の燃焼特性に及ぼす燃料性状の影響について

313 非定常流中での 2 液滴列の燃焼特性に及ぼす燃料性状の影響について

302 低酸素濃度雰囲気中での 2 液滴列の燃焼特性に関する研究

302 低酸素濃度雰囲気中での 2 液滴列の燃焼特性に関する研究

Deformation and breakup behavior of a small droplet impinging upon a hot surface.

The phenomenon of a small droplet impinging upon a hot surface is applied in various industries. Such applications are divided into those employing atomization by the impingement of the droplet and those employing the heat transfer from surface to the droplet. The purpose of this paper is to obtain fundamental information concerning the heat transfer process and breakup behavior characteristics of individual small droplets impinging upon a hot surface. A uniform sized water droplets array at room temperature under atmospheric pressure was produced by the vibratory method to impinge upon a heated flat copper surface. And then, the deformation and the breakup behavior owing to the impingement of the droplet in observed by means of a drum camera recording high-speed microscopic photographs. The transient change in the diameter of the radial film which is formed after the droplet impinges on a surface is adjusted with the Weber number, and it is revealed that contact resistance in solid-liquid interface varies with surface temperature. The breakup form of the impinged droplet is classified into 7 types: R, RB, B, N, H, V, and F. The changes in the Sauter mean diameter of breakup droplets and the volume distribution of breakup droplets are examined.