Microfluidic devices obtained by thermal toner transferring on glass substrate

A new process for the manufacture of microfluidic devices based on deposition of laser-printing toner on glass substrates is described. It is an alternative method to the toner on polyester film (toner-polyester) one, previously introduced. Commercial laser printers cannot print directly on glass, thus the toner must first be printed on a special paper and then transferred by heating under pressure to the glass surface. Although this procedure is more complex than the toner-polyester one, it can be repeated several times, yielding multiple toner layers. Even without special alignment equipment, up to four layers could be satisfactorily piled up. Characterization tests revealed that the toner-glass devices have similar behavior as toner-polyester ones regarding the toner layer porosity. The main advantages of the toner-glass technology are improved mechanical stability, possibility of multiple toner layers, augmented electroosmotic flow (EOF), and improved heat transfer. On the other hand, toner adhesion to glass is weaker than to polyester, which limits the device lifetime and usable liquid media. The measured EOF mobility (3.5 x 10(-4) cm2.V(-1).s(-1) for pH 7) suggests that it is mainly determined by the glass surface, being little influenced by the toner walls. Microchip electrophoresis with contactless conductivity detection and photometric detection were implemented using toner-glass devices.     

Simple and rapid methods for the fabrication of polymeric and glass chips for using in analytical chemistry

This paper describes simple and rapid methods for the fabrication of glass and polymeric chips for routine analytical applications. The methods are easily interfaced to the general laboratory environment and do not require special clean room facilities or expensive instruments. Glass microchips were fabricated by etching with HF solution. Microfluidic channels were designed with CAD program and transferred onto a sheet of commercial polymeric self-adhesive (PSA) film by a cutter plotter. The PSA film was used as a mask for etching process. The etching rate was about 7 μm min⁻¹. A cover glass plate was sealed on the top of etched substrate by using polycellulose (cellophane). Polymeric microchips were fabricated by sawing with a jigsaw. Commercial polycarbonate (PC) was used as a substrate and two iron sheets were used as leader masks. While this restricts us to the fabrication of straight channels, it is however, much faster and less complicated than the other methods. The chip comprised three polymeric plates and the channels were created in the middle plate. Thermal bonding was used to bond three layers of the microfluidic chip. With this method, we could achieve simple channels with the width of about 200 μm. The channel depth depends on the polymeric plate thickness. Fabricated channels were accurate without any sinuosity or sideshow.     

A glass microfluidic chip for continuous blood cell sorting by a magnetic gradient without labeling

This paper presents a microfluidic chip for highly efficient separation of red blood cells (RBCs) from whole blood on the basis of their native magnetic properties. The glass chip was fabricated by photolithography and thermal bonding. It consisted of one inlet and three outlets, and a nickel wire of 69-microm diameter was positioned in the center of a separation channel with 149-microm top width and 73-microm depth by two parallel ridges (about 10 microm high). The two ridges were formed simultaneously during the wet etching of the channels. The nickel wire for generating the magnetic gradient inside the separation channel was introduced from the side of the chip through a guide channel. The external magnetic field was applied by a permanent magnet of 0.3 T placed by the side of the chip and parallel to the main separation channel. The RBCs were separated continuously from the 1:40 (v/v) diluted blood sample at a flow rate in the range 0.12-0.92 microL/min (9-74 mm/min) with the chip, and up to 93.7% of the RBCs were collected in the middle outlet under a flow rate of 0.23 microL/min. The cell sedimentation was alleviated by adjusting the specific density of the supporting media with bovine serum albumin. Quantum dot labeling was introduced for visual fluorescence tracking of the separation process. The uneven distribution phenomenon of the blood cells around the nickel wire was reported and discussed.     

Glass microfabricated nebulizer chip for mass spectrometry

A microfluidic nebulizer chip for mass spectrometry is presented. It is an all-glass device which consists of fusion bonded Pyrex wafers with embedded flow channels and a nozzle at the chip edge. A platinum heater is located on the wafer backside. Fabrication of the chip is detailed, especially glass deep etching, wafer bonding, and metal patterning. Various process combinations of bonding and metallization have been considered (anodic bonding vs. fusion bonding; heater inside/outside channel; metallization before/after bonding; platinum lift-off vs. etching). The chip vaporizes the liquid sample (0.1-10 microL min(-1)) and mixes it with a nebulizer gas (ca. 100 sccm N2). Operating temperatures can go up to 500 degrees C ensuring efficient vaporization. Thermal insulation of the glass ensures low temperatures at the far end of the chip, enabling easy interconnections.     

Electrophoresis microchip fabricated by a direct-printing process with end-channel amperometric detection

We describe the development of an electrophoresis microchip fabricated by a direct-printing process, based on lamination of printed polyester films with end-channel amperometric detection. The channel structures are defined by polyester (base and cover) and by a toner layer (walls). The polyester-toner devices presented an electroosmotic flow (EOF) magnitude of approximately 10(-5) cm2 V(-1) s(-1), which is generated by a polymeric mixture of the toner and polyester composition. The microelectrodes used for detection were produced combining this laser-printer technology to compact discs. The performance of this device was evaluated by amperometric detection of iodide and ascorbate. The detection limits found were 500 nmol.L(-1) (135 amol) and 1.8 micromol.L(-1) (486 amol) for iodide and ascorbate, respectively.     

Patterning, integration and characterisation of polymer optical oxygen sensors for microfluidic devices

This paper describes a process for the layer-by-layer fabrication and integration of luminescent dye-based optical oxygen sensors into microfluidic devices. Application of oxygen-sensitive platinum(ii) octaethylporphyrin ketone fluorescent dye dissolved in polystyrene onto glass substrates by spin-coating was studied. Soft lithography with polydimethylsiloxane (PDMS) stamps and reactive ion etching in oxygen plasma were used to produce sensor patterns with a minimum feature size of 25 microm. Sensors patterns were integrated into a PDMS microfluidic device by plasma bonding. No degradation of the sensor response as a result of the lithography and pattern-transfer processes was detected. Gaseous and dissolved oxygen (DO) detection was characterised using fluorescence microscopy. The intensity signal ratio of the sensor films was found to increase almost two-fold from 3.6 to 6.8 by reducing film thickness from 1.3 microm to 0.6 microm. Calibration of DO measurement showed linear Stern-Volmer behaviour that was constant for flow rates from 0.5 to 2 mL min(-1). The calibrated sensors were subsequently used to demonstrate laterally resolved detection of oxygen inside a microfluidic channel. The fabrication process provides a novel, easy to use method for the repeatable integration of optical oxygen sensors into cell-culture and lab-on-a-chip devices.     

Prototyping disposable electrophoresis microchips with electrochemical detection using rapid marker masking and laminar flow etching

Two novel methods are described for the fabrication of components for microchip capillary electrophoresis with electrochemical detection (microchip CEEC) on glass substrates. First, rapid marker masking is introduced as a completely nonphotolithographic method of patterning and fabricating integrated thin-film metal electrodes onto a glass substrate. The process involves applying the pattern directly onto the metal layer with a permanent marker that masks the ensuing chemical etch. The method is characterized, and the performance of the resulting electrode is evaluated using catecholamines. The response compares well with photolithographically defined electrodes and exhibits detection limits of 648 nM and 1.02 microM for dopamine and catechol, respectively. Second, laminar flow etching is introduced as a partially nonphotolithographic method of replicating channel networks onto glass substrates. The replication process involves applying a poly(dimethylsiloxane) (PDMS) mold of the channel network onto a slide coated with a sacrificial metal layer and then pulling solutions of metal etchants through the channels to transfer the pattern onto the sacrificial layer. The method is tested, and prototype channel networks are shown. These methods serve to overcome the time and cost involved in fabricating glass-based microchips, thereby making the goal of a disposable high performance lab-on-a-chip more attainable.     

Spreading of individual toner particles studied using in situ optical microscopy

This study develops and tests an experimental method to monitor in situ the dynamic spreading of individual toner particles on model substrates during heating, to simulate on laboratory scale the fusing sub-processes occurring in electrophotographic printing of paper. Real toner particles of cyan, magenta, yellow and black are transformed to perfect spheres by a temperature pre-treatment, then applied to the substrate, either high-energy clean glass or low-energy hydrophobised glass, and heated at rates up to 50 degrees C/min. The subsequent spreading as a function of time (and temperature) is recorded by an optical microscope and CCD camera mounted above the substrate, with the measured drop covering area used to calculate the corresponding toner-substrate-air contact angle. On the hydrophobic substrate the spreading is limited and equal for all four colours, while the substantially greater spreading on the hydrophilic substrate is accompanied by significant differences between the toner colours. In particular, the cyan and black toners are found to spread to almost twice the extent of the yellow particles. The dynamic spreading behaviour is interpreted in terms of complementary measurements of substrate and toner surface energy components and bulk toner rheology, and a simple empirical relation is proposed that fits very well the measurements for all toner and substrate types tested. In particular, the spreading relation is found to be determined only by the toner surface energy and its equilibrium contact angle, with no explicit dependence on toner viscosity.     

玻璃微流控芯片廉价快速制作方法的研究

研究了一种玻璃微流控芯片的快速、低成本制作工艺和方法. 该方法采用商品化的显微载玻片(soda-lime玻璃)作为芯片基质材料, 利用AZ 4620光刻胶代替传统工艺中的溅射金属层或多晶硅/氮化硅层作为玻璃刻蚀的掩膜层, 同时利用一种紫外光学胶键合方法代替传统熔融键合方法实现芯片的键合, 整个工艺对玻璃基质材料要求低, 普通微流控芯片(深度小于50 μm)制作流程仅需约3.5 h, 可降低制作成本, 缩短制作周期. 还系统地研究了光刻胶厚度、光刻胶硬烘时间和玻璃腐蚀液配比对玻璃微流控芯片制作的影响, 获得了优化的工艺参数.     

Quick production of gold electrode sets or arrays and of microfluidic flow cells based on heat transfer of laser printed toner masks onto compact discs

A process is described to speedily produce in the laboratory, single or multiple coplanar gold electrodes of any shape and with sizes ranging from 100 μm to 10 cm, as well as to assemble microfluidic flow cells with them. The innovative combination of simple processes for ad hoc design and production uses readily available equipment and inexpensive materials, like recordable compact disks of the gold sputtered type. The following steps are involved: drawing of the electrode(s) on a microcomputer; laser printing of the design on wax paper; heat-transfer of the toner onto the gold surface of a peeled CD-R; etching of the gold layer from unprinted regions; removal of the toner with a solvent; activation; and use in conventional batch or flow cells. To obtain microfluidic flow cells with 7–12 μm interlayer gap, a gasket spacer of the desired shape is drawn and laser printed, the toner layer is heat transferred onto one CD piece with pre-etched electrodes and a second CD section is heat-sealed on top of it. The functionality of these electrodes as well as of the microfluidic flow cells is demonstrated by voltammetry and flow injection amperometric analysis.     

Chemical stability of midazolam injection by high performance liquid chromatography

The chemical stability of midazolam hydrochloride injection, undiluted or diluted with dextrose sterile solution, was studied at different storage conditions by LC. The study was performed at room temperature (23 +/- 2 degrees C) under light exposure and light protection, +8 +/- 1 degrees C and -20 +/- 0.5 degrees C, in glass and plastic containers over 14 days with midazolam hydrochloride injection, undiluted or diluted with 5% dextrose sterile solution. Chromatographic separation was carried out on a RP-18(e) column, using a mobile phase consisting of ACN-phosphate buffer (pH 3.3; 0.1 M) (30:70 v/v) at a flow rate of 1.0 mL/min and UV detection at 220 nm. The concentrations of all samples remained greater than 90% of the original concentration. The chromatographic assay exhibited an adequate linearity (r(2) >0.999), selectivity, precision (RSD <3.1), and accuracy (recoveries from 100.46 to 101.40%). Injectable midazolam hydrochloride was chemically stable in all conditions that were studied.     

Flash hydrolysis deinking of laser print using degradable toner resin

The choice of vinyl polymers as the plastic matrix for the pigment in xerographic toner did not anticipate the deinking thrust which has swept the paper industry. The hydrolytic stability of the carbon-carbon bond in vinyl and diene copolymers has prevented the use of a plastic degradation strategy for toner removal. New toner resins based on alkali degradable plastics have been shown to allow up to 97% toner removal. Based on polyimide and polyesterimide toners (either magnetic or non-magnetic) developed by Xerox, this study uses flash hydrolysis in the presence of 0.5% alkali to repulp. The process operates on 200-300 second batches at 190−210°C. The best results were obtained using alkaline repulping and magnetic deinking coupled with washing. The alkali also inhibits the hydrolytic degradation of cellulose although it negatively impacts the brightness. Thus the use of a polymer resin containing a chemically sensitive function allows conversion of the toner to pigment fragments and water soluble oligomers. The former is best separated by magnetic deinking while the latter is removed by washing.     

Shear-driven pumping and Fourier transform detection for on chip circular chromatography applications

A circular, shear-driven pumping system combined with Fourier Transform detection has been developed for the application of chip based cyclic chromatography. Using this system, it is possible to perform an injection of a sample plug into a circular micro-channel and then drive the sample through the channel, using shear flow induced by a rotation stage. High pumping rates at uniform speeds are attainable with this system with very little heat production. Typical pumping rates of up to 1.423 mm s(-1) +/- 2 microm s(-1) were used in experiments although much higher rates >14 mm s(-1) are also possible with this system. Fluorescence detection was used to detect a sample plug of Coumarin dyes, flowing around the channel. A coating of porous polymethacrylate was used to immobilise RP-HPLC beads onto the glass surface and was applied to the glass micro-channel by selective photopolymerisation. This coating acted as a stationary phase and differences in retention time were observed for an injection of Coumarin dyes for different methanol-water, mobile phase ratios. Full sample retention occurred for 30 : 70 (v/v) methanol-water whereas no retention occurred for 92 : 8 (v/v) methanol-water which can be expected for such a reverse phase, open tubular system. Fourier transform detection applied to the fully retained and non-retained cases showed frequency domain data from a single detection point corresponding to that which may be expected from shear flow theory.     

Anisotropic etching of silicon in hydrazine

This paper contains a detailed discussion of the practical issues related to the anisotropic etching of single crystal silicon using a 5050 hydrazinewater solution. Characteristics of the etchant, etching reactor design, etch procedures, safety precautions, etch rate data for typical samples and appropriate etch-masks are among the topic discussed. The etching process is carried out in a atmospheric reflux reactor, continuously purged with nitrogen. The etch rate of (100) silicon at 115°C in this hydrazine solution is nearly 3 μm/min, which is much higher than that of ethylenediaminepyrocatecholwater (EDP) solutions. Silicon dioxide, silicon nitride and most metallic thin films, except aluminium, can be used to mask the etching process. The etch rate is reduced significantly in highly-boron-doped silicon; a boron concentration of 1.5 × 10²⁰ cm⁻³ practically stops the etch. The use of the hydrazine solution for micromachining thin silicon diaphragms, cantilevers and fibers is demonstrated.     

On-line chemiluminescence detection for isoelectric focusing of heme proteins on microchips

In this paper we present a sensitive chemiluminescence (CL) detection of heme proteins coupled with microchip IEF. The detection principle was based on the catalytic effects of the heme proteins on the CL reaction of luminol-H2O2 enhanced by para-iodophenol. The glass microchip and poly(dimethylsiloxane) (PDMS)/glass microchip for IEF were fabricated using micromachining technology in the laboratory. The modes of CL detection were investigated and two microchips (glass, PDMS/glass) were compared. Certain proteins, such as cytochrome c, myoglobin, and horseradish peroxidase, were focused by use of Pharmalyte pH 3-10 as ampholytes. Hydroxypropylmethylcellulose was added to the sample solution in order to easily reduce protein interactions with the channel wall as well as the EOF. The focused proteins were transported by salt mobilization to the CL detection window. Cytochrome c, myoglobin, and horseradish peroxidase were well separated within 10 min on a glass chip and the detection limits (S/N=3) were 1.2x10(-7), 1.6x10(-7), and 1.0x10(-10) M, respectively.     

Fabrication of immunosensor microwell arrays from gold compact discs for detection of cancer biomarker proteins

A simple method is reported to fabricate gold arrays featuring microwells surrounding 8-electrodes from gold compact discs (CDs) for less than $0.2 per chip. Integration of these disposable gold CD array chips with microfluidics provided inexpensive immunoarrays that were used to measure a cancer biomarker protein quickly at high sensitivity. The gold CD sensor arrays were fabricated using thermal transfer of laserjet toner from a computer-printed pattern followed by selective chemical etching. Sensor elements had an electrochemically addressable surface area of 0.42 mm(2) with RSD <2%. For a proof-of-concept application, the arrays were integrated into a simple microfluidic device for electrochemical detection of cancer biomarker interleukin-6 (IL-6) in diluted serum. Capture antibodies of IL-6 were chemically linked onto the electrode arrays and a sandwich immunoassay protocol was developed. A biotinylated detection antibody with polymerized horseradish peroxidase labels was used for signal amplification. The detection limit of IL-6 in diluted serum was remarkably low at 10 fg mL(-1) (385 aM) with a linear response with log of IL-6 concentration from 10 to 1300 fg mL(-1). These easily fabricated, ultrasensitive, microfluidic immunosensors should be readily adapted for sensitive detection of multiple biomarkers for cancer diagnostics.     

Porous polymer monolith assisted electrospray from a glass microdevice

The coupling of a lab-on-a-chip microfluidic device to a nanoelectrospray ionization mass spectrometer has the potential to automate many routine analytical procedures and produce a powerful analytical tool. However, past coupling strategies have relied on complex manufacturing steps including drilling and etching the device to attach a capillary or building a nanospray emitter directly into the device. This study shows that a nanospray emitter can be easily fabricated using a porous polymer monolith (PPM) at the end of a glass microdevice. These devices are able to obtain a stable electrospray at a variety of flow rates (50-500 nL/min) but optimal results are obtained at lower flow rates (50-100 nL/min) compatible with electroosmotic flow processes. The PPM is photo-patterned so that it can be placed in any position within the channel of the device with no dead volume. The porous character and the hydrophobic nature of the PPM both aid in development of a stable electrospray process. Total ion current traces for the constant infusion of leucine-enkephalin and PPG show relative standard errors as low as 4%, and produce mass spectra with good signal-to-noise (S/N 43) from only 2 fmol of material. In addition, multiple experiments in a given day show good repeatability with variability as low as 13%, and the multiple flow paths inherent in the PPM limit sprayer clogging.     

Formation of masking pattern by electron beam-induced vapor deposition

The dry resist-free process of electron beam-induced masking via chemical vapor deposition from a hydrocarbon precursor was studied. It was shown that the obtained mask exhibited a low selectivity during ion beam etching with SF₆ ions. It was found that, during mask deposition, a thin (of the order of 1 nm) boundary layer is formed on the SiO₂ plate surface; the layer had a substantially higher plasma resistance and, hence, high selectivity upon ion beam etching of SiO₂. Certain features of the masking process and the properties of the mask material were studied.     

Fabrication of two-weir structure-based packed columns for on-chip solid-phase extraction of DNA

Microchip-based packed column SPE of DNA was performed using the microfabricated two-weir structure within a microchannel. We developed two methods to fabricate the two-weir structured glass chips: a "two-side etching/alignment" method and a simplified "one-side/two-step etching" method. The former method required a straightforward alignment step, while the latter approach comprised a simplified wet etching process using paraffin wax as the temporary protective layer. Both methods were convenient and rapid as compared to the previous approaches. Through a reversibly sealed bead-introduction channel, beads can be fed into or out of the chip columns, thus enabling refreshment of the packing materials. Using the proposed chip columns, highly efficient lambda-DNA extractions (average recovery >80%) were performed with good chip-to-chip reproducibility (RSD <10%). The on-chip SPE procedure was completed within 15 min at the flow rate of 3 microL/min and the bulk of the loaded DNA was eluted within a small volume of approximately 8 microL. Application of the microchip-based packed columns was demonstrated by purifying PCR-amplifiable genomic DNA from human hepatocellular carcinoma (HepG2) cells and human whole blood samples.     

Direct Toner Printing: A Versatile Technology for Easy Fabrication of Flexible Miniaturized Electrodes

We reported here three simple, low cost and easy to accomplish strategies for the fabrication of microelectrodes and other conductive patterns using ordinary office laser‐printers. In this work, toner patterns were directly printed onto the flexible substrate, acting as a mask to create the intended conductive design. To highlight the versatility of such technology, toner‐printed patterns were employed in two diverse ways: one in which the patterned toner had the exact design of the electrode and other employing a reverse toner‐printed pattern. The first one was used for the adaptation of the well‐known printed circuit board (PCB) fabrication technique, but using direct toner printing (DTP) in an already conductive flexible substrate. The second was employed for the two remaining strategies: one based on the deposition of conductive film, followed by lift‐off process; and another based on drop‐casting of a conductive ink into the formed toner cavities, followed by thermal cure. As proof‐of‐concept, all three DTP strategies were used for the fabrication of miniaturized gold electrodes in polyimide substrate, and electrochemical performance of each obtained electrode was evaluated by cyclic voltammetry. Insights about DTP technology, alignment issues, advantages, limitations and resolution of each presented approach were provided. Finally, direct toner printing showed to be a simple, affordable and quite promising technology for the fabrication of low cost point‐of‐care electrochemical devices using flexible platforms.