Glass Microchannel Research Articles

Assessing Stability, Durability, and Protein Adsorption Behavior of Hydrophilic Silane Coatings in Glass Microchannels

Microfluidics-based separation of biomolecules has numerous applications, including fundamental characterization of biomolecules, sequencing of genomes for biological functions, biometric fingerprinting, and identification of pathogens and genetic diseases. One of the main drawbacks, however, for making microfluidic based separations more commercially viable is the non-specific adsorption of biomolecules at the channel walls during separations. Herein, we compare five commonly employed surface coatings, and evaluate their performance in terms of successful silanization of channel surface walls, long term stability, and antifouling performance, using BSA or IgG as model proteins. We compare adsorption of fluorescently-tagged proteins on glass slides with those confined within channels, showing similar behavior with static measurements, but differences when incorporating electrokinetic flow. Based on these data, we find that MPEG is an effective surface coating for applications where long term stability is critical. However, for separation experiments, where the channel is used shortly after coating, a silanized zwitterionic sultone has superior anti-fouling characteristics.

Power law fluid viscometry through capillary filling in a closed microchannel

In this work we analyze the capillary filling dynamics of non-Newtonian fluids that can be modeled with a power law constitutive equation. We solve the Poiseuille equations for an hydrophilic closed channel where capillary pressures drives the fluid in until a rest position given by the barometric pressure is reached. We show that this dynamics can be used to measure both the coefficient k and exponent n, that describes the power law fluid viscosity and we ran tests on Soda Lime Glass microchannels. Using a simple experimental setup with a USB Microscope and a custom image processing software we were able to measure the power law parameters of whole blood, wall varnish and DI water.The exponents were also obtained from the velocity profiles inside the microchannel using a custom μPIV setup matching both results with those measured with a standard Brookfield Rotational Microviscometer.

Atomic layer deposition of alternative glass microchannel plates

The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm2). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm−2 s−1), and low gain variation (±5%).

Determination of droplet contours in liquid-liquid flows within microchannels

An experimental analysis of the droplet regime with a silicone oil-water two-phase flow within a micro cross-junction, varying the average velocity of the fluids, has been carried out. The micro cross-junction is made as intersection of two glass microchannels with a stadium-shaped cross-section with height H=190 μm and width Wj=195 μm within the junction and W=390 μm before and after the junction. The water flow rate is broken in droplets having spherical shape with dimensions and velocity that depend on the average velocity ratio imposed. Different kinds of intermittent droplets have been observed, in the ranges of average velocity (0.0105-0.042) m/s and (0.0004-0.0050) m/s for oil and water, respectively. The droplet velocity has been calculated starting from the detection of the shape of the droplets and then by the evaluation of the displacement of the droplets in the unit of time. The images of the droplets have been obtained from a high-speed camera, connected to an inverted microscope. The procedure of water phase contour detection is based on Matlab Image Toolbox scripts.

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.

Channel polymer optical waveguides embedded in glass: Design, fabrication and characterization

In this work, the design, fabrication and experimental evaluation of new channel polymer optical waveguides embedded in glass are reported. We show that high quality microchannels in glass, without roughness on the walls, make possible the fabrication of new channel optical waveguides by filling the microchannels with a polymer. Guided light through those new optical waveguides is demonstrated experimentally. The commercial software OlympIOs was used to design multimode and monomode channel polymer optical waveguides. The microchannels in glass substrate were fabricated by using a laser lithography system and wet-etching procedures. The spin-coating technique was applied to deposit the polymer inside the microchannels. The end-coupling method was implemented for the waveguides characterization. Theoretical and experimental results have confirmed light confinement as well as guided modes propagation by these new channel optical waveguides.

Limitations to laser machining of silicon using femtosecond micro-Bessel beams in the infrared

We produce and characterize high-angle femtosecond Bessel beams at 1300-nm wavelength leading to nonlinearly ionized plasma micro-channels in both glass and silicon. With microjoule pulse energy, we demonstrate controlled through-modifications in 150-μm glass substrates. In silicon, strong two-photon absorption leads to larger damages at the front surface but also a clamping of the intensity inside the bulk at a level of ≈4 × 1011 W cm−2 which is below the threshold for volume and rear surface modification. We show that the intensity clamping is associated with a strong degradation of the Bessel-like profile. The observations highlight that the inherent limitation to ultrafast energy deposition inside semiconductors with Gaussian focusing [Mouskeftaras et al., Appl. Phys. Lett. 105, 191103 (2014)] applies also for high-angle Bessel beams.

Electrophoretic extraction of low molecular weight cationic analytes from sodium dodecyl sulfate containing sample matrices for their direct electrospray ionization mass spectrometry.

While the use of sodium dodecyl sulfate (SDS) in separation buffers allows efficient analysis of complex mixtures, its presence in the sample matrix is known to severely interfere with the mass-spectrometric characterization of analyte molecules. In this article, we report a microfluidic device that addresses this analytical challenge by enabling inline electrospray ionization mass spectrometry (ESI-MS) of low molecular weight cationic samples prepared in SDS containing matrices. The functionality of this device relies on the continuous extraction of analyte molecules into an SDS-free solvent stream based on the free-flow zone electrophoresis (FFZE) technique prior to their ESI-MS analysis. The reported extraction was accomplished in our current work in a glass channel with microelectrodes fabricated along its sidewalls to realize the desired electric field. Our experiments show that a key challenge to successfully operating such a device is to suppress the electroosmotically driven fluid circulations generated in its extraction channel that otherwise tend to vigorously mix the liquid streams flowing through this duct. A new coating medium, N-(2-triethoxysilylpropyl) formamide, recently demonstrated by our laboratory to nearly eliminate electroosmotic flow in glass microchannels was employed to address this issue. Applying this surface modifier, we were able to efficiently extract two different peptides, human angiotensin I and MRFA, individually from an SDS containing matrix using the FFZE method and detect them at concentrations down to 3.7 and 6.3 μg/mL, respectively, in samples containing as much as 10 mM SDS. Notice that in addition to greatly reducing the amount of SDS entering the MS instrument, the reported approach allows rapid solvent exchange for facilitating efficient analyte ionization desired in ESI-MS analysis.

Flow patterns of an air–water mixture at the exit of a micro T-junction

An experimental investigation of typical flow patterns in adiabatic gas–liquid mixture (air-water) generated in a micro T-junction varying the superficial velocity of the fluids is presented. The micro T-junction is made as intersection of two glass microchannels with a rectangular cross-section having a width of 300μm and a height of 256μm. The air–water mixture is obtained by means of an injection of air in perpendicular direction with respect to a straight stream of water. The air flow is broken in slugs having geometrical characteristics depending on the superficial velocity ratio imposed. Changing the air and water superficial velocity from 0.005m/s up to a maximum value of 0.15m/s, different kinds of intermittent slugs have been observed. In this way, a flow pattern map has been generated in order to reword the main characteristics of the intermittent slug flow generated after the T-junction as a function of the superficial air–water velocity ratio. In order to build the flow pattern map, 256 experimental runs characterized by different values of superficial velocity have been made. Different kinds of Taylor bubble flows have been observed during this experimental campaign: for a fixed low value of the air flow rate, by increasing the water flow rate it has been evidenced how the formation of the bubbles becomes faster and the length of the single bubble becomes shorter. A detailed discussion of the impact of the superficial air to water velocity ratio on the observed flow patterns is given.

Novel windows for "solar commodities": a device for CO2 reduction using plasmonic catalyst activation.

A novel plasmonic reactor concept is proposed and tested to work as a visible energy harvesting device while allowing reactions to transform CO2 to be carried out. Particularly the reverse water gas shift (RWGS) reaction has been tested as a means to introduce renewable energy into the economy. The development of the new reactor concept involved the synthesis of a new composite capable of plasmonic activation with light, the development of an impregnation method to create a single catalyst reactor entity, and finally the assembly of a reaction system to test the reaction. The composite developed was based on a Cu/ZnO catalyst dispersed into transparent aerogels. This allows efficient light transmission and a high surface area for the catalyst. An effective yet simple impregnation method was developed that allowed introduction of the composites into glass microchannels. The activation of the reaction was made using LEDs that covered all the sides of the reactor allowing a high power delivery. The results of the reaction show a stable process capable of low temperature transformations.

In-channel integration of designable microoptical devices using flat scaffold-supported femtosecond-laser microfabrication for coupling-free optofluidic cell counting

The high-precision integration of three-dimensional (3D) microoptical components into microfluidics in a customizable manner is crucial for optical sensing, fluorescence analysis, and cell detection in optofluidic applications; however, it remains challenging for current microfabrication technologies. This paper reports the in-channel integration of flexible two-dimensional (2D) and 3D polymer microoptical devices into glass microfluidics by developing a novel technique: flat scaffold-supported hybrid femtosecond laser microfabrication (FSS-HFLM). The scaffold with an optimal thickness of 1–5 µm is fabricated on the lower internal surface of a microfluidic channel to improve the integration of high-precision microoptical devices on the scaffold by eliminating any undulated internal channel surface caused by wet etching. As a proof of demonstration, two types of typical microoptical devices, namely, 2D Fresnel zone plates (FZPs) and 3D refractive microlens arrays (MLAs), are integrated. These devices exhibit multicolor focal spots, elongated (>three times) focal length and imaging of the characters ‘RIKEN’ in a liquid channel. The resulting optofluidic chips are further used for coupling-free white-light cell counting with a success rate as high as 93%. An optofluidic system with two MLAs and a W-filter is also designed and fabricated for more advanced cell filtering/counting applications. By fabricating microscale polymer lenses in hollow glass microchannels, scientists realize an optofluidic chip that detects and counts cells. This scheme works by employing a femtosecond laser to ‘grow’ by two-photon polymerization various three-dimensional optical structures, such as microlens arrays, on a flat polymer scaffold on the internal surface of a microfluidic channel. White light is then shone through the lenses and the presence of cells in the optical path is detected by a drop in light transmission. Dong Wu and co-workers from RIKEN’s Laser Technology Laboratory in Japan and Jilin University in China say that this fabrication approach could also prove useful for constructing a variety of active and passive micro-optic devices, such as optical switches, on-chip microlasers and amplifiers for lab-on-a-chip applications.

ZnO as an Efficient Nucleating Agent for Rapid, Room Temperature Synthesis and Patterning of Zn-Based Metal–Organic Frameworks

The use of ZnO particles as efficient agents for seeding, growing, and precisely positioning metal–organic frameworks (MOFs) is described. Ceramic seeds have been successfully used for the preparation of Zn-based MOFs with a number of different carboxylic acids: terephthalic acid, 2-aminoterephthalic acid, 1,3,5-benzenetricarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid. In situ synchrotron small-angle X-ray scattering and electron microscopy experiments were employed to determine the effect of the concentration of ZnO nanoparticles, temperature, and time on MOF growth. Under optimized conditions, MOF crystals were found to form in several minutes. This unprecedented capacity to seed MOF formation was used to control the growth of crystals in precise locations. Accordingly, we employed this seeding technique to position porous MOF crystals on paper strips (lateral flow), or within glass and PDMS microchannels (120 μm width and 100 μm height). These data demonstrate tha...

Application of atomic layer deposited microchannel plates to imaging photodetectors with high time resolution

Novel microchannel plates have been constructed using borosilicate glass micro-capillary array substrates with 20µm and 10µm pores and coated with resistive, and secondary electron emissive, layers by atomic layer deposition. Microchannel plates in 33mm, 50mm and 20cm square formats have been made and tested. Although their amplification, imaging, and timing properties are comparable to standard glass microchannel plates, the background rates and lifetime characteristics are considerably improved. Sealed tube detectors based on the Planacon tube, and a 25mm cross delay line readout tube with a GaN(Mg) opaque photocathode deposited on borosilicate microchannel plates have been fabricated. Considerable progress has also been made with 20cm microchannel plates for a 20cm format sealed tube sensor with strip-line readout that is being developed for Cherenkov light detection.

Reconstructing the 3D shapes of droplets in glass microchannels with application to Bretherton’s problem

The outstanding potential of absorbance imaging for the 3D shape analysis of dynamic scenes in multiphase flows is demonstrated and experimentally confirmed. The experimental procedures and workflows have been extended and applied to the 3D shape analysis of droplets moving in microchannels. Using this technique, the problem of measuring the thickness of the lubrication layer and the droplet geometry with sub-\(\upmu\)m resolution could be solved. The obtained data generally conform to models based on Bretherton’s theory and allow its extension even for non-circular microchannel geometries.

Wave propagation of induced radiation in microcapillary holes of a glass microchannel plate

Soft x-ray reflection and transmission spectra of radiation propagating inside microchannel plates have been analyzed in the framework of the wave approximation. X-ray and fluorescence yields due to the grazing incidence reflection phenomenon have been investigated with respect to the geometry of the channel walls. We also discuss x-ray absorption near-edge structure spectra collected at the exit of microcapillaries under the total x-ray reflection condition, taking into account a surface transition layer at the sample surface. The fine structures and the angular distribution of the transmitted radiation have been interpreted in the energy range of the anomalous dispersion of the Si L2,3 edges.

Photopatterning of poly(N-isopropylacrylamide) membranes for a high level of enrichment and cleanup of nucleic acids in microfluidic chips.

An ideal nanoporous poly(N-isopropylacrylamide) membrane has been fabricated in glass microchannels by means of spatially controlled photopatterning technology for a high level of enrichment and cleanup of nucleic acids.

A glass microchip device for conducting serological survey of West Nile viral antibodies.

Serological surveys are vital to determining the prevalence of a disease and/or the immunity status against it in any population. However, the relatively large sample volume requirement (1-10mL) in traditional serum-based assays demands that blood draw camps be set up by medical professionals to obtain samples for these studies which significantly increases the time and cost associated with them. Here we address these drawbacks of a serosurvey by reducing the whole blood requirement in its diagnostic procedures down to 10μL using the microfluidic platform. Such a miniaturization approach was demonstrated in our current work by developing a microchip based serological device for determining the serum levels of West Nile (WN) viral antibodies (IgG and IgM) to assess the immunity status against WN virus in Fremont County, Wyoming. Enzyme-linked immunosorbent assays (ELISA) were developed for these target analytes in glass microchannels to accomplish this task using antibodies/assay reagents purchased from commercial sources. The reported assays were directly quantitated using a fluorescence microplate reader which to our knowledge is the first account of signal measurement in a microchip based ELISA procedure using this standard instrument. To enable this quantitation method, the assay channels on our device were spaced identically as the wells on a commercial microplate, and a holder having the dimensions of this plate was used to accommodate the microchips. Our microfluidic assays showed an excellent correlation with the results from the microwell plate based experiments for significantly lower incubation periods and using only 3μL of the ELISA reagents.

Use of the μPIV technique for an indirect determination of the microchannel cross-section passage geometry

In this work the possible use of the μPIV technique for the experimental determination of the microchannel cross-section geometry has been investigated by means of a blind test in which a series of experimental measurements obtained using glass microchannels having a declared rectangular cross-section with a depth of 100 μm and width of 300 μm and a square microchannel with a 300 μm side have been compared with the direct SEM visualisation of the real cross section of the microchannels. For the (oPIV measurements water is used as working fluid. The laminar fully developed 2D velocity profile has been reconstructed by moving the focal plane of the microscope objective from the bottom to the top of the microchannel. The results shown in this paper demonstrate that the real cross section geometry of the microchannel can be predicted by minimizing the difference between the theoretical and the experimental 2D velocity profiles. When the right passage geometry is determined, the average difference between the theoretical and the experimental velocity is within 4-6%.

Experimental Determination of the 2D Velocity Laminar Profile in Glass Microchannels using μPIV

In this work an experimental campaign for the determination of the 2D velocity profile in laminar regime of water flowing through glass microchannels is described. Two channels are considered: a microchannel with a side of 300μm (test #1) having an aspect ratio (height/width) equal to 1 and a microchannel having a width of 300μm and a height of 100μm (test #2). Firstly, the real cross section of the glass microchannels has been determined by means of a Scanned Electron Microscope (SEM). The SEM images of the cross sections highlight how the real cross section of these channels differs from the cross section declared by the manufacturer. In particular, both the tested glass microchannels have evidenced a trapezoidal cross section and not a rectangular one as specified in the manufacturer data sheet. For both the channels, the experimental velocity data acquired by using the μPIV system have been compared with the theoretical values obtained by solving the Navier-Stokes equation for a incompressible fluid under steady state conditions. The results have evidenced that μPIV is able to determine the velocity profile within the glass microchannel with an average relative difference with respect the theoretical values of the order of 1-4% depending on the aspect ratio of the channel in the central part of the channels. On the contrary, moving towards the walls, the relative difference between the theoretical and experimental velocity grows up by reaching the maximum values close to the walls. The results presented in this paper are used in order to discuss how the accuracy of the velocity measurements obtained byμPIV can be optimized.

Characterisation of Micro Channels in Electrochemical Discharge Machining Process

Micromachining techniques has increased the demand for precise and accurate instruments which are used in many industries. Glass materials offer higher challenges in micro machining as they are tough, non-conducting and difficult to machine with conventional machining operations. Electro Chemical Discharge Machining (ECDM) is a new non-conventional hybrid machining process which combines the features of Electrical Discharge Machining (EDM) and Electro Chemical Machining (ECM) to machine both conducting and nonconducting materials. In the present paper effect of various process parameters like voltage, concentration of electrolyte, duty factor and temperature on ECDM process are studied to obtain desired micro channels in soda lime glass. Design of Experiment (DOE) is used to plan and conduct the experiments. The Response Surface Modelling (RSM) is used for characterising non linear output responses in terms of material removal rate and surface finish. Modeled results are validated with experimental values.