This work was supported by the Department of Bioengineering and Therapeutic Sciences at UCSF, the California institute for Quantitative Biosciences (QB3), and the Bridging the Gap Award from the Rogers Family Foundation.

1. Design Device Dimensions and Topologies Based on Experimental Needs Using Computer Aided Design (CAD) Software
Note: Select emulsion channel diameters smaller than those of the spherical droplets. This forces the droplets into a cylindrical or &#34;sausage&#34; shape and allows for more effective picoinjection. For our purposes, we designed 30 x 30 &#956;m channels for droplets that were 50 &#956;m in diameter.
<ol>
	<li>Model picoinjection site(s) after those described by Abate et al.3 with the exception that the channels for the metal electrodes are removed, as they are unnecessary.</li>
	<li>Add channels to serve as the Faraday Moat (Figure 1)&#160;that run between picoinjection site(s) and the upstream emulsion such that they shield the droplets from the electric field. 
	Note: This prevents unintended merging.</li>
</ol>
2. Fabricate Devices Using Soft Photolithographic Techniques
<ol>
	<li>Generate a transparency photolithography mask based on the CAD file using existing commercial services.</li>
	<li>With the photomask, cure photoresist on silicon wafers to produce a device master, as described previously4.</li>
	<li>Pour PDMS mixed with curing agent (11:1 ratio) over the device master contained in a 5 cm polystyrene Petri dish.</li>
	<li>Place the master with PDMS in a vacuum desiccator for roughly 15 min&#160;to remove any air bubbles.</li>
	<li>Cure the PDMS device by placing it in a 95&#160;&#176;C oven for 1 hr. Alternatively, the PDMS will cure at RT after 24 hr.</li>
	<li>Remove the device by cutting around the perimeter with a surgical blade and carefully peeling the device from the master.</li>
	<li>Punch inlet and outlet holes into the PDMS using a 0.5 mm biopsy punch.</li>
	<li>Bond the device to a glass microscope slide using a plasma bonder4.</li>
</ol>
3. Prepare an Air Pressure Control Pump to Pressurize a Reservoir Containing the Fluid
<ol>
	<li>Modify the pump output such that the pressurized air exits through a length of 2.7 mm inner diameter polyethylene tubing.</li>
	<li>Construct it such that the tubing terminates at a luer-lock syringe tip by fitting the lumen over the nipple on the rear of the luer-lock.</li>
	<li>Seal by filling the space between the luer-lock threads and the tubing with epoxy.</li>
	<li>Attach a 27.5 G needle.</li>
</ol>
4. Prepare a Monodisperse Emulsion of Aqueous (Water-in-oil) Droplets Suspended in an Inert Fluorinated Carrier Oil with 2% (wt/wt) Dissolved Biocompatible Surfactant7
The specific reagents contained in these droplets depend on the application
<ol>
	<li>In preparation for reinjection, load the emulsion into a 1 ml syringe with a 27.5 G needle.</li>
	<li>Secure the syringe in a syringe pump and orient the pump vertically (needle upward). 
	Note: This orientation causes the droplets to pack in a layer above the carrier oil. When the pump is started, the droplets will be pushed out of the syringe at high volume fraction by the oil layer under them.</li>
</ol>
5. Prepare Reagents for Introduction to the Microfluidic Chip
<ol>
	<li>Punch three 0.5 mm holes into the cap of a 15 ml centrifuge tube (any container with a screw cap will suffice) using a biopsy punch, needle, or drill.</li>
	<li>Insert a 0.5 mm diameter wire electrode and a ~20 cm length of PE-2 tubing through two of the holes so that they reach the bottom of the tube.</li>
	<li>In the remaining hole, thread a ~2.5&#160;cm of a ~20 cm length of PE tubing such that it will rest above the fluid level.</li>
	<li>Seal any gaps on the top of the cap with UV-cured epoxy.</li>
	<li>Fill the tube with the picoinjection fluid and screw on the cap.</li>
	<li>Connect the output from the air-pressure control pump to the shorter length of tubing by inserting the needle into the lumen. The needle should fit snugly.</li>
	<li>Fill a 1 ml syringe with 1 M NaCl to serve as the Faraday Moat.</li>
	<li>Connect a 27.5 G needle and secure the syringe in a syringe pump.</li>
	<li>Fill another 1 ml syringe with carrier/spacer oil, connect a 27.5 G needle, and secure it in a syringe pump.</li>
</ol>
6. Prepare the Microfluidic Device for Picoinjection
<ol>
	<li>Connect the output tubing (longer length) from the injection fluid container to the inlet port of the picoinjection fluid on the microfluidic chip.</li>
	<li>Connect the syringe containing the 1 M NaCl to the inlet port for the Faraday Moat on the microfluidic chip with a length of PE tubing.</li>
	<li>Connect the syringe containing the carrier oil to the inlet port of the microfluidic chip with a length of PE tubing.</li>
	<li>Insert PE tubing into the emulsion outlet port on the microfluidic chip. The tubing should terminate in an emulsion collection vessel, normally a 1.5 ml centrifuge tube.</li>
	<li>Insert PE tubing into the outlet port for the Faraday Moat on the microfluidic chip. The tubing should terminate in a non-conducting and electrically isolated container to prevent a short circuit.</li>
	<li>Connect the output of the high-voltage (HV) amplifier via alligator clip to the metal electrode submerged in the picoinjection fluid.</li>
	<li>Connect the ground electrode of the HV amplifier via alligator clip to the metal of the syringe needle containing the 1 M NaCl.</li>
</ol>
7. Infuse Reagents into Microfluidic Chip
<ol>
	<li>Introduce the 1 M NaCl (Faraday Moat) to the device at a rate of 100 &#956;l/hr.</li>
	<li>Introduce the droplet emulsion and carrier oil at rates suitable for the device dimensions. For our demo device, we introduce the drops and oil at 200 and 400 &#956;l/hr, respectively. The flow rates should allow the droplets to pass the picoinjector at regular intervals separated by a gap of carrier oil.</li>
	<li>Adjust the pressure applied to the picoinjection fluid such that the fluid pressure at the picoinjection orifice is in mechanical equilibrium with the droplet channel. 
	Note: At this pressure (the Laplace pressure), the injection fluid should bulge into the droplet channel without budding off and forming its own drops (Figure 2). At these flow rates described above, we apply a pressure of ~13 psi to the injection fluid to achieve equilibrium at the injection site.</li>
</ol>
8. Begin Picoinjection
<ol>
	<li>As droplets pass the injection orifice, apply a 0-10 V, 10 kHz, AC signal amplified 1,000x by the HV-amplifier (Figure 3).</li>
	<li>Modulate the injection volume by changing the amplitude of the applied voltage. 
	Note: Higher voltages should allow for more fluid to be introduced to the droplets. In our testing, we observe stable and consistent injection at voltages between 100 and 3,000 V using injection solutions of NaCl ranging from 10-500 mM (Figure 4).</li>
</ol>

<ol>
	<li>Kritikou, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=It's+cheaper+in+the+Picolab.">It's cheaper in the Picolab.</a> Nat. Rev. Genet. 6 (9), (2005).</li><li>Ahn, K., Agresti, J., Chong, H., Marquez, M., Weitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrocoalescence+of+drops+synchronized+by+size-dependent+flow+in+microfluidic+channels.">Electrocoalescence of drops synchronized by size-dependent flow in microfluidic channels.</a> Appl. Phys. Lett. 88 (26), (2006).</li><li>Abate, A. R., Hung, T., Mary, P., Agresti, J. J., Weitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+injection+with+microfluidics+using+picoinjectors.">High-throughput injection with microfluidics using picoinjectors.</a> Proc. Natl. Acad. Sci. U S A. 107, 19163-19166 (2010).</li><li>Harris, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+a+microfluidic+device+for+the+compartmentalization+of+neuron+soma+and+axons.">Fabrication of a microfluidic device for the compartmentalization of neuron soma and axons.</a> J. Vis. Exp. (7), (2007).</li><li>Duffy, D. C., McDonald, J. C., Schueller, O. J., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+prototyping+of+microfluidic+systems+in+poly(dimethylsiloxane).">Rapid prototyping of microfluidic systems in poly(dimethylsiloxane).</a> Anal. Chem. 70 (23), 4974-4984 (1998).</li><li>O'Donovan, B., Eastburn, D. J., Abate, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrode-free+picoinjection+of+microfluidic+drops.">Electrode-free picoinjection of microfluidic drops.</a> Lab on a Chip. 12 (20), 4029-4032 (2012).</li><li>Holtze, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biocompatible+surfactants+for+water-in-fluorocarbon+emulsions.">Biocompatible surfactants for water-in-fluorocarbon emulsions.</a> Lab on a Chip. 8 (10), 1632-1639 (2008).</li><li>Chung, C., Lee, M., Char, K., Ahn, K., Lee, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Droplet+dynamics+passing+through+obstructions+in+confined+microchannel+flow.">Droplet dynamics passing through obstructions in confined microchannel flow.</a> Microfluid. Nanofluid. 9, 1151-1163 (2010).</li><li>Herminghaus, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamical+instability+of+thin+liquid+films+between+conducting+media.">Dynamical instability of thin liquid films between conducting media.</a> Phys. Rev. Lett. 83 (12), 2359-2361 (1999).</li><li>Priest, C., Herminghaus, S., Seemann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+electrocoalescence+in+microfluidics:+Targeting+a+single+lamella.">Controlled electrocoalescence in microfluidics: Targeting a single lamella.</a> Appl. Phys. Lett. 89 (13), 134101-134103 (2006).</li><li>Florent, M., Siva, A. V., Hao, G., Dirk, E., Frieder, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrowetting-controlled+droplet+generation+in+a+microfluidic+flow-focusing+device.">Electrowetting-controlled droplet generation in a microfluidic flow-focusing device.</a> J. Phys: Condens. Matter. 19 (46), (2007).</li><li>Eastburn, D. J., Sciambi, A., Abate, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Picoinjection+enables+digital+detection+of+RNA+with+droplet+rt-PCR.">Picoinjection enables digital detection of RNA with droplet rt-PCR.</a> PLoS ONE. 8 (4), (2013).</li></ol>

We do not fully understand exact physical mechanism behind the relationship between the applied voltage and injection volume observed in our experiments. The lab&#39;s interests and relevant areas of expertise are not well-suited for pursuing this lingering question. We encourage those with more physics and engineering acumen to explore this phenomenon.

The relationship between injection volume and applied voltage is dependent on many factors including device dimensions, length of the tubing carrying the picoinjection fluid to the device, molarity of picoinjection fluid, and the velocity of the droplets as they pass they injector. For this reason we recommend that the volume/voltage relationship be characterized before each run of picoinjection by measuring injection volumes at the edges of the working ranges of voltage and molarity. Additionally, at higher voltages and...

In droplet-based microfluidics, micron-scale aqueous droplets are used as &#34;test tubes&#34; for biological reactions. The advantage to performing reactions in the tiny droplets is that each drop uses only a few pl of reagent and, with microfluidics, the drops can be formed and processed at kilohertz rates1.&#160;Combined, these properties allow millions of reactions with individual cells, nucleic acid molecules, or compounds to be performed in a matter of min&#160;with &#956;l&#160;of total material.
To use drops for applications like these, techniques are needed for adding controlled volumes of reagents to the drops; such operations are analogous to pipetting into test tubes. One method for accomplishing this is electrocoalescence, wherein a drop of reagent is merged with the target drop by applying an electric field. The electric field disrupts the arrangement of surfactant molecules on the interfaces of the drops, inducing a thin-film instability and triggering coalescence in emulsions that are otherwise stable2. Electrically-induced merging is also exploited in the design of the picoinjector, a device that injects reagents into drops as they flow past a pressurized channel3. To apply the electric field, picoinjector devices utilize metal electrodes, but the integration of metal electrodes into microfluidic chips is often a complex and error-prone process as the liquid-solder wires are easily compromised by air bubbles or dust and other debris in the channel, as well as fractures from stress or bending during device setup.
Here we present a method to perform picoinjection without the use of metal electrodes, making the fabrication simpler and more robust. To trigger picoinjection, we instead use the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. We also add a &#34;Faraday Moat&#34; to shield sensitive regions of the device and act as a universal ground (Figure 1). The moat electrically isolates the droplets upstream of the picoinjection site by providing a ground, preventing unintended droplet merger. An added benefit of our technique is that the volume injected into the drops depends on the magnitude of the applied voltage, allowing it to be adjusted by tuning the applied signal.
We fabricate our devices in poly(dimethylsiloxane) (PDMS) using soft photolithographic techniques4,5. Our approach is compatible with devices fabricated in other materials, like resins, plastics, and epoxies. The channels have heights and widths of 30&#160;&#956;m, which are optimal for working with droplets 50 &#956;m in diameter (65 pl). We introduce reagents via polyethelene tubing (0.3/1.09 mm inner/outer diameter) inserted into ports created during device fabrication with 0.50 mm biopsy punches, similar to methods described previously5. The exact makeup of the injection fluid depends on the specific application. The fluid need only contain dissolved electrolytes at concentrations high enough to yield sufficient conductivity for the electrical signal to be transmitted to the picoinjector. In bench testing, we have found that ionic concentrations greater than 10 mM should suffice6, though this value and fluid conductivities depend on the specific device dimensions and magnitude of the applied voltage.

<table border="0" cellpadding="0" cellspacing="0" width="1000">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">1 mL Leur-Lok&#8482; syringes</td>
			<td style="width:143px;">BD Medical</td>
			<td align="right" style="width:160px;">309628</td>
			<td style="width:415px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LocTite UV-cured adhesive</td>
			<td style="width:143px;">Henkel</td>
			<td align="right">35241</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:283px;">PE-2 Tubing</td>
			<td style="width:143px;">Scientific Commodities</td>
			<td>BB31695-PE/2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Novec HFE-7500</td>
			<td>3M</td>
			<td style="width:160px;">98-0212-2928-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">NaCl</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td style="width:160px;">S9888</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">1.5 mL centrifuge tubes</td>
			<td style="width:143px;">Eppendorf</td>
			<td align="right" style="width:160px;">22363531</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">BD Falcon 15 ml tube</td>
			<td style="width:143px;">BD Biosciences</td>
			<td align="right" style="width:160px;">352097</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:283px;">Air Pressure Control Pump</td>
			<td style="width:143px;">Control Air Inc.</td>
			<td style="width:160px;"></td>
			<td style="width:415px;">We recommend one under the control of DAQ and control software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Syringe Pumps</td>
			<td>New Era</td>
			<td style="width:160px;"></td>
			<td>Must be capable of holding 1ml syringes and flowing at rates as low as 100 uL/hr</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">HV-Amplfier</td>
			<td style="width:143px;"></td>
			<td style="width:160px;"></td>
			<td>Must be capable of 1000x amplification of signals between 0.01 and 10 V</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Plasma Bonder/Cleaner</td>
			<td style="width:143px;">Harrick Plasma</td>
			<td style="width:160px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3&#8221; silicon wafers</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td align="right" style="width:160px;">647535</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PDMS</td>
			<td style="width:143px;">Dow Corning</td>
			<td style="width:160px;"></td>
			<td>Sylgard 184 with curing agent should be included</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">SU-8 Photoresist</td>
			<td style="width:143px;">MicroChem</td>
			<td style="width:160px;"></td>
			<td>Viscocity depends on device dimensions</td>
		</tr>
	</tbody>
</table>

picoinjection of microfluidic drops without metal electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.

Microscopic images taken at the picoinjection site show that electrification of the picoinjection fluid is enough to trigger injection (Figure 2). The injected volume can be controlled by modulating the amplitude of the applied voltage, with higher voltages allowing for higher injection volumes. We plot the injection volume versus the magnitude of the applied voltage for three representative molarities of injection fluid in (Figure 3). To demonstrate the speed our method, we selectively ...

Watch this Scientific Journal Video about Picoinjection of Microfluidic Drops Without Metal Electrodes at JoVE.com

Picoinjection of Microfluidic Drops Without Metal Electrodes

We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use.

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of ...

picoinjection-of-microfluidic-drops-without-metal-electrodes

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11.0K Views.  Unversity of California, San Francisco. We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use. 

Video: Picoinjection of Microfluidic Drops Without Metal Electrodes

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within &#177;2 &#176;C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.

Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...

Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of electrospun titanium dioxide nanofibers (TiO2-NFs) on top of a blocking layer made of commercially available titanium dioxide nanoparticles (TiO2-NPs). This is achieved by first electrospinning a solution of titanium (IV) butoxide, polyvinylpyrrolidone (PVP), and glacial acetic acid in ethanol to obtain composite PVP/TiO2 nanofibers. These are then calcined at 500 &#176;C to remove the PVP and to obtain pure anatase-phase titania nanofibers. This material is characterized using scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The photoanode is prepared by first creating a blocking layer through the deposition of a TiO2-NPs/terpineol slurry on a fluorine-doped tin oxide (FTO) glass slide using doctor blading techniques. A subsequent thermal treatment is performed at 500 &#176;C. Then, the light-scattering layer is formed by depositing a TiO2-NFs/terpineol slurry on the same slide, using the same technique, and calcinating again at 500 &#176;C. The performance of the photoanode is tested by fabricating a dye-sensitized solar cell and measuring its efficiency through J-V curves under a range of incident light densities, from 0.25-1 Sun.

The overall goal of this project was to use electrospinning to fabricate a photoanode with improved performance for dye-sensitized solar cells.

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film.
The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in ...

Fused Filament Fabrication (FFF) of Metal-Ceramic Components

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.

Fused Filament Fabrication FFF of Metal-Ceramic Components

This study shows multi-material additive manufacturing (AM) using fused filament fabrication (FFF) of stainless steel and zirconia.

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with ...