Lab on a Chip Blog

Over the years, the materials used to make microfluidic devices have dictated the progress of the field. The development of early silicon and glass devices progressed very slowly because the fabrication methods required to make these devices were prohibitively expensive and inaccessible.¹ Since the arrival of polydimethylsiloxane (PDMS)-based devices made by elastomeric micromolding or “soft lithography” in 1998,² the pace of microfluidic technology development has increased dramatically. For example, between 1998 and 2010, the number of microfluidic-related publications increased from hundreds to thousands per year.³ These developments were fueled by the simplicity of PDMS-soft lithography, and more importantly, the ability of PDMS to form pneumatic valves and pumps.⁴

Although soft lithography has become one of the most popular methods for microfluidic fabrication, clean room processes are still needed to make a micromold, and PDMS is not compatible with existing high-throughput manufacturing methods.¹ For these reasons and others, researchers are developing alternative methods for device fabrication. For example, Dr. Cooksey at the National Institute of Standards and Technology, Gaithersburg and Prof. Atencia at the University of Maryland developed techniques to create microfluidic devices from cut-off laminates and double-sided tapes.⁵ Their article, which featured as a cover in Lab on a Chip, showed how these film-based devices can be rapidly fabricated without a cleanroom using in-expensive materials and widely available equipment (e.g. razor cutter, laser cutter).

Like conventional PDMS-devices, these film-based devices can support pneumatic valves and pumps by sandwiching a thin layer of PDMS between two layers of film with cut-out channels. Accurate alignment between these layers is achieved using a self-alignment strategy, in which features of adjacent layers are mirrored across a folding line on a single piece of tape. To demonstrate valve functionality, Cooksey and Atencia created a device that uses 3 valves to control flow from 3 fluidic inputs, and one that uses 8 valves to control a 2-inlet rotary mixer.

One interesting feature of this technology is that very thin devices can be formed (less than 0.5 mm), which enables the fabrication of devices with many layers. For example, using the self-alignment strategy, the researchers fabricated a 6-layer device comprising a valve layer and five fluidic layers that form liquid chambers of varying heights.

Perhaps the most fascinating trait of this technology is the ability to fold devices into 3D structures with fully functioning valves. As shown in the figure below, the researchers assembled a 3D microfluidic cube that can deliver reagents to specific locations on the cube using the fluid channels routed through the walls. The researchers filled the cube with agar and used it to study the chemotaxis of C. elegans. Within two hours, the worms migrated from the center of the cube toward the face introduced with food, and promptly moved away when the food was switched to a repellent.

In summary, Dr. Cooksey and Prof. Atencia developed a rapid prototyping technique that can create film-based devices with the similar valve functionalities as conventional PDMS-based devices. But because these devices are very thin, more complicated and unique devices structures can be created. This technology has the potential uncover new applications for microfluidics, and make microfluidic technologies more accessible to non-engineers (e.g. biologists and clinicians).

1.            E. K. Sackmann, A. L. Fulton and D. J. Beebe, Nature, 2014, 507, 181-189.

2.            D. C. Duffy, J. C. McDonald, O. J. A. Schueller and G. M. Whitesides, Analytical Chemistry, 1998, 70, 4974-4984.

3.            E. Berthier, E. W. K. Young and D. Beebe, Lab on a Chip, 2012, 12, 1224-1237.

4.            M. A. Unger, H.-P. Chou, T. Thorsen, A. Scherer and S. R. Quake, Science, 2000, 288, 113-116.

5.            Pneumatic valves in folded 2D and 3D fluidic devices made from plastic films and tapes, Gregory A. Cooksey and Javier Atencia, Lab on a Chip, 2-14, 14, 1665-1668

To accurately diagnose a disease or monitor the effectiveness of a treatment, patient samples (e.g. blood, saliva, or urine) must be analyzed in a central laboratory. After collection, the samples will begin to degrade due to chemical, bacterial, and enzymatic interactions.¹ These changes can compromise the integrity of the analyte and introduce errors during analysis. Thus, stabilization techniques are necessary to preserve the diagnostic value of patient samples.

Typically, analyte stabilization is achieved by transporting and storing samples at low temperature using dry ice, refrigerators, freezers, or liquid nitrogen. Unfortunately, low-temperature preservation is costly to implement, requiring substantial infrastructure, specialized equipment, and trained personnel. It becomes particularly expensive for applications involving bio surveillance, long-term sample archiving, and clinical diagnostics in low-resource settings.

To address this challenge, a research team, led by Prof. Ismagilov at the California Institute of Technology, developed a microfluidic device that can preserve biological samples in the dry state. The device relies on pre-loaded desiccants to rapidly (~30 min) dry samples in a stabilization matrix, protecting the analyte from enzymatic degradation and light or heat activated reactions.² Importantly, the device is simple to use, allowing minimally trained users to collect and preserve samples without worrying about the precision of the input volume.

The device, based on SlipChip technology,³ was formed by stacking three layers of subassemblies: the top layer has through-holes for sample loading and recovery, the middle layer has channels for sample storage, and the bottom layer houses the desiccants for drying. With the help of a lubricant between each layer, the middle layer can be horizontally moved (slipped), relative to the other layers, allowing the device to be reconfigured into different states.

The device has three states, each with a specific function: loading, drying, and recovery (see figure 1). In the loading state, the loading inlet is connected to the sample storage channel.  An untrained user will place the sample in the inlet and close the lid to create a tight seal. This generates an air pressure that pushes the sample through the channels. To initiate the preservation process, the user will slip the device into the drying state. Here, the sample is disconnected from the inlet and is placed into vapor contact with the desiccant through a porous membrane. At this stage, the device can be stored or transported without the use of low-temperature preservation equipment. Just before analysis in the laboratory, a trained user will use a special tool to slip the device into the recovery state. Here, the sample is disconnected from the desiccant chamber and is connected to the recovery inlets. Using a pipette and water, the samples can be rehydrated and recovered for quantitative analysis.

As a validation, the device was subjected to an accelerated aging test (50^oC for 5-weeks) while preserving samples containing control RNA or HIV-1 RNA. Remarkably, the RNA samples stored in the device were indistinguishable from the ones stored in the freezer at -80^oC, as tested by electrophoresis and RT-qPCR. In contrast, significant degradation was observed in samples stored in the liquid state at 50^oC. These results suggest that the RNA may be stable at room temperature in the device for at least up to 8 months.

In summary, the research team developed and validated a microfluidic device that can preserve biological samples in the dry state, eliminating the need for low-temperature equipment. The device is compact, easy to use, making it compatible for challenging applications such as clinical diagnostics in remote, resource-limited settings. The reduction of cost in transport, sample collection, and storage can open up many new possibilities in health care, diagnostics, and beyond.

To access the full article, click the following link: A microfluidic device for dry sample preservation in remote setting, Stefano Begolo, Feng Shen and Rustem F. Ismagilov.

1.            G. V. Iyengar, K. S. Subramanian and J. R. W. Woittiez, Element Analysis of Biological Samples: Principles and Practice, CRC Press, Boca Raton, New York, 1998.

2.            E. Wan, M. Akana, J. Pons, J. Chen, S. Musone, P. Y. Kwok and W. Liao, Current Issues in Molecular Biology, 2010, 12, 135-142.

3.            W. Du, L. Li, K. P. Nichols and R. F. Ismagilov, Lab on a Chip, 2009, 9, 2286-2292.

Researchers from the University of Tokyo and the CEA-Leti research institute in France have designed a platform that allows channels to be written and rewritten at will in a fluid layer atop a grid of electrodes.

In their recent cover article in Lab on a Chip, Raphael Renaudot and colleagues describe this novel device, which is based on the Electrowetting on Dielectric (EWOD) and Liquid Dielectrophoresis (LDEP) phenomena¹. Their goal was to create a flexible, reusable platform that would enable the creation of microfluidic devices without the use of expensive microfabrication techniques. The fluid layer of the device is filled with liquid paraffin, which can easily be solidified and re-melted via thermoelectric cooling and heating (its melting temperature is 35° C.) Water is injected into the paraffin layer, and its flow path is controlled via the underlying electrode layer, which is made up of a grid of 83 electrodes (the small squares seen in the figure). By tuning the interfacial tension between the water and the surface of each electrode via the independently controlled electrode voltages, it is possible to guide a channel (or “finger”) of water along the desired path on the grid (see figure).

After the water is guided into the desired path, the device is cooled, solidifying the paraffin and setting the channels in place. Later, the device can be reheated to erase the existing channels, and a new design can be drawn. The chip can be reused multiple times, reducing waste and making it very useful for prototype testing and low-cost applications. The authors demonstrated two chip designs using the reconfigurable platform: a droplet generator and a device for E. coli confinement within a fluidic cavity.

A water channel is drawn through a paraffin matrix via control of an underlying grid of electrodes (from Figure 2b)

Read this HOT article in Lab on a Chip today!

A Programmable and Reconfigurable Microfluidic Chip, Raphael Renaudot, Vincent Agache, Yves Fouillet, Guillaume Laffite, Emilie Bisceglia, Laurent Jalabert, Momoko Kumemura, Dominique Collard and Hiroyuki Fujita. DOI: 10.1039/c3lc50850a

References:

1. T. B. Jones and K. L. Wang, Langmuir 2004, 20 (7), 2813–2818.