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paper-based microfluidics

Random Laser Emission From a Paper-Based Device

Rahil Jain
23 February 2014

Paper is such a versatile material that it never ceases to amaze. It was not until recently that its potential in developing low-cost microfluidic diagnostic technologies started being utilized [1]. In yet another intriguing demonstration of the use of paper, a group at Istituto Nanoscienze, CNR in Italy realized lasing with paper as the substrate [2]. Paper, with its complex network of randomly distributed fibers, may seem like an odd choice with which to realize a laser, which traditionally required a gain medium of controlled purity, periodicity, size, concentration, and shape. However, the incipient technique of random lasing [3], which employs scattering processes of light for optical gain and doesn’t rely on external feedback to achieve above unity gain, can be implemented on a low-ordered substrate, such as paper. When imbibed with a fluorescent lasing dye like Rhodamine B (RhB), paper provides a randomly distributed network of scatterers (fibers) in an optical gain medium (dye) required for random lasing. The emission spectrum of a paper-based random laser was found to be dependent on laser-dye characteristics, microfluidic channel dimensions, and the shape, pore-size, local refractive index, and functionalization of the substrate (Fig 1). With a tunable spectral response and susceptibility to a variety of channel properties, random lasers may find application as an optical transducer or sensor in biosensing and diagnostics. The disadvantage of random lasing is loss of coherence in light output and the requirement of optical pumping. The understanding of physics behind this observation is still in its incipient stage and further work in lasing in paper is warranted.

Figure 1: Methods and results of paper-based laser. (a) The microfluidic circuit is realized lithographically on a single layer chromatography paper and is filled by capillary driven laser dye (RhB). Inset shows true colors of channel wetting. (b) shows variation in emission peak intensity as a function of optical pumping energy for channels of different widths compared to native non-patterned paper.  (c-d) demonstrates variation in emission characteristics with functionalization of surface with high refractive index TiO2 and channel shape respectively. (e) shows emission spectra for 100μm wide channel and in the inset the emission spectra of pure RhB in ethylene glycol. Pictures adapted without permission from [2]. 

References:

[1] Martinez, Andres W., et al. "Diagnostics for the developing world: microfluidic paper-based analytical devices." Analytical Chemistry 82.1 (2009): 3-10.

[2]Viola, Ilenia, et al. "Random laser emission from a paper-based deviceJournal of Materials Chemistry C 1.48 (2013): 8128-8133.

[3]Gottardo, Stefano, et al. "Resonance-driven random lasing." Nature Photonics 2.7 (2008): 429-432.

Author: Rahil Jain is a graduate student in the Electrical Engineering department at UW, Seattle. His work in the Lutz Lab focusses on developing microfluidic technologies for application in low-cost diagnostics. 

Paper-Based Visual Detection of DNA

Koji Abe
7 January 2014

Rapid and inexpenive nucleic acid assays are challenging to achieve but highly needed for low-cost and point-of-care diagnostics. Yajing Song and co-workers published a paper addressing the above issue by developing a paper-based DNA assay visualized by the naked eye. Their study in the ACS journal Analytical Chemistry demonstrates a novel filter paper-based tool using streptavidin-coated micrometer-sized beads to couple with DNA. Hybridization of the targets was performed by capillary transport through the filter paper array and generated specific signals within 2 min. The resulting signals were detected by the naked eye, as well as measured by a molecular imager. This strategy for visual detection of DNA can be applied not only in a forensic setting but also for point-of-care diagnostics.

Illustration of the use of filter paper for the detection of target DNA with visual readout by the naked eye. Song et al., "Visual Detection of DNA on Paper Chips," Analytical Chemistry, Just Accepted Manuscript (January 2, 2014). © 2014 American Chemical Society.

New Paper Device for Timing-Based Quantitative Assay

Koji Abe
2 November 2013

In making progress toward an inexpensive paper-based point-of-care device with no electronics required, Scott T. Phillips and coworkers developed a new device that simply relies on keeping track of time. Their study in the ACS journal Analytical Chemistry describes a strategy for quantitative measurement of enzyme analytes in the low to mid femtomolar range. After applying a sample with enzyme analyte to the device, a white assay region turns green, followed by a control region. The user only needs to measure the time for the control region to turn green relative to the assay region. Since the temperature, humidity, and viscosity of the sample will affect the measurement for both the control and assay regions, the control region serves to normalize the output of the assay to account for the effects of these factors. This strategy for a timing-based quantitative assay has great potential for use in remote settings of the world where sophisticated instruments are not options. 

Illustration of the paper device for a timing-based quantitative assay.  Gregory G. Lewis, Jessica S. Robbins, and Scott T. Phillips, "Point-of-Care Assay Platform for Quantifying Active Enzymes to Femtomolar Levels Using Measurements of Time as the Readout", Analytical Chemistry Article ASAP, 2013. © American Chemical Society 2013

Thumbs Up from George Whitesides on Sugar Delays

Carly Holstein
8 October 2013

In a recent issue of Lab on a Chip, renowned chemist and MF2.0 pioneer George Whitesides provided his "Viewpoint" on the use of sugar delays in paper-based tests. This sugar delay work, performed by our own Yager, Lutz, and Fu labs, was published in Lab on a Chip earlier this year and featured in our blog here. In his current "Viewpoint" article, Dr. Whitesides discusses the need for "simplicity in diagnostics" and commends Lutz et al.'s elegant approach to designing simple but automated paper diagnostics that are actually appropriate for point-of-care settings. He also praises the "quantitative engineering footing" on which the sugar delay work was based. While he notes that further development is of course needed to bring this technology to use, he asserts that this work is a step in the right direction for low-cost testing. Kudos to the authors of the work (Dr. Barry Lutz, Tinny Liang, Dr. Elain Fu, Sujatha Ramachandran, Peter Kauffman, and Dr. Paul Yager), and thank you to Dr. Whitesides for the kind words!

Article citation: Whitesides, George M., "Viewpoint on 'Dissolvable fluidic time delays for programming multi-step assays in instrument-free paper diagnostics'," Lab on a Chip 13 (20): 4004-4005 (2013).

Automated paper-based device for sequential multistep ELISA

Koji Abe
21 March 2013

In their recent paper published in Lab on a Chip, Amara Apilux and colleagues demonstrate automated paper-based devices for one-step quantitative sandwich ELISA-based analysis.  Two different designs of the patterned nitrocellulose membrane illustrate a potential for creating delayed fluid flow and allowing a multistep process (e.g. preconcentration and washing) with a single-step application of the sample solution. The authors achieved a limit of detection for hCG (8.1 mIU/mL) that is lower than measurable levels of conventional pregnancy test kits (20-100 mIU/mL), resulting from optimization of the pattern design using inkjet printing. This technology has the potential to simplify the efforts of complicated and time-consuming multistep biochemical analyses in the future.

Apilux et al., “Development of automated paper-based devices for sequential multistep sandwich enzyme-linked immunosorbent assays using inkjet printing”, Lab Chip, 2013, 13, 126.

Fun Times at MF2.0 in Boston!

Gina Fridley
11 December 2012

Last week some of us had the pleasure of visiting Boston for the 2012 Workshop on Capillary-based Microfluidics for Bioanalysis, hosted by Dr. Cathie Klapperich’s group at Boston University. As those of you who were there or watched the live stream [1] know, there was an incredible line-up of some of the best ideas that paper microfluidics has to offer. This community is using these paper technologies to address a huge range of problems, from identification of counterfeit drugs [2] to inexpensive solar power [3]. Inexpensive and easy-to-use devices are improving our ability to detect antibiotic resistance [4] and monitor water quality [5], while on-paper electrochemical detection [6] and nucleic acid amplification [7] increase the sensitivity achievable in these paperfluidic devices. We heard about the challenges and successes involved when testing new devices in the field [8] and got to experience do-it-yourself fabrication of little devices [9] and tests for TB drug adherence [10].

I didn’t get to see most of the demos on Day 2, because I was busy with the demos from our lab. I heard from other participants that the hand-on experiences were fantastic, and I know that we all had a great time sharing our lab’s work with the group.  One our demos demonstrated a method for visualizing flow through paper networks of arbitrary geometry [11], and the other featured some of my thesis work rehydrating dry reagents from storage depots patterned on assay membranes [12]. 

Thank you Cathie for carrying on the torch… and we’re hoping one of you MF2.0 fans out there will continue the tradition!

[1]      Videos of the talks are still available on the Klapperich lab website

[2]      Dr. Marya Lieberman

[3]      Dr. Karen Gleason

[4]      Dr. Ratmir Derda

[5]      Dr. John Brennan

[6]      Dr. Richard Crooks

[7]      Our own Dr. Barry Lutz!

[8]      Dr. Bernhard Weigl and Diagnostics for all

[9]      Jose Gomez-Marquez

[10]  Adher.io TB with Dr. Jackie Linnes

[11]  Visualizing flow in paper networks and Kauffman, P.; Fu, E.; Lutz, B.; Yager, P., Visualization and measurement of flow in two-dimensional paper networks. Lab on a Chip 2010, 10 (19), 2614-2617.

[12]  Fridley, G.; Le, H.; Fu, E.; Yager, P., Controlled release of dry reagents in porous media for tunable temporal and spatial distribution upon rehydration. Lab on a Chip 2012, 12(21),4321-4327.

Distributed Analysis of Environmental Pollutants Using Microfluidics

Luke Allpress
3 October 2012

A group in Denmark recently published an article in Lab on a Chip detailing the application of microfluidic gold enhancement processes to environmental pollutant analysis. The devices use a digital camera as the optical sensor to detect the gold nanoparticles bound to pollutants such as mercury.

With detection limits as low as 0.6 µg/L for mercury, this technology will simplify the efforts of deep field analytics for environmental pollution. The application of gold nanoparticle technology to contaminants shows potential to create more rapid, accurate analytics for field research in the future.

Article citation: Lafleur, Josiane, et. al, "Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants." Lab on a Chip, Advance Article, 20 Jun 2012.

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