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.
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.
In an effort to fully represent the Microfluidics 2.0 community, we are seeking blog posts from guest contributors. If you are a member of the Microfluidics 2.0 community and would like to write a blog post about your work, other MF2.0 work you find interesting, or other topics relevant to the MF2.0 world, please let us know! If interested, send us an email (yagerlab at gmail dot com) with your name, affiliation, and a brief description of the topic you'd like to write about. Looking forward to your contributions!
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!
Professors Barry Lutz, Elain Fu, Paul Yager, and colleagues have published their work on sugar-based time delays for paper devices in the most recent issue of Lab on a Chip. This work describes the use of dissolvable sugar barriers to create and control fluidic time delays in paper microfluidic devices. This technique can be used to program multi-step assays that enable automated, easy-to-use paper diagnostic tests. What a “sweet” example of MF2.0!
Paul Farmer, co-founder of Partners in Health and Chair of the Department of Global Health and Social Medicine at Harvard Medical School, has just released a collection of short speeches: To Repair the World: Paul Farmer Speaks to the Next Generation. He began his humanitarian work in Haiti and has been a long-term advocate of grassroots, community-based aid over donation-based aid. The most recent issue of Time Magazine features an article entitled “10 Questions for Paul Farmer” in which he addresses how we think about humanitarian aid. If you don’t have access to the magazine you can watch the interview here. On Health and Science day he also sat down to answer questions at the Nobel Peace Prize Forum in which he also addresses issues of health care and aid. One of the most interesting points he makes is the new focus on “global health equity” rather than “international health.” Check it out! To read more about Paul Farmer you can also check out the book Mountains Beyond Mountains by Tracy Kidder, which chronicles Farmer’s work with Partners in Health.
I am excited to announce that our review article on nitrocellulose is now available in the latest issue of MRS Bulletin! This special issue is devoted to "Paper-Based Technology" and includes several great articles that highlight key aspects of this Microfluidics 2.0 technology! The article written by Gina Fridley, Shefali Oza, Paul Yager, and I describes "The Evolution of Nitrocellulose as a Material for Bioassays," including a brief history of the material, an overview of its physical properties, and considerations for assay development. Since nitrocellulose is one of the most common "paper" substrates for bioassays, we hope you will find this review useful!
Figure from our article illustrating (A) the porous nature of nitrocellulose, (B) the traditional use of nitrocellulose in a lateral flow test, and (C) the emerging use of nitrocellulose in MF2.0-based assays, such as 2DPNs. Fridley et al., MRS Bulletin 38 (4): 326-330 (April 2013).