Thread as a Matrix for Biomedical Assays
Original Entry: Peter Foster, AP 225, Fall 2011 In progress...
Authors: Meital Reches, Katherine A. Mirica, Rohit Dasgupta, Michael D. Dickey, Manish J. Butte, and George M. Whitesides
Publication: Reches et al. Thread as a Matrix for Biomedical Assays. Acs Appl Mater Inter (2010) vol. 2 (6) pp. 1722-1728
This paper details a fairly ingenious application of the capillarity of cotton string. The general idea is that one can think of string like a one dimensional microfluidic device. When one end of the string makes contact with a (water based) liquid, capillary effects will pull the fluid up through the string. Strings can be chemically treated so that they will change their color in the presence of a given chemical and thus can serve as a biomedical diagnostic tool.
Mercerized cotton (diameter = 0.3 mm) was chosen as the thread because of its ready availability and the reasonable rate at which water flows up the string ( ~0.23 cm/s). Three different layouts for the string are shown in Figure 1. In Figure 1 (A), the strings are sandwiched in parallel between two pieces of tape, with one end of each string exposed. They term this the "woven array". Figure 1 (B) shows the "branching array". The design is similar to the woven array, but instead of having multiple strings laid out in parallel, there is a single input that travels to a branching point, from which liquid can travel down other strings to different detection zones. The advantage of the branching array is that because the strings aren't laid out in parallel, one can put the same number of tests on one device with a smaller footprint compared with the woven array. Figure 1 (C) shows the "sewn array". Here, the string is simply sewn through a piece of plastic. Clear nail polish was used in order to seals the holes left from sewing to ensure that liquid can only travel through the string. This advantage of this assay is that the device could be sewn into almost anything (bandages, diapers, etc.).
 Reches et al. Thread as a Matrix for Biomedical Assays. Acs Appl Mater Inter (2010) vol. 2 (6) pp. 1722-1728