title: Sample pre-concentration with high enrichment factors at a fixed location in paper-based microfluidic devices.
abstract: The lack of sensitivity is a major problem among microfluidic paper-based analytical devices (μPADs) for early disease detection and diagnosis. Accordingly, the present study presents a method for improving the enrichment factor of low-concentration biomarkers by using shallow paper-based channels realized through a double-sided wax-printing process. In addition, the enrichment factor is further enhanced by exploiting the ion concentration polarization (ICP) effect on the cathodic side of the nanoporous membrane, in which a stationary sample plug is obtained. The occurrence of ICP on the shallow-channel μPAD is confirmed by measuring the current-voltage response as the external voltage is increased from 0 to 210 V (or the field strength from 0 to 1.05 × 10(4) V m(-1)) over 600 s. In addition, to the best of our knowledge, the electroosmotic flow (EOF) speed on the μPAD fabricated with a wax-channel is measured for the first time using a current monitoring method. The experimental results show that for a fluorescein sample, the concentration factor is increased from 130-fold in a conventional full-thickness paper channel to 944-fold in the proposed shallow channel. Furthermore, for a fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) sample, the proposed shallow-channel μPAD achieves an 835-fold improvement in the concentration factor. The concentration technique presented here provides a novel strategy for enhancing the detection sensitivity of μPAD applications.
authors.affiliation: Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan. rjyang@mail.ncku.edu.tw.
authors.forename: Shih-Hao
authors.initials: SH
authors.lastname: Yeh
authors.affiliation: Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan. rjyang@mail.ncku.edu.tw.
authors.forename: Kuang-Hua
authors.initials: KH
authors.lastname: Chou
authors.affiliation: Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan. rjyang@mail.ncku.edu.tw.
authors.forename: Ruey-Jen
authors.initials: RJ
authors.lastname: Yang
mesh_terms: D000818:Animals; D002417:Cattle; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000737:chemistry; D056656:Lab-On-A-Chip Devices; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods; D010209:Paper; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: C039217:fluorescein isothiocyanate bovine serum albumin; D012710:Serum Albumin, Bovine; D016650:Fluorescein-5-isothiocyanate