title: Dissolvable fluidic time delays for programming multi-step assays in instrument-free paper diagnostics.
abstract: Lateral flow tests (LFTs) are an ingenious format for rapid and easy-to-use diagnostics, but they are fundamentally limited to assay chemistries that can be reduced to a single chemical step. In contrast, most laboratory diagnostic assays rely on multiple timed steps carried out by a human or a machine. Here, we use dissolvable sugar applied to paper to create programmable flow delays and present a paper network topology that uses these time delays to program automated multi-step fluidic protocols. Solutions of sucrose at different concentrations (10-70% of saturation) were added to paper strips and dried to create fluidic time delays spanning minutes to nearly an hour. A simple folding card format employing sugar delays was shown to automate a four-step fluidic process initiated by a single user activation step (folding the card); this device was used to perform a signal-amplified sandwich immunoassay for a diagnostic biomarker for malaria. The cards are capable of automating multi-step assay protocols normally used in laboratories, but in a rapid, low-cost, and easy-to-use format.
authors.affiliation: University of Washington, Department of Bioengineering, 3720 15th Ave NE, Box 355061, Seattle, WA 98195, USA. blutz@uw.edu
authors.forename: Barry
authors.initials: B
authors.lastname: Lutz
authors.forename: Tinny
authors.initials: T
authors.lastname: Liang
authors.forename: Elain
authors.initials: E
authors.lastname: Fu
authors.forename: Sujatha
authors.initials: S
authors.lastname: Ramachandran
authors.forename: Peter
authors.initials: P
authors.lastname: Kauffman
authors.forename: Paul
authors.initials: P
authors.lastname: Yager
mesh_terms: D019411:Clinical Laboratory Techniques / Q000295:instrumentation* / Q000379:methods*; D003101:Collodion / Q000737:chemistry; D004867:Equipment Design; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation* / Q000379:methods*; D010209:Paper; D019095:Point-of-Care Systems; D012995:Solubility; D013395:Sucrose / Q000737:chemistry; D013997:Time Factors
chemical_list: D013395:Sucrose; D003101:Collodion