Fluidic Timers for Time-Dependent, Point-of-Care Assays on Paper

摘要

This article describes an integrated approach to trackingnthe end point of a time-based assay that is conducted onnan analytical device made out of paper. The timingnmechanism is built directly into a paper-based analyticalndevice and does not require starting, stopping, resetnbuttons, batteries, or maintenance; the timer simply startsnonce the sample is added to the device. These “fluidicntimers” are composed of paraffin wax and a signalingnfeature (e.g., a dye). The timing function is made possiblenby the specific time required for a liquid sample to wicknthrough predefined regions in the device. This time periodncan be anywhere between 1 min and 2 h and is controllednby the quantity of wax present in the timer. Because bothnthe fluidic timers and paper-based assays depend on thenwicking rate of the sample, the fluidic timers automaticallyncalibrate themselves (relative to the assay) to account forndifferences in wicking rates that are caused by variationsnin humidity. Fluidic timers are 97% accurate (with respectnto the time required for the assay) and provide slightlynbetter accuracy than an external timer when used to tracknan assay that measured the level of glucose in a sample.