Quantifying Colorimetric Assays in Paper-Based Microfluidic Devices by Measuring the Transmission of Light through Paper

This article describes a point-of-care (POC) system—comprising a microfluidic, paper-based analytical device (μ-PAD) and a hand-held optical colorimeter—for quantifying the concentration of analytes in biological fluids. The μ-PAD runs colorimetric assays, and consists of paper that has been (i) patterned to expose isolated regions of hydrophilic zones and (ii) wet with an index-matching fluid (e.g., vegetable oil) that is applied using a disposable, plastic sleeve encasement. Measuring transmittance through paper represents a new method of quantitative detection that expands the potential functionality of μ-PADs. This prototype transmittance colorimeter is inexpensive, rugged, and fully self-contained, and thus potentially attractive for use in resource-limited environments and developing countries.