This communication describes the first paper-based microfluidic device that is capable of generating its own power when a sample is added to the device. The microfluidic device contains galvanic cells (that we term ''fluidic batteries'') integrated directly into the microfluidic channels, which provides a direct link between a power source and an analytical function within the device. This capability is demonstrated using an example device that simultaneously powers a surface-mount UV LED and conducts an on-chip fluorescence assay.

Fluorescence assays often require specialized equipment and, therefore, are not easily implemented in resource-limited environments. Herein we describe a point-of-care assay strategy in which fluorescence in the visible region is used as a readout, while a camera-equipped cellular phone is used to capture the fluorescent response and quantify the assay. The fluorescence assay is made possible using a paper-based microfluidic device that contains an internal fluidic battery, a surface-mount LED, a 2-mm section of a clear straw as a cuvette, and an appropriately-designed small molecule reagent that transforms from weakly fluorescent to highly fluorescent when exposed to a specific enzyme biomarker. The resulting visible fluorescence is digitized by photographing the assay region using a camera-equipped cellular phone. The digital images are then quantified using image processing software to provide sensitive as well as quantitative results. In a model 30 min assay, the enzyme β-D-galactosidase was measured quantitatively down to 700 pM levels. This Communication describes the design of these types of assays in paper-based microfluidic devices and characterizes the key parameters that affect the sensitivity and reproducibility of the technique.

Microfluidic devices fabricated out of paper (and paper and tape) have emerged as promising platforms for conducting multiple diagnostic assays simultaneously in resource-limited settings. Certain types of assays in these devices, however, require a source of power to function. Lithium ion, nickel-cadmium, and other types of batteries have been used to power these devices, but these traditional batteries are too expensive and pose too much of a disposal hazard for diagnostic applications in resource-limited settings.To circumvent this problem, we previously designed a ''fluidic battery'' that is composed of multiple galvanic cells, incorporated directly into a multilayer paper-based microfluidic device. We now show that multiple cells of these fluidic batteries can be connected in series and/or in parallel in a predictable way to obtain desired values of current and potential, and that the batteries can be optimized to last for a short period of time (,1 min) or for up to 10-15 min. This paper also (i) outlines and quantifies the parameters that can be adjusted to maximize the current and potential of fluidic batteries, (ii) describes two general configurations for fluidic batteries, and (iii) provides equations that enable prediction of the current and potential that can be obtained when these two general designs are varied. This work provides the foundation upon which future applications of fluidic batteries will be based.

This chapter describes a method for fabricating three-dimensional (3D), paper-based microfluidic devices that contain internal timers for running quantitative, time-based assays. The method involves patterning microfluidic channels into paper, and cutting double-sided adhesive tape into defined patterns. Patterned paper and tape are assembled layer by layer to create 3D microfluidic devices that are capable of distributing microliter volumes of a sample into multiple regions on a device for conducting multiple assays simultaneously. Paraffin wax is incorporated into defined regions within the device to provide control over the distribution rate of a sample, and food coloring is included in defined regions within the device to provide an unambiguous readout when the sample has reached the bottom of the device (this latter feature is the endpoint of the timer).