Implementation of Laser-Printed Paper-Based Analytical Devices for Colorimetric Assay of Metals in the Teaching Laboratory

Microfluidics is a quickly growing discipline in analytical chemistry, biochemistry, and diagnostic medicine. Paper-based analytical devices, also known as microPADs (mu PADs), show marked ease of construction, low cost, and portability and can be used to measure analyte concentrations in tiny amounts of fluids based on colorimetric detection. The channel-defining hydrophobic boundary can be fabricated out of many different materials, with wax printing being the most used. Recently, a polyester-based laser printer toner has been employed to construct the boundary to form laser-printed paper-based analytical devices (LP-mu PADs). However, no applications of these simple devices in undergraduate teaching laboratories have been reported. Here, we describe a set of activities in which students first learn to fabricate LP-mu PADs using different types of paper and then characterize the conditions leading to optimal hydrophobic boundaries and flow. Finally, the students used their fabricated devices along with their smartphone to develop colorimetric assays for iron(II) and nickel(II) in aqueous solutions. From the easy and very inexpensive fabrication method described in this work, this activity provides a simple and accessible way to introduce microfluidics in the teaching laboratory. In general, this activity is suitable for students with a foundational knowledge of chemistry in laboratories focusing on analytical chemistry techniques.