Design considerations for reducing sample loss in microfluidic paper-based analytical devices

The field of microfluidic paper-based analytical devices (μPADs) is most notably characterized by portable and low-cost analysis; however, struggles to achieve the high sensitivity and low detection limits needs required for many environmental applications hinder widespread adoption of this technology. Loss of analyte to the device material represents an important problem impacting sensitivity. Critically, we found that at least 50% of a Ni(II) sample is lost when being transported down a 30 mm paper channel that is representative of structures commonly found in μPADs. In this work, we report simple strategies such as adding a waste zone, enlarging the detection zone, and using an elution step to increase device performance. A μPAD combining the best performing functionalities led to a 78% increase in maximum signal and a 28% increase in sensitivity when transporting Ni(II) samples. Using the optimized μPAD also led to a 94% increase in maximum signal for Mn(II) samples showing these modifications can be applied more generally.