Microfluidic paper-based analytical devices (µPADs) have emerged as viable multiplexable platforms with the potential to transcend existing analytical techniques in resource-limited settings. µPADs are fabricated by patterning hydrophobic materials on hydrophilic paper. Reproducibility in fabrication is essential in a myriad of applications and particularly, in the development of point-of-care (POC) diagnostic devices that utilize paper-based platforms. A critical step in fabrication involves the wax heating process that determines the channel dimensions and the depth at which hydrophobic wax material permeates paper to create barriers. In this paper, we assess µPAD viability by examining two fabrication parameters that affect wax ink spreading and permeation using a commercial heat press: temperature and time of heating. Analysis of the µPADs revealed that functional chips could be fabricated at temperatures between 143 and 215 °C and time of heating between 50 and 135 s, while non-functioning chips were obtained at temperatures between 76 and 140 °C and time of heating between 5 and 45 s. Wax ink spread and permeated paper consistently between 143 and 215 °C. Also shown is a simple three dimensional (3D) microfluidic channel fabricated in a single sheet of cellulose paper utilizing the fabrication conditions described herein. This work demonstrates that controlling the extent of wax printing in the fabrication process of a µPAD can yield versatile and interesting devices for use in both resource-rich and -limited settings.
Wilson Lee and Frank A. Gomez *
Department of Chemistry and Biochemistry, California State University, Los Angeles, 5151 State University Drive, Los Angeles, CA 90032-8202, USA
Micromachines 2017, 8(4), 99; doi:10.3390/mi8040099