Microfluidic paper-based analytical device (μPAD) fabricated by wax screen printing technique for the determination of nitrite and nitrate ion in water samples

A microfluidic paper-based analytical device (mu PAD) is a new technology platform for extremely low-cost sensing applications. This study aimed to explore for an inexpensive alternative fabrication method. Accordingly, a simple wax screen printing fabrication manageable with locally available materials has been elaborated and successfully demonstrated for the determination of nitrite and nitrate ion(s) in water samples. The operational parameters such as sample and Griess reagent volume, color development time, and zinc powder loading were optimized. Applying the optimal conditions, the limits of detection for nitrite and nitrate ion were found to be 0.16 and 0.87 ppm, respectively. The level of sensitivity observed in mu PAD is adequate to determine the threshold concentration limit for nitrite (1 ppm) and nitrate (50 ppm) in drinking water set by WHO. The mu PAD revealed 95% recovery compared with the standard method UV-vis spectrophotometry (> 96%), which indicates the validity of the developed method. Furthermore, the application of mu PADs and UV-vis spectrophotometry for the analysis of Dire Dawa groundwater samples showed below the detection limit for nitrite. In contrast, 71 ppm of nitrate concentration was found in the ground water by using both methods. The concentration measured using mu PADs was in an excellent agreement with the values obtained from UV-vis spectrophotometry. This implies a potential use of the mu PADs for environmental monitoring of nitrate and nitrite in resources limited areas without the need for expensive benchtop analytical devices.

Automated summary

This study developed a simple and low-cost wax screen printing technique for the fabrication of microfluidic paper-based analytical devices (mu PADs). The mu PADs were successfully used for the determination of nitrite and nitrate ions in water samples, with detection limits that meet the concentration limits set by the WHO for drinking water. The mu PADs showed a high level of recovery compared to the standard UV-vis spectrophotometry method. Additionally, the mu PADs demonstrated potential for environmental monitoring in resource-limited areas.