Novel microfluidic paper-based analytical devices (µPADs) for the determination of nitrate and nitrite in human saliva.

ABSTRACT

In this work, two different microfluidic paper-based analytical devices (µPADs) were developed for the quantification of nitrite and nitrate in human saliva samples, in order to aid in the diagnosis of some diseases and health conditions associated with these ions. The development of these nitrite and nitrate µPADs involved several studies to optimize their design and construction, including an interference assessment and stability studies. These µPADs allowed a nitrite determination in a range of 5-250 µM with limits of detection and quantification of 0.05 µM and 0.17 µM, respectively, and a nitrate determination in the range 0.2-1.2 mM with limits of detection and quantification of 0.08 mM and 0.27 mM, respectively. As for the stability, both of the µPADs were stable when stored in vacuum at 4 °C (the nitrite µPAD for at least 60 days and the nitrate µPAD for at least of 14 days) and, after the sample placement, the nitrite and nitrate µPADs could be scanned within the first 4 and 2 h, respectively. The nitrite µPAD measurements were compared with the ones obtained from the standard colorimetric method and there were no statistically significant differences between these two methods. To evaluate the accuracy of nitrate µPAD measurements, 4 certified water samples were used and recovery studies using saliva samples were performed.