Determination of nitrate and nitrite in human saliva with a specially designed microfluidic paper-based analytical device (μPAD)

The concentration of nitrite and nitrate anions in human saliva has been primarily believed to be correlated with oral cancer and other disfunctions and infections in the mouth. However, newly found benefits to the presence of these ions in the oral cavity have been reported in a few recent studies. In any case, there is a connection between the NOx salivary concentration and the human health and therefore it has become more and more relevant to understand this connection. In this context, the objective of this work was to develop microfluidic paper-based analytical devices (μPADs) for nitrite and nitrate determination (Figure 1) in human saliva samples. The choice of this type of approach is justified by the advantages provided by these devices, which make them ideally suited to conduct on-hand analyte determinations. While many of the current monitoring techniques require specialized skills, laborious laboratory processes, or/and expensive equipment, μPADs provide a very quick and cheap analytical measurement. Also, the minimal use of reagent and sample, coupled to its portability, makes the developed devices ideally suited for unskilled operators and regular monitoring. In this work, the determination of the nitrite and nitrate anions was based upon the modified colorimetric Griess reaction, in which the conversion of nitrate to nitrite was achieved using zinc powder.