Colorimetric determination of nitrite in clinical, food and environmental samples using microfluidic devices stamped in paper platforms

This study reports the use of microfluidic paper-based analytical devices (mPADs) associated with colorimetric detection for the determination of nitrite in clinical, food and environmental samples. mPADs were fabricated by a simple and fast stamping process in a geometry containing eight circular detection zones and one central zone to sample inlet interconnected by microfluidic channels. The colorimetric determination of nitrite was performed through the modified Griess reaction. Detection zones were spotted with a 0.75 mL aliquot of a solution containing 50 mM sulfanilamide, 1.2 M hydrochloric acid and 4 mM N-(1-naphthyl) ethylenediamine. The monitoring of the background colorimetric response revealed good stability over 12 h for devices stored in the absence of light. After the addition of standard or real samples, the resulting images were captured with a scanner, converted to a color scale and analyzed in the magenta channel. The analytical sensitivity and the limit of detection achieved after a preconcentration stage were 0.56 (AU mu M-1) and 5.6 mu M, respectively. The preconcentration provided an enrichment factor of ca. 3.2 times. The concentration levels of nitrite were successfully determined in saliva, preservative water, ham, sausage and river water samples. The concentration levels attained for each sample using mPADs were compared to the values found by spectrophotometry and there was no significant difference from one another at a confidence level of 95%.