Thread-based platform for nitrite detection based on a modified Griess assay

A new thread-based platform for colorimetric detection of nitrite was developed based on a modified Griess assay. Cellulose thread was chemically modified with a p-aminobenzoyl group and impregnated with chromotropic acid as a coupling reagent. The functionalization of the thread was confirmed by Raman spectroscopy. The diazotization and coupling reaction occurred along the length of the thread to produce a colored band in the presence of nitrite. This allowed the measurement of the length of thread in relation to nitrite concentration. In this method, the optimum concentration of chromotropic acid for nitrite detection was 5 mM in 0.10 M sulfuric acid mixed with 0.2 M citric acid. With a sample volume of 15 mu L, the obtained working range for nitrite detection was from 50 to 1000 mu M, where the lowest nitrite concentration that could produce color on the platform was 25 mu M. The proposed method was successfully used to detect nitrite in three different types of samples with acceptable recoveries (92.4-115.4 %) and Relative Standard Deviation (RSD) (4.3-10.4 %).