A smartphone-assisted ratiometric fluorescence and colorimetric detection of nitrite based on 2, 3-diaminonaphthalene and gold nanoclusters paper strip

A smartphone-assisted fluorescent and colorimetric detection method for nitrite based on 2,3-diaminonaphthalene (DAN) and gold nanoclusters (AuNCs) paper strip was developed. DAN reacts with NO 2 - via a coupling reaction under acidic conditions to generate naphthotriazole (NAT), emitting strong blue fluorescence at 435 nm. The red fluorescence of AuNCs at 650 nm is quenched by the reduction of nitrite. The ratio of fluorescent intensity (I 435 /I 650 ) exhibits a good linear relationship with NO 2 - concentration (0.01–9.0 μg/mL), with LOD and LOQ of 2.3 μg/L and 8.7 μg/L, respectively. The fluorescent detection mode was successfully applied to the determination of nitrite in water and food samples, with recoveries ranging from 80.0 % to 103.0 %. Furthermore, a smartphone-integrated paper strip platform was designed for on-site colorimetric analysis. It was noteworthy that the strip's fluorescence color transitions dynamically from red to blue under ultraviolet light, thereby enabling visual semi-quantification.