Colorimetric and fluorogenic detection of nitrite anion in water and food based on Griess reaction of fluorene derivatives

New Griess reagents for nitrite determination were developed using two fluorene derivatives; 2-amino-7-bromofluorene (ABF) and 2-amino-7-bromo-9,9-dimethylfluorene (ABDF). The system of ABF is colorimetric sensor while the ABDF system is a dual-mode colorimetric and fluorogenic sensor. The diazotization reaction of ABF, NO2- , and beta-naphthol in acid solution provided azo-dye product and led to an obvious color change from colorless to pink. The same reaction with ABDF displayed the color change to pink and a fluorescence quenching of ABDF emission. Under the optimal condition, colorimetric response, fluorogenic response, anion competition and detection limitation toward NO2- were determined using naked eye observation, UV-Vis and fluorescence technique. The lowest LOD (0.0007 mg L-1) was obtained from fluorescent method of ABDF. In addition, nitrite anion in different ham types were successfully analyzed using ABDF and fluorescent method which presented satisfactory performance parameters such as working range (0.0024 - 0.020 mg L-1), %recovery (83.36-107.68) and %RSD (0.26-3.77). According to paired t-test at a 95% confidence level, there was no significant differences between the results from the ABDF and those from the reference method. The practical application of ABF/ABDF sensors based on hydrogel indicator can be used for on-site monitoring of NO2- with a high sensitivity and selectivity by showing the same results of naked-eye color change and fluorescence turning off.