Chemical switch based reusable dual optoelectronic sensor for nitrite

An optical sensor was developed for sensing of nitrite based on the monotonous decrease in absorbance of Rhodamine 6G at 525 nm (the absorbance maximum of dye) with increasing concentration of nitrite. This sensor also permits naked eye detection. Various parameters like concentrations of sulphuric acid and Rhodamine 6G, response time and stability were varied and optimal conditions are reported. Under these conditions, the developed sensor enables the determination of nitrite in the concentration range 0–12.18 μmol L−1. The nitrite response is selective as 60–2.5 × 105 fold amounts of several anions and cations have no deleterious effect. The addition of nitrite to Rhodamine 6G dye causes hypsochromic shift from 525 to 385 nm while several other anions like I−, SCN−, ClO4−, [HgI4]2− and [Zn (SCN)4]2− showed a bathochromatic shift from 525 to 575 nm. The sequential addition of nitrite and sulphamic to Rhodamine 6G in 0.75 mol L−1 sulphuric acid solution results in switching of “ON” and “OFF” absorbance. The time elapse and concentration of sulphamic acid required for chemical switching was also established. Similar “ON” and “OFF” switching behaviour was observed in fluorescence studies also. This enabled the design and development of reusable chemical switch based dual optoelectronic sensor, for monitoring of traces of nitrite in environmental and food samples. The plausible mechanism for above switching behaviour is also proposed.