1-m-Nitrobenzoyl semicarbazide: reversible colorimetric cascade indicators for fluoride and moisture

Abstract

Colorimetric indicators can provide quick results for instant, in-field detection of analytes without expensive equipment and expertise. A simple, cost-effective 1-m-nitrobenzoyl semicarbazide based indicator has been developed for reversible colorimetric cascade detection of fluoride and moisture. The detection is highly selective for fluoride over other halides and different anions. On addition of fluoride, a sharp brown colour appeared immediately and fluorescence quenching was observed. The fluorescence turn off is due to complex formation with fluoride, almost immediately and can be observed with the naked eye, which is necessary for a real-time sensor without any sophisticated and expensive instruments and quicker response time. Moreover the 1-m-nitrobenzoyl semicarbazide–fluoride complex acts as a reusable probe for moisture showing high selectivity, sensitivity, instant response and stability. In the presence of moisture, the sharp brown colour disappears immediately and the fluorescence bounces back. The entire detection process is reversible in nature and helps to develop a re-writable device and an encryption–decryption system as security ink.