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A benzothiazole-azo based sensor (BTAN) was developed for rapid and on-site detection of arginine. The sensor's selectivity in a semi-aqueous medium was thoroughly investigated, focusing on the colorimetric response to arginine in the presence of 11 different amino acids. Notably, the limit of detection (LOD) for arginine was determined to be 0.7 μM. The underlying sensing mechanism was addressed using 1 H-NMR and UV-vis spectroscopy. BTAN exhibited significant changes in both absorption as well as emission spectra exclusively in the presence of arginine. Furthermore, the arginine sensing capability was extended to the solid state by immobilizing BTAN into a starch-PVA hydrogel matrix as well as paper strips. The hydrogel film of BTAN enabled effective on-site sensing of arginine in a 100% aqueous medium. Moreover, the practicability of the sensor was demonstrated by detecting arginine in human blood samples.

The use of formalin to preserve raw food items such as fish, meat, vegetables etc . is very commonly practiced in the present day. Also, formaldehyde (FA), which is the main constituent of formalin solution, is known to cause serious health issues on exposure. Considering the ill effects of formaldehyde, herein we report synthesis of highly sensitive triphenylmethane based formaldehyde (FA) sensors from a single step reaction of inexpensive reagents namely 4-hydroxy benzaldehyde and 2,6-dimethyl phenol. The synthetic method also provides highly pure product in bulk quantity. The analytical activity of the triphenylmethane sensor 1 with a limit of detection (LOD) value of 2.31 × 10 -6 M for FA was significantly enhanced through induced deprotonation and thereafter a LOD value of 1.82 × 10 -8 M could be achieved. To the best of our knowledge, the LOD value of the deprotonated form (sensor 2) for FA was superior to those of all the FA optical sensors reported so far. The mechanism of sensing was demonstrated by 1 H-NMR titration and recording mass spectra before and after addition of FA to a solution of sensor 2. Both sensor 1 and sensor 2 exhibit quenching in emission upon addition of FA. A fluorescence study also demonstrates enhancement in analytical activity of the sensor upon induced deprotonation. Then the sensor was effectively immobilized into a hydrophilic and biocompatible starch-PVA polymer matrix which enabled detection of FA in a 100% aqueous system reversibly. Again, quick and effective sensing of FA in real food samples (stored fish) with the help of a computational application was demonstrated. The sensors have significant practical applicability as they effectively detect FA in real food samples qualitatively and quantitatively.

A novel colorimetric BODIPY-based probe for selective detection of fluoride and cyanide has been developed. The color of the solution significantly changes upon addition of fluoride and cyanide ions with detection limits of 2.2 × 10 -7 and 1.8 × 10 -7 M calculated by UV-vis absorption method for F - and CN - respectively. An unprecedented phenomenon about the interaction of cyanide ions with the probe was discovered which has not been reported yet. The green color of the paper strip in the presence of cyanide ions changes with time. This observation indicates that unlike fluoride, the cyanide ion interaction with the probe is beyond mere deprotonation of the phenolic group rather envisaged as nucleophilic addition reaction. The phenomenon was also observed in the solution phase and subsequently the reaction order and rate constant of the reaction were determined from absorption versus time graph which were found to be first order and 0.3465 s -1 respectively. The emission spectra also showed different behavior of interaction with time for the two ions. The rate of the reaction was found to be independent of the solvent polarity. The plausible mechanism of the reaction between cyanide and fluoride ions with the probe was proposed based on 1 H NMR titration experiments and mass spectrometry., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)