A novel ratiometric colorimetric sensor for detecting hypochlorite and ascorbic acid based on cascade reaction.

Hypochlorite and ascorbic acid (AA), play an indispensable role in numerous physiological activities. Herein, a ratiometric colorimetric sensing strategy for the determination of hypochlorite and AA was developed via the catalytic oxidation and reduction of 3,3',5,5'-tetramethylbenzidine (TMB). Interestingly, in the presence of Fe3O4-MOF-5(Fe) and hypochlorite, TMB complexes in acidic environments were oxidized to blue oxidized TMB and further diazotized to produce yellow-green diazotized TMB, resulting in the hypochlorite concentration-dependent ratiometric variation for the absorbance at 652 and 450 nm (A450/A652). Moreover, the diazotized TMB was restored to colorless TMB due to the reducibility of AA, and the detection limit of hypochlorite and AA were 0.027 and 0.677 µM, respectively. The ratiometric colorimetric sensing platform offered higher sensitivity and better selectivity because of the specific hypochlorite-induced reaction and the excellent peroxidase-like activity of Fe3O4-MOF-5(Fe). The proposed novel strategy provided the guidance to develop sensors for successive detection of hypochlorite and AA in complicated samples.

ß-CD@AgNPs with peroxisase-like activity for colorimetric determination of chiral tryptophan.

Different enantiomer forms of amino acids play different roles in multifarious fields, and improper use will cause irreversible effects. Therefore, the identification of chiral amino acids is a vital issue in the field of pharmaceutical analysis. Herein, a chiral sensing system of ß-cyclodextrin coated silver nanoparticle (ß-CD@AgNPs) with peroxidase-like activity was designed for the fast and efficient colorimetric identification of tryptophan (Trp) enantiomers based on the difference in binding capacity between D/L-Trp and ß-CD. The results showed the satisfactory linearity for detecting D/L-Trp over the concentration range from 0.2 to 4 mM with a LOD of 0.16 and 0.18 mM, respectively. Moreover, the absorbance increased linearly with the rise of D-Trp concentration percentage in the Trp enantiomer mixture. The proposed method avoided the use of natural enzymes and improved the stability due to the protective effect of cyclodextrin, which provided a new idea for selective colorimetric recognition and detection of D/L-Trp based on cyclodextrin.