A smartphone-assisted ratiometric colorimetric and fluorescent probe for triple-mode determination of nitrite based on MnO2 nanoparticles and carbon quantum dots

A triple-mode colorimetric and fluorescent sensing scheme based on manganese dioxide nanoparticles (MnO2NPs) and carbon quantum dots (CQDs) were developed to determine nitrite. MnO2NPs can oxidize 3,3 ',5,5 '-tetramethylbenzidine (TMB) into a blue oxidation product (TMBox), which is further oxidized into a yellow diimine derivative by nitrite. The ratio of absorbance at 652 nm to 452 nm was monitored as signal response for UV-vis detection mode. A turn-off CQDs fluorescence probe was also constructed for fluorescent detection mode. Smartphone tool kit was used to capture the color of sample for smartphone-based measure-ment. Various analytical performance under different detection modes were obtained and compared. The pro-posed methods were applied to food samples with satisfactory recoveries (83.3-106 %). The results were validated with AOAC standard spectrophotometric method. The current triple-mode detection were accurate, convenient, low-cost and fast for analyzing nitrite in foods and water samples on-site.

Automated summary

A triple-mode colorimetric and fluorescent sensing scheme based on manganese dioxide nanoparticles (MnO2NPs) and carbon quantum dots (CQDs) was developed for nitrite determination. The proposed methods, including UV-vis detection mode and fluorescent detection mode using a smartphone-based measurement, showed accurate and convenient detection of nitrite in food and water samples. The results were validated with the AOAC standard spectrophotometric method.