Dual Colorimetric and Ratiometric Fluorescent Responses for the Determination of Glutathione Based on Fluorescence Quenching and Oxidase-Like Activity of MnO₂ Nanosheets

Abstract

A dual colorimetric and ratiometric fluorescent assay is constructed for the detection of glutathione (GSH) based on MnO 2 nanosheets (MnO 2 NS). Amplex Red (AR) and curcumin (CUR) fluorescence-pairing probes have opposite responses to MnO 2 NS with fluorescence quenching and oxidaselike property. MnO 2 nanosheets can largely quench the fluorescence of curcumin. However, the fluorescence of oxidized AR (oxAR) was obviously raised via the catalytic oxidation reaction of no fluorescent AR. The color of the solution gradually changes from yellow to orange. However, MnO 2 nanosheets lose the fluorescence quenching capacity and oxidase-like property after the addition of GSH. Therefore, the fluorescence intensity of curcumin shows an obvious increase and the intensity of oxAR a decrease, accompanied by the restoration of the solution color from orange to yellow. For MnO 2 nanosheets, the linear relationship between the absorbance ratio of the two substrates and the GSH concentration (50−15 000 nM) is obtained with the detection limit of 16 nM. Besides, the ratiometric fluorescent method has a good linear range from 10 to 5000 nM for GSH. The detection limit is as low as 4.2 nM. Further, this method can not only be used for the determination of GSH in an aqueous solution but also shows a high responsive ability to GSH in human serum. This result indicates its potential in bioanalysis and disease diagnosis.

Au Nanocrystals@Defective Amorphous MnO2 Nanosheets Core/Shell Nanostructure with Effective CO2 Adsorption and Activation toward CO2 Electroreduction to CO

“…For Au NCs@a-MnO 2 -60 NSs, two peaks at 84.0 and 87.7 eV in Au 4f spectrum were Au 4f 7/2 and Au 4f 5/2 of Au 0 , respectively (Figure a) . The Mn 2p doublets at 642.1 and 653.9 eV were Mn 2p 3/2 and Mn 2p 1/2 of Mn 4+ , respectively, with the satellite peak of Mn 4+ at 644.6 eV (Figure b). , In the O 1s XPS spectrum, the binding energies at 529.7 and 532.9 eV were the metal–O bonds and hydroxide species at the product’s surface, respectively, whereas the peak at 531.3 eV corresponded to defect sites with low oxygen coordination (Figure c). − Notably, the binding energies of Au 4f in Au NCs@a-MnO 2 -60 NSs and Au NCs@c-MnO 2 NSs shifted to lower values than those of Au NCs (Figure d), whereas the binding energies of Mn 2p in Au NCs@a-MnO 2 -60 NSs and Au NCs@c-MnO 2 NSs shifted to higher values compared to those in a-MnO 2 NSs and c-MnO 2 NSs (Figure e). These results demonstrated that the electrons were transferred from Mn to Au in Au NCs@a-MnO 2 -60 NSs and Au NCs@c-MnO 2 NSs, making Au NCs core electron-rich and MnO 2 NSs shell electron-deficient.…”

Universal Nanoplatform for Formaldehyde Detection Based on the Oxidase-Mimicking Activity of MnO2 Nanosheets and the In Situ Catalysis-Produced Fluorescence Species

“…24 Moreover, the strategy of using the nanoprobes such as AuNCs and fluorescence polydopamine nanoparticles was relatively complex and their fluorescence properties may be greatly affected by the microenvironment. 25 Another unique property of MnO 2 nanosheets or nanoflakes is their oxidase (OXD)-or peroxidase-like activity, which has also attracted much attention. 26,27 The mimicking properties can be used in construction of colorimetric sensors for the rapid qualitative analysis of various substrates.…”

“…26,27 The mimicking properties can be used in construction of colorimetric sensors for the rapid qualitative analysis of various substrates. 28,29 Compared with the colorimetric sensing, fluorescence analysis is more sensitive. Meanwhile, in situ formation of fluorescence species as the signal output based on the nanozyme activity of MnO 2 may be more convenient because there is no need to synthesize fluorescent nanoprobes with higher purity.…”

“…In many of these MnO 2 -based systems, luminescent probes were utilized, whose fluorescence intensity may be greatly affected by the quencher of MnO 2 nanosheets . Moreover, the strategy of using the nanoprobes such as AuNCs and fluorescence polydopamine nanoparticles was relatively complex and their fluorescence properties may be greatly affected by the microenvironment . Another unique property of MnO 2 nanosheets or nanoflakes is their oxidase (OXD)- or peroxidase-like activity, which has also attracted much attention. , The mimicking properties can be used in construction of colorimetric sensors for the rapid qualitative analysis of various substrates. , Compared with the colorimetric sensing, fluorescence analysis is more sensitive.…”

“…Moreover, the strategy of using the nanoprobes such as AuNCs and fluorescence polydopamine nanoparticles was relatively complex and their fluorescence properties may be greatly affected by the microenvironment . Another unique property of MnO 2 nanosheets or nanoflakes is their oxidase (OXD)- or peroxidase-like activity, which has also attracted much attention. , The mimicking properties can be used in construction of colorimetric sensors for the rapid qualitative analysis of various substrates. , Compared with the colorimetric sensing, fluorescence analysis is more sensitive. Meanwhile, in situ formation of fluorescence species as the signal output based on the nanozyme activity of MnO 2 may be more convenient because there is no need to synthesize fluorescent nanoprobes with higher purity.…”