Two novel fluorescent probes were designed to detect the biothiol in foods using the highly efficient Michael addition reaction between maleimide-derived probes and the biothiol. First, maleimide functionalized GQDs (M-GQDs) were synthesized and used for biothiol identification according to the Michael addition principle. The biothiol can be detected in the range of 5 × 10 −9 to 4 × 10 −7 mol/L and the detection limit was 1.69 × 10 −9 mol/L. Then, a fluorescence resonance energy transfer (FRET) system between M-GQDs and tetrakis (4-aminophenyl) porphyrin (TAPP) for biothiol detection was developed. However, the process of FRET was switched off in the presence of biothiols due to the switch of M-GQDs fluorescence emission to the“ON” mode following the Michael addition mechanism. The system could quickly and accurately detect the biothiol with a detection range of 6.7 × 10 −10 to 2 × 10 −7 mol/L and a detection limit of 2.34 × 10 −10 mol/L. Compared to the single detection system, the FRET system had a wider detection range and lower detection limit, and the related biomolecules did not interfere with the quantitative identification of the biothiol. The proposed method was successfully applied for the determination of the biothiol in foods and human blood samples.
The authors describe a photometric method for the determination of free cholesterol based on the oxidation of cholesterol by the catalytic action of the enzyme cholesterol oxidase. The hydrogen peroxide formed is used to oxidize the chromogenic compound 3,3′,5,5′-tetramethylbenzidine (TMB) by exploiting the peroxidase-like activity of carbon nanotube-supported Prussian blue (PB). This enzyme mimic was synthesized from a mixture of ferric chloride and hexacyanoferrate(III) in the presence of intrinsically reducing multi-walled carbon nanotubes. The composite can trigger the formation of a blue-green dye from TMB in the presence of H 2 O 2 . The findings were exploited to design a photometric (652 nm) assay that has a linear response in the 4 to 100 μM cholesterol concentration range and a 3 μM detection limit. The practicability of the method was verified by the successful analysis of free cholesterol in human blood samples.
Schematic of a carbon nanotube-supported Prussian blue (PB/MWCNT) hybrid used as a promising peroxidase mimic. It has the advantages of low cost, simple synthesis, high activity, and good stability. PB/MWCNTs along with cholesterol oxidase (ChOx) are used in a colorimetric assay for the determination of free cholesterol.
Shuo Liu,Jianwen Wang,Yu-e Shi,Yongqing Zhai,Yun-kai Lv,Peng Zhang,Zhenguang Wang
Sulfur quantum dots (S-dots) show great potential for applications in various field, due to their favorable biocompatibility, high stability, and antibacterial properties. However, the use of S-dots in chemical sensing is limited by the lack of functional groups on the surface. In this work, a fluorescence glutathione (GSH) assay is developed based on the GSH modulated quenching effect of Cu 2 O nanoparticles (NP) on S-dots. The fluorescence of S-dots is effectively quenched after forming complex with Cu 2 O NP through a static quenching effect (SQE). Introducing of GSH can trigger the decomposition of Cu 2 O NP into GSH-Cu(I) complex, which leads to the weaken of SQE and the partial recover of the fluorescence. The intensity of recovered fluorescence shows a positive correlation with the concentration of GSH in the concentration range of 20 to 500 μM. The fluorescence GSH assay shows excellent selectivity and robustness towards various interferences and high concentration salt, which endow the successful detection of GSH in human blood sample. The presented results provide a new door for the design of fluorescence assays, which also provides a platform for the applications in nanomedicine and environmental science.
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