Fluorescence Turn-On Detection of Ascorbic Acid Using a Self-Assembled Lanthanide Polymer Nanoparticle

A novel biosensor for detecting vitamin C in milk powder based on Hg2+-mediated DNA structural changes

Background:

Detection of Vitamin C (Vc) is very important to protect human health. A lot of methods have been developed for the detection of Vc. However, many methods require complex material preparation and skilled operators. Thus, a simple, label-free biosensor is still urgently needed.

Methods:

In this work, N-methylmesoporphyrin IX (NMM)/G-quadruplex pair was used as a label-free signal reporter. Without Vc, the G-quadruplex DNA and its incomplete complementary chain could form duplex structure by T-Hg(II)-T mismatch. In this case, the G-quadruplex structure could not be formed. When Vc was added, the Hg2+ was reduced to Hg(0). Then, the G-quadruplex DNA became free and formed G-quadruplex structure to emit fluorescence signal.

Results:

Under optimal conditions, this biosensor showed a good linear response in the range of 0.2 - 4.0 μM and a low limit of detection (19.9 nM). This biosensor also had good selectivity towards Vc. Meanwhile, the satisfactory recovery rates (93.2%-102.8%) suggested that this biosensor had attractive potential for measuring Vc in real samples.

Conclusion:

In this work, a simple label-free fluorescent biosensor for the detection of Vc based on Hg2+-mediated DNA structural changes had been developed. The whole experiment was simple and all reagents were commercialized. The label-free detection was realized by NMM/G-quadruplex as a signal reporter. This biosensor was very sensitive with a low limit of detection. And it had a potential practical application for the Vc detection in milk powder.

Ratiometric fluorescence detection of sulfide ions based on lanthanide coordination polymer using guanosine diphosphate as ligand

The efficiency of energy transfer from guanine nucleotide to terbium ion (Tb³⁺) is affected by the phosphate group significantly. Compared with the biomolecules 5'-GMP (guanosine monophosphate), guanosine diphosphate (GDP) exhibits better sensitize ability to Tb³⁺ ions luminescence. Assisted with the carboxycoumarin ligand, we synthesized a more stable optical Coumarin@GDP-Tb polymer with the characteristic emission peaks located on 440 nm and 545 nm in this work. The Coumarin@GDP-Tb polymer is not only rich in metal binding sites, but also maintains a moderate ionic binding force, which helps metal ions to bind or leave it easily. Experiment result shows that Coumarin@GDP-Tb polymer has the appropriate binding force for Fe²⁺ ions, which can be destroyed by sulfur ions (S^2-) as the formation of FeS precipitation. Based on this, Coumarin@GDP-Tb was designed as the ratio fluorescence probe for sulfur ions detection, where the fluorescence at 545 nm can be selectively quenched by Fe²⁺ ions, while that at 440 nm was unaffected, in the presence of S^2- ions, the quenched fluorescence can be recovered remarkably. With the increasing S^2- ions from 0.1-45 μM, the ratio of fluorescence intensity at 545 nm to 440 nm (F₅₄₅/F₄₄₀) is linear to S^2- concentration, and the detection limit of S^2- was calculated to be 0.073 μM. Contrast to those fluorescence probes with single wavelength emission, Coumarin@GDP-Tb displays a comparable sensitivity, the introduced self-adjust wavelength improved the detection accuracy efficiently. The above 98.1 % recovery rates of S^2- ions in the actual water sample demonstrated the practicability of Coumarin@GDP-Tb fluorescence probe.