A Ratiometric Fluorescence Biosensor for Detection of Alkaline Phosphatase Via an Advanced Chemometric Model.

In this paper, a ratiometric fluorescence biosensor was introduced for alkaline phosphatase (ALP) detection based on 2-aminopurine (2-Amp) and thioflavin T (ThT)-G-quadruplex system. We designed a special DNA (5'-AGGGTTAGGGTTAGGGTTAGGGAAA/i2-Amp/AAAA-PO4-3', AP) modified with a phosphate moiety at the 3'-end, G-quadruplex at the 5'-end, and a fluorophore (2-Amp) in the middle. In the absence of ALP, the G-rich AP strand could be prone to fold into G-quadruplex structures in the presence of K+. Then, ThT combined with G-quandruplex, resulting in the enhancement of fluorescence emission peak at 485 nm. However, ALP-mediated hydrolysis of the 3'-phosphoryl end promoted the cleavage of AP by the exonuclease I (Exo I), releasing 2-Amp which displayed a strong fluorescence emission peak at 365 nm. Moreover, the quantitative fluorescence model (QFM) was derived for the analysis of the fluorescence measurements obtained by the proposed ratiometric fluorescent biosensor. With the aid of the advanced model, the proposed ratiometric fluorescent biosensor possessed satisfactory results for the detection of ALP in the human serum samples, with accuracy comparable to that of the reference method-the commercial ALP assay kit. Under the optimized experimental conditions, this method exhibited good selectivity and higher sensitivity, and the detection limit was found to be as low as 0.017 U/L. Therefore, it is reasonable to expect that the method had a great potential to detect ALP quantitatively in clinical diagnosis.

[Magnetic/luminescent quantum dots bifunctional nanoparticles labeling of rat bone mesenchymal stem cells].

OBJECTIVE: To evaluate the dual-labeling efficiency of magnetic and luminescent quantum dots bifunctional nanoparticles to rat bone mesenchymal stem cells (BMSC). METHODS: Rat BMSC were isolated, purified, and expanded. Magnetic/luminescent bifunctional nanoparticles (Fe(3)O(4)@CdTe@SiO(2)), were prepared by using silicon dioxide (SiO(2)) to encapsulate simultaneously Fe(3)O(4) and CdTe quantum dots. BMSC were incubated with the Fe(3)O(4)@CdTe@SiO(2) nanoparticles which iron concentration was 25 microg/ml. Fluorescence microscope was used to detect the fluorescence of the intracellular nanoparticles. The dual-labeled BMSC with various concentration underwent ex vivo MR imaging with T(1)WI, T(2)WI and T(2)(*)WI sequences. To show the intracellular iron of labeled cells, prussian blue stain was performed. Spectrophotometer was used to detect the iron concentration in the cells. RESULTS: Intracellular red fluorescence of Fe(3)O(4)@CdTe@SiO(2) can be observed via fluorescent microscopy. Rat BMSC could be effectively dual-labeled with approximately 90% efficiency. The MR images with T(2)WI and T(2)(*)WI sequences, especially with T(2)(*)WI sequence, showed that the signals of the dual-labeled BMSC were lower than those of the unlabeled cells. Cellular total iron is 14.05 + or - 4.15 pg per cell. Iron containing intracytoplasmic vesicles could be observed with Prussian blue staining. CONCLUSION: Rat BMSC can be dual-labeled successfully with Fe(3)O(4)@CdTe@SiO(2) magnetic/luminescent bifunctional nanoparticles successfully, and might serve as a tool for magnetic resonance imaging and in vivo optical imaging.

Amplification of fluorescence detection of DNA based on magnetic separation.

A novel nanoparticles-based fluorescence detection method has been developed by taking advantage of magnetic separation and amplified fluorescence detection. This DNA sensor relies on a "sandwich" hybridization strategy, in which the DNA targets are first hybridized to captured oligonucleotide probes immobilized on magnetic nanoparticles, and then hybridized with thiol-modified oligonucleotide probes immobilized on gold nanoparticles. Subsequently, the amplified DNA signals are detected in the form of bio-bar-code DNA using a chip-based fluorescence detection method. The result showed that the detection limit of target DNA probes is 1 pM. Complementary and mismatched sequences were clearly distinguished, and the ratio of the background-subtracted fluorescence values for complementary and single-base mismatched oligonucleotide was 2.12:1. This new system can be applied to both DNA detection and immunoassay, and has broad potential applications in disease diagnosis and immunoassay.