DNA Labeling Generates a Unique Amplification Probe for Sensitive Photoelectrochemical Immunoassay of HIV-1 p24 Antigen.

Photoelectrochemical (PEC) immunoassay is an attractive methodology as it allows for an elegant and sensitive protein assay. However, advanced PEC immunoassay remains challenging and the established amplifications rely almost exclusively on the labeling of various enzymes, which usually suffer the inferior stabilities. Here we report the development and validation of the DNA labeling that leads to a unique amplification probe for the sensitive PEC immunoassay of HIV-1 capsid protein, p24 antigen, an important biomarker of human immune deficiency virus (HIV). Following the sandwich immunobinding, the DNA tags could be released and the subsequent dipurinization of the oligonucleotide strands enables the easy oxidation of free nucleobases at a CdTe quantum dots (QDs) modified ITO transducer. Such DNA tags induced PEC amplification and readout permits the exquisite assay of HIV-1 p24 antigen with high sensitivity. As compared to the existing method of enzymatic labeling, the easy preparation and stability of these labels make them very suitable for PEC amplification. Another merit of this method is that it separates the immunobinding from the PEC transducer, which eliminates the commonly existing affection during the biorecognition processes. This work paves a new route for the PEC immunoassay of HIV-1 p24 antigen and provides a general format for the PEC biomolecular detection by means of the DNA labeling.

[Phenolic constituents of Ampelopsis grossedentata from zhangjiajie].

OBJECTIVE: To study the phenolic constituents from Ampelopsis grossedentata. METHODS: Compounds were isolated using column chromatographic techniques (silica gel, polyamide gel, Sephadex LH-20) and semi-preparative HPLC. Structures were elucidated on the basis of spectral data (NMR and HR-MS). RESULTS: Eight compounds were isolated and identified as ampelopsin (I), 5, 7, 3',4',5'-pentahydroxyflavanone (II), galloyl-beta-D-glucopyranoside (III), gallic acid (IV), ethyl gallate (V), myricitrin (VI), (2R, 3S)-5,7,3',4',5'-pentahydroxyflavanonol (VII) and myricetin (VIII). CONCLUSION: Compounds II and VII are obtained from this genus for the first time.

[Content determination of two isomers containd in Garcinia hanburyi by HPLC].

OBJECTIVE: To establish a method for determing the content of two isomers containd in Garcinia hanburyi by HPLC. METHOD: Chromatographic column of SunFire (Waters) C8 (2.1 mm x 150 mm, 3.5 microm) was adopted, with acetonitrile-methanol-0.3% trifluoroacetic acid (36: 37:27) as the mobile phase. The detection wavelength was 360 nm,the flow rate was 0.3 mL x min(-1), and the column temperature was 28 degrees C. RESULT: The linear regression equation of r-gambogic acid was Y = 2.87 x 10(6) X - 2.24 x 10(5), r = 0.999 9. The linear regression equation of S-gambogic acid was Y = 3.31 x 10(6) X - 1.44 x 10(5), r = 0.999 9. The average recoveries were 100.0% and 100.9%, with RSD being 2.1% and 2.5% (n = 6), respectivley. The average contents of two gambogic acid in G. hanburyi were 30.06% and 21.45%, respectively. CONCLUSION: The method was so convenient and stable that it can be used for identification and content determination of two isomers containd in G. hanburyi.

[Determination of the total content of astragaloside IV in Radix Astragali].

OBJECTIVE: To determine the total content of astragaloside IV in Radix Astragali. METHODS: The measurement conditions were used as follows: Irregular C18 (4.6 mm x 250 mm, 5 microm) column; mobile phase: acetonitrile-water (32:68); flow rate: 1.0 ml/min; detector: ELSD 2000; the temperature of drift tube: 100 degrees C; gas flow: 2.7 L/min. RESULTS: Eight batches of Radix Astragali from different sources were determined. The stability, precision and reproducibility of the method were studied, RSD <3%. CONCLUSION: There is great difference between the content of astragaloside IV in Radix Astragali by different processing methods.

Stable Molecular Diodes Based on π-π Interactions of the Molecular Frontier Orbitals with Graphene Electrodes.

In molecular electronics, it is important to control the strength of the molecule-electrode interaction to balance the trade-off between electronic coupling strength and broadening of the molecular frontier orbitals: too strong coupling results in severe broadening of the molecular orbitals while the molecular orbitals cannot follow the changes in the Fermi levels under applied bias when the coupling is too weak. Here, a platform based on graphene bottom electrodes to which molecules can bind via π-π interactions is reported. These interactions are strong enough to induce electronic function (rectification) while minimizing broadening of the molecular frontier orbitals. Molecular tunnel junctions are fabricated based on self-assembled monolayers (SAMs) of Fc(CH2 )11 X (Fc = ferrocenyl, X = NH2 , Br, or H) on graphene bottom electrodes contacted to eutectic alloy of gallium and indium top electrodes. The Fc units interact more strongly with graphene than the X units resulting in SAMs with the Fc at the bottom of the SAM. The molecular diodes perform well with rectification ratios of 30-40, and they are stable against bias stressing under ambient conditions. Thus, tunnel junctions based on graphene with π-π molecule-electrode coupling are promising platforms to fabricate stable and well-performing molecular diodes.