[en] The authors describe an aptamer based fluorometric assay for the determination of ATP. It is based on deoxyribonuclease I-aided target recycling and signal amplification. The DNA probe consists of two regions (sequences) that represent the capture probe and the signal probe, respectively. In the absence of ATP, the probe is adsorbed by the surface of graphene oxide (GO) via π-stacking interactions. This results in quenching of the fluorescent label (carboxyfluorescein) and protects it from being cleaved by DNase. Upon adding ATP, the probe will be repelled by GO because ATP binds to the aptamer. This triggers an increase in fluorescence as measured at excitation/emission wavelengths of 480/514 nm. The detection limit is as low as 0.2 nM, and the calibration plot is linear in the 10 to 400 nM ATP concentration range. The assay is specific and sensitive, and in our perception has a large potential in terms of detecting other species including pathogenic microorganisms, small molecules, metal ions, and proteins. < Image>.

[en] Silver nanoellipsoids (Ag NEs) with about 40 nm diameter minor axis and 100 nm major axis were prepared by a typical polyol process in the presence of poly(vinyl pyrrolidone), using Cl⁻ as etching agent at the early stage of synthesis and poly(ethylene glycol) at the later stage to control the size. A suspension of these kinds of Ag NEs can resist the coffee-ring effect and deposit uniform films after drying. By contrast, suspensions of spherical silver nanoparticles suffer the coffee-ring effect badly, always leaving a ring on the edge of patterns after evaporation is complete. The reasons behind these phenomena can be mainly attributed to the long-ranged interparticle attraction between Ag NEs that preserves them from being transported by Marangoni flows during the drying process. These Ag NEs will be very useful in the preparation of conductive inks. They can perform well in the solidification process of printed patterns, forming uniform and smooth films, greatly enhancing the printing efficiency. (paper)

[en] A graphene oxide (GO)–based fluorescent bioassay was developed to quantify agrA gene transcription (its mRNA) in methicillin-resistant Staphylococcus aureus (MRSA). This method is based on the use of Klenow fragment (KF)–assisted target recycling amplification and hybridization chain reaction (HCR). A triple complex was designed that contained a capture probe (CP), a trigger probe (TP), and a help probe (HP), which were partially complementary to one another. In the absence of the target, all the oligonucleotides labeled with carboxyfluorescein (FAM) are adsorbed onto the surface of GO by π-stacking interactions. This adsorption quenches the FAM signal. On the contrary, the target RNA causes the triple complex to disintegrate and initiates strand-displacement polymerization reaction (SDPR) and HCR in the presence of the appropriate raw materials, including the primer, KF, dNTPs, hairpin 1 (H1), and hairpin 2 (H2), generating double-stranded DNA (dsDNA) products. These dsDNA products are repelled by GO and produce strong fluorescence, measured at excitation/emission wavelengths of 480/514 nm. The fluorescent signal is greatly amplified by SYBR Green I (SGI) due to the synergistic effect of dsDNA-SGI. The target was assayed with this method at concentrations in the range 10 fM to 100 pM, and the detection limit (LOD) was 10 fM. This method also displayed good applicability in the analysis of real samples. It provides a new way of monitoring biofilm formation and studying the mechanisms of drug actions.