Jinhua Liu

Graphene Signal Amplification for Sensitive and Real-Time Fluorescence Anisotropy Detection of Small Molecules

Fluorescence anisotropy (FA) is a reliable, sensitive, and robust assay approach for determination of many biological targets. However, it is generally not applicable for the assay of small molecules because their molecular masses are relatively too small to produce observable FA value changes. To address this issue, we report herein the development of a FA signal amplification strategy by employing graphene oxide (GO) as the signal amplifier. Because of the extraordinarily larger volume of GO, the fluorophore exhibits very high polarization when bound to GO. Conversely, low polarization is observed when the fluorophore is dissociated from the GO. As proof-of-principle, the approach was applied to FA detection of adenosine triphosphate (ATP) with a fluorescent aptamer. The aptamer exhibits very high polarization when bound to GO, while the FA is greatly reduced when the aptamer complexes with ATP, which exhibits a maximum signal change of 0.316 and a low detection limit of 100 nM ATP in buffer solution. Successful application of this strategy has been demonstrated that it can be constructed either in a signal-off or in a signal-on detection scheme. Moreover, because FA is less affected by environmental interferences, FA measurements could be conveniently used to directly detect as low as 1.0 μM adenosine triphosphate (ATP) in human serum. The universality of the approach could be achieved to detect an array of biological analytes when complemented with the use of functional DNA structures.

Silver ions-mediated conformational switch: facile design of structure-controllable nucleic acid probes.

Conformationally constraint nucleic acid probes were usually designed by forming an intramolecular duplex based on Watson-Crick hydrogen bonds. The disadvantages of these approaches are the inflexibility and instability in complex environment of the Watson-Crick-based duplex. We report that this hydrogen bonding pattern can be replaced by metal-ligation between specific metal ions and the natural bases. To demonstrate the feasibility of this principle, two linear oligonucleotides and silver ions were examined as models for DNA hybridization assay and adenosine triphosphate detection. The both nucleic acids contain target binding sequences in the middle and cytosine (C)-rich sequences at the lateral portions. The strong interaction between Ag(+) ions and cytosines forms stable C-Ag(+)-C structures, which promises the oligonucleotides to form conformationally constraint formations. In the presence of its target, interaction between the loop sequences and the target unfolds the C-Ag(+)-C structures, and the corresponding probes unfolding can be detected by a change in their fluorescence emission. We discuss the thermodynamic and kinetic opportunities that are provided by using Ag(+) ion complexes instead of traditional Watson-Crick-based duplex. In particular, the intrinsic feature of the metal-ligation motif facilitates the design of functional nucleic acids probes by independently varying the concentration of Ag(+) ions in the medium.

Green chemistry for large-scale synthesis of semiconductor quantum dots.

Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190-230 degrees C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs.

Microwave-mediated nonaqueous synthesis of quantum dots at moderate temperature.

The use of microwave irradiation to accelerate both inorganic and organic chemical reactions has attracted widespread attention. Generally, microwave-mediated synthesis of quantum dots (QDs) has been conducted in aqueous solution. Here, using commercial diesel and glycerol as reaction medium, a microwave-mediated nonaqueous method toward CdSe QDs with size-tunable photoluminescent properties produces oleic-acid-protected QDs at moderate reaction temperatures of 50-140 degrees C, which are much lower than the current temperature necessary for the synthesis of CdSe QDs in organic solvents. The appropriate condition optimization for high-quality CdSe QDs shows that different sizes of CdSe QDs with emission wavelengths between 450 and 600 nm have been synthesized through varying time, temperature, feed ratio, and reaction medium.

Fluorescence turn-on and colorimetric dual readout assay of glutathione over cysteine based on the fluorescence inner-filter effect of oxidized TMB on TMPyP.

Quantitative fluorescence turn-on and colorimetric detection of glutathione (GSH) with rapid speed, low cost have attained much attention. Herein, we developed a sensitive fluorescence turn-on and colorimetric sensor for GSH based on the inner-filter effect (IFE), which is the first time to select oxTMB and TMPyP as the IFE absorber and fluorophore pair, respectively. The absorption band of oxTMB matches well with the emission band of TMPyP in the IFE-based fluorescent assay. In the absence of GSH, the absorption peak of oxTMB at 652nm significantly overlaps with the emission of TMPyP, resulting in the efficient IFE and inhibition of the fluorescence of TMPyP. In the presence of GSH, the absorption intensity at 652nm decreases, generating the recovery of the fluorescence of TMPyP. Therefore, this approach is demonstrated to be a novel candidate for detection of GSH, with high sensitivity and selectivity. The linear dynamic range for the concentrations of GSH is between 0.1μM to 20μM along with a limit of detection (LOD) of about 30nM (calculated LOD as 3σ/slope). Finally, this novel sensor was successfully applied for GSH detection in fetal calf serum, and satisfactory recovery was achieved.

A facile and rapid route for synthesis of g-C3N4 nanosheets with high adsorption capacity and photocatalytic activity

A graphitic carbon nitride (g-C3N4) nanosheet and its nanocomposites have recently attracted increasing interest due to their massive potentials in applications ranging from fluorescence imaging to solar energy conversion. An economical mass-production method for the synthesis of g-C3N4 nanosheets is urgently needed for the application of these intriguing nanomaterials. Here we develop a facile and rapid route to synthesize g-C3N4 nanosheets by using chemical exfoliation followed by extraction and thermal treatment. The feature of this approach lies in its rapid speed with exfoliation time of only about one minute and facile operation free of long-time ultrasonication or stirring, filtration and repeated washing processes to remove the residual acid. Moreover, the method is high-yield and easily upscalable. Meanwhile, the exfoliated g-C3N4 nanosheets exhibit high adsorption capability and photocatalytic activity due to the synergistic effects of large surface area, decreased recombination probability of photoinduced electron–hole pairs and enlarged band gap. This simple and rapid route enables the possibility of large-scale synthesis of g-C3N4 nanosheets with high yield, thus promoting their application in environmental purification and solar energy conversion.

Molecule-binding dependent assembly of split aptamer and γ-cyclodextrin: a sensitive excimer signaling approach for aptamer biosensors.

A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively.

Noncovalent assembly of carbon nanoparticles and aptamer for sensitive detection of ATP

Coupling carbon nanomaterials with biomolecular recognition events for sensor design has attracted great interest in the development of efficient bioanalytical tools. Here, based on competitive interaction of electrostatic repulsion and π–π stacking, noncovalent assembly of carboxylated carbon nanoparticles (cCNPs) with aptamer that allows sensitive and selective detection of ATP is reported. The sensor exhibits minimal background fluorescence, due to the extraordinarily high quenching efficiency of cCNPs with a spherical structure. Importantly, the quenched fluorescence is recovered with the addition of ATP within several minutes; the limit of detection is as low as 0.1 μM in the range of 0.1–300 μM, since only one end of the aptamer needs the modification, the present approach is simple and cost-effective. Furthermore, compared to the analog design based on the “pre-mixing” strategy, the assay of the “post-mixing” strategy increases by approximately 1.5 times in signal-to-background (S/B) and possesses a quicker response time (within two minutes). Depending on the spherical structure of the cCNPs and the rapid kinetic response, this assay can be expected to provide a new and ultrasensitive platform for the detection of various small molecules.

Signal-amplification and real-time fluorescence anisotropy detection of apyrase by carbon nanoparticle

Carbon nanomaterial combined with aptamer has been developed as an efficient bioanalytical method in sensor design. Herein, depending on carbon nanoparticle (cCNP)-enhanced fluorescence anisotropy (FA), a novel aptamer-based sensor (aptasensor) enabling signal-amplification and real-time detection of apyrase is reported. The foundation of our sensor design based on ATP-aptamer(P) can be adsorbed on the surface of cCNPs, resulting in the increase of FA due to the mass of cCNPs, and P-ATP complex has weak binding ability to cCNPs with minimal change of FA. Apyrase, being an integral membrane protein, can hydrolyze ATP and make P-ATP complex disassemble, and thus lead to the increasing of FA. Therefore, this approach is demonstrated to be a novel candidate for the detection of apyrase, with high sensitivity and selectivity. The linear dynamic range for the concentrations of apyrase is between 0.1 and 0.5 U/μL along with a detection limit of 0.05 U/μL. Furthermore, these results indicated that our design is a flexible and sensitive method for biomolecule analysis, which makes it promising for practical biomolecule analyses.

Local atomic structures of amorphous Pd80Si20 alloys and their configuration heredity in the rapid solidification

ABSTRACT The local atomic structures of amorphous Pd80Si20 alloys and their configuration heredity in the rapid solidification are investigated by a molecular dynamics simulation with the help of cluster-type index method based on Honeycutt–Anderson bond-type index and an inversely tracking technique of atomic trajectories. Their short-range orders are found to be various Kasper clusters as well as their distorted configurations, and among which (10 2/1441 8/1551) bi-capped square Archimedean anti-prism (BSAP) clusters are dominated, e.g. Si-centred Pd10Si1 clusters. These Kasper clusters mainly exist in the form of isolated basic clusters. Few medium-range orders can be detected, especially for Si-centred Kasper clusters. Similarly to icosahedrons of Cu–Zr amorphous alloys, their sustainable configuration heredity also occurs firstly in the super-cooled liquid region, and BSAP clusters have higher onset temperature Tonset and bigger descendible fraction F than other Kasper clusters in the rapid solidification of Pd80Si20 alloys.