Leilei Tian

Graphene Oxides for Homogeneous Dispersion of Carbon Nanotubes

Graphene oxides (GOs) in terms of both structure and property are essentially polyelectrolytes in a two-dimensional sheet configuration. As is well-established in the literature, polyelectrolytes are, in general, good dispersion agents for single-walled carbon nanotubes (SWNTs), which are otherwise in bundles because of strong van der Waals interactions. We report here a study in which GOs were used to disperse SWNTs, both as-purified and separated semiconducting SWNTs, for solution-like homogeneous suspensions. As a demonstration for their potentials, the optically transparent dispersions were used in a more accurate determination of the absorptivities for the band-gap transitions in semiconducting SWNTs. Results on exploration of the use of the GO-dispersed SWNTs in the development of unique carbon nanocomposite materials are also presented and discussed.

Real-time detection of telomerase activity using the exponential isothermal amplification of telomere repeat assay.

As crucial pieces in the puzzle of cancer and human aging, telomeres and telomerase are indispensable in modern biology. Here we describe a novel exponential isothermal amplification of telomere repeat (EXPIATR) assay--a sensitive, simple, and reliable in vitro method for measuring telomerase activity in cell extracts. Through a strategically designed path of nucleic acid isothermal amplifications, EXPIATR abandons the expensive thermal cycling protocol and achieves ultrafast detection: telomerase activity equivalent to a single HeLa cancer cell can be detected in ∼25 min.

Enhancing-effect of gold nanoparticles on DNA strand displacement amplifications and their application to an isothermal telomerase assay

The exciting applications of gold nanoparticles (AuNPs) in bio-diagnostics are not limited to use as signal transduction probes; the fascinating effect of AuNPs on enhancing the reactions of nucleic acids has also been increasingly recognized. Herein, we explored the power of AuNPs and their enhancing effect on isothermal amplification reactions. The EXPIATR assay, based on a programmed path of isothermal strand displacement amplifications, has been proven to be a sensitive assay for telomerase activity. However, the assay is not applicable to the complex, protein-rich samples which more closely resemble real clinical specimens, since the abundant cellular proteins in the complex samples can impair the specificity of the amplification reactions. In the presence of AuNPs, the sensitivity of the detection of telomerase activity in complex samples is improved five-fold compared with the traditional assay, providing an efficient way to enhance the reliability of the EXPIATR assay to a new level. In addition to the situation of low-specificity caused by the external interference of cell lysates, it was further demonstrated that AuNPs showed a similar effect on improving the low-specificity caused by the polymerase, which implies that AuNPs affect the amplification reactions in a very fundamental way, presumably by enhancing the activity and stability of the amplification enzymes. By revealing and demonstrating the beneficial role of AuNPs in nucleic-acid reactions, this study provides a new avenue to promote the clinical applications of isothermal nucleic acid amplification.

Effective purification of single-walled carbon nanotubes with reversible noncovalent functionalization.

An effective purification method for single-walled carbon nanotubes (SWNTs) based on a combination of oxidative acid treatment and reversible noncovalent functionalization with 1-pyreneacetic acid is reported. The functionalization was selective toward the nanotubes, allowing a nearly complete removal of residual metal catalysts and carbonaceous impurities. The resulting highly pure SWNTs remained solvent-dispersible, a valuable feature to potential applications that require solvent-based processing. The functionalization agent could be recovered quantitatively and reused. Effects of the purification process on the composition and properties of the nanotube sample were evaluated.

Efficient blue organic light-emitting devices based on oligo(phenylenevinylene)

Highly bright and efficient blue organic light-emitting devices based on two oligo(phenylenevinylene) derivatives, 1,4-di(4′-N,N-diphenylaminostyryl)benzene (DPA-DSB) and 2,5,2′,5′-tetrastyryl-biphenyl (TSB), are fabricated. Using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) combined with 4,4′,4″-tri(N-carbazolyl) triphenylamine as the hole-transporting layer and DPA-DSB doped TSB as the blue emitter, a maximum luminous efficiency of 12.2 cd/A (corresponding to an external quantum efficiency of 6.2%) and a maximum power efficiency of 6.39lm∕W are obtained. The maximum brightness of 17350cd∕m2 is attained. These fairly high brightness and efficiencies are due to the efficient energy transfer from TSB to DPA-DSB and depression of concentration quenching by doping.

Fluorescence quenching effect of metal ions for α,α′-diamine containing conjugated polymers in solid films

The fluorescence quenching effect of the conjugated polymers P1 and P2 (the molecular recognitions are twisted 2,2′-bipyridine (bpy) and planar 1,10-phenanthrolin (phen), respectively) films upon the addition of metal ions has been studied. And the results showed that P2 exhibited stronger fluorescence quenching ability upon the addition of both transition metal ions and main group metal ions compared with that of P1. The 20° twist angle between the two consecutive pyridine rings of bpy unit in the P1 main chain is the reason for the weaker fluorescence quenching ability compared with P2, in which the planar phen unit can chelate with metal ions relatively freely without the conformational transition. So P2 is a kind of material with better properties for solid film devices, such as sensors for metal ions recognition.

DNA Hydrogel with Tunable pH-Responsive Properties Produced by Rolling Circle Amplification

Recently, smart DNA hydrogels, which are generally formed by the self-assembly of oligonucleotides or through the cross-linking of oligonucleotide-polymer hybrids, have attracted tremendous attention. However, the difficulties of fabricating DNA hydrogels limit their practical applications. We report herein a novel method for producing pH-responsive hydrogels by rolling circle amplification (RCA). In this method, pH-sensitive cross-linking sites were introduced into the polymeric DNA chains during DNA synthesis. As the DNA sequence can be precisely defined by its template, the properties of such hydrogels can be finely tuned in a very facile way through template design. We have investigated the process of hydrogel formation and pH-responsiveness to provide rationales for functional hydrogel design based on the RCA reaction.

Construction of Thermo-Responsive Elastin-Like Polypeptides (ELPs)-Aggregation-Induced-Emission (AIE) Conjugates for Temperature Sensing

In this work, an aggregation-induced emission (AIE) molecule (tetraphenylethene derivative, TPE-COOH) was conjugated to elastin-like polypeptides (ELPs40) via an amide bond to form ELPs40-TPE. The successful synthesis of ELPs40-TPE was confirmed by Circular Dichroism spectroscopy, gel electrophoresis, UV-vis absorption, and fluorescence emission spectroscopy. ELPs40-TPE possessed both amphiphilicity and the features of an AIE, and the fluorescence intensity was dependent on the local temperature. The Hela cells imaging indicated that ELPs40-TPE has great potential for bio-imaging applications because of its advantages of high fluorescence intensity, good water-solubility, and remarkable biocompatibility.

Highly Stable and Multiemissive Silver Nanoclusters Synthesized in Situ in a DNA Hydrogel and Their Application for Hydroxyl Radical Sensing

Oligonucleotide-stabilized silver nanoclusters (AgNCs) show promising applications in bioimaging and bio-/chemo-sensing. However, their unsatisfactory photostability limits their practical applications. In this work, fluorescent AgNCs were synthesized in situ in a DNA hydrogel, consisting of cross-linked enzymatically amplified polymeric DNAs with cytosine-rich sequences in the presence of Ag+. The fluorescence property of the resultant AgNCs was optimized by a rational design of the DNA sequences to cover a broad spectrum with comparable green and red emissions. Under the protection of the DNA hydrogel, the AgNCs showed significantly improved photostability in an ambient oxygen environment, as well as low cytotoxicity even at a high concentration. Therefore, these properties show the rolling-circle-amplification-stabilized AgNCs to be a promising possible fluorescent probe for the detection of reactive oxygen/nitrogen species (ROS/RNS) in live cells because red-emitting species are susceptible to oxidation and consequently convert to green-emitting species. Finally, the as-prepared AgNCs were demonstrated to be a sensitive and specific probe for cellular imaging and the monitoring of ROS/RNS levels, which broadens the applications of AgNCs and provides a new tool for related biological investigations.

Magnesium Stabilized Multifunctional DNA Nanoparticles for Tumor-Targeted and pH-Responsive Drug Delivery

Functional nucleic acids, which can target cancer cells and realize stimuli-responsive drug delivery in tumor microenvironment, have been widely applied for anticancer chemotherapy. At present, high cost, unsatisfactory biostability, and complicated fabrication process are the main limits for the development of DNA-based drug-delivery nanocarriers. Here, a doxorubicin (Dox)-delivery nanoparticle for tumor-targeting chemotherapy is developed taking advantage of rolling circle amplification (RCA) technique, by which a high quantity of functional DNAs can be efficiently collected. Furthermore, Mg2+, a major electrolyte in human body showing superior biocompatibility, can sufficiently condense the very long sequence of an RCA product and better preserve its functions. The resultant DNA nanoparticle exhibits a high biostability, making it a safe and ideal nanomaterial for in vivo application. Through cellular and in vivo experiments, we thoroughly demonstrate that this kind of Mg2+-stabilized multifunctional DNA nanoparticles can successfully realize tumor-targeted Dox delivery. Overall, exploiting RCA technique and Mg2+ condensation, this new strategy can fabricate nanoparticles with a nontoxic composition through a simple fabrication process and provides a good way to preserve and promote DNA functions, which will show a broad application potential in the biomedical field.