Yuxin Pei

A fluorescent probe for hydrazine and its in vivo applications

In aqueous solution, probe 1 selectively reacts with hydrazine (N2H4), leading to a 30.5-fold turn-on fluorescence response at 560 nm. Probe 1 can detect hydrazine in both solution and gas state by color changes from readily prepared strips. Furthermore, it was found that probe 1 is able to detect hydrazine in Hela cells.

Real-time and label-free analysis of binding thermodynamics of carbohydrate-protein interactions on unfixed cancer cell surfaces using a QCM biosensor.

A novel approach to the study of binding thermodynamics and kinetics of carbohydrate-protein interactions on unfixed cancer cell surfaces using a quartz crystal microbalance (QCM) biosensor was developed, in which binding events take place at the cell surface, more closely mimicking a biologically relevant environment. In this study, colon adenocarcinoma cells (KM-12) and ovary adenocarcinoma cells (SKOV-3) grew on the optimized polystyrene-coated biosensor chip without fixation. The association and dissociation between the cell surface carbohydrates and a range of lectins, including WGA, Con A, UEA-I, GS-II, PNA and SBA, were monitored in real time and without label for evaluation of cell surface glycosylation. Furthermore, the thermodynamic and kinetic parameters of the interaction between lectins and cell surface glycan were studied, providing detailed information about the interactions, such as the association rate constant, dissociation rate constant, affinity constant, as well as the changes of entropy, enthalpy and Gibbs free energy. This application provides an insight into the cell surface glycosylation and the complex molecular recognition on the intact cell surface, which may have impacts on disease diagnosis and drug discovery.

Polytriazole bridged with 2,5-diphenyl-1,3,4-oxadiazole moieties: a highly sensitive and selective fluorescence chemosensor for Ag+

Fluorescent conjugated polytriazoles (FCP 1–4) containing both 2,5-diphenyl-1,3,5-oxadiazole (OXD) and 1,2,3-triazole moieties in the main chain were synthesized from aromatic diazide (1) and dialkynes (2–5) via click polymerization, respectively. In the polymers, OXDs (fluorophores) and triazole rings (generated via CuAAC acting as metal ion ligands) comprise a fluorescent system. The polytriazoles displayed relatively strong emission with quantum yields in the range of 0.20–0.28 at room temperature in DMF. The study on their ion-responsive properties showed that, although all four FCPs have good selectivity for Ag+, the integration of alkoxy side groups (methoxy for FCP 2, hexyloxy for FCP 3 and 2-ethylhexyloxy for FCP 4) to the main chains of the polytriazoles decreased their sensitivity for Ag+ via alteration of the polymer aggregation status and electron density of the main chains. Thus FCP 1 is highly sensitive for Ag+, where its Ksv is as high as 1.44 × 105 M−1 and its lowest detection limit is in the ppb range (4.22 × 10−7 M). This study provides an efficient click approach to the synthesis of a novel fluorescence sensor for Ag+ detection, which could expand the application of click polymerization in designing fluorescence sensors based on the triazole unit.

Highly selective turn-on detection of (strept)avidin based on self-assembled near-infrared fluorescent probes

Selective detection and visualization of specific proteins are important in clinical diagnostics and biological research. For protein sensing, small-molecule-based fluorescent turn-on probes are preferable because of their high sensitivity, simplicity and detection with high-throughput. Herein we demonstrated a small molecular fluorescent dye (SQ-Biotin) which can self-assemble into a non-fluorescent probe in aqueous solution for near infrared turn-on detection of avidin protein. This probe consisting of a hydrophobic squaraine (SQ) as a fluorophore and a specific and strong protein ligand (biotin) formed self-assembled aggregates in aqueous solution (fluorescence off), and the aggregates of the probe disassembled in response to the target protein (avidin) through the specific protein–ligand interaction (fluorescence on). The conversion of the aggregation of SQ-Biotin was confirmed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The fluorescence intensities at 665 nm were linearly proportional to the concentration of avidin over the range of 0.76–1.46 μM. The detection limit was calculated to be about 70 nM. SQ-Biotin showed good selectivity to avidin over other proteins, enabling turn-on fluorescent detection of avidin in the near infrared region. The strategy demonstrated the great potential applicability of the self-assembled small-molecule-based fluorophores for protein sensing in clinical diagnosis.

Morphology-controlled dual clickable nanoparticles via ultrasonic-assisted click polymerization

Morphology-controlled dual clickable nanoparticles (DCNPs) were synthesized in one step via ultrasonic-assisted azide–alkyne click polymerization. The morphology of DCNPs was strongly dependent on the solvent and the co-monomer structure. Numerous unreacted alkynyl and azido groups on the surface of DCNPs facilitated the nanocarrier platforms for further functionalization via click chemistry.

One-step synthesis of dual clickable nanospheres via ultrasonic-assisted click polymerization for biological applications.

Dual clickable nanospheres (DCNSs) were synthesized in one step using an efficient approach of ultrasonic-assisted azide-alkyne click polymerization, avoiding the need of surfactants. This novel approach presents a direct clickable monomer-to-nanosphere synthesis. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and dynamic laser scattering (DLS) were used to characterize the synthesized DCNSs. Numerous terminal alkynyl and azide groups on the surface of DCNSs facilitate effective conjugation of multiple molecules or ligands onto a single nanocarrier platform under mild conditions. To exemplify the potential of DCNSs in biological applications, (1) multivalent glyconanoparticles (GNPs) were prepared by clicking DCNSs with azide-functionalized and alkyne-functionalized lactose sequentially for the determination of carbohydrate-galectin interactions with quartz crystal microbalance (QCM) biosensor. Using protein chip (purified galectin-3 coated on chip) and cell chip (Jurkat cells immobilized on chip), the QCM sensorgrams showed excellent binding activity of GNPs for galectins; (2) fluorescent GNPs were prepared by clicking DCNSs with azide-functionalized Rhodamine B and alkyne-functionalized lactose sequentially in order to target galectin, which is overexpressed on the surface of Jurkat cells. The fluorescent images obtained clearly showed the cellular internalization of fluorescent GNPs. This fluorescent probe could be easily adapted to drugs to construct lectin-targeted drug delivery systems. Thus, DCNSs prepared with our method may provide a wide range of potential applications in glycobiology and biomedicine.

Facile fabrication of glycopolymer-based iron oxide nanoparticles and their applications in the carbohydrate–lectin interaction and targeted cell imaging

A novel method for facile fabrication of glycopolymer-based iron oxide nanoparticles (GIONs) is developed. Via perfluorophenylazide photochemically induced C–H insertion, alkynyl groups were introduced onto the polymer which was precoated on the iron oxide nanoparticle surface. GIONs were then prepared by conjugating the azide-functionalized carbohydrate to the introduced alkynyl groups via click chemistry. Polyvinyl alcohol-coated and dextran-coated iron oxide NPs were chosen as scaffolds to attach two different carbohydrates, α-D-mannose and β-D-glucose, to fabricate multivalent GIONs, respectively. The multivalent GIONs demonstrated high binding affinities towards the corresponding lectins in both protein and cell chips. As a proof of concept, fluorescent GIONs (Gal-RhB-IONPs) were fabricated, which showed selective and efficient internalization by ASGP-R overexpressing HepG2 cells targeted.

Regioselective Benzoylation of Diols and Carbohydrates by Catalytic Amounts of Organobase.

A novel metal-free organobase-catalyzed regioselective benzoylation of diols and carbohydrates has been developed. Treatment of diol and carbohydrate substrates with 1.1 equiv. of 1-benzoylimidazole and 0.2 equiv. of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN under mild conditions resulted in highly regioselective benzoylation for the primary hydroxyl group. Importantly, compared to most commonly used protecting bulky groups for primary hydroxyl groups, the benzoyl protective group offers a new protection strategy.

Highly efficient green synthesis and photodynamic therapeutic study of hypericin and its derivatives

A highly efficient synthetic pathway for hypericin (7a) was achieved under mild conditions with an overall yield over two steps of 92% using emodinanthrone as a starting material, where protohypericin, a key precursor of hypericin, was synthesized in water with microwave assistance, which was then photocyclized to hypericin with a high yield via 1 h irradiation in a visible light reactor equipped with 575 nm monochromatic lamps. In addition, the method could be used to synthesize hypericin derivatives (7b–d) with similar overall yields. Furthermore, their effects of photodynamic therapy (PDT) were evaluated on A431, HepG-2, and MCF-7 cell lines. The PDT of 7b was better than that of 7a, whereas 7c and 7d were worse. Unlike other cell lines, MCF-7 was not sensitive to any of 7a–d at the same concentrations.

Optimization of 3D Surfaces of Dextran with Different Molecule Weights for Real-Time Detection of Biomolecular Interactions by a QCM Biosensor

Quartz crystal microbalance (QCM) has been extensively applied in real-time and label-free biomolecular interaction studies. However, the sensitive detection by QCM technology remains challenging, mainly due to the limited surface immobilization capacity. Here, a three-dimensional (3D) carboxymethyl dextran coated gold sensor chip surface was successfully fabricated with dextran of different molecular weight (100, 500 and 2000 kDa, respectively). To evaluate the 3D carboxymethyl dextran surface immobilization capacity, the 3D surface was used for studying antigen–antibody interactions on the QCM biosensor. The results showed that the protein immobilization capacity of the 3D carboxymethyl dextran (2000 kDa) surface exceeded more than 4 times the capacity of the 2D carboxyl surface, and 2 times the capacity of the traditional 3D carboxymethyl dextran (500 kDa) surface. Furthermore, the kinetic and affinity properties of antigen–antibody interactions were performed. Most notably, the optimized 3D carboxymethyl dextran (2000 kDa) surface could be used for small molecule detection, where the binding of biotinylated oligo (0.67 kDa) reached 8.1 Hz. The results confirmed that a 3D carboxymethyl dextran (2000 kDa) surface can be exploited for sensitive detection of low molecular weight analytes, which have great potential applications for characterizing the interactions between small molecule drugs and proteins.