Guolin Zhang

Carbon nanodots as a fluorescence sensor for rapid and sensitive detection of Cr(VI) and their multifunctional applications

In this work, carbon nanodots (CDs) were prepared via a green and convenient microwave assisted pyrolysis of ionic liquids (ILs) and ethylenediamine. It was found that the synthesized IL-based CDs (ILCDs) exhibited a superior selective sensitivity for Cr(VI). Photoluminescence (PL) properties of the ILCDs were applied to determine the concentration of Cr(VI), which showed a wide linear range and a low detection limit. We also received promising results by using the ILCDs for Cr(VI) detection in real samples. Moreover, the synthesized ILCDs can also work as a PL nanosensors to determine temperature and pH value in solution.

Carbon Nanodots-Based Fluorescent Turn-On Sensor Array for Biothiols

Biothiols play important roles in biological processes. In this study, a novel sensor array-based method was proposed to detect and differentiate biothiols. The sensor array was constructed using three kinds of Ag+-sensitive carbon nanodots (CDs). The CDs were synthesized with amino acids and urea as carbon sources via a simple microwave method. Results revealed that Ag+ can bind with CDs and depress the fluorescence of CDs, while the subsequently joined biothiols can take Ag+ away from CDs and recover the fluorescence of CDs. Due to the different binding ability between Ag+ and various CDs, as well as Ag+ and various biothiols, the CD-Ag+ array exhibits a unique pattern of fluorescence variations when interacting with six biothiol samples (cysteamine, dithiothreitol, mercaptosuccinic acid, glutathione, mercaptoacetic acid, and mercaptoethanol). Principal component analysis (PCA) was applied to analyze the pattern and generate a clustering map for a clearer identification of these biothiols. PCA can also be employed to simplify the established three-sensor array into a two-sensor array. Both the three- and two-sensor arrays can identify these biothiols in a wide biothiol concentration range (>10 μM).

Synthesis and self-assembly of new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) block copolymers via the combination of ring-opening polymerization and click chemistry

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by click reaction with alkynyl-terminated poly(N-vinylcaprolactam) (PNVCL-C ≡ CH) and azido-terminated poly(ε-caprolactone) (N3-PCL). The structures of the polymers were determined by proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC) measurements. The fluorescence technique was used to determine the critical micelle concentrations (CMC) of copolymer solutions. The factors affecting the lower critical solution temperature (LCST) of the copolymers were studied by UV-visible analysis. The diameters and distribution of the micelles were characterized by dynamic light scattering (DLS), and their shapes were observed by transmission electron microscopy (TEM). The results showed that these copolymers could self-assemble into nano-micelles in water. The CMC values of the copolymer solutions and the sizes of micelles reduced with increasing proportion of hydrophobic parts. TEM images demonstrated that the micelles are all spherical. On the other hand, the UV–visible measurements showed that these block copolymers exhibit a reproducible temperature-responsive behavior with a LCST that is tunable by block composition.

Preparation of poly(ionic liquids)-functionalized polypyrrole nanotubes and their electrocatalytic application to simultaneously determine dopamine and ascorbic acid

Novel poly(ionic liquids) functionalized polypyrrole nanotubes (PILs/PPyNTs) were successfully synthesized. 1-Vinyl-3-ethylimidazole bromide (VEIB) was polymerized on the surface of novel polymerizable vinyl imidazolium-type IL modified PPyNTs prepared by a covalent method. Due to the modification of PILs, the dispersibility of PILs/PPyNTs in aqueous solution was significantly improved and their surface charge properties were obviously changed to electropositivity. Because of the synergetic effects of conductive PPyNTs and biocompatible PILs, excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA) were achieved using a PILs/PPyNTs modified glassy carbon electrode (GCE), which gave a large potential difference enough to well distinguish DA from AA, with excellent sensitivity and good stability, for the simultaneous detection of DA and AA. The existence of PILs effectively improved the transmission mode of electrons of DA and AA oxidation on the electrode and resulted in their different electrocatalytic performance.

Microwave synthesis of carbon dots with multi-response using denatured proteins as carbon source

A new synthetic strategy has been developed for facile and green fabrication of highly photoluminescent carbon dots (CDs) via a one-step microwave treatment of the denatured proteins in aqueous solution. The as-prepared CDs, possessing excellent up-conversion fluorescent properties, can serve as a multifunctional fluorescent nanosensor for pH and temperature. CDs prepared from various protein carbon source can be sensitive to a specific metal ion.

Synthesis and self-assembly of a new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) block copolymer

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by ring-opening polymerization of ε-caprolactone with hydroxy-terminated poly(N-vinylcaprolactam) (PNVCL-OH) as a macroinitiator. The structures of the polymers were confirmed by IR, 1H NMR and GPC. The critical micelle concentrations of copolymer in aqueous solution measured by the fluorescence probe technique reduced with the increasing of the proportion of hydrophobic parts, so did the diameter and distribution of the micelles determined by dynamic light scattering. The shape observed by transmission electron microscopy (TEM) demonstrated that the micelles are spherical. On the other hand, the UV–vis measurement showed that polymers exhibit a reproducible temperature-responsive behavior with a lower critical solution temperature (LCST). The LCST of PNVCL-OH can be adjusted by controlling the molecular weights, and that of copolymers can be adjusted by controlling the compositions and the concentration. Variable temperature TEM measurements demonstrated that LCST transition was the result of transition of individual micelles to larger aggregates.

Poly(ionic liquid) functionalized polypyrrole nanotubes supported gold nanoparticles: An efficient electrochemical sensor to detect epinephrine

Poly(ionic liquids) (PILs) have been applied as the linkers between Au nanoparticles (NPs) and polypyrrole nanotubes (PPyNTs) for the synthesis of Au/PILs/PPyNTs hybrids. Due to the presence of PILs, high-density and well-dispersed Au NPs have been deposited on the surface of PILs/PPyNTs by anion-exchange with Au precursor and the in-situ reduction of metal ions. The obtained Au/PILs/PPyNTs hybrids can be used as a good steady electrode material for sensitively and selectively detecting epinephrine (EP). The catalytic oxidation peak currents obtained from differential pulse voltammetry (DPV) increased linearly with increasing EP concentrations in the range of 35-960μM with a detection limit of 298.9nM according to the criterion of a signal-to-noise ratio=3 (S/N=3), respectively, which showed the excellent electrocatalytic activity towards this significant hormone in human life.

Fluorescent nanothermometers based on mixed shell carbon nanodots

A novel kind of nanothermometer was prepared, which has potential to monitor the temperature variation in the nano regime. The nanothermometer was based on biocompatible fluorescent carbon nanodots (CDs) via one-step microwave assisted synthesis, and two kinds of polymers, including thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) and non-thermo-sensitive polyethylene glycol (PEG), were used simultaneously to modify the CDs. Therefore, the as-prepared nanothermometer possesses a CD core and a mixed shell consisting of PEG and PNIPAM chains. The elaborately-designed nanostructure endows the nanothermometer with both temperature sensing capacity and the solution stability. When heating up above the lower critical solution temperature (LCST) of PNIPAM, hydrophobic phase transition occurred to PNIPAM, and the nanothermometer evolved into the core–shell-corona structure, with a freshly-formed and collapsed PNIPAM shell. Meanwhile, the fluorescence behavior of the nanothermometer changed along with the structure transition reversibly without fluorescence decay. The detection temperature of the nanothermometer is consistent with the LCST of the applied thermo-sensitive polymer passivating agents. Moreover, this nanothermometer can remain stable without aggregation and fluorescence quenching whether below or above the LCST due to the stabilizing effect of the PEG chains. Furthermore, the nanothermometer could be endocytosed by cells with negligible cytotoxic effects. In view of the excellent sensitivity and reversibility, preferable biocompatibility as well as nano-scale structure, this nanothermometer shows great potential applications in intracellular imaging and temperature sensing.

Microwave Assisted Synthesis of a New Triplet Iridium(III) Pyrazine Complex

A new cyclometalated iridium(III) complex Ir(DPP)3 (DPP = 2,3-diphenylpyrazine) was prepared by reaction of DPP with iridium trichloride hydrate under microwave irradiation. The structure of the complex was confirmed by elemental analysis, 1H NMR, and mass spectroscopy. The UV-Vis absorption and photoluminescent properties of the complex were investigated. The complex shows strong 1MLCT (singlet metal to ligand charge-transfer) and 3MLCT (triplet metal to ligand charge-transfer) absorption at 382 and 504 nm, respectively. The complex also shows strong photoluminescence at 573 nm at room temperature. These results suggest the complex to be a promising phosphorescent material.

Multicompartment micelles based on hierarchical co-assembly of PCL-b-PEG and PCL-b-P4VP diblock copolymers

Multicompartment micelles are prepared via the hierarchical co-assembly of two diblock copolymers, poly(e-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and poly(e-caprolactone)-b-poly(4-vinylpyridine) (PCL-b-P4VP) in aqueous solution. These two polymers first assemble into mixed shell micelles through hydrophobic interaction among PCL chains. PCL chains form the micellar core, while PEG and P4VP chains form the micellar shell. Regulating the pH value above the pKa of P4VP can induce hydrophobic phase-segregated P4VP patches forming on the surface of mixed shell micelles. When hydrophilic PEG chains cannot stabilize theses micelles with hydrophobic patches, they will furthermore assemble as the subunits into MMs with different morphologies. These MMs can be revealed by transmission electron microscopy through P4VP chains positive staining.