Qingling Xu

Polydiacetylene-Based Colorimetric and Fluorescent Chemosensor for the Detection of Carbon Dioxide

We developed a colorimetric and fluorescent turn-on carbon dioxide sensor that relies on a polydiacetylene, PDA-1, functionalized with amines and imidazolium groups. The pendant amines react with CO2 under basic conditions to form carbamoate anions, which partially neutralize the polymers positive charges, inducing a phase transition. PDA-1 allows for the selective sensing of CO2 with high sensitivity, down to atmospheric concentrations. Naked-eye detection of CO2 is accomplished either in water solutions of PDA-1 or in the solid state with electrospun coatings of PDA-1 nanofibers.

Development of Imidazoline‐2‐Thiones Based Two‐Photon Fluorescence Probes for Imaging Hypochlorite Generation in a Co‐Culture System

We designed and prepared the imidazoline-2-thione containing OCl(-) probes, PIS and NIS, which operate through specific reactions with OCl(-) that yield corresponding fluorescent imidazolium ions. Importantly, we demonstrated that PIS can be employed to image OCl(-) generation in macrophages in a co-culture system. We have also employed two-photon microscopy and PIS to image OCl(-) in live cells and tissues, indicating that this probe could have wide biological applications.

A water-soluble boronate-based fluorescent probe for the selective detection of peroxynitrite and imaging in living cells

A water-soluble boronate-based fluorescent probe was evaluated for the detection of peroxynitrite (ONOO−) in the presence of a monosaccharide. The enhanced fluorescence of the probe when bound with D-fructose was switched off in the presence of peroxynitrite. In contrast, other reactive oxygen/nitrogen species (ROS/RNS) led to only slight fluorescence decreases due to protection by an internal N–B interaction. The interaction of the probe with D-fructose not only strengthens the fluorescence signal, but also protects the boronic acid from oxidation by other ROS/RNS. Therefore, under conditions generating various ROS/RNS, the boronate-based saccharide complex preferentially reacts with peroxynitrite. The probe was used in cell imaging experiments for the detection of endogenous and exogenous peroxynitrite. The sensor displays good “on–off” responses towards peroxynitrite, both in RAW 264.7 cells and HeLa cells.

Visual detection of copper ions based on azide- and alkyne-functionalized polydiacetylene vesicles

A new method for visual detection of Cu2+ based on azide- and alkyne-functionalized polydiacetylene (PDA-aa) vesicles has been developed. In the presence of ascorbic acid, Cu2+ can be reduced to Cu+ and catalyze the click reaction between the two functional groups. After incubation with Cu2+ and ascorbic acid, a PDA-aa solution changed its color from blue to red, which was attributed to conformational transition of the conjugated backbone. Other metal ions were explored but only induced negligible color changes. This method provides a naked eye detection of Cu2+ in water without the aid of complex instruments.

A Selective Imidazoline-2-thione-Bearing Two-Photon Fluorescent Probe for Hypochlorous Acid in Mitochondria

Hypochlorite (OCl(-)) plays a key role in the immune system and is involved in various diseases. Accordingly, direct detection of endogenous OCl(-) at the subcellular level is important for understanding inflammation and cellular apoptosis. In the current study, a two-photon fluorescent off/on probe (PNIS) bearing imidazoline-2-thione as an OCl(-) recognition unit and triphenylphosphine (TPP) as a mitochondrial-targeting group was synthesized and examined for its ability to image mitochondrial OCl(-) in situ. This probe, based on the specific reaction between imidazoline-2-thione and OCl(-), displayed a selective fluorescent off/on response to OCl(-) with the various reactive oxygen species in a physiological medium. PNIS was successfully applied to image of endogenously produced mitochondrial OCl(-) in live RAW 264.7 cells via two-photon microscopy.

Sensing and antibacterial activity of imidazolium-based conjugated polydiacetylenes

In the current study, we report the first example of polydiacetylenes (PDAs), where our PDA-based system acts as both a sensing probe and killer for bacteria. The contact of imidazolium and imidazole-derived PDA with various bacterial strains including MRSA (methicillin-resistant Staphylococcus aureus) and ESBL-EC (extended-spectrum β-lactamase-producing Escherichia coli) results in a distinct blue-to-red colorimetric change of the solution as well as a rapid disruption of the bacterial membrane, which is demonstrated by transmission electron microscopy and confocal microscopy. Zeta potential analysis supports that antibacterial activity of the PDA solution originates from an electrostatic interaction between the negatively charged bacterial cell surface and the positively charged polymers. These results suggest that the PDA has a great potential to carry out the dual roles of a probe and killer for bacteria.

Ratiometric Two-Photon Fluorescent Probe for Detecting and Imaging Hypochlorite

The ratiometric fluorescent probe B6S, which contains pyrene as a fluorophore and imidazoline-2-thione as a reactive site, was developed for detection of hypochlorite (OCl-). B6S displays a high specificity toward OCl- in contrast to other reactive oxygen species and reactive nitrogen species. The probe has a low detection limit and operates under biological conditions. Moreover, the low cytotoxicity of B6S enables it to be utilized effectively for OCl- imaging in living cells and tissues by using two-photon microscopy. The findings indicate that B6S has the capability of serving as a probe to explore the biological functions of OCl- in living systems.

Thermal design of BESIII magnet

Publisher Summary This chapter presents the thermal analysis of Beijing Spectrometer Magnet (BESIII Magnet) which is used as a superconducting detector magnet in BEPC-II. There are mainly five kinds of heat loads when BESIII Magnet is in static operating condition: Joule heating of the joint turns, radiation heat leak, heat leak through axial and radial supports, current leads heat leak, and measuring wires heat leak. BESIII superconductor is composed of three long conductors, design data of electric resistance of the joint turn is 10-9 Ω. The static temperature distribution of BESIII magnet can be calculated with a commercial FE method software-Ansys. BESIII Magnet is cooled by forced flow of two phase helium and the inner winding technique is adopted in the coil winding process. A 3D model of calculation for the magnet is also presented. The heat load and the temperature distribution of the magnet is analyzed by a finite element method, and the upper limits of several heat leak sources are calculated.