Synthesis of amphiphilic triblock copolymers as multidentate ligands for biocompatible coating of quantum dots

One barrier to apply current tri-octylphosphine oxide (TOPO) based quantum dots (QDs) to biomedical imaging is that the TOPO on TOPO-QDs can be replaced by the proteins in living system, which may cause the degradation of QDs and/or deactivation of protein. In order to develop biocompatible optical imaging agents, a novel triblock copolymer, designed as a multidentate ligand, was synthesized to coat quantum dot nanocrystals (QDs). The copolymer consists of a polycarboxylic acid block at one end and a polythiol block at the other end with an intervening cross-linked poly(styrene-co-divinylbenzene) block bridging the ends. The multiple mercapto groups from the polythiol block act as multidentate ligands to stabilize QDs, while the polycarboxylic acid block improves the water solubility of QDs and offers reaction sites for surface modification or conjugation with bimolecules. The cross-linked poly(styrene-co-divinylbenzene) block provides a densely compacted hydrophobic shell. This shell will act as a barrier to inhibit the degradation of QDs by preventing the diffusion of ions and small molecules into the core of QDs. This new multidentate polymer coating facilitates the transfer of QDs from organic solvent into aqueous phase. The QDs directly bound to multidentate mercapto groups instead of TOPO are less likely to be affected by the mercapto or disulfide groups within proteins or other biomolecules. Therefore, this research will provide an alternative coating material instead of TOPO to produce QDs which could be more suitable for in vivo use under complex physiological conditions.     

Constructing center-stable tori

We show that certain derived-from-Anosov diffeomorphisms on the 2-torus may be realized as the dynamics on a center-stable or center-unstable torus of a 3-dimensional strongly partially hyperbolic system. We also construct examples of center-stable and center-unstable tori in higher dimensions.     

From MOF-74-Zn to Triazolate-Directed Nonsymmetric Assembly of Chiral Zn6@Zn6 Clusters

The creation of new cluster building blocks, as well as new ligand coordination modes, are among the most effective ways to develop new framework materials. Yet, large and chiral clusters are both difficult to create and relatively few. Here, by studying the competing coordination of different azolates against carboxylate and combined carboxylate/phenolate, it is shown that the impact of azolates in the MOF-74 synthesis system differs dramatically, leading to the synthesis of MOF-74, UTSA-74, and CPM-72 for 2-methylimidazole, 1,2,4-triazole, and 1,2,3-triazole, respectively. The new CPM-72 contains a novel chiral Zn₁₂ triazolate cluster, which features a trigonal-prismatic Zn₆ core inside an octahedral Zn₆ shell. In contrast with MOF-74 with fully deprotonated and symmetrically bonded 2,5-dihydroxyterephthalic acid (H₄DOBDC), H₄DOBDC adopts an unusual nonsymmetric bonding mode in CPM-72 (carboxylate only at one end and carboxylate/phenolate at the other), resulting in a highly porous and intrinsically chiral 3D framework. The nonsymmetric bonding mode by H₄DOBDC, apparently dictated by the chiral Zn₁₂ cluster, can be replicated with 2-hydroxyterephthalic acid (H₃OBDC), leading to the synthesis of porous isoreticular CPM-73.     

Nonlinear refractive indices of nonlinear liquids: wavelength dependence and influence of retarded response

We use liquid-filled capillary fibers with different core diameters to precisely characterize the nonlinear refractive index of the highly nonlinear liquids carbon disulfide, nitrobenzene, and toluene. We present measurements with two different femtosecond pump sources at wavelengths of 1032 and 1560 nm. The large nonlinearity of the liquids results from the retarded nonlinear optical response of the liquid molecules which includes a strong non-instantaneous contribution due to molecular reorientation. The nonlinear refractive index of the liquids is determined by fitting numerical simulations based on solving the generalized nonlinear Schrödinger equation including retarded response to the measured broadened output spectra. Our work is important for the novel field of near- and mid-IR supercontinuum generation in liquid-core optical fibers.     

Multi-objective optimisation of positively homogeneous functions and an application in radiation therapy

Unconstrained multi-objective optimisation problems with p$p$ positively homogeneous objective functions are considered. We prove that such problems reduce to multi-objective optimisation problems with p−1$p-1$ objectives and a single equality constraint. Thus, problems with two objectives can be solved with standard single objective optimisation methods and, for problems with p>2$p>2$ objectives, we can compute infinitely many efficient solutions by solving a finite number of single objective problems. The proposed procedure is applied on radiotherapy for cancer treatment.     

Direct-write,Well-aligned Chitosan-Poly(ethylene oxide) Nanofibers Deposited via Near-field Electrospinning

A continuous near-field electrospinning (NFES) process has been demonstrated to be able to achieve direct-write and well-aligned chitosan/poly(ethylene oxide) nanofibers. The ability to precisely control and deposit chitosan-based nanofibers in a direct-write manner is favorable in manipulating cells attachment and proliferation at a preferred position. Experimental results show that fiber diameters can be reliably controlled in the range of 265–1255 nm by adjusting various operating parameters of the NFES processes. These prescribed patterns of nanofibers exceed tens of centimeters long and complex configurations such as grid arrays and arc shapes are assembled at specified separations as small as 5 μm. FTIR analysis reveals that NFES nanofibers have a similar morphology and composition as conventional electrospinning counterpart and constitute all components formerly present in the polymer solution. The versatile functionality to fabricate chitosan-based nanofibers with controllable size and directional alignment as well as highly ordered and customized patterns may represent an ideal candidate of a functional biomaterial and in tissue-engineering scaffolds that are predominantly representative of extracellular matrix (ECM).     

Scaling effect of flexoelectric (Ba,Sr)TiO3 microcantilevers

The flexoelectric microcantilever offers an alternative approach for the development of micro/nano‐sensors. The transverse flexoelectric coefficients µ₁₂ of barium strontium titanate microcantilevers were measured at room temperature, and found to keep the same value of 8.5 µC/m for microcantilevers with thickness ranging from 30 µm to 1.4 mm. The calculated effective piezoelectric coefficient and electrical energy density of flexoelectric cantilevers are superior to those of their piezoelectric counterparts, suggesting that the flexoelectricity‐induced polarization can be significantly increased as structures are scaled down due to the scaling effect of strain gradient, holding promise for flexoelectric micro/nano cantilever sensing applications. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detection of carcinoembryonic antigen using functional magnetic and fluorescent nanoparticles in magnetic separators

We combined a sandwich immunoassay, anti-CEA/CEA/anti-CEA, with functional magnetic (~80 nm) and fluorescent (~180 nm) nanoparticles in magnetic separators to demonstrate a detection method for carcinoembryonic antigen (CEA). Determination of CEA in serum can be used in clinical diagnosis and monitoring of tumor-related diseases. The CEA concentrations in samples were deduced and determined based on the reference plot using the measured fluorescent intensity of sandwich nanoparticles from the sample. The linear range of CEA detection was from 18 ng/mL to 1.8 pg/mL. The detection limit of CEA was 1.8 pg/mL. In comparison with most other detection methods, this method had advantages of lower detection limit and wider linear range. The recovery was higher than 94%. The CEA concentrations of two serum samples were determined to be 9.0 and 55 ng/mL, which differed by 6.7% (9.6 ng/mL) and 9.1% (50 ng/mL) from the measurements of enzyme-linked immunosorbent assay (ELISA), respectively. The analysis time can be reduced to one third of ELISA. This method has good potential for other biomarker detections and biochemical applications.