Template-Monomer Interaction in Molecular Imprinting: Is the Strongest the Best?

Molecularly imprinted polymers (MIPs) represent a new class of materials possessing high selectivity and affinity for the target molecule. They have been utilized as sensors, catalysts, sorbents for solid-phase extraction, stationary phase for liquid chromatography, mimics of enzymes, receptors, and antibodies. In this research, molecular imprinted polymers (MIPs) for luteolin were prepared using acrylamide, 4-vinylpyridine and 1-allyl-piperazine as functional monomers and ethylene glycol dimethacrylate as cross-linker by non-covalent imprinting method. UV-visible spectra were used to evaluate the interaction strength between the template and the monomers. The composites of the polymers were calculated from elementary analysis. The porous properties of the imprinted polymers have been determined from nitrogen adsorption-desorption isotherms. The imprinting efficiency of the prepared MIPs was evaluated by selective adsorption for luteolin and its structural analogues. Although the interaction strength of monomers to the template was in the order 1-ALPP > 4-VP > AA, the binding affinity of the imprinted polymers towards luteolin was in the order MIP 2 > MIP 3 > MIP 1. Our results demonstrated that the imprinting efficiency was depending not only on the interaction strength between the template and the monomer, but also on the fidelity in transferring the complex into the polymer.

Temperature-driven reversible structural transformation and conductivity switching in ultrathin Cu_(9)S_(5)crystals

Two-dimensional(2D)materials with reversible phase transformation are appealing for their rich physics and potential applications in information storage.However,up to now,reversible phase transitions in 2D materials that can be driven by facile nondestructive methods,such as temperature,are still rare.Here,we introduce ultrathin Cu_(9)S_(5)crystals grown by chemical vapor deposition(CVD)as an exemplary case.For the first time,their basic electrical properties were investigated based on Hall measurements,showing a record high hole carrier density of~1022 cm^(-3) among 2D semiconductors.Besides,an unusual and repeatable conductivity switching behavior at~250 K were readily observed in a wide thickness range of CVD-grown Cu_(9)S_(5)(down to 2 unit-cells).Confirmed by in-situ selected area electron diffraction,this unusual behavior can be ascribed to the reversible structural phase transition between the room-temperature hexagonalβphase and low-temperatureβ’phase with a superstructure.Our work provides new insights to understand the physical properties of ultrathin Cu_(9)S_(5)crystals,and brings new blood to the 2D materials family with reversible phase transitions.

Bending strain effects on the optical and optoelectric properties of GaN nanowires

Elastic strain has been an important method to regulate the electronic structures and physical properties of nanoscale semiconductors due to the promising potentials in improving the performance of their optoelectronic devices.Here,we report the investigation of bending strain effects on the optical and optoelectric properties of individual gallium nitride(GaN)nanowires(NWs).By charactering the near-band emission spectrum of individual GaN NWs at different bending strains with low temperature cathodoluminescence(CL),we reveal that the near-band emission splits into two peaks,where the low energy peak displays a linear redshift with increasing the bending strain while the high energy one shows a slight blueshift.Further localized ultraviolet(UV)photoresponse measurements illustrate that the photoresponse of the GaN NWs shows a linear increase with the bending train,and the maximum enhancement is more than two orders of magnitude.The experimental observations are well interpreted by theoretical calculations on the strain modulation on the electronic band structure of GaN combined with analysis of carrier dynamics and optical waveguide effect in the bending strain field.Our results not only shed light on the bending strain effects on the optical and optoelectric properties of semiconductors,but also hold potential to help the future design of high performance nano-optoelectric devices.