Yihua Zhao

What makes efficient circularly polarised luminescence in the condensed phase: aggregation-induced circular dichroism and light emission

In this contribution, we conceptually present a new avenue to construction of molecular functional materials with high performance of circularly polarised luminescence (CPL) in the condensed phase. A molecule (1) containing luminogenic silole and chiral sugar moieties was synthesized and thoroughly characterized. In a solution of 1, no circular dichroism (CD) and fluorescence emission are observed, but upon molecular aggregation, both the CD and fluorescence are simultaneously turned on, showing aggregation-induced CD (AICD) and emission (AIE) effects. The AICD effect is supported by the fact that the molecules readily assemble into right-handed helical nanoribbons and superhelical ropes when aggregated. The AIE effect boosts the fluorescence quantum efficiency (ΦF) by 136 fold (ΦF, ∼0.6% in the solution versus ∼81.3% in the solid state), which surmounts the serious limitations of aggregation-caused quenching effect encountered by conventional luminescent materials. Time-resolved fluorescence study and theoretical calculation from first principles conclude that restriction of the low-frequency intramolecular motions is responsible for the AIE effect. The helical assemblies of 1 prefer to emit right-handed circularly polarised light and display large CPL dissymmetry factors (gem), whose absolute values are in the range of 0.08–0.32 and are two orders of magnitude higher than those of commonly reported organic materials. We demonstrate for the first time the use of a Teflon-based microfluidic technique for fabrication of the fluorescent pattern. This shows the highest gem of −0.32 possibly due to the enhanced assembling order in the confined microchannel environment. The CPL performance was preserved after more than half year storage under ambient conditions, revealing the excellent spectral stability. Computational simulation was performed to interpret how the molecules in the aggregates interact with each other at the molecular level. Our designed molecule represents the desired molecular functional material for generating efficient CPL in the solid state, and the current study shows the best results among the reported organic conjugated molecular systems in terms of emission efficiency, dissymmetry factor, and spectral stability.

A Gold Nanocrystal/Poly(dimethylsiloxane) Composite for Plasmonic Heating on Microfluidic Chips

Microfluidic chips, on which fluids can be controlled and analyzed within microscale channels, have received intensive interest from both industrial and academic communities. The benefits of miniaturization, integration, and automation facilitate their potential uses in areas ranging from materials synthesis, bioanalysis, point-of-care diagnostics to drug discovery.[1–5] In many of these applications, heating is of vital importance for the overall chip performance. For example, heating is crucial in capillary electrophoresis[6] and cell culturing.[3] It is also essential for on-chip polymerase chain reactions[7,8] and analyses involving DNA binding and melting.[9] Furthermore, precise and localized heating can generate thermocapillary driving forces, which is useful for manipulating bubbles and droplets.[10] Up to date, on-chip heating has relied mainly on resistive[11] and optical means.[12,13] The use of resistance elements limits the spatial resolution of localized heating, and the required wiring increases the complexity of microchip fabrication. The optical means need no electric connections, and the heating locations are more controllable owing to the elimination of resistive electrodes. However, strongly light-absorbing materials are often needed to enhance the heating efficiency. The use of these materials introduces additional fabrication steps and often interferes with on-chip optical analyses. As a result, simple and economical means of photothermal conversion on microfluidic chips without interference with analyses are strongly desired. Noble metal nanocrystals (NCs) exhibit rich plasmonic properties. They possess extremely large absorption cross sections at their plasmon wavelengths. Under resonant excitation, a small number of metal NCs can absorb a large amount of light and convert it into heat nearly completely. The fundamental aspects of the photothermal conversion arising from the localized plasmon resonances of metal nanocrystals have been carefully studied.[14–17] Plasmonic photothermal conversion has also been widely applied to biotechnological applications, such as photothermal imaging,[18] cancer therapy,[17,19,20] and gene delivery.[21] Moreover, the plasmon wavelengths of metal NCs can be synthetically tuned over a wide spectral range,[22] which

L-Valine methyl ester-containing tetraphenylethene: aggregation-induced emission, aggregation-induced circular dichroism, circularly polarized luminescence, and helical self-assembly

L-Valine methyl ester-containing tetraphenylethene (Val-TPE) has been designed and synthesized. This novel molecule exhibits aggregation-induced emission (AIE), aggregation-induced circular dichroism (AICD), circularly polarized luminescence (CPL) and the capacity to self-assemble into helical nanofibers.

Fabrication of a microfluidic Ag/AgCl reference electrode and its application for portable and disposable electrochemical microchips

This report describes a convenient method for the fabrication of a miniaturized, reliable Ag/AgCl reference electrode with nanofluidic channels acting as a salt bridge that can be easily integrated into microfluidic chips. The Ag/AgCl reference electrode shows high stability with millivolt variations. We demonstrated the application of this reference electrode in a portable microfluidic chip that is connected to a USB‐port microelectrochemical station and to a computer for data collection and analysis. The low fabrication cost of the chip with the potential for mass production makes it disposable and an excellent candidate for real‐world analysis and measurement. We used the chip to quantitatively analyze the concentrations of heavy metal ions (Cd2+ and Pb2+) in sea water. We believe that the Ag/AgCl reference microelectrode and the portable electrochemical system will be of interest to people in microfluidics, environmental science, clinical diagnostics, and food research.

Convenient Method for Modifying Poly(dimethylsiloxane) To Be Airtight and Resistive against Absorption of Small Molecules

In this paper we present a simple and rapid method of modifying poly(dimethylsiloxane) (PDMS) surfaces with paraffin wax. PDMS that contains a layer of paraffin wax at its surface resists the absorption of hydrophobic molecules; we used fluorescence microscopy to confirm that paraffin-modified PDMS resists the absorption of rhodamine B. Furthermore, we demonstrated that microfluidic devices made from PDMS that contains a surface layer of paraffin wax prevent efficiently the transport of gas molecules through the bulk and into microchannels. We characterized the surface of PDMS that contains paraffin wax using the water contact angle, optical transmission, and X-ray photoelectron spectroscopy. We show that PDMS that contains paraffin wax can be substituted for native PDMS; specifically, we fabricated peristaltic valves in PDMS that contains paraffin wax, and the valves showed no degradation in performance after multiple open/close cycles. Finally, we show how to use PDMS that has been treated with paraffin wax as a mold for the fabrication of PDMS replicas; this approach avoids silanization of PDMS, which is a time-consuming step in soft lithography. The wax-modified PDMS channels also show performance superiro to that of bare PDMS in micellar electrokinetic chromatography for quantitative analysis.

Gradient-Regulated Hydrogel for Interface Tissue Engineering: Steering Simultaneous Osteo/Chondrogenesis of Stem Cells on a Chip

Injury to articular cartilage, especially the defects induced by degenerative diseases has presented insurmountable challenges. Elaborating a replacement of articular cartilage using biomimic tissue-engineering strategies provides a promising remedy. However, none of the previous osteo/chondrogenic methodologies can not only simultaneously induce osteo/chondrogenesis of stem cells in one scaffolding niche, but also generate a biomimic interface between the formed osteogenic and chondrogenic zones. We report here an innovative method using biomicrofluidic techniques to simultaneously steer distinct specialized differentiation of stem cells into chondrocytes and osteoblasts in one hydrogel slab. Importantly, a gradient that mimics the interface of bone-to-cartilage was generated in the middle of the hydrogel slab. We compared this format with the conventional method for osteochondrogenesis; this format using the gradient-generating microfluidic device indicated outstanding superiorities in stem cell culture and differentiation. Our findings will have a major impact on the design of versatile biomicrofluidic devices for interfacial tissue regeneration.

Enhanced Osteogenesis by a Biomimic Pseudo‐Periosteum‐Involved Tissue Engineering Strategy

Elaborating a bone replacement using tissue-engineering strategies for bone repair seems to be a promising remedy. However, previous platforms are limited in constructing three-dimensional porous scaffolds and neglected the critical importance of periosteum (a pivotal source of osteogenic cells for bone regeneration). We report here an innovative method using the periosteum as a template to replicate its exquisite morphologies onto the surfaces of biomaterials. The precise topographic cues (grooved micropatterns) on the surface of collagen membrane inherited from the periosteum effectively directed cell alignment as the way of natural periosteum. Besides, we placed the stem-cell and endothelial-cell-laden collagen membrane (pseudo-periosteum) onto a three-dimensional porous scaffold. The pseudo-periosteum-covered scaffolds showed remarkable osteogenesis when compared with the pseudo-periosteum-free scaffolds, indicating the significant importance of pseudo-periosteum on bone regeneration. This study gives a novel concept for the construction of bone tissue engineering scaffold and may provide new insight for periosteum research.

A convenient platform of tunable microlens arrays for the study of cellular responses to mechanical strains

In this paper, we present an array of tunable microlenses on polydimethylsiloxane (PDMS) microfluidic chips as a convenient platform for the study of cell responses to mechanical strains. This array of microlenses is an array of microwells covered with a thin PDMS membrane that are connected by microfluidic channels. The deformation of the PDMS membrane on the microlenses is tuned by external hydraulic pressure that is introduced through the microchannels. The degree of deformation of the PDMS membrane can be estimated from the focal length of the microlens, and the corresponding mechanical strain that is caused can be calculated from finite element simulation. We demonstrate the capability of this array of microlenses as a general platform for studying the influence of mechanical strain on adherent cells by using NIH 3T3 fibroblasts and HeLa cells as our models.

Engineering a Freestanding Biomimetic Cardiac Patch Using Biodegradable Poly(lactic‐co‐glycolic acid) (PLGA) and Human Embryonic Stem Cell‐derived Ventricular Cardiomyocytes (hESC‐VCMs)

Microgrooved thin PLGA film (≈30 μm) is successfully fabricated on a Teflon mold, which could be readily peeled off and is used for the construction of a biomimetic cardiac patch. The contraction of it is studied with optical mapping on transmembrane action potential. Our results suggest that steady-state contraction could be easily established on it under regular electrical stimuli. Besides, the biomimetic cardiac patch recapitulates the anisotropic electrophysiological feature of native cardiac tissue and is much more refractory to premature stimuli than the random one constructed with non-grooved PLGA film, as proved by the reduced incidence of arrhythmia. Considering the good biocompatibility of PLGA as demonstrated in our study and the biodegradability of it, our biomimetic cardiac patch may find applications in the treatment of myocardial infarction. Moreover, the Teflon mold could be applied in the fabrication of various scaffolds with fine features for other tissues.

One-step generation of engineered drug-laden poly(lactic-co-glycolic acid) micropatterned with Teflon chips for potential application in tendon restoration.

Regulating cellular behaviors such as cellular spatial arrangement and cellular phenotype is critical for managing tissue microstructure and biological function for engineered tissue regeneration. We herein pattern drug-laden poly(lactic-co-glycolic acid) (PLGA) into grooves using novel Teflon stamps (that possess excellent properties of resistance to harsh organic solvents and molecular adsorption) for engineered tendon-repair therapeutics. The drug release and biological properties of melatonin-laden PLGA grooved micropatterns are investigated. The results reveal that fibroblasts cultured on the melatonin-laden PLGA groove micropatterns not only display significant cell alignment that mimics the cell behavior in native tendon, but also promote the secretion of a major extracellular matrix in tendon, type I collagen, indicating great potential for the engineering of functional tendon regeneration.