Qiuquan Guo

Synthesis of Ag?TiO2 composite nano thin film for antimicrobial application

TiO2 photocatalysts have been found to kill cancer cells, bacteria and viruses under mild UV illumination, which offers numerous potential applications. On the other hand, Ag has long been proved as a good antibacterial material as well. The advantage of Ag-TiO2 nanocomposite is to expand the nanomaterials antibacterial function to a broader range of working conditions. In this study neat TiO2 and Ag-TiO2 composite nanofilms were successfully prepared on silicon wafer via the sol-gel method by the spin-coating technique. The as-prepared composite Ag-TiO2 and TiO2 films with different silver content were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) to determine the topologies, microstructures and chemical compositions, respectively. It was found that the silver nanoparticles were uniformly distributed and strongly attached to the mesoporous TiO2 matrix. The morphology of the composite film could be controlled by simply tuning the molar ratio of the silver nitrate aqueous solution. XPS results confirmed that the Ag was in the Ag(0) state. The antimicrobial effect of the synthesized nanofilms was carried out against gram-negative bacteria (Escherichia coli ATCC 29425) by using an 8 W UV lamp with a constant relative intensity of 0.6 mW cm(-2) and in the dark respectively. The synthesized Ag-TiO2 thin films showed enhanced bactericidal activities compared to the neat TiO2 nanofilm both in the dark and under UV illumination.

A lab-on-CD prototype for high-speed blood separation

Blood separation is the first step for subsequent blood tests in clinical diagnosis. Lab-on-a-chip technology provides an automatic, cost-effective and fast solution for a wide variety of blood analyses. The objective of this work is to design a new lab-on-CD microstructure capable of separating blood cells from the whole blood into different reservoirs directly. A CD platform including a microchannel network consisting of a straight main microchannel, a curved microchannel and a branching microchannel has been proposed. The merits of this design are its simple structure, less operating time and high separation efficiency because it utilizes multiple separation mechanisms, for instance, two centrifugal forces and Coriolis force. One centrifugal force is due to the system rotation; the other centrifugal force is due to the curvature of the specifically designed curved channel. In this work, systematical evaluation on the functionality and performance of such a design has been done. Ninety-nine per cent separation efficiency is achieved for diluted blood of 6% hematocrit.

Ultrathin low-frequency sound absorbing panels based on coplanar spiral tubes or coplanar Helmholtz resonators

Performance of classic sound absorbing materials strictly depends on their thickness, with a minimum of one-quarter wavelength to reach full sound absorption. In this paper, we report ultrathin sound absorbing panels that completely absorb sound energy with a thickness around one percent of wavelength. The strategy is to bend and coil up quarter-wavelength sound damping tubes into 2D coplanar ones, and embed them into a matrix to form sound absorbing panel. Samples have been designed and fabricated by 3D printing. Efficacies of sound absorption by these panels were validated through good agreement between theoretical analysis and experimental measurements.

Fabrication of flexible copper-based electronics with high-resolution and high-conductivity on paper via inkjet printing

Flexible and printable electronics are attractive techniques which have potential for broad applications not only in flexible but also in large area electronics. An effective and convenient method of fabricating high-resolution copper patterns with high conductivity and strong adhesion on flexible photopaper is demonstrated in this paper. Functional photopaper was prepared with inkjet printing of a palladium salt solution onto its surface, followed by electroless deposition of copper. Parameters of the printing process, such as voltage control waveform, temperature of printhead and substrate, meniscus vacuum level, printing height, etc. were optimized to obtain a robust and high resolution printing with feature dimensions down to 50 μm. Through a unique thermal sintering process, printed copper lines showed excellent conductivity of up to 3.9 × 107 S m−1 (>65% of bulk copper). The developed technique was successfully applied for fabricating paper based functional flexible circuits such as RFID antennae, micro-inductive coils and complex circuit boards.

Initiator-Integrated 3D Printing Enables the Formation of Complex Metallic Architectures

Three-dimensional printing was used to fabricate various metallic structures by directly integrating a Br-containing vinyl-terminated initiator into the 3D resin followed by surface-initiated atomic-transfer radical polymerization (ATRP) and subsequent electroless plating. Cu- and Ni-coated complex structures, such as microlattices, hollow balls, and even Eiffel towers, were prepared. Moreover, the method is also capable of fabricating ultralight cellular metals with desired structures by simply etching the polymer template away. By combining the merits of 3D printing in structure design with those of ATRP in surface modification and polymer-assisted ELP of metals, this universal, robust, and cost-effective approach has largely extended the capability of 3D printing and will make 3D printing technology more practical in areas of electronics, acoustic absorption, thermal insulation, catalyst supports, and others.

i3DP, a robust 3D printing approach enabling genetic post-printing surface modification

Initiator integrated 3D printing, namely i3DP, was developed by incorporating a vinyl-terminated initiator into UV curable resin to make functional structural materials that enable genetic post-printing surface-initiated modification. Taking advantage of 3D printing and surface-initiated ATRP, the feasible i3DP makes 3D printed complex architectures possible for nearly any desired surface modification for various applications, for example, even pouring water into a sieve was readily achieved.

Characterization of cell elasticity correlated with cell morphology by atomic force microscope

Biomechanical properties of cells have been identified as an important factor in a broad range of biological processes. Based on measurements of mechanical properties by atomic force microscopy (AFM) particularly cell elasticity has been linked with human diseases, such as cancer. AFM has been widely used as a nanomechanical tool to probe the elasticity of living cells, however, standard methods for characterizing cell elasticity are still lacking. The local elasticity of a cell is conventionally used to represent the mechanical property of the cell. However, since cells have highly heterogeneous regions, elasticity mapping over the entire cell, rather than at a few points of measurement, is required. Using human aortic endothelial cells (HAECs) as a model, we have developed in this study a new method to evaluate cell elasticity more quantitatively. Based on the height information of the cell, a new characterization method was proposed to evaluate the elasticity of a cell. Using this method, elasticities of cells on different substrates were compared. Results showed that the elasticity of HAECs on softer substrate also has higher value compared to those on harder substrate given a certain height where the statistical distribution analysis confirmed that higher actin filaments density was located. Thus, the elasticity of small portions of a cell could not represent the entire cell property and may lead to invalid characterization. In order to gain a more comprehensive and detailed understanding of biomechanical properties for future clinical use, elasticity and cell morphology should therefore be correlated with discussion.

High-yield synthesis of graphene quantum dots with strong green photoluminescence

A facile and high-yielding hydrothermal method for synthesizing graphene quantum dots (GQDs) from glucose is presented. The GQDs, with fluorescence quantum yield (FL QY) of 44.3%, demonstrate strong green photoluminescence (PL) and excitation-independent PL emission characteristics.

Direct Pen Writing of Adhesive Particle-Free Ultrahigh Silver Salt-Loaded Composite Ink for Stretchable Circuits

In this article, we describe a writable particle-free ink for fast fabrication of highly conductive stretchable circuits. The composite ink mainly consists of soluble silver salt and adhesive rubber. Low toxic ketone was employed as the main solvent. Attributed to ultrahigh solubility of silver salt in short-chain ketone and salt-assisted dissolution of rubber, the ink can be prepared into particle-free transparent solution. As-prepared ink has a good chemical stability and can be directly filled into ballpoint pens and use to write on different substrates to form well adhesive silver salt-based composite written traces as needed. As a result of high silver salt loading, the trace can be converted into highly conductive silver nanoparticle-based composites after in situ reduction. Because of the introduction of adhesive elastomeric rubber, the as-formed conductive composite written trace can not only maintain good adhesion to various substrates but also show good conductivity under various deformations. The conductivity of written traces can be enhanced by repeated writing-reduction cycles. Different patterns can be fabricated by either direct handwriting or hand-copying. As proof-of-concept demonstrations, a typical handwriting heart-like circuit was fabricated to show its capability to work under different deformations, and a pressure-sensitive switch was also manufactured to present pressure-dependent change of resistance.

Micro-electromechanical film bulk acoustic sensor for plasma and whole blood coagulation monitoring

Monitoring blood coagulation is an important issue in the surgeries and the treatment of cardiovascular diseases. In this work, we reported a novel strategy for the blood coagulation monitoring based on a micro-electromechanical film bulk acoustic resonator. The resonator was excited by a lateral electric field and operated under the shear mode with a frequency of 1.9GHz. According to the apparent step-ladder curves of the frequency response to the change of blood viscoelasticity, the coagulation time (prothrombin time) and the coagulation kinetics were measured with the sample consumption of only 1μl. The procoagulant activity of thromboplastin and the anticoagulant effect of heparin on the blood coagulation process were illustrated exemplarily. The measured prothrombin times showed a good linear correlation with R2=0.99969 and a consistency with the coefficient of variation less than 5% compared with the commercial coagulometer. The proposed film bulk acoustic sensor, which has the advantages of small size, light weight, low cost, simple operation and little sample consumption, is a promising device for miniaturized, online and automated analytical system for routine diagnostics of hemostatic status and personal health monitoring.