Microfluidic Plasma-Based Continuous and Tunable Synthesis of Ag–Au Nanoparticles and Their SERS Properties

Silicon dioxide layer thickness-dependent Aunanocube@mSiO2@Ag with surface enhanced Raman scattering for trace detection of harmful substances

Aunanocube@mSiO2@Ag nanocomposites were synthesized by layer-by-layer assembly with an Au nanocube core, an Ag shell, and mesoporous silica as a spacer. The thickness of the mesoporous silica layer was controlled simply by changing the amount of silica precursor. The SERS activity of the nanocomposites varied with the thickness of the SiO2 spacer layer, and the strongest SERS effect was observed when the optimized silica layer thickness was about 6 nm. The sensitivity of the synthesized nanocomposites was tested using typical representatives of organic dyes and pesticides (rhodamine 6G, crystal violet, and thiram) as probes, which have very low detection limits of 10-12, 10-11 and 10-9 M, respectively, and good stability was observed. The SERS performance of Aunanocube@mSiO2@Ag changed with the change of the thickness of SiO2, and Aunanocube@mSiO2@Ag with appropriate SiO2 thickness showed excellent SERS performance. When the thickness of the SiO2 layer is 6.0 nm, the SERS signal is strongest. It has the advantages of a fast response speed, simple operation, low detection limit and good pollutant detection ability.

Microreactor designed for efficient plasma-liquid segmented flows

Microreactors were designed for gas-liquid plasma chemical processes and operated under segmented flows in a high aspect ratio (8.76) rectangular microchannel. First, the hydrodynamics of the gas-liquid flows generated at a T-junction was investigated for fifteen solvents commonly used in organic synthesis. The classical literature scaling laws were revised to describe the dependence of bubble and slug lengths, and bubble residence time on the liquid nature by introducing their liquid vapour pressure. Liquid film thickness and liquid residence time were estimated from residence time distribution experiments. Secondly, plasma could be successfully generated in these segmented flows for all the liquids. Due to the plasma dissipation of thermal energy, gas phase temperature increased and induced the lengthening of bubbles and the decrease in bubble residence time. The flow pattern was also impacted by the gas temperature increase. A flow map describing the evolution of the flow pattern under plasma conditions was built, enabling prediction of the flow pattern based on the liquid boiling point and dielectric constant. These microreactors have demonstrated great potential, and by adapting the synthesis solvent or the operating plasma conditions, they could find promising applications in gas-liquid plasma chemical processes.

Optically controlled coalescence and splitting of femtoliter/picoliter droplets for microreactors

Microreactor technology has attracted tremendous interest due to its features of a large specific surface area, low consumption of reagents and energy, and flexible control of the reaction process. As most of the current microreactors have volumes of microliters or even larger, effective methods to reduce the microreactors' sizes and improve their flexibility and controllability have become highly demanded. Here we propose an optical method of coalescence and splitting of femto-/pico-liter droplets for application in microreactors. Firstly, two different schemes are adopted to stably trap and directionally transport the microdroplets (oil and water) by a scanning optical tweezing system. Then, optically controlled coalescence and splitting of the microdroplets are achieved on this basis, and the mechanism and conditions are explored. Finally, the microdroplets are used as microreactors to conduct the microreactions. Such microreactors combine the advantages of miniaturization and the multi-functions of microdroplets, as well as the precision, flexibility, and non-invasiveness of optical tweezers, holding great potential for applications in materials synthesis and biosensing.

Optical trapping, transportation, coalescence and splitting of femto-/pico-liter microdroplets are realized based on a scanning optical tweezing system. On this basis, the microdroplets are used as microreactors to conduct the microreactions.