Controlled vibration selectively propels multiple microliter-sized drops along microstructured tracks, leading to simple microfluidic systems that rectify oscillations of the three-phase contact line into asymmetric pinning forces that propel each drop in the direction of higher pinning.

Printable electronics and the increased use of nanoparticle products (e.g. quantum dots) has resulted in the rapid development of nanoparticle inks. Microfl uidic reactors -or microreactors -show promise to provide advanced control over size, size distribution and shape for commercial-scale synthesis of nanoparticles. Compared to batch-wise synthesis techniques primarily in use today, microfl uidic technology can provide better control of the reaction conditions, which is the key to controlling the product characteristics. [ 1 ] Handling small volumes of liquid allows better control of mixing, and hence yields more uniform chemical composition. For thermally activated syntheses, reagents can be heated and cooled rapidly and uniformly, avoiding the large thermal gradients typically found throughout the reaction volume in batch techniques. Several high-temperature microreactors for synthesizing nanoparticles have been described in the literature. [ 2 ] Almost all microreactors described to date have a single heated zone where nucleation and growth of particles as well as reaction processes which should be controlled at different temperatures for proper completion, are executed at the same temperature. In order to obtain monodisperse or near-monodisperse size distributions, the nucleation and growth stages must be separated. [ 3 ] LaMer et al. discussed this concept for the reduction of thiosulphate to sulphur, in terms of the concentration of sulphur monomers. [ 4 ] The rate at which thiosulphate is reduced, and hence the sulphur monomer concentration at a given time, is temperature dependent. The principles elucidated by LaMer are broadly applicable to thermally activated syntheses. Of the few reactors with multiple temperature zones, Yang et al. introduced a capillary-based microreactor. [ 2l ] However due to the lack of thermal isolation between these two zones, it was not possible to quench nucleation. This paper focuses on the design and fabrication of an ideal, functioning Multi-Temperature zone Microreactor (MTM) on a silicon substrate, built upon theoretical concepts introduced by Winterton et al. [ 5 ] As discussed by Winterton et al., the necessary concentration profi les can be controlled by controlling the temperature as a function of time. [ 5 ] Ideally, one needs a very short zone of the reactor at a high temperature, to trigger nucleation, followed by a longer duration at a lower temperature where growth occurs to ensure narrow nanoparticle distributions. However Winterton et al. did not fabricate a microreactor to base their ideas. The MTM is the fi rst fabricated and experimentally tested microreactor in literature that has multiple thermally isolated heated and cooled zones designed to separate nucleation and growth as well as to provide a platform for carrying out a systematic study on the effects of temperature and residence time on nanoparticle formation. In this work, TiO 2 nanoparticles were selected as a model system to demonstrate the functionality of the microreactor.The MTM utilizes t...

The realization of high‐quality lasers in microfluidic devices is crucial for numerous applications, including biological and chemical sensors and flow cytometry, and the development of advanced lab‐on‐chip (LOC) devices. Herein, an ultralow‐threshold microfluidic single‐mode laser is proposed and demonstrated using an on‐chip cavity. CdSe/CdS@CdxZn1−xS core/crown@gradient‐alloyed shell colloidal semiconductor quantum wells (CQWs) dispersed in toluene are employed in the cavity created inside a poly(dimethylsiloxane) (PDMS) microfluidic device using SiO2‐protected Ag mirrors to achieve in‐solution lasing. Lasing from such a microfluidic device having CQWs solution as a microfluidic gain medium is shown for the first time with a record‐low optical gain threshold of 17.1 µJ cm−² and lasing threshold of 68.4 µJ cm−² among all solution‐based lasing demonstrations. In addition, air‐stable SiO2 protected Ag films are used and designed to form highly tunable and reflective mirrors required to attain a high‐quality Fabry–Pérot cavity. These realized record‐low thresholds emanate from the high‐quality on‐chip cavity together with the core/crown@gradient‐alloyed shell CQWs having giant gain cross‐section and slow Auger rates. This microfabricated CQW laser provides a compact and inexpensive coherent light source for microfluidics and integrated optics covering the visible spectral region.