A novel fluid micromixer based on pneumatic perturbation and passive structures was developed. This micromixer facilitates integration and is applicable to fluid mixing over a wide range of flow rates. The microfluidic mixing device consists of an S-shaped structure with two mixing chambers and two barriers, and two pneumatic chambers designed over the S-shaped channel. The performance of the micromixer for fluids with wide variation of flow rates was significantly improved owing to the integration of the pneumatic mixing components with the passive mixing structures. The mixing mechanism of the passive mixing structures was explored by numerical simulation, and the influencing factors on the mixing efficiency were investigated. The results showed that when using a gas pressure of 0.26 MPa and a 100 pm-thick polydimethylsiloxane （PDMS） pneumatic diaphragm, the mixing of fluids with flow rates ranging from 1 to 650 ~tL/min was achieved with a pumping frequency of 50 Hz. Fast synthesis of CdS quantum dots was realized using this device. Smaller particles were obtained, and the size distribu- tion was greatly improved compared with those obtained using conventional methods.
WANG XinMA XiuFengAN LanLanKONG XiangWeiXU ZhangRunWANG JianHua
Highly efficient and rapid proteolytic digestion of proteins into peptides is a crucial step in shotgun-based proteome-analysis strategy. Tandem digestion by two or more proteases is demonstrated to be helpful for increasing digestion efficiency and de- creasing missed cleavages, which results in more peptides that are compatible with mass-spectrometry analysis. Compared to conventional solution digestion, immobilized protease digestion has the obvious advantages of short digestion time, no self-proteolysis, and reusability. We proposed a multiple-immobilized proteases-digestion strategy that combines the ad- vantages of the two digestion strategies mentioned above. Graphene-oxide （GO）-based immobilized trypsin and endoprotein- ase Glu-C were prepared by covalently attaching them onto the GO surface. The prepared GO-trypsin and GO-Glu-C were successfully applied in standard protein digestion and multiple immobilized proteases digestion of total proteins of Thermoan- aerobacter tengcongensis. Compared to 12-hour solution digestion using trypsin or Glu-C, 14% and 7% improvement were obtained, respectively, in the sequence coverage of BSA by one-minute digestion using GO-trypsin and GO-GIu-C. Multiple immobilized-proteases digestion of the total proteins of Thermoanaerobacter tengcongensis showed 24.3% and 48.7% en- hancement in the numbers of identified proteins than was obtained using GO-trypsin or GO-Glu-C alone. The ultra-fast and highly efficient digestion can be contributed to the high loading capacity of protease on GO, which leads to fewer missed cleavages and more complete digestion. As a result, improved protein identification and sequence coverage can be expected.
