| We have performed chemistry on the scale used by living cells, worked toward selectively delivering chemicals to single cells and subcellular components, and measured biochemical kinetics in containers as small as subcellular components. In the latter, interactions between reagents and the walls of their containers likely become more important than for reactions within laboratory flasks and beakers. Our approach is to use liposomes as biomimetic microreactors that can be fused together or fused to individual cells. Fusion is achieved using electric fields (i.e., electrofusion; EF). We have demonstrated the initiation of chemical interactions after electrofusing together individual pairs of liposomes, monitored chemical kinetics inside of single liposomes, and made progress in single-pair cell-cell and liposome-cell EF. We have also developed nanoengineered pipets to optimize these processes, utilizing the new pipet design to perform single-cell electroporation (EP) and liposome EF with significantly greater fusion yield than previously possible.; We have also used electric fields to induce coupled electrorotation (CER) between latex microspheres and between microspheres and a small amount of glass (such as a sealed pipet tip) or the corner of a block of polydimethylsiloxane (PDMS). When microspheres of different sizes were coupled to each other they rotated in registry at different rates. A change in the rate of microsphere CER can be used to determine the torque applied to that microsphere by a nearby object (and, hence, the torque applied on the object by the microsphere). A sealed pipet tip was used to apply 40 zN-m of torque on a microsphere (and vice versa). We developed a microchip to optimize the use of CER for sensing local changes in ionic concentration, viscosity, and pH. The microchip was also used to demonstrate microfluidic mixing induced by CER between a microsphere and a PDMS microstructure.; CER allows for microfluidic mixing and sensing. EP and EF allow for biorelevant femtoliter chemical mixing and chemical kinetics measurements. Microscale EP, EF, and CER are simple, versatile techniques using similar experimental tools. Taken together, these techniques allow for sensitive microscale chemical manipulations and measurements relevant to both living systems and nanotechnology. |
