Electroosmotic glass microreactor

Watts et al. demonstrated multi-step solution-phase synthesis of peptides in a glass microreactor with quantitative yield in 20 min [94]. This should be compared with batch reactions where only moderate yields (40-50%) were obtained in 24 h. Common protecting groups were used, viz. Fmoc was selected for N-protection and Dmab ester for protection of the carboxylic add. The reaction was carried out in the microreactor under electroosmotic flow. Deprotection, which is required to extend the peptide chains beyond dipeptides, was also demonstrated with quantitative yield in the microreactor. In this first microreactor demonstration, only alanine-based peptides were synthesized in later work other amino acids were also used ]95, 96]. 

There are a number of materials used for the fabrication of pTAS devices. Perhaps the most common is glass due to its low cost, ease of machining, and suitability for electrophoresis and electroosmotic flow (EOF) applications without requiring surface modifications. It is also chemically inert to most reagents (apart from hydrofluoric acid and concentrated alkali). Silicon is also a valuable material that has similar chemical inermess and can easily be machined by chemical etching. While it is more expensive, it can be easily chemically etched to yield far higher aspect ratios than are possible with glass. Silicon is not suitable for electrophoresis or EOF applications without surface pretreatment. Devices fabricated from polymers such as polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) are also frequently used due to the low cost of the material (especially important for disposable devices) and the ease of fabrication. Perhaps one drawback with polymers is their incompatibility with solvents. They are suited to electrophoretic applications but frequently require surface modification to support EOF. Occasionally, metals are used however, these are far more frequently encountered in chemical microreactors. 

---